General principles 39
3.1.1 Structural diagnosis 39
3.1.2 Functional diagnosis of spinal column mobility (kinematics) 40
3.1.3 Functional diagnosis of body statics 40
3.2 Technique in functional diagnosis 40
Manual techniques call for an accurate understanding of anatomy, especially when treating the spinal column. Textbooks of radiology are interested mainly in morphology, while our concern is mainly with function, the consistent focus of the present book. The use of radiology for functional studies can greatly improve our understanding in manual diagnosis. However, if we are to be able to interpret radiographic images from the functional point of view, we need a good knowledge of X-ray anatomy, such as we present here, as well as certain requirements as regards technique.
3.1. General principles
For our purposes, X-ray diagnosis fulfills three basic tasks:
1. Structural diagnosis.
2. Functional diagnosis of spinal column mobility (kinematics).
3. Functional diagnosis of body statics (interpretation of curvatures of the spinal column).
3.1.1. Structural diagnosis
Structural diagnosis provides information about the morphology of the bony structures. This is the essential focus of classic X-ray diagnosis, which is mainly concerned with form and structure and constitutes the basis of our knowledge. This type of diagnosis is very important for manual therapy in that it alerts us to potential serious errors of diagnosis, providing a warning against manual therapy where inflammation, tumors, fractures, or other contraindications are present. It also reveals abnormalities and changes in structure, such as asymmetries, which can be significant for function. Diagnosis of structure can be found in the classic textbooks of radiology, so we shall deal here only with those morphological changes that are important for an understanding of dysfunctions.
3.1.2. Functional diagnosis of spinal column mobility (kinematics)
Functional diagnosis in the narrower sense involves movement studies of the spinal column in which X-rays are taken in end of range positions, in ante- and retroflexion (extension), side-bending and, less frequently, rotation. Examination of this kind is the only approach that can provide direct information about dysfunctions in the motion segment. It can also be used before and after treatment. It is of value for documentation and assessment, but is too time-consuming and uneconomical and the radiation exposure is too great for use as a routine procedure. Since manual therapy examination gives good information on mobility and disturbances of mobility, it is generally possible to dispense with movement studies. They do have an important role to play in research, however, and provide an understanding of the biomechanics of movement processes.
3.1.3. Functional diagnosis of body statics
Although movement studies come first to mind when we think of functional diagnosis, it is no less important to diagnose disturbances of body statics. The images used to assess this must be taken standing (or, for the cervical spine, sitting), under static loading and under standard conditions. The curvatures of the spine, as explained below, should mainly be assessed from the point of view of static function. This applies not only to the sagittal but also the frontal plane, in which every obliquity (e.g. of the pelvis during walking) produces a corresponding scoliotic curvature and rotation. Curvature may be regular or irregular, so that a marked deviation may be observed in one particular segment. This may be scoliotic, increased lordosis or kyphosis, rotation, or lateral shift (‘offset’).
The significance of these signs of irregularities in the position of neighboring vertebrae (relational diagnosis) is highly controversial, and closely connected with the discredited subluxation theory. It is also closely linked to the problem of asymmetry, bearing in mind the fact that a degree of asymmetry is the rule rather than the exception. Jirout (1978) has shown that asymmetry of the position of the atlas in relation to the axis is present in the majority of adults. In a study to compare children of various ages, he found that its incidence increases with age. This can be shown particularly easily by observing the position of the spinous processes. He concluded that these asymmetries were the result of asymmetrical pull of the muscles due to the dominance of one cerebral hemisphere.
From this we can conclude that asymmetry and other kinds of irregularity are not in themselves pathological, although they can be the expression of functional asymmetries. We know, for example, that if the axis is asymmetrically rotated in neutral position, the entire cervical spine will rotate asymmetrically during side-bending. In general it is advisable to be cautious when drawing conclusions about examples of asymmetry observed on an X-ray film, and always to take the clinical findings into account when interpreting the radiographic findings.
One advantage of static functional diagnosis is that the examination is economical: only two X-rays are required, two projections, which must correspond to each other vertically. Standard conditions must be observed as regards static loading. As individual posture is highly characteristic, it also remains fairly constant. Gutmann & Véle (1978) said of static function: ‘The dominating principle of the spinal column is body statics. All other functions are subordinate to the requirements of upright posture on two legs. The human body is more ready to accept loss of mobility or painful impingement of nerve roots than to sacrifice erect posture.’
3.2. Technique in functional diagnosis
Since the spinal column is a functional unit, the most appropriate format for the X-ray examination is to show the entire spinal column on a single film. An AP and a lateral view with the patient standing are required, with the feet placed in a standardized position. If this cannot be done, the sections of the spinal column that have been imaged need to be assessed in the light of the clinical findings. These can then make good whatever is missing in the X-ray.
3.3. The lumbar spine and pelvis
3.3.1. X-ray of the lumbar spine and the pelvis
The imaging projections needed for routine examination of the static function and morphological changes of the spinal column are simply one AP and one lateral view with the patient standing. This is done using a device described by Gutmann (1970), in which a plumb line indicates the vertical line from the head. The procedure is illustrated in Figure 3.1 A–D and is as follows:
 |
| Figure 3.1
X-ray technique for the lumbar spine after Gutmann (1970). (A) Positioning of the plumb line for the head and (B) patient position during radiography, as prepared for the AP view. (C) Positioning of the plumb line for the head and (D) patient position during radiography, as prepared for the lateral view.
|
A line which corresponds to the center of the cassette is drawn on the floor in front of the middle of the stand. For the AP view the patient places one foot symmetrically on each side of the line, and is requested to distribute the weight of standing equally between both feet, with legs straight, so as to rest on a base that is in line with the center of the cassette. A plumb line extended downward from the center of the cassette will therefore meet the floor at the mid point between the patient’s heels, setting the base line. A movable plumb line of metal wire (so as to create contrast) is attached to the screen. The cassette is first raised to the level of the patient’s occiput and this metal wire plumb line moved to a point precisely below the middle of the occipital squama, where the external occipital protuberance can be palpated. This sets the plumb line that marks the head position. The cassette is then adjusted (taking care not to displace it to the side) to the height required to take a view of the lumbar region and the pelvis (with the central ray of the X-ray beam and the center of the cassette roughly at the height of the navel). By setting up the AP view in this way, the shadow of the metal wire marks the plumb line representing the head position, and the center of the film represents that of the base line.
The same procedure is used for the lateral view of the lumbar spine, except that this time the patient stands with feet across the line on the floor that represents the center of the cassette, with ankles one finger’s breadth behind the line. The plumb line for the head is positioned at a point in line with the external acoustic meatus. Here – as in the procedure described for the cervical spine – it is helpful to align the central ray below rather than on the center of the cassette, directing the beam off-center to focus approximately on the lumbosacral junction, midway between the iliac crest and the greater trochanter. This technique has two great advantages:
1. There is considerably greater absorption of radiation at the lumbosacral junction (on which the pelvis is superimposed) than in the lumbar spine. If the central ray is aligned as usual on the middle of the lumbar spine, the result is either under-exposure of the lumbosacral junction, while the rest of the lumbar spine is correctly exposed, or over-exposure of the lumbar spine while exposure of the lumbosacral junction is good. Aligning the beam on the lumbosacral junction evens out the exposure, and has the additional advantage of providing good imaging of the hip joints (see Figure 3.2).
2. If the beam is aligned to the center of the cassette (middle of the lumbar spine), the effect is to project the iliac crests away from each other, lying well apart as they do, although they are very important for body statics. The projection error produced at the much slimmer lumbar spine, on the other hand, is only slight.
For both projections the focus-film distance should be as great as possible, depending on the power of the apparatus and the corpulence of the patient, the ideal distance being at least 2m (78inches). For technical reasons, the patient needs to stand with arms folded in front of the chest (see Figure 3.1 D). The final step, once the apparatus and the patient’s position have been set up, is to tape the wire to the cassette so that it cannot be displaced, and then instruct the patient to lean against the screen so as to remain steady during the long film exposure.
3.3.2. X-ray evaluation of lumbar spinal statics
The purpose of the films taken in the standing position is mainly to study body statics. The only structures in the frontal plane that can be assessed by clinical examination are the occipital protuberance, spinous processes, iliac crests, intergluteal cleft, and the midpoint between the heels. In the sagittal plane, clinical examination can show the posture of the head, position of the shoulders, the trochanters and the heels in relation to the plumb line, which takes the line from a fixed point at the external auditory meatus. Clinical examination cannot provide information about the position and inclination of the sacrum and the most caudal vertebrae (which mark the true base of the spinal column), information which is essential for a full understanding and evaluation of spinal statics.
This may explain why clinicians interested in body statics have devoted their attention mainly to the question of body equilibrium as a whole, studying deviation of the head and deviation from the line of gravity by means of statovectography. However, Rash & Burke (1971) pointed out that with static load each body segment should be vertically above the center of the segment on which it rests. The principle is violated if tension of the ligaments or excessive muscular contraction are required to maintain balance. X-ray examination under static conditions provides information on precisely this type of static disturbance.
The mechanism of body statics differs considerably in the frontal and the sagittal planes. One way to appreciate this is to observe the effect of a heel insert, a pad or block placed under one foot. A healthy subject experiences a height difference of as little as 1cm as uncomfortable, whereas if a heel insert of 1cm is placed under both feet it is hardly noticed. This is because in the frontal plane the center of gravity lies over both feet, such that body equilibrium is (relatively) stable. As a result, any mechanical change (the insert under the foot) has an immediate effect. In the sagittal plane, in contrast, body equilibrium is labile, over the two perfectly round surfaces of the hip joints. A slight mechanical change has little effect, because it is dynamic muscle function that is maintaining balance in this plane. The muscular force required should, however, be minimal.
Lumbar spinal statics in the frontal plane
In the ‘ideal’ case the pelvis and spinal column lie symmetrically in a straight line in the AP view. The external occipital protuberance, spinous processes, pubic symphysis, and coccyx lie in the midline. Such a spinal column is the exception in real life; people simply do not place their weight symmetrically on both feet, but stand in a relaxed posture in which the weight is taken mainly on one leg. During walking, the pelvis constantly swings from one side to the other. The result is the constant creation of oblique planes. The main concern in assessing these is to discover how the spinal column reacts to obliquity in the frontal plane.
The physiological reaction to obliquity can be seen by performing a test in healthy subjects: the subject must first relax, stand with legs straight, and rest the weight of the body on both feet; a block of wood is then placed under one foot. The subject’s pelvis then shifts to the higher side (see Figure 3.3).
The radiographic image shows not only the shift to the side, but also scoliosis and rotation to the lower side. The summit of the scoliotic curve is usually at the mid-lumbar region, with the thoracolumbar junction vertically above the sacrum. The degree of rotation depends on the degree of lordosis of the lumbar spine. If there is no lordosis – as is often the case in acute lumbago – there is also no rotation. If there is kyphosis, there may even be rotation to the same side as the concavity.
Reaction by the spinal column to an oblique plane is normal if:
• scoliosis to the lower side results
• there is rotation to the same side (when there is lordosis)
• the thoracolumbar junction is vertically above the sacrum
• the pelvis shifts to the higher side (see Figure 3.4).
Slight thoracic scoliosis occurs in the opposite direction.
These features reflect normal spinal statics and are closely associated with the problem of difference in leg length. From the point of view of body statics, a difference in leg length becomes significant only when accompanied by obliquity of the base of the spinal column (see Figure 3.5).
In the light of this fact, the age-old dispute over how to measure a difference in leg length is beside the point. While it is possible clinically to establish the presence of pelvic tilt, we cannot determine the position of the sacrum relative to the sacral promontory and the lumbar vertebrae that constitute the base of the spinal column proper, as the pelvis may be straight while the sacrum is tilted, or vice versa. The determining factor in spinal column and body statics is the base of the spinal column. The only way to establish the position of these, and find how the spinal column reacts to an oblique base, is by X-ray examination with the patient standing (see Figure 3.6).
The most important findings where there is a disturbance of body statics are:
• obliquity of the base of the spine without scoliosis or with inadequate scoliosis, so that the thoracolumbar junction is not vertically above the lumbosacral
• no lateral pelvic shift to the higher side
• no rotation when there is scoliosis together with lordotic posture of the lumbar spine or even rotation in the direction of the concavity.
The practical decision to be made is whether to order a corrective heel insert. This is primarily a clinical decision, although the X-ray can provide useful clues. The following radiological criteria show when a heel insert can be helpful in the case of obliquity of the base of the spine:
• If scoliosis is not sufficient to bring the thoracolumbar junction into a position vertically above the lumbosacral, or if scoliosis is absent. Use of a heel insert to raise one heel should bring the thoracolumbar junction to the vertical, or at least nearly so.
• If the pelvis is shifted, usually toward the higher side, it should then return to the midline.
• If the scoliosis was statically balanced, it should decrease.
These criteria should all be checked again by X-ray. The spinal column may react positively or negatively to the heel insert, either ‘accepting’ or ‘rejecting’ the correction. If the response is negative it would be wrong to force correction upon the patient, because this would only worsen the situation at the base (see Figure 3.7).
The typical reaction to obliquity as seen radiographically has been studied by Illi (1954) and Edinger & Biedermann (1957), with the subject walking on the spot. At each step, oblique planes appeared together with corresponding scoliosis to the side concerned; the summit of the scoliotic curve appeared at L3. The thoracolumbar junction remained vertically above the sacrum. Above T12 there was a scoliosis of the thoracic spine to the opposite side, but it was shallow. According to Edinger & Biedermann (1957), the thoracolumbar junction forms a kind of point of interchange, and should not swing more than 4cm from one side to the other.
The relation of the scoliosis to rotation and its dependence on the presence of curvature in the sagittal plane was studied by Lovett (1907), who found that rotation of the lumbar spine (in the sense of scoliosis) occurs if lordosis is present, but not in kyphosis. The explanation for this lies in the fact that, whereas the vertebral bodies have good mobility during side-bending, the joints of the vertebral arches are forced together in lordosis and so resist movement. In contrast, in kyphosis there is less close contact between the joints of the vertebral arches; but the vertebral bodies are pressed more firmly against each other, so that these are less free to side-bend. As a result, either there is no rotation at all or rotation occurs in the opposite direction. This is sometimes the case in patients with acute lumbago or in radicular compression syndrome (see Figure 3.8). The situation can also be found clinically in healthy subjects. On passive side-bending of a subject in lordosis, the spinous processes remain in the midline, and the vertebrae rotate in the sense of scoliosis. If the same is done in kyphosis, the spinous processes form a scoliotic curve: in other words, they move in parallel with the vertebral bodies.
Lumbar spinal statics in the sagittal plane
In the sagittal plane, we often speak of ‘normal’ curvatures; these are generally held to be the convex cervical curve (lordosis), concave thoracic curve (kyphosis), convex lumbar curve (lordosis), and concave sacral curve (kyphosis). Sollmann & Breitenbach (1961) demonstrated on the basis of 1000 X-ray films in the sagittal plane that there is no such thing as a general norm; at best we can speak of an ‘individual norm.’ They do not, however, lay down any criteria for this kind of norm.
Cramer (1958) showed, on the basis of 150 measurements of the lumbar spine with the subject standing, that there is a constant correlation between the tilt of L5 and that of T12, and more important still, that the T12 vertebra lies an average of 4cm dorsally to L5. The results of our own study (Lewit 1973) gave complete confirmation of Cramer’s findings and also showed that the plumb line for the head follows a line down from the external acoustic meatus exactly to the navicular bone. We found that the sacral promontory lay an average of 4mm anterior to this plumb line, and the transverse axis of the hip joints 12mm anterior to the plumb line.
Deviations from this norm indicate a disturbance of body statics as a result of lack of muscle coordination. This is most evident in muscle spasm due to acute lumbago or radicular pain, when there is forward-thrust posture (see Figure 3.9), in which the thoracolumbar junction lies exactly over or ventral to the lumbosacral junction. The reverse is found in ‘flabby’ posture, in which the sacral promontory lies well forward of the plumb line for the head, and T12 lies dorsal to L5 by some distance (see Figure 3.10).
 |
| Figure 3.9 |
‘Flabby’ posture is the expression of imbalance of the muscles of the pelvic girdle; it may be the result of weakened abdominal and gluteal muscles, but equally well of hyperactive hip flexors.
The curvature of the lumbar spine is of course also dependent on pelvic tilt which, in turn, varies according to the ‘type’ of pelvis, as is shown in the following section.
One further point to note is that a slight curvature (a ‘flat’ spine) goes hand in hand with hypermobility and lack of stability, while greater curvature (in both the sagittal and the coronal plane) corresponds to stability and less mobility.
The curvatures of the spine are an expression of static function, and should therefore be interpreted in terms of whether they fulfill this function. In the frontal plane, balance is relatively stable; in the sagittal plane, muscle activity is the determining factor. Curvature of the lumbar spine in the sagittal plane is normal if the thoracolumbar junction is dorsal to the lumbosacral, if there is no forward shifting of the sacral promontory (no more than 8cm in front of the center of the cassette, which is double the average). The position of the thoracolumbar junction vertically above the lumbosacral is also the most important criterion in the frontal plane. If there is obliquity at the base, the normal reaction is scoliosis and rotation of the spinal column (if lordosis is present) and a shift of the pelvis to the higher side.
3.3.3. The pelvis
The pelvis and the spinal column together constitute a functional unity, in which the pelvis serves both as the base of the column and at the same time as the connection with the lower limbs. The pelvis transmits motion from the lower limbs, at the same time acting as a shock-absorber. The spinal column rests on the pelvis much as the mast of a boat rests securely on the firm base of the mast step (Benninghoff, 1944). The sacroiliac joints and the pubic symphysis allow for a degree of mobility with enough spring to act as a buffer while also providing adequate stability.
Pelvic types
The function of the pelvis and its influence on body statics depend largely on its type; we owe the recognition of this relationship to Erdmann & Gutmann (1965). The variability observed here is evidence of the phylogenetic instability of this region; evidence of this variability can be seen in our description of the last lumbar vertebra as a ‘transitional’ vertebra; it is difficult here to speak of any such thing as a ‘norm.’ If the variations are asymmetrical as between the two sides, this results in obliquity at the base of the spinal column, and the effects on spinal statics are considerable. If the variations are symmetrical, this affects the length of the sacrum, which is closely associated with its position and inclination.
Erdmann & Gutmann (1965) distinguish the following pelvic types with respect to the associated mechanism of pathology (see Figure 3.11 and Table 3.1). The authors call these Hohes Assimiliationsbecken (high promontory assimilation pelvis), Normalbecken (normal pelvis) and Überlastungsbecken (overload pelvis):
• High promontory: the ‘assimilation’ type presents a long sacrum and high sacral promontory, with a tendency to hypermobility (see Figure 3.17)
• Normal type: this is of average length, with a tendency to restrictions.
• Low promontory: the ‘overload’ type has a low promontory and marked inclination of the sacrum.
All the points summarized in Table 3.1 should be borne in mind when evaluating X-ray films; it will be seen that the type of pelvis affects the spinal curvatures, the height of the last intervertebral disk, and the shape of the vertebral bodies, and therefore also the mobility of the most caudal motion segments. The assessment to be made when hyperlordosis is found will therefore be different in the case of a high promontory (assimilation) type and in that of a low promontory (overload) type. Similarly, a low L5/S1 intervertebral disk will be differently assessed.
Identification of pelvic type (see Figure 3.11 and Table 3.1) is extremely important for the assessment of dysfunctions, especially in the lumbar and pelvic region.
| High promontory (assimilation) | Normal | Low promontory (overload) | |
|---|---|---|---|
| Inclination of sacrum | 50°–70° | 35°–50° | 15°–30° |
| Inclination of end-plate of S1 | 15°–30° | 30°–50° | 50°–70° |
| Position of L4 disk | Above the line of the iliac crests | At the height of the iliac crests | Below the line of the iliac crests |
| Position of the promontory in the pelvic girdle | Eccentric (dorsal) | At the center | At the center or ventral |
| Shape of L5 vertebra | Rectangular | Trapeze shaped | Trapeze shaped |
| Shape of L5 disk | Rectangular and higher than L4 | Wedge shaped and thinner than L4 | Wedge shaped and thinner than L4 |
| Segment with maximum mobility | L5/S1 | L4/L5 | L4/L5 |
| Effect of iliolumbar ligament | Slight fixation of L5 | Good fixation of L5 | Good fixation of L4 and L5 |
| Weight-bearing structure | End-plate of S1 | End-plate of S1 | L5/S1 joints and sacroiliac joint |
| Spinal curvature | Flat | Average | Considerable |
| X-ray statics | Promontory and hip joints lie in front of plumb line for head | Promontory and hip joints almost on line of plumb line for head | Promontory and hip joints lie behind plumb line for head |
| Clinical signs | Hypermobility, pathological changes of L5 disk; ligament pain | Restrictions, pathological changes of L4 disk | Arthroses of L5/S1, sacroiliac joint and hip |
The sacroiliac joints
There is some mobility of the otherwise firm pelvic girdle, due to the role of the sacroiliac joints and the pubic symphysis. The major role is that of the sacroiliac joints.
The sacrum is wedge shaped in two directions; first the whole structure tapers in the caudal direction. A double contour is usually seen in the AP view, since there is another wedge in the ventrodorsal direction; the sacrum is somewhat broader ventrally, at least in its craniad part, although in this respect too there are considerable variations. It is helpful to note that the greater the distance between the two contours of the joint, the narrower the joint space appears. If on the other hand we see only one contour, the joint space appears to be wide and clearly defined. This is often the case with the high promontory type, and is a further sign of hypermobility.
It is important to point out that, despite its unusual shape and limited mobility and the fact that there are no muscles to move the sacrum against the ilium, the sacroiliac joint is a true synovial joint (Colachis et al 1963; Duckworth 1970; Mennell 1952; Weisl 1954). According to Duckworth, the sacrum rotates relative to the ilia around an axis corresponding to the shortest sacroiliac ligaments, at the level of S2. This movement is one of nutation; with each step taken during walking, the weight of the spinal column produces a forward nodding motion of the sacrum, together with the sacral promontory, acting as a shock-absorber. This mobility of the sacrum within the pelvic girdle is easily palpated and is familiar to gynecologists in the management of labor. Perpendicular to this ‘functional’ motion, the joint play consists in a springing, wing-like motion about a craniocaudal axis, the effect of which is a distraction of the joint.
The degree of mobility in the sacroiliac joint should be as little as possible, yet never to the point of restriction, just as a shock-absorber is firm but never immobile.
It is appropriate at this point to deal with a condition described as pelvic distortion, which requires explanation from the functional anatomical point of view. The finding on palpation is that the posterior superior iliac spine (PSIS) is lower on one side than the other. The finding is the same if the finding is made at the posterior border of the iliac crests at the point where they can be palpated in the vertebral region. Ventrally the opposite is found: on the side where the PSIS is lower, the anterior superior iliac spine (ASIS) is
found to be higher than on the contralateral side, and vice versa. The ventral parts of the iliac crests behave in the same way as the anterior iliac spines. The middle portion of the iliac crests may be symmetrical, although this need not be so. On first impression it seems as if one ilium is twisted relative to the other about a frontal transverse axis, although this is in fact impossible if the pubic symphysis is intact.The functional anatomy involved can best be illustrated anatomically by Cramer’s diagram (1965) (Figure 3.12). This shows a one-sided nutation of the sacrum brought about by its rotation between the ilia around its longitudinal axis. This in turn results in rotation of one ilium about a horizontal axis and of the other about a vertical one.
 |
| Figure 3.12 |
All attempts to visualize these changes radiographically have remained without success as far as we know. However, we have been successful in showing X-ray evidence of a disturbance of body statics in the presence of pelvic distortion (see Figure 3.13). The pelvis was found to be shifted toward the higher side, and there was deviation of the angle between the sacrum and the lumbar spine. This disappeared following treatment of the atlanto-occipital and atlantoaxial joints. Lewit & Rosina (1999) were able to induce pelvic distortion by rotating the head to one side and then the other, but radiographic examination showed this effect to have been a palpatory illusion.
3.3.4. The lumbar spine
Although only a little shorter than the thoracic spine, the lumbar spine consists of only five vertebrae. However, in ante- and retroflexion as well as in side-bending, the corresponding motion segments play a significant part in ensuring the mobility of the trunk. Meanwhile the inferior part of the lumbar spine also carries the weight of the trunk, so the vertebral bodies and articular processes of the lumbar spine are the most robust.
The joints of the vertebral arches form massive gliding surfaces that can enable considerable excursion and also provide stability. The greater part of the articular facets runs vertically, almost in the sagittal plane. Ventrally, the smaller part is turned almost at a right angle to point medially, in the frontal plane. Frequently, however, the articular facets simply form an arc, whose concave aspect faces dorsally. If the two parts do stand at right angles to each other, the joint spaces can be easily visualized by X-ray; if they form an arc, this cannot be done. Given that the joints of the vertebral arches only develop their final shape after birth, during the first years of life there is considerable variation in this respect.
The shape of the joints determines the function of the lumbar spine; it mainly allows for ante- and retroflexion and tends to inhibit side-bending, which occurs in combination with rotation. The joints inhibit rotation about a sagittal axis. Just as side-bending happens in combination with rotation, so rotation of the trunk produces the effect of lateral flexion.
If the joints of the vertebral arches determine the quality of the movements of the lumbar spine, its great mobility depends on the thickness of the lumbar intervertebral disks. Their thickness usually increases from L1 down to L4; consequently maximum mobility is usually found at the L4/5 segment. Only in the ‘high promontory’ pelvic type is maximum thickness and mobility found at L5/S1. Retroflexion, however, is usually most extensive in the L5/S1 segment.
X-ray anatomy of the lumbar spine
The oval shadow of the pedicles of the vertebral arches are the most striking feature in the AP views of the lumbar spine (see Figure 3.14 and Figure 3.15). The last pedicles (only) are projected onto the lateral edge of the fifth lumbar vertebra; they are also less distinct. This is partly owing to the triangular shape of the spinal canal in the inferior lumbar spine. Taking the pedicle as a starting point, it is possible to identify the lamina of the vertebral arch and trace it along to the spinous process. Lateral to and above the pedicle we find the superior articular processes; from the vertebral arch downwards and below the pedicle, the inferior articular processes can be traced in a caudal and lateral direction toward the superior articular processes of the next vertebra below. The two inferior articular processes form an arch; this, together with the spinous process of the caudal neighboring vertebra, forms a frame around a lucency which offers a glimpse into the spinal canal. At this point the canal is not covered by bone, and this is the location where lumbar puncture can be performed. Where both articular processes meet is the joint space. It is possible to see into the joint space if part of it is aligned in the sagittal plane.
The lateral view (see Figure 3.16) also shows the thick pedicles, situated immediately behind the bodies of the vertebrae. The superior and inferior articular processes arise from the pedicles. It is often also possible to see the joint space if the medial part of the joint lies in the frontal plane. Between the superior and inferior articular processes is the pars interarticularis (pars isthmica), which tends to be the site of spondylolysis in true spondylolisthesis. Between the pedicles of adjacent vertebrae can be seen the intervertebral foramen, dorsal to the vertebral bodies and intervertebral disk and bordered dorsally by the articular processes. It lies almost exactly in the frontal plane, and its width is almost that of the spinal canal. The lamina is covered by the articular processes, and dorsal to these can be seen the massive spinous processes. The transverse processes are projected onto the articular processes, appearing as a thick shadow.
The fifth (last) lumbar vertebra occupies a special position in that it serves a transitional function between the mobile lumbar spine and the rigid pelvis. In terms of its shape, it is therefore adapted to the base (craniad end) of the sacrum. In the lateral view, the vertebral body of L5 is trapezoid. An important point to note is that the powerfully developed transverse processes of L5 – often resembling the pars lateralis of the sacrum – provide attachment to the iliolumbar ligaments, which stabilize the last lumbar vertebra in the pelvis. L5 therefore plays a part in the shock-absorbing function of the pelvis. The intervertebral foramen of L5 is usually narrower than the others of the lumbar spine, despite the generally powerfully developed pedicle of L5. This vertebra is usually considerably inclined, so the L5/S1 joints usually lie in the frontal plane, to prevent forward gliding.
The most important anomalies of the lumbosacral junction have already been dealt with under ‘pelvic types’ (see Section 3.3.3). When there is a transitional vertebra, it can be difficult to decide whether this is a sacralized L5 or a lumbarized S1. It is especially difficult if the image shows six vertebrae with lumbar characteristics and the task is to decide whether the last is indeed a lumbar vertebra or a lumbarized sacral vertebra. In cases where a neurosurgical intervention is to be carried out, this decision can be very important. The most reliable criterion to use is an imaginary line drawn between the two iliac crests: this line usually corresponds to the fourth intervertebral disk (see Figure 3.17). If, however, this line projects across the middle of a vertebral body, the identification becomes well-nigh impossible, unless an X-ray of the thoracic spine is also available. Sometimes, instead of the massive transverse process of L5, a transitional lumbosacral vertebra may have a pars lateralis which forms a pseudarthrosis with the pars lateralis of S1, and may even cause clinical symptoms.
The most serious anomaly, clinically, is probably spinal canal stenosis. In the lateral view the usual finding shows massive vertebral bodies with short, stubby pedicles and markedly narrow intervertebral foramina. The line of the inferior articular processes is noticeably steep. In the AP view the massive appearance of the articular processes is striking, it is possible to see clearly into the joint space, and the lucency between the inferior articular processes below the spinous process is particularly narrow. The effect is to give the spinal canal a trefoil shape. CT offers the best insight into the anatomical relations in the spinal canal; it can also visualize the narrow lateral recesses and the narrowed, trefoil-shaped spinal canal. A narrow spinal canal adversely affects root compression and is often accompanied by radicular claudication.
It is of course important to be able to assess the thickness of the intervertebral disks correctly. Straightforward disk hypoplasia is a quite common anomaly, and should not be confused with disk degeneration. This is especially true in the case of an L5 transitional disk. If this vertebra shows no signs of degenerative changes and no shift that might indicate laxity, the practitioner should not be too hasty in diagnosing a narrow disk as degeneration. A useful sign of disk hypoplasia is a finding that shows abbreviated end-plates either side of a narrow disk. Although we usually rely on lateral views for the assessment of disks, marked asymmetry in the AP view can be a useful sign, particularly for the L5/S1 disk, where anomalies are frequently found (asymmetrical L5/S1 disk, see Figure 3.18).
Evaluation of function from X-rays
In order to evaluate radiographic films from the point of view of function, they must be taken under standard conditions. The film must be taken with the patient standing erect, and if possible using the technique described in Section 3.3.1. A functional evaluation of the lumbar spine can only be done if the pelvis, hip joints and pubic symphysis are included on the film. A 30×40 format is therefore recommended for both projections, so that the entire sacrum and hip joints can also be seen in the lateral projection. A focus-film distance of at least 1.5 meters is needed to keep distortion to a minimum.
Careful assessment of rotation can be important, because rotation is to some extent related to scoliosis and the degree of lordosis; if the relationship is disproportionate, this can be a sign of dysfunction. Rotation of a vertebra is recognized by a deviation of the spinous process and the pedicles in the direction opposite to that of rotation. On the side of rotation the pedicle appears wider and it is easier to see into the joint space; the transverse process is slightly shorter (because it is nearer the cassette). Deviation of the spinous process alone should never be taken to be a sign of rotation; absence of the other criteria, especially the corresponding asymmetry of the pedicles and the row of transverse processes, etc., indicates that the deviation observed is simply asymmetry and not rotation. Scoliosis should always be assessed according to the principles of body statics.
The lateral view is used to assess lordosis, kyphosis and ventral or dorsal shift. If an apparently blocked position is found, this can also be significant. Slight shifting (ventrally or dorsally) is a sign of instability. This may become more marked during ante- or retroflexion. However, very slight, proportional shifts in ante- or retroflexion, especially in young patients, may be normal. There are two potential pitfalls to beware of:
1. Incongruence of the end-plates of two adjacent vertebrae, most frequently observed between L5 and S1 in the lateral view. In such cases the superior end-plate of S1 is usually slightly longer than the inferior end-plate of L5, and the shift that is observed can be seen either only at the dorsal or ventral edge of the adjacent vertebra.
2. Slight rotation in patient positioning: here the shadows of the anterior and posterior borders form a double contour which can be mistaken for a shift.
Slight shifts due to hypermobility or slight instability need to be distinguished from true spondylolisthesis (with spondylolysis) and from degenerative ‘pseudospondylolisthesis or spondylotic listhesis’ as described by Junghanns (1930), in which the superior articular process of the adjacent vertebra below (most frequently L5) is bent in the ventral direction, so that the vertebra above it (usually L4) glides ventrally over it.
Radiographic movement studies
Films taken in erect posture may not always provide any clues to disturbed function, which only becomes evident in movement studies. These are usually performed to study ante- and retroflexion and side-bending. In the normal case, movement is fluid and all segments of the lumbar spine participate. Where there is disturbed function, it is possible to distinguish segments of reduced or increased mobility. We find a sign of reduced mobility at a block vertebra position, and the segment concerned does not participate in the movement. Where there is increased mobility, local ventral or dorsal shifts may be observed in ante- and retroflexion. In young and hypermobile subjects, slight step-like shifting of vertebrae and shifting that occurs to an equal degree in all segments may be considered normal (Jirout 1956). Even the formation of an exaggerated sharp bend is a sign of local hypermobility. However, if this sharp bend is accompanied by a ventral narrowing of the disk in anteflexion, without a corresponding dorsal widening, this is indicative of a disk lesion. The same can be said if it is accompanied by dorsal narrowing of the disk without a corresponding widening ventrally (Jirout 1965).
In the lumbosacral segment a ‘paradoxical’ shift sometimes occurs; instead of the ventral shift in anteflexion and dorsal shift in retroflexion that is observed in the other segments, there is a ventral shift during retroflexion and dorsal shift during anteflexion (Jirout 1957). This presumably occurs as a kind of leverage mechanism.
Movement studies are mainly indicated where there is a clinical reason for doing so; usually where particular movements give rise to symptoms. These studies are particularly important in order to find out whether or not spondylolisthesis is already fixed. In side-bending, the main object is to look for asymmetry and to assess the relationship between flexion and rotation.
3.4. The thoracic spine
3.4.1. Functional anatomy
The thoracic spine is the longest section of the spinal column, but also the one with the least mobility. The main reason for this is its firm, though jointed, connection to the relatively rigid thoracic cage. The narrowness of the intervertebral disks is the morphological expression of this minimal mobility. In the frontal plane the joint spaces are almost vertical, but laterally they fall away anteriorly, as if on the periphery of a circle (cylinder) whose center is ventral to the vertebral body. This arrangement would allow for considerable rotation in the thoracic region were it not for the ribs and the intervertebral disks.
Side-bending, and to some degree also anteflexion, are similarly limited by the thoracic cage. Anteflexion is also held in check by the tension of the inter- and supraspinal ligaments. Retroflexion is limited mainly by the articular and the spinous processes, which overlie each other in the manner of tiles on a roof. At a certain point in retroflexion this arrangement therefore obstructs bending in this direction.
Transitional regions
One important reason for the significance of the thoracolumbar junction is that there is a sudden change in joint structure occurring in the region of a single vertebra (T12): whereas the articular processes above this point are those of the thoracic spine, those below it have the form and mechanical features of the lumbar spine. During walking on the spot, the thoracolumbar junction acts as a fixed point, where scoliosis of the lumbar spine to one side changes to scoliosis of the thoracic spine to the opposite side.
The anatomists’ view that trunk rotation takes place mainly in the thoracolumbar junction was refuted by Singer & Giles (1990). They demonstrated directly by means of CT during trunk rotation that the rotation occurring in this segment was hardly any greater than that in the neighboring thoracic and lumbar motion segments. We confirmed these findings using AP films of trunk rotation taken in the sitting position with fixed pelvis. We demonstrated that scoliosis with rotation occurs in the entire lumbar spine (see Figure 3.19).
Just as side-bending (scoliosis) of the trunk is combined with rotation, so rotation of the trunk is accompanied by side-bending. In principle, movement of the spine occurs by coupled movements in all three planes.
Another transition region which is commonly the site of dysfunctions is the cervicothoracic junction down to T3/T4; this is where movements of the head and neck end, as is most clearly seen in ante- and retroflexion. The same is true for side-bending and rotation, though it is evident only in erect posture. One possible reason for the frequency of dysfunctions in this region may be that it is the point of transition between the most mobile section of the spine and the least mobile section. Another is that this is the site where the powerful muscles and tendons of the upper limbs have their origin.
The middle thoracic spine is an important transitional region, because this is where the cervical erector spinae muscle ends and the lumbar portion of the muscle begins. Around T5, therefore, the apex of the thoracic curvature of the spine, is the weakest point of the muscles of the back.
All transitional regions are rich in anomalies. There may be rudimentary ribs at T12 or lumbar ribs at L1; cervical ribs at C7 or enlarged transverse processes at C7 are quite common. It is rare, on the other hand, for the first rib at T1 to be absent. The uncinate process at C7 may sometimes be absent on one or both sides.
The ribs
The ribs articulate with the vertebrae at the costovertebral and costotransverse joints. The head of the rib articulates with the superior border of the body of the corresponding vertebra and with the inferior border of the next vertebral body above. The tip of the head of the rib (crista capituli) is attached to the intervertebral disk by ligaments. The third rib therefore articulates with the bodies of T2 and T3, and is attached to the T2 intervertebral disk. Exceptions to this rule are the first rib, which articulates exclusively with the body of the first thoracic vertebra, and the last two floating ribs, which are attached simply by a syndesmosis to the rudimentary transverse processes of the corresponding last thoracic vertebrae.
Rib movement occurs about an axis running from the head of the rib through the neck of the rib to the costotransverse joint. In the upper thoracic spine, this axis is horizontal in the frontal plane. The movement about this axis causes the thorax to rise and fall and the sternum to undergo a pumping motion. In the inferior thoracic spine, the axis runs in an oblique, laterodorsocaudal direction, and produces a wing-like movement. At the last floating ribs there is no joint, so there will be no motion restriction here. If pain occurs here it is due to muscle attachments, especially that of the quadratus lumborum. The articulation between the ribs and sternum is often painful; this too is usually due to muscle attachments with TrPs in the pectoralis and scalene muscles.
3.4.2. X-ray anatomy of the thoracic spine
X-ray imaging of the thoracic spine demonstrates the structural details less clearly than imaging of the lumbar spine. In the AP view (see Figure 3.20) the vertebral bodies, pedicles, and spinous processes can be clearly seen. The joint spaces are not visible because they lie in the frontal plane; the laminae of the vertebral arches and the superior and inferior articular processes can also not be seen. The spinous processes are angled downward. As a result, from about T4 to T10 the tip of the spinous process is projected onto the body of the next vertebra below.
The characteristic feature of the thoracic spine is the costovertebral joint. The head of the rib can be seen in close contact with the intervertebral disk and, laterally to it, the neck and tubercle of the rib are superimposed on the transverse process. The costotransverse joint space usually runs at a steep angle from dorsocranial to ventrocaudal, so is difficult to visualize much or at all. Sometimes, especially in the lower thoracic region, the joint space runs more dorsoventrally and horizontally, and is then easily seen. In this case the superimposed rib lies approximately on the transverse process.
The first rib articulates only with the first thoracic vertebra. The two last ribs only contact the rudimentary transverse processes of the last thoracic vertebrae. The sternum and sternocostal joints are not generally visualized when the usual technique is used.
In the lateral view (see Figure 3.21) the ribs and structures of the lungs are superimposed on the vertebral bodies and disks. At the vertebral arches this superimposition is still more troublesome. Nevertheless, if the film is technically successful enough to give good visualization, the pedicles and intervertebral foramen are easily seen. The foramen opens ventrally at an angle of approximately 15° to the frontal plane, but there need be little distortion if the lateral projection is set up accurately. The joint space and articular processes are clearly visualized. The ribs are superimposed on the laminae and the greater part of the spinous processes, although the tips of the spinous processes can be seen if the image is good. The superior portion of the thoracic spine (approximately above T3) is completely hidden in the lateral projection and can only be demonstrated using oblique views or by tomography.
It can sometimes be difficult to identify which thoracic vertebra is which in the lateral view, as T1 cannot be seen and it is hard to be sure of identifying T12, because the last rib can sometimes be rudimentary. It is therefore useful to look for the inferior angle of the scapula (which is usually at the level of T7), the bifurcation of the trachea (approximately at T5), the arch of the aorta (level with T4), and the dome of the diaphragm (usually level with T10).
3.4.3. Evaluating functional aspects
The curvatures of the spine are important here as they are in all sections of the spinal column. Scoliosis and increased kyphosis are the most frequent findings. It is always useful to know whether the curvatures are in static equilibrium. For this, the films must be taken under static conditions. It is important to note that the greater the curvature, the less the mobility and the greater the stability. Conversely, if the curve is flat, this indicates hypermobility and a tendency to instability.
Dysfunctions may be associated with rotation, in which a sudden deviation is found in the line of the spinous processes (see Figure 3.20). The asymmetrical position of the spinous process is insufficient on its own to enable a diagnosis of rotation to be made; for this, there must also be a shift in the position of the pedicles in the same direction (see Figure 3.22).
In the lateral view of the thoracic spine it is rare to see shifts between two adjacent vertebrae, or a lordotic or kyphotic deviation between neighboring vertebrae in cases of simple dysfunction. Kyphotic deformity, on the other hand, whose cause is morphological, does frequently occur here in the context of juvenile osteochondrosis (Scheuermann’s disease), following a traumatic compression fracture, or as a consequence of osteoporosis.
Dysfunctions of the ribs can be recognized by changes in the spaces between them.
3.5. The cervical spine
The cervical spine is the most mobile section of the whole spinal column; it is also the most vulnerable. This region is the richest in afferent proprioceptive nerves, which exercise an effect on the entire locomotor system. Dysfunctions here are therefore particularly important, and their treatment is correspondingly rewarding.
3.5.1. X-ray technique
A suitable and effective technique is essential in order to obtain pictures that can be evaluated for function. The usual technique, which usually produces very poor visualization of the upper portion of the cervical spine in the lateral view and does not visualize it at all in the AP one, is not even adequate for morphological diagnosis and is completely useless for the evaluation of function.
The Sandberg–Gutmann technique (Sandberg 1955) (see Figure 3.23 A) best meets the requirements for a successful image in the AP projection. For this, the patient is supine. Positioning is done using the following technique, so as to represent the patient’s posture accurately: the patient begins by sitting on the X-ray table, intergluteal cleft exactly on the midline of the table and legs extended, symmetrically side by side. Only then is the patient requested to lie down. Ask your patient to do so without use of the arms, looking straight ahead and in a completely natural manner. To check that the finding is representative rather than chance, this procedure may be repeated. If the head regularly deviates to one side, this must not be corrected; instead you should adjust the cassette and the X-ray tube accordingly. If you correct the head position you might either correct or artificially produce cervical scoliosis and at the same time induce axis rotation and lateral deviation of the atlas.
The film format used is either 18×24cm or 15×40cm; it can be helpful to include the upper thoracic spine as well. Position the cassette so as to be able to assess the upper margin of the foramen magnum, the front incisors and, caudally, at least T1. This is usually achieved when the upper edge of the cassette is aligned slightly craniad to the patient’s external ear.
Ask the patient to open her mouth as wide as possible and place a cork between her front teeth. The patient should then draw in her chin until the forehead (glabella) and upper lip (filtrum) are on the same horizontal plane. For this, a pillow beneath the head is often necessary, except when the patient is a child.
Now the X-ray tube can be centered. The central ray must be aligned through a point one finger’s breadth below the upper premolars to a point one finger’s breadth above the palpable inferior border of the occiput (posterior margin of the foramen magnum) in the midline. Either a light field indicator or a piece of string running from the center of the focal spot to the appropriate position on the patient’s face can be used for this alignment. The X-ray tube is then aligned so that the line of the central ray is an extension of that of the string (or light) (see Figure 3.23 A). For edentulous patients, the central ray is aligned through a point one finger’s breadth below the maxilla to the border of the occipital squama, and in infants who do not yet have teeth, from the inferior border of the maxilla to the border of the occipital squama. Finally, correct any rotation of the patient’s head since this would make the film hard to evaluate.
This projection can also be taken with the patient seated, aligning the beam in an analogous manner. This approach is slightly more difficult but has the advantage of being performed under static conditions. Nevertheless, there can be an advantage in having taken the AP projection with the patient supine and the lateral one with the patient seated, if the findings reveal discrepancies. It is always possible then to perform an additional AP view taken in the sitting position.
One objection to the open-mouth technique is that the mandible is superimposed on the mid-cervical spine. This problem can be avoided if the patient rapidly opens and shuts her mouth while the film is being taken; in this way the shadow of the mandible is blurred. The risk in this case is that there will be slight associated movement of the head, which might cause blurring of the image at the craniocervical junction.
For the lateral view the patient is seated relaxed in front of a vertical stand (see Figure 3.23 B). The film may be 18×24cm or 24×30cm, and must be placed so that the image demonstrates the cranial base as far as the sella turcica, and the cervical spine down to the cervicothoracic junction. In subjects with very tapering shoulders it will also be possible to include the first thoracic vertebra. The patient’s gaze should be fixed on a distant object at eye level, maintaining the hard palate horizontal. Take care that there is no inclination or rotation of the patient’s head, so that the two mandibles are exactly superimposed. This is necessary for accurate assessment of the film.
Do not align the central ray on the mid-cervical region as is usually done, but on the tip of the mastoid process. The light field indicator can be used for this. It is best to use a film-focus distance of 1.5 meters or more. This produces an undistorted image of the cranial base and the entire cervical spine and also evens the exposure; the density of the cranial base means that it demands more irradiation than the cervical spine.
X-ray films of the cervical spine that do not provide good visualization of the atlanto-occipital and atlantoaxial joints and cranial base and of the cervicothoracic junction are inadequate for the evaluation of function.
3.5.2. Assessment of X-ray films
The technique described here provides sufficient criteria to evaluate all the images and to repeat them for comparison, even if all structures are asymmetrical. In the AP projection (see Figure 3.24) the first task is to make sure that both occipital condyles, the atlas, and the axis are well visualized, and whether it is possible to look into both foramina transversaria (which give passage to the vertebral artery). At the caudal end, ensure that at least the first thoracic vertebra is included in the image. Next the centering should be checked, to make sure that the image is straight. If the positioning is correct, the middle point between the incisors should be vertically in line with the middle of the dens of the axis and of the occipital squama. The tip of the chin will be projected onto the middle of the cervical spine, which must run symmetrically between the two rami of the mandible.
The position of the mastoid processes should also be symmetrical. In order to evaluate the inferior part of the cervical spine, it is necessary to ensure that the superior thoracic spine is not rotated.
In the lateral projection (see Figure 3.25), first ensure that the cranial base, including the sella turcica and hard palate, can all be seen. If possible the cervical spine should be shown as far down as C7, although this is often not possible in heavily built patients or those with high shoulders. Check that the alignment is perfect before beginning to evaluate the findings on the film. It is particularly important that the line of the hard palate should be horizontal. Fineman et al (1963) showed that a difference of only 10° in inclination of the head is sufficient to change lordotic to linear posture, or even to change it to the extent that lordosis becomes kyphosis. It is important that the two halves of the mandible should overlie each other exactly. If the vertical borders of the rami appear projected side by side, the head is rotated to one side. Projection of the horizontal line of the mandible one above the other indicates that the head is inclined to one side. Another sign of rotation is if the shoulders are projected apart.
The oblique projection (for which the patient adopts a position turned at an angle of 45°) gives the clearest imaging of the intervertebral foramina. This projection is indicated especially for radicular syndromes and vertebral artery syndrome. As recommended by Gutmann (1956), this projection should be taken with the patient’s head in retroflexion, because this more clearly displays any narrowing of the intervertebral foramen. It is also recommended to take it not with the patient’s back to the cassette, but with the patient facing toward it (see Figure 3.26).
3.5.3. Functional anatomy of the cervical spine
The cervical spine has two distinct sections: the atlanto-occipital and atlantoaxial joints, and the rest of the cervical spine from C3 to C7; nevertheless it is a functional unity, since all the movements it performs originate at the atlanto-occipital and atlantoaxial joints, these movements being anticipated by eye movements. The anatomical description will accordingly be treated in separate sections. The function of the cervical spine will then be dealt with as a whole.
Functional anatomy of C3–C7
As in other parts of the spinal column, the degree of mobility in the cervical spine corresponds to the thickness of the intervertebral disk, which is greatest in the segments C3/C4 and C4/C5. The characteristic feature of the cervical spine is the raised lateral margins of the vertebral bodies, the uncinate processes. The disk therefore thins laterally, with the consequence that thinning of the disk brings about contact in this lateral region. This is where early degenerative changes occur, tending to form uncovertebral joints (neoarthroses). The position of these is very close to the intervertebral foramen. The significance for cervical function is that the shape of the vertebrae with their lateral margins limits side-bending and favors ante- and retroflexion.
The intervertebral joints are almost parallel, inclined at an angle of about 45° from ventrocranial to dorsocaudal. The angle is greatest at C2/C3. In this segment the joints are frequently not parallel but arranged as if on the circumference of a cylinder with its center behind the vertebra; it is therefore not pathological if the joint space at C2/C3 is less clearly delineated than in the other segments of the cervical spine in the lateral projection. As a general principle, laterally the joints in the lordotic section of the cervical spine are inclined slightly posteriorly and in the kyphotic section slightly anteriorly. According to Janda (2002) the transition from the one to the other occurs roughly at C3/C4. The inclination of the intervertebral joints in the sagittal plane means that side-bending produces rotation, the two kinds of movement being coupled. Similarly, rotation brings about side-bending, always to the same side (see Figure 3.30 A and B).
During anteflexion, a slight ventral shift of the cranial partner vertebra relative to its caudal neighbor is often observed. In retroflexion there is a slight caudad shift. This too is associated with the inclination of the joints. Penning (1968) describes this motion as a rotation of the upper vertebra relative to the lower one, around a frontal axis in the dorsal part of the vertebral body. Experience shows this motion to be physiological, as long as it occurs evenly in the motion segments of the cervical spine. It is regularly seen in young subjects with good mobility. If it is not observed in less mobile, older patients, this absence is not pathological. The shift is greatest between C2/C3 (see Figure 3.32 B and D) where the range of motion is least in adulthood.
It is also important to note that the cervical spinal canal lengthens considerably during anteflexion, shortening during retroflexion. This produces a significant movement of the meninges and dural sheaths of the nerve roots relative to the spinal cord, which becomes longer and thinner in anteflexion and shorter and thicker in retroflexion.
The course of the vertebral artery also has an important role. This enters its bony canal at C6, passing upward through the intervertebral foramina in close contact with the intervertebral joints and uncinate processes almost at right angles to the course of the nerve roots. Therefore, as the intervertebral foramen (canal) narrows in retroflexion, this may affect both the nerve root and the vertebral artery.
Functional anatomy of the craniocervical junction
In order to understand function it is important to look first at the anatomy of the individual articular structures and ligaments. The superior articular surfaces of the atlas run obliquely from dorsolateral to ventromedial. The facets are oval in shape, converging anteriorly like a section of the surface of a sphere with its center located above both articular surfaces. The most important movement of the atlanto-occipital joint is ante- and retroflexion of about 16° (see Figure 3.27). Gliding of the occipital condyles occurs in the dorsal direction during anteflexion and in the ventral direction during retroflexion. Very slight rotation is also possible, which Jirout (1981) was able to demonstrate as a synkinetic movement during side-bending of the head. Slight side-bending is also possible, coupled with rotation in the opposite direction.
 |
| Figure 3.27 |
The atlantoaxial joint is made up of the articulation between the anterior arch of the atlas and the dens of the axis, between the dens and the transverse ligament of the atlas with its articular cartilage, and between the lateral mass of the atlas and the body of the axis. Its main function is that of rotation, and it also performs ante- and retroflexion. All these articulations participate in rotation. On one side the lateral mass of the atlas glides ventrally on the body of the axis, rising as it does so, while on the other side the lateral mass of the atlas glides dorsally and downward. The rotation is limited by the joint capsules and the strong alar ligaments, which have their attachment to the margins of the foramen magnum. The average range of motion of this rotation (our own results) is 25° in each direction, although we have found a range of motion up to as much as 40° (see Figure 3.28). Dvorák, using CT, even obtained average measurements of 41.1° to the right and 44° to the left. Huguenin, on the other hand, in measurements made using CT, obtained figures corresponding to our own.
Ante- and retroflexion between atlas and axis is considerable, amounting on average to 15°. The anterior arch of the atlas slides up and down on the dens of the axis, while the atlas itself performs a tipping motion (see Figure 3.29).
Kinematics of the cervical spine
Rotation
Rotation begins between the atlas and the axis and the movement takes place mainly there until the range of motion in this segment is exhausted, that is to about 25° to each side. Up to this point the head rotates about a vertical axis in the horizontal plane. From this point onwards the other segments participate in succession in the rotation movement, from C2/C3 to C6/C7, as long as the cervical spine is in a position of slight kyphosis. If the neck is completely upright the cervicothoracic junction also rotates, down to and including T3. In passive rotation there is still some slight additional rotation between the atlas and the occiput. The moment rotation below C2 begins, the inclined course of the intervertebral joints brings about simultaneous lateroflexion to the same side unless the subject deliberately resists this synkinesis.
Side-bending
Side-bending can be studied only by X-ray, hence the decision to deal with it under functional radiographic studies (see Figure 3.30). Like rotation, it begins at the atlanto-occipital and atlantoaxial joints. This can be demonstrated by looking at the craniocervical region in passive side-bending (‘side-nodding’). This shows that side-bending starts with rotation of the axis relative to the atlas. At the same time we find a synkinesis in which the atlas shifts relative to the occipital condyles and C2 in the direction of the side-bending (see Figure 3.30 C).
During this side-bending the cervical spine rotates, maximum rotation occurring at C2. Jirout (1968) demonstrated that this rotation is absent in the lower cervical spine during side-bending to the right, but during side-bending to the left it continues down into the upper thoracic spine. He explains this as being due to the stronger pull of the muscles of the shoulder girdle on the right side, whose attachment to the spinous processes exerts a pull to the right and so brings about left rotation. This combination of side-bending and rotation is consistent with the positioning of the intervertebral joints, although this cannot be the true cause, as is usually thought, because the side-bending originates at the axis. This rotates even with the slightest side-bending, followed by the other segments. If rotation of the axis does not take place, there is no rotation of the rest of the cervical spine (see Figure 3.47 B).
According to Jirout (1968), the forces that bring about axis rotation are the product of side-bending of the head (see Figure 3.31). Side-bending of the head involves rotation of the head about a sagittal axis at the level of the root of the nose. This creates a pull on the spinous process of the axis, which causes rotation of the axis with simultaneous tipping in the sagittal direction. This tipping motion in the sagittal plane, which takes place both in side-bending and in rotation, is, according to Jirout (1968), the joint play of the cervical spine. The sideways shift of the spinous process can easily be palpated, and occurs as soon as the subject’s head inclines to the side even to a slight degree. Interestingly, Gaymans (1973) demonstrated that a shifting of the spinous process of the axis (rotation of the axis) occurs even on mere leaning against slight resistance in the neutral position and with minimum pressure, thus simply through the pull of the muscles. He obtained radiological evidence of this.
Rotation of the axis on side-bending of the cervical spine is not simply the combined result of rotation movements of the individual vertebrae, due to the inclination of the zygapophysial joints of C7, C6, etc.; on the contrary it results from the inclination of the head itself, in which the head rotates about a sagittal axis and exerts a pull on C2. If there is no rotation of the axis, there is also no rotation of the other vertebrae of the cervical spine during side-bending. At the same time there is a tipping motion in the sagittal plane, so that the movement occurs in a coupled way in all three planes.
 |
| Figure 3.31
Mechanism of side-bending of the cervical spine according to Jirout (1968). During side-bending the head inclines about a sagittal axis (x) passing through the anterior cranial fossa. The diagram shows how the cranial base, together with the occipital condyles, shifts relative to the atlas in the opposite direction to the side-bending, and how the axis, together with the lower cervical vertebrae, is brought into rotation in the direction of the side-bending, while the axis is tilted ventrally by a cranial pull on the spinous process.
|
Anteflexion and retroflexion
Two distinct kinds of anteflexion should be distinguished. The first is a nodding movement limited to the atlanto-occipital and atlantoaxial joints. The other is a forward flexion involving the entire cervical spine. This distinction does not exist for retroflexion. The two kinds of anteflexion of the head are to some extent mutually exclusive. If we draw the chin in toward the chest (forward nodding), this usually inhibits full anteflexion. If we drop the head far forward in anteflexion, this renders nodding more difficult except in hypermobile subjects. The explanation lies in the tipping mechanism of the atlas.
The following changes can be observed in X-ray studies of anteflexion and retroflexion (see Figure 3.32):
• In the erect posture (see Figure 3.32 A), the atlas is already in a position of slight retroflexion with an average angle of about 5°.
• During forward nodding (see Figure 3.32 B), anteflexion of the atlas increases only slightly. This movement causes an anteflexion of the head (the plane of the foramen magnum); in the erect posture the head had been in a position of anteflexion relative to the atlas. In this position the atlanto-occipital and atlantoaxial joints are in maximum anteflexion.
• In maximum anteflexion (see Figure 3.32 C), the cervical spine is almost horizontal; there is a proportional slight ventral shift of the individual cervical vertebrae up to C2. Anteflexion between C1 and C2 is at its maximum. In contrast to the situation in the erect posture and in forward nodding there is now retroflexion of the head relative to the atlas, which can be greater than in retroflexion with the subject seated. Anteflexion of the atlanto-occipital and atlantoaxial joints is thus reduced as compared to forward nodding, closer to the degree of anteflexion in the erect posture. Consequently the angle between the clivus and dens is usually the same with the head erect as during maximum anteflexion. There is also a forward shift of the clivus (basion), together with the atlas, relative to the tip of the dens.
• In maximum retroflexion with the subject seated (see Figure 3.32 D), there is maximum retroflexion of the atlas (relative to the axis). Retroflexion of the cranium, on the other hand, is seldom at its maximum (it is usually very little greater than during anteflexion of the head). Here, too, we see a proportional dorsal shift of the individual cervical vertebrae from C7 to C2 and of the clivus and atlas relative to the tip of the dens.
• In passive retroflexion with the subject side-lying and so without the effect of gravity (see Figure 3.32 E), there is now maximum retroflexion of the head relative to the atlas, while retroflexion of the atlas relative to C2 is even less than in the erect posture. There is no dorsal shift of the basion with the atlas.
The mechanism underlying these processes, which appear paradoxical at first sight, has been termed the tipping of the atlas. It is based on the following (see Figure 3.33): in anteflexion with the subject sitting, as soon as the center of gravity of the head shifts ventrally, the occipital condyles exert pressure on the anterior, rising part of the concave articular surface of the atlas. This causes the atlas to tip forward and downward. There is an analogous process in retroflexion with the subject sitting: the atlas tips backward. This does not happen, however, with the subject lying on one side, which explains why in this case retroflexion of the occiput relative to the atlas attains its maximum.
3.5.4. X-ray anatomy of the cervical spine
Anteroposterior view
The AP view (see Figure 3.34 and Figure 3.35) shows the arc of the anterior margin of the foramen magnum, at the cranial end of the cervical spine. Its superior border is formed by the clivus and its lateral part by the occipital condyles. Beneath the condyles lie the two articulations of the atlanto-occipital joint, meeting at an angle of about 125–130°. Below the condyles, to either side of the dens of the axis, can be seen the lateral masses of the atlas. These are wedge shaped, tapering towards their medial border. Close to this border we often see a medial lucency which should be interpreted as a normal finding. Laterally to the lateral mass, the transverse processes can be seen. It is sometimes possible to see into the foramen transversarium, which gives passage to the vertebral artery. The spindle-like posterior arch (broadest in its medial portion) can be traced from one transverse process to the other. It separates the ‘lateral triangle’ from the lateral mass. Sometimes the anterior arch can also be seen, projected across the tip of the dens.
The inferior contour of the lateral mass forms the superior articular surface of the joint between C1 and C2. At the medial border of the joint facet of the axis there is a tiny notch marking the border of the dens. The tip of the dens usually lies well below the superior border of the foramen magnum. Just below the lateral end of the superior joint facets of the axis is the foramen transversarium. Medial to this foramen, the point-like projection of the pedicles of the axis can be seen. From here can be traced the shadow of the arch of the axis on both sides, through to the spinous process. If there is hyperlordosis it is sometimes possible to see into the spinal canal above the arch of the axis.
Below the axis can be seen the typical cervical vertebrae with their characteristic uncinate process either side. This causes the intervertebral disk to be much higher medially than laterally. Beneath the unciform processes lies the shadow of the point-like pedicles. The spinous processes can be seen in the midline and the lateral contour is formed by the transverse processes. The intervertebral foramen is visible, but less clearly. Rarely, the intervertebral joint space can be seen.
Lateral view
The lateral view (see Figure 3.36) offers an undistorted image of the cranial base and the atlanto-occipital and atlantoaxial joints. The clivus can be followed in its entirety down from the sella turcica to the anterior margin of the foramen magnum (basion) which is situated directly above the tip of the dens. The posterior margin of the foramen magnum (opisthion) cannot always be clearly distinguished from the squama of the occipital bone; it helps to follow the posterior margin of the cervical spinal canal from caudad to craniad. Where the arc-shaped prolongation of this margin meets the occiput is the opisthion.
The mastoid process frequently overlaps the condyle and atlanto-occipital joint; therefore this joint is not always visualized in the lateral view, although it is often clearly seen (see Figure 3.37).
 |
| Figure 3.37 |
The plane of the foramen magnum can be established by drawing a line from the basion to the opisthion on the posterior margin of the foramen magnum. The plane of the atlas corresponds to a straight line through the middle of the anterior and posterior arches of the atlas. The plane of the axis lies on a straight line linking the inferior border of the transverse processes and the inferior border of the spinous process. These lines are used to determine the ante- or retroflexion of the occiput, atlas, and axis (see Figure 3.25 and Figure 3.38).
 |
| Figure 3.38 |
The dens of the axis is projected just behind the anterior arch of the atlas. The tip of the dens is usually at the same level as the superior border of the anterior arch of the atlas. It should not be much above the palato-occipital line; this is the case in basilar impression.
In this section of the spinal column, unlike the others, the pedicles and transverse processes are projected onto the vertebral bodies in the lateral view but not in the AP view, because here the spinal canal is wider than the vertebral bodies. The superior border of the transverse processes lies slightly above the superior end-plate of the vertebral bodies, which can cause them to appear somewhat blurred. In the lower cervical spine the shadow of the transverse processes lies more in the dorsal direction and in the superior cervical spine more ventrally; at C2 the position of this shadow of the transverse process is such that its anterior border overlies the anterior border of the vertebral body.
The shadows of the articular processes and joint spaces are projected behind the vertebral bodies. If the projection is well executed, all that can be seen is a lucency, showing that the joints are essentially parallel. This need not be so at C2/C3, where it can be quite normal to see some fuzziness of outline. The posterior margin of the spinal canal corresponds to a line linking the bases of the spinous processes (posterior border of the vertebral arch) – a rule that thus also applies to the atlas, which does not have a spinous process. If, however, this shadow is absent at the atlas, this is a sign of spina bifida atlantis, a frequently-found anomaly.
3.5.5. Evaluation with respect to functional implications
The most characteristic disturbance of statics in the cervical region is the forward-drawn posture (see Figure 3.39). Even when statics are normal, the centre of gravity of the head is slightly in front of its support, so that electromyographic studies reveal a slight degree of muscular activity in the nuchal muscles even with the subject in normal erect posture. As soon as there is any forward inclination (not flexion!), whether of the entire body or of the neck alone, tension can immediately be palpated in the muscles of the back of the neck. The forward-drawn position therefore creates overload of the cervical spine and compensatory hyperlordosis at the atlanto-occipital and atlantoaxial joints, and tension in the short extensor muscles of the neck.
In order to demonstrate the patient’s natural posture radiographically, lateral projections should be taken with the subject seated in a relaxed manner, in a backless chair, as described by Gaizler (1973). It is important to ensure that the patient remains relaxed, with gaze fixed on an object at eye level, so that there is no anteflexion of the head despite the natural posture. We took projections of a group of 50 patients with the patients in erect posture (kneeling), and sitting both upright and relaxed. Whereas with the subject sitting upright the external auditory meatus was projected almost exactly above the anterior border of C7, in the erect posture it was 7mm in front of C7, and sitting relaxed it was projected forward by 16mm; in individual cases even by 5cm. This was particularly the case where a patient’s relaxed sitting position involved lumbar kyphosis.
In addition to disturbances of statics, localized irregularities can be observed. Examples of these are slight relative shifts in neighboring vertebrae or local lordotic or kyphotic deviations. In the craniocervical region the atlas may be in a position of ante- or retroflexion in relation to the axis. The older expressions ‘atlas superior’ or ‘atlas inferior,’ which were adopted by chiropractors, are less appropriate because they refer to the position of the atlas relative to the occiput rather than the axis, whereas the criterion being assessed in the rest of the spine is always the position of the upper of two vertebrae relative to the one below it. The tipping of the atlas means that the atlas is usually in a slightly retroflexed position if there is cervical lordosis, with the occiput in anteflexion; if the posture is kyphotic the atlas would be in anteflexion and the occiput in retroflexion (see Figure 3.33, Figure 3.39 and Figure 3.40).
 |
| Figure 3.39 |
Other frequent findings are the rotation of several vertebrae (see Figure 3.46) and, in the region of the atlanto-occipital and atlantoaxial joints, lateral shifting, an asymmetrical position of the condyles relative to the atlas, and of the atlas in relation to the axis. This is often described as a shift of the atlas to one side relative to the condyles and to the axis, which is not quite appropriate: the description should always be given in terms of the upper element relative to the lower. The description in this case would not be of the atlas to the right relative to the condyles and axis, but of the atlas to the right relative to the axis, and the condyles to the left relative to the atlas (see Figure 3.41, Figure 3.42 and Figure 3.43).
Isolated rotation of the atlas in relation to both the occiput and the axis is fairly uncommon. The joint space between atlas and axis is narrower on the side of rotation, the lateral triangle of the lateral mass becomes larger, the center of the posterior arch is shifted in the opposite direction to the rotation, and the lateral mass becomes larger on the side opposite to rotation.
Much more frequent than rotation of the atlas is axis rotation in neutral posture (see Figure 3.44). A 5° or occasionally even 10° rotation of the axis is not unusual. Interestingly, the rotation of the axis is caudally transmitted, down to the rest of the cervical vertebrae and even down as far as the cervicothoracic junction, particularly when rotation is to the left. This can happen even in the simple case of lateral deviation of the spinous process. The mechanism clearly seems to be the same as that discussed in connection with side-bending, which brings about left rotation of the lower cervical spine and cervicothoracic junction.
The characteristic features of axis rotation in the AP view are the deviation and position of the pedicles and the spinous process to that of rotation. The foramen transversarium widens on the side of rotation and the joint space narrows on the opposite side.
Rotation of the other cervical vertebrae is characterized not only by the deviation of the spinous process and rotation of the pedicles to the opposite side, but also by distortion of the unciform processes (see Figure 3.45). In the lateral view, the structures that usually overlap are projected apart. This applies particularly to the joint spaces, together with the articular processes and transverse processes. At C2 one transverse process is projected in front of the vertebral body (see Figure 3.46).
An important sign of static disturbance is discrepancy between the AP view taken with the patient supine and the lateral view with the patient sitting, in particular if there is rotation in the view taken sitting and none at all in the AP view with the patient supine. The cause may be an oblique plane below the cervical spine.
3.5.6. Movement studies
Radiographic movement studies are used to investigate restrictions and hypermobility. X-rays are taken in ante- and retroflexion and side-bending. Rotation is less studied by this method because interpretation is difficult.
The physiological reaction of the cervical spine during side-bending has been described in Section 3.5.3. The study of side-bending is useful in the diagnosis of movement restrictions. We find that if there is no rotation of the axis, there will be none in the rest of the cervical spine (see Figure 3.47). Even if, on side-bending, an asymmetrical spinous process of the axis fails to reach any further than the midline, the rest of the cervical spine will not rotate. This demonstrates that the rotation is transmitted through the spinous processes in a caudal direction. Lack of rotation in the lower cervical spine does not in any way impair rotation above the restriction (Jirout 1972) (Figure 3.48).
Although lateral shifting of the atlas occurs in side-bending, this shifting can sometimes be absent without implying any movement restriction, especially if there is marked asymmetry. More importantly, the shifting may still be seen in the radiographic image even in cases where there is restriction. If there is restriction blocking axis rotation, no side-bending occurs at the atlanto-occipital and atlantoaxial joints (see Figure 3.49). This is in keeping with the fact that in cases of atlas assimilation, side-bending at the craniocervical junction occurs in the normal way.
This raises the question as to whether restriction between occiput and atlas on side-bending can be demonstrated radiographically at all. We have shown this to be possible (Lewit & Krausová 1967) with the head rotated to the side, locking the atlas/axis motion segment. This is necessary to obtain an accurate diagnosis.
It is not usually difficult to demonstrate a restriction of side-bending between the atlas and axis. When this is done, rotation is (also) seen to be blocked (see Figure 3.47 and Figure 3.49). The radiological evidence of restriction in the other motion segments of the cervical spine is much more difficult to achieve. According to Jirout (1971) side-bending is accompanied by slight synkineses in the sagittal plane, consisting of ante- and retroflexion movements that can be recognized by a change in the position of the spinous processes relative to the vertebral bodies. Comparison of the films taken before and after manipulation found a more marked reaction of these synkineses in restrictions than actual side-bending as seen radiographically.
To summarize:
• Lateroflexion of the head against the cervical spine (side-bending; ‘side-nodding’) is mainly performed by means of rotation of the axis relative to the atlas. Normalization of side-bending at the atlanto-occipital and atlantoaxial joints also normalizes this rotation.
• Lateroflexion between occiput and atlas can be established radiographically and clinically only if the more mobile segment (C1/C2) is locked, that is if the head and atlas are rotated by at least 45°. The movement restriction between occiput and atlas does not affect side-bending in the frontal plane or the synkinesis between occiput and atlas during side-bending in the sense of a lateral shift accompanied by simultaneous rotation of the axis.
• Ante- and retroflexion is the movement most frequently examined by X-ray. The disadvantage of this examination from the point of view of manipulation therapy is that this is the movement most frequently and preferentially performed and so the least susceptible to dysfunction. Hypermobility, on the other hand, is more readily revealed here. This can reveal increased shift between neighboring vertebrae, increased lordosis or kyphosis between neighboring vertebrae, and the following signs of hypermobility at the craniocervical junction:
– Laxity of the transverse ligament of the atlas and a widening of the joint space between the anterior arch of the atlas and the dens of the axis, especially the superior part (see Figure 3.50). As a consequence the basion also shifts anteriorly. During anteflexion the distance between the anterior arch of the atlas and the dens and the angle between the clivus and the dens decreases. This happens not only on forward-nodding, but also anteflexion (see Figure 3.51).
– Hypermobility between the occipital condyles and the atlas without laxity of the transverse ligament of the atlas can be recognized by a shift of the basion and opisthion in relation to the dens of the axis (see Figure 3.52).
3.5.7. Morphological changes
It is not the task of this book to deal in detail with morphological and structural changes; nor is it necessary to do so, since this field forms the subject of textbooks of radiology and orthopedics. Therefore only certain aspects, the limited number of those that are particularly important from the point of view of manual medicine, are touched on here.
Anomalies
Block vertebrae
Block vertebrae lead to a compensatory hypermobility in the neighboring segments. The coalescence may be complete or partial, or sometimes simply consist of a hypoplastic intervertebral disk, in which case the vertebral bodies adjacent to the hypoplastic disk are narrower (see Figure 3.53). This occurs because the adjacent end-plates – between which the hypoplastic disk lies – are also the zone of growth. This anomaly could easily be confused with the consequences of childhood rheumatoid arthritis (Still’s disease). The difference lies in the obliteration of the joints, while the vertebral arches and spinous processes are normally developed.
Cervicothoracic transitional vertebra
A transitional C7 cervicothoracic vertebra with a very large transverse process or with a cervical rib is another frequent anomaly. There may also be an absence of the unciform process on one or both sides. A transitional T1 vertebra is however rare.
Spinal canal stenosis
A narrow spinal canal is particularly important clinically, because it is the most important cause of cervical myelopathy. From the practical point of view in diagnosis it is more helpful to look at the change in the proportions of the individual anatomical structures than to measure the sagittal diameter of the spinal canal; the proportions of the structures can be seen at first glance. Normally, in the cervical spine, the spinal canal is wider than the vertebral bodies. In spinal canal stenosis this is not so; also (if there is no rotation in the radiograph) the articular processes overlie the entire width of the spinal canal (see Figure 3.54).
Basilar impression
As a region of transition, the craniocervical junction, the region of the atlanto-occipital and atlantoaxial joints, is the site of many anomalies. Probably the most important of these is basilar impression (see Figure 3.55), which is the result of hypoplasia of the basiocciput. In this condition the occipital part of the clivus is shortened and therefore the dens axis appears as if shifted into the foramen magnum, so as to lie above the palato-occipital line in the lateral view (see Figure 3.55 A). In the AP view the dens can be above the occipital condyles, placing it well above the line between the mastoid processes and digastric muscles (see Figure 3.55 B). At the same time the foramen magnum may be narrower than usual, unless there is also an Arnold–Chiari malformation, in which case displacement of the tonsils of the cerebellum below the foramen magnum has the effect of widening it. These changes can cause syndromes associated with compression of the medulla oblongata, similar to those of spinal canal stenosis in the cervical region.
 |
| Figure 3.55
Basilar impression. (A) The lateral view shows hypoplasia of the clivus, and the dens high in the foramen magnum. (B) In the AP view the dens of the axis is again seen in a high position. (C) Diagram: a, sphenoid part of the clivus; b, occipital part of the clivus; c, palato-occipital line; d, distance (according to Klaus 1974) of the dens of the axis from a line joining the tuberculum sellae and the internal occipital protuberance; e, plane of the foramen magnum.
|
Frequently basilar impression is accompanied by hypoplasia or assimilation of the atlas to the occipital bone and its condyles. Less frequently there can be a block vertebra involving coalescence of the axis with a lateral mass of the atlas.
All the anomalies listed here are frequently asymmetrical, so that lateral displacement of the atlas and also rotated positions of the axis can be found simultaneously. In addition there can also be hyperlordosis. It is therefore little wonder that these anomalies often also lead to dysfunctions which in turn cause pain.
Hypoplasia of the dens of the axis
Hypoplasia of the dens or especially the os odontoideum leads to pathological instability (see Figure 3.56). Another anomaly deserving of mention is reclination of the dens (Gutmann 1981), which results in retroflexion of the atlas and therefore places increased strain on the transverse ligament of the atlas during head anteflexion.
Degenerative changes
Degenerative changes can be of clinical significance, especially if they affect the intervertebral foramen, if they are closely associated with the nerve root and the vertebral artery, or if they cause additional narrowing of an already narrow spinal canal. These changes mainly develop in the region of the uncinate processes when there is thinning of the disk, bringing the uncinate processes into close contact with the body of the vertebra above. This can lead to the formation of uncovertebral joints (neoarthroses) and osteophytes.
Degeneration of the articular processes also has an effect on the intervertebral foramina. Arthroses of the zygapophysial joints often occur as a consequence of their horizontal position, whether this has come about as an anomaly or in the case of hyperlordosis. In such cases the joint facets, rather than the end-plates of the vertebral bodies, become the weight-bearing structures. This causes a broadening and condensation of these joints, and they can therefore be clearly seen in the AP view (see Figure 3.57) as well as the lateral view.
Finally, the significance of a divergent course of the paired joints in the cervical spine needs to be highlighted. This change can clearly be seen in a well-centered lateral view. It causes rotation of the upper of two neighboring vertebrae, relative to the caudally adjacent one, during retroflexion, and consequent narrowing of the intervertebral foramen on the side of the rotation (see Figure 3.58).
