Setting the pelvis square

This is an important preliminary step. Determine from the position of the anterior superior iliac spines whether or not the pelvis is lying square with the limbs (Fig. 17.1). If it is not, an attempt is made to set it square. If this is impossible it means that there is incorrectable adduction or abduction at one or other hip (or, rarely, a severe and rigid curvature of the spine): in that event the fact that the pelvis is tilted should be noted and borne in mind during the subsequent steps of the examination.

Fig. 17.1 First step in the clinical examination of the hip: determining the lie of the pelvis.

Measuring the length of the limbs

Methods of measuring the lower limbs are often confusing to the uninitiated, but it is important that they should be properly understood. Accuracy in measurement is of more than academic significance; it is of practical importance when corrective operations or adjustments to the shoes are contemplated. Limb length can be measured clinically within an error of one centimetre. If greater accuracy is needed, radiographic measurement (scanography) is recommended.

It is necessary to measure, first, the real or true length of each limb. Secondly, it is necessary to determine whether there is any ‘apparent’ or false discrepancy in the length of the limbs from fixed pelvic tilt (Fig. 17.2). Whereas it is always necessary to measure the true length, it is necessary to measure ‘apparent’ discrepancy only when there is an incorrectable tilt of the pelvis.

Fig. 17.2 ‘Apparent’ or false discrepancy in limb length is caused entirely by incorrectable lateral tilting of the pelvis, which effectively abducts one hip and adducts the other hip A. If the pelvis is square with the limbs there can be no ‘apparent’ discrepancy in limb length B.

Measurement of true length. Ideally it would be desirable to measure from the normal axis of hip movement – that is, the centre of the femoral head – but since there is no surface landmark at that point it is impracticable to do so clinically. The measurement is therefore taken from the nearest convenient landmark – namely, the anterior superior spine of the ilium. Distally, measurement is usually made to the medial malleolus.

It should be noted that the anterior superior spine is well lateral to the axis of hip movement. This is of no consequence if the angle between limb and pelvis is the same on each side. But it will render the measurements fallacious if the angle between limb and pelvis is not the same on each side. This will be understood best by reference to Fig. 17.3A. It will be seen that abduction of a limb brings the medial malleolus nearer to the corresponding anterior superior spine, whereas adduction of the limb carries the medial malleolus away from the anterior superior spine. Thus if measurements are made while the patient lies with one hip adducted and the other abducted (a common posture in cases of hip disease) inaccurate readings will be obtained: the length will be exaggerated on the adducted side and underestimated on the abducted side.

Fig. 17.3 A Since the anterior superior spine is lateral to the hip joint abduction approximates the foot to it and adduction carries the foot away from it. For this reason measurements of true length, taken from the anterior superior spine, are inaccurate if the angle of abduction or adduction is not equal on the two sides. B Correct way of measuring the true length when there is a fixed adduction deformity of one hip. The other hip must be adducted through an equal angle. (Position of tape measure shown by interrupted lines.)

The rule is, therefore, that to obtain an accurate comparison of their true length by surface measurement the two limbs must be placed in comparable positions relative to the pelvis. Thus if one limb is adducted and cannot be brought out to the neutral position, the other limb must be adducted through a corresponding angle by crossing it over the first limb before the measurements are taken (Fig. 17.3B). Similarly, if one hip is in fixed abduction the other must be abducted through the same angle before the measurements of true length are made.

Fixing the tape measure at the anterior superior spine. A flat metal end (as found on the ordinary tailor’s measure) is essential. The metal end is placed immediately distal to the anterior superior spine and is pushed up against it. The thumb is then pressed firmly backwards against the bone and the tape end together (Fig. 17.4). This gives rigid fixation of the tape measure against the bone and minimises any error in measurement.

Fig. 17.4 Fixing the tape measure at the anterior superior spine.

Taking the reading at the medial malleolus. The tip of the index finger is placed immediately distal to the medial malleolus and pushed up against it. The thumb nail is brought down against the tip of the index finger so that the tape measure is pinched between them (Fig. 17.5). The point of measurement is indicated by the thumb nail.

Fig. 17.5 Taking the measurement at the medial malleolus.

Determining the site of true shortening. If measurements reveal real shortening of a limb it is necessary to determine whether the shortening is above the trochanteric level (suggesting an affection in or near the hip), or below the trochanteric level (suggesting a disorder of the limb bones).

Shortening above the greater trochanter. Tests for shortening above the trochanteric level are: the measurement of Bryant’s triangle, Nelaton’s line, or Schoemaker’s line.

In modern practice these tests are seldom used, since the information they provide can be supplied from simpler clinical observations or more accurately from radiographic measurements. They all depend on comparing the relative distance between the tip of the greater trochanters and the iliac crests. This can be quickly achieved with the patient supine, by using both hands with the thumbs placed on the greater trochanters and the tips of the index fingers on the anterior superior iliac spines. Any discrepancy between the two sides should then become apparent.

Shortening distal to the trochanter. True shortening is sometimes caused by an abnormality below the trochanteric level, such as a congenital defect of development, impaired epiphysial growth, or a previous fracture with overlapping of the fragments. To investigate this possibility individual measurements should be made of the femur (tip of greater trochanter to line of knee joint) and of the tibia (line of knee joint to medial malleolus) on each side and by flexing the knees to 90 ° and observing whether the shortening lies above the knee or below it (Gallenzi test).

Measurement of ‘apparent’ discrepancy in limb length. ‘Apparent’ or false discrepancy in limb length is due entirely to incorrectable sideways tilting of the pelvis (Fig. 17.2A). The usual cause is a fixed adduction deformity at one hip, giving an appearance of shortening on that side, or a fixed abduction deformity, giving an appearance of lengthening. Exceptionally, fixed pelvic obliquity is caused by severe lumbar scoliosis.

To measure apparent discrepancy the limbs must be placed parallel to one another and in line with the trunk. Measurement is made from any fixed point in the midline of the trunk (for example, the xiphisternum) to each medial malleolus (Fig. 17.6).

Fig. 17.6 For correct measurement of ‘apparent’ discrepancy in limb length the limbs must be parallel and in line with the trunk. (Position of tape-measure shown by interrupted lines.) In this example the pelvis is raised on the left, a situation that is commonly due to fixed adduction at the hip.

If there is a discrepancy of true length it must be allowed for when ‘apparent’ discrepancy is determined. As already noted above, there is no need to measure for apparent discrepancy if the pelvis lies square with the limbs, as determined from the position of the two iliac crests.

Examination for fixed deformity

Contracture of the joint capsule or of muscles may cause fixed deformity at the hip, preventing its being placed in a neutral position. Fixed flexion, fixed adduction, and fixed lateral rotation are common in some forms of arthritis.

Fixed adduction deformity. This is detected by judging the relationship between pelvis and limbs. It will already have been noted at an earlier stage of the examination. If fixed adduction is present the transverse axis of the pelvis (as indicated by a line joining the two anterior superior spines) cannot be set at right angles to the affected limb, but lies at an acute angle with it.

Fixed abduction deformity. The angle between the transverse axis of the pelvis and the limb is greater than 90 °.

Fixed flexion deformity. This is determined by a manoeuvre known as Thomas’s test.

Principle of Thomas’s test. If there is a fixed flexion deformity at the hip the patient compensates for it, when lying on the back, by arching the spine and pelvis into exaggerated lordosis, as shown in Fig. 17.7A. This allows the affected limb to lie flat on the couch. To measure the angle of fixed flexion deformity it is necessary to correct the lumbo-pelvic lordosis. This is done by flexing the pelvis (and with it the lumbar spine) by means of the fully flexed sound limb (Fig. 17.7B).

Fig. 17.7 Thomas’s test for fixed flexion deformity. A Flexion deformity masked by arching of spine and pelvis. B Deformity revealed by flexing the sound hip and, by continuing the flexion force, correcting the arching of spine and pelvis.

Technique of the manoeuvre. One hand is placed behind the lumbar spine (between it and the couch) to assess the degree of lumbar lordosis. If there is no lordosis when the affected limb lies flat on the couch there can be no fixed flexion deformity and there is no need to proceed with the test. If there is excessive lordosis, as indicated by arching of the back (Fig. 17.7A), it is corrected in the following way: The sound hip is flexed to the limit of its range. The limb is then pushed further into flexion, thereby rotating the pelvis on a horizontal transverse axis until the arching of the spine is obliterated. During this manoeuvre the thigh of the disordered limb, if in fixed flexion, is automatically raised from the couch as the lumbar lordosis is reduced (Fig. 17.7B). The angle through which the thigh is raised from the couch is the angle of fixed flexion deformity.

Fixed rotation deformity. The most reliable index of the rotational position of the thigh is the patella, which normally points forwards when the hip is in the neutral position. If there is fixed lateral rotation or fixed medial rotation the limb cannot be rotated to the neutral position, with the patella directed forwards. The angle by which it falls short of the neutral when rotated as far as possible is the angle of fixed rotation deformity.

Movements

The accurate determination of hip movements demands much care, because restriction of hip movement is easily masked by movement of the pelvis. It is therefore essential to place one hand upon the pelvis to detect any movement there, while the other guides and supports the limb.

Flexion. The range of hip flexion is best demonstrated by flexing the hip and knee together; not by lifting the leg with the knee straight. Movement of the pelvis is best detected by grasping the crest of the ilium (Fig. 17.8). Only in this way is it possible to distinguish between true hip movement and the false flexion imparted by rotation of the pelvis. The normal range of true hip flexion is about 130 °, but it varies according to the build of the patient.

Fig. 17.8 Testing hip flexion. The right hand supports the limb while the left hand grips the ilium to detect incipient rotation of the pelvis. Hip and knee are flexed together.

Abduction. The limb to be tested is supported by one hand while the other hand bridges the pelvis from anterior superior spine to anterior superior spine (Fig. 17.9). In this way true abduction at the hip can be differentiated from the false abduction that is imparted by tilting of the pelvis. The normal range of true abduction at the hip is 30 ° to 35 ° (more in children).

Fig. 17.9 Testing abduction of the hip. The right hand supports the limb while the left, bridging the two anterior superior spines, is ready to detect tilting of the pelvis. Adduction is tested in the same way.

Abduction in flexion. This is often the first movement to suffer restriction in arthritis of the hip. The patient flexes his hips and knees by drawing the heels towards the buttocks. He then allows the knees to fall away from one another towards the couch (see Fig. 17.11B). The normal range is about 70 ° (90 ° in young children).

Fig. 17.10 A Negative Trendelenburg test. The hip abductors are acting normally, tilting the pelvis upwards when the opposite leg is raised from the ground. B Positive Trendelenburg test. The hip abductors are unable to control the dropping of the pelvis when the opposite leg is raised. The pelvis tilts down instead of upwards.

Adduction. The limb to be examined is crossed over the other limb. Again care must be taken to differentiate between true adduction and the false movement imparted by tilting of the pelvis. The normal range of adduction is about 25–30 °.

Lateral rotation and medial rotation. Judge the range by an imaginary pointer thrust axially into the patella, not by the position of the foot. The normal range both of medial and of lateral rotation is about 40 °.

Extension. Contrary to what has often been written, the range of extension at the hip is nil. Extension of the hip joint beyond the neutral position is prevented by the strong anterior capsule and reinforcing Y-shaped ligament. Seeming backward movement of the thigh is in fact contributed entirely by rotation of the pelvis and extension of the spine, not by extension at the hip joint proper.

Examination for abnormal mobility

In cases of marked instability of the hip longitudinal movement or ‘telescoping’ can sometimes be demonstrated – especially in children with developmental (congenital) dislocation of the hip. To carry out the test the limb is grasped firmly in one hand and alternately pushed and pulled in its long axis, the trunk being steadied by the examiner’s other hand upon the iliac crest.

In infants it is important to examine for dislocation by the click tests of Ortolani and Barlow. These are described on page 344.

Examination for postural stability: the Trendelenburg test

The Trendelenburg manoeuvre is a test of the stability of the hip, and particularly of the ability of the hip abductors (gluteus medius and gluteus minimus) to stabilise the pelvis upon the femur when the subject is standing upon the one leg.

Principle of the test. Normally, when one leg is raised from the ground the pelvis tilts upwards on that side, through the action of the hip abductors of the standing limb (Fig. 17.10A). (This automatic mechanism allows the lifted leg to clear the ground in walking.) If the abductors are inefficient they are unable to sustain the pelvis against the body weight and it tilts downwards instead of rising up on the side of the lifted leg (Fig. 17.10B).

Fig. 17.11 Congenital dislocation of the right hip. A The right lower limb was slightly shorter than the left, as suggested here by the typical extra skin folds in the thigh. B shows the reduced range of abduction of the affected hip – another typical and important diagnostic feature.

Technique. Stand behind the patient. Instruct him first to stand upon the sound limb and to raise the other from the ground. Having thus got the idea of what he is required to do, he should now stand on the affected leg and lift the sound leg from the ground. By inspection, or by palpation with a hand upon the iliac crest, observe whether the pelvis rises or falls on the lifted side. Remember that the limb upon which the patient stands is the one under test. If the pelvis rises on the opposite side (normal) the test is negative (Fig. 17.10A). If it falls, the test is positive (Fig. 17.10B); in other words the abductor muscles are incapable of stabilising the pelvis upon the femur.

Causes of positive Trendelenburg test. There are three fundamental causes:

Sometimes two of these factors may operate together: for instance, in a case of upward dislocation of the hip there may be an unstable fulcrum as well as approximation of the origin of the abductor muscles to their insertion.

Gait

Watch how the patient stands and observe his gait on walking. Note that a patient with an unstable or painful hip prefers to use a stick in the opposite hand, and tends to shorten the period of weight-bearing on the affected limb (‘antalgic gait’). Characteristic gait patterns that are recognised include:

The patient’s ability to negotiate stairs must also be tested. A disability of the hip often precludes the normal rhythm of ascent and descent: on ascending, the foot of the sound leg is advanced first, and that of the affected side is then brought up to it. On descent, the affected leg is put down first and the sound leg is brought down to it.

Extrinsic causes of pain in the hip region

If examination of the hip itself fails to reveal abnormalities sufficient to account for the patient’s symptoms, possible causes outside the hip must be investigated. Attention should be directed particularly to the spine and sacro-iliac joints (including a neurological survey of the lower limbs), to the abdomen and pelvis (including rectal or bimanual examination if necessary), and to the vascular system (state of the peripheral pulses).

Imaging

Radiographic examination. Plain radiographs should include an antero-posterior projection showing the whole pelvis with both hips, and lateral films of each hip separately. It is recommended that the lateral films be obtained by slightly abducting the affected hip and directing the X-ray beam horizontally beneath the opposite flexed thigh. In special cases there is a place for arthrography (that is, radiography after the injection of radio-opaque fluid into the joint). When there is a possibility that the symptoms may be referred from the back radiographs of the spine and sacro-iliac joints must be obtained.

Radioisotope bone scanning. This is of value especially in the diagnosis of inflammatory lesions in or about the hip. It may also be helpful in the early detection of metastatic neoplastic deposits in the pelvis or upper end of the femur.

Computerised tomography (CT scanning) provides clear cross-sectional images of the pelvis or thigh and is useful in special circumstances. For instance, it can show accurately the orientation (degree of anteversion) of the acetabulum or of the neck of the femur. Or it may be used to outline bony or soft-tissue tumours in or about the pelvis or hip (see Fig. 2.3, p. 15).

Magnetic resonance imaging (MRI) is of particular value in showing the extent of soft-tissue changes – for instance in the case of an invasive tumour. It may also allow early detection of bone necrosis in the femoral head.

Ultrasound is now used increasingly in babies and young infants for the detection of developmental dysplasia before ossification of the femoral head allows radiological assessment.

Arthroscopy. Arthroscopic inspection of the interior of the hip is a useful supplementary method of investigation in adults, and it is now used increasingly in diagnosis and treatment.