CHAPTER 8 The thoracic and lumbar spine
Fig. 8.A
The Spine: Anatomical Features
The complex relationships of the components of a typical vertebra may be illustrated by an exploded diagram (shown here after Kapandji). The bony elements comprise the vertebral body (1), composed of cancellous bone covered with an outer shell of cortical bone; the horseshoe-shaped neural arch (2); two articular masses or processes (3) which take part in the facet (interarticular) joints; the transverse processes (4); and the spinous processes (5). When these components are brought together they form a protective covering for the cord (6) and issuing nerve roots (7). The neural arch (2) is divided by the articular processes (3) into pedicles (8) and laminae (9).
Each vertebra articulates with the one above and below by means of the facet joints and the intervertebral discs. Each disc, lying between the hyaline cartilage endplates of adjacent vertebral bodies, is composed of a nucleus pulposus (NP) surrounded by concentric sheets of fibrous tissue (annulus fibrosis) (AF).
Movements between the vertebrae are possible in several planes, and the axes of these movements pass through the approximate centres of the intervertebral discs. At all levels of the spine, flexion (F) and extension (E), and lateral flexion (LF) to both sides are possible. In the thoracic spine, the plane of the facet joints lies in the arc of a circle which has its centre in the nucleus pulposus (CNP); as a result, (axial) rotation (AR) is possible in this part of the spine. In contrast, the orientation of the facet joints (FJ) in the lumbar region is such that rotation is blocked, i.e. virtually no vertebral rotation occurs in the lumbar spine.
As a result of the elasticity of the annulus the nucleus pulposus is under constant pressure, and may (uncommonly) herniate into a vertebral body anteriorly (A), or centrally (Schmorl’s node) (SN). A much more common occurrence is for the annular fibres to tear (as a result of trauma or degenerative changes) so that the nucleus can bulge posteriorly (P) or laterally (L): (’slipped discs’ – central or lateral protrusions). A posterior (central) disc protrusion may affect the cord directly (or the cauda equina in the lower lumbar spine); this may lead to bilateral lower limb signs with or without bladder involvement. With lateral protrusions the neurological disturbance usually results from pressure on one or two nerve roots only, so that the effects are more localised and usually predominate on one side. In the neural canals (NC, circled, top right) the space for the segmental nerves is restricted, and in this region symptoms may be caused not only by disc prolapse but by any other pathology compromising the space available (e.g. arthritic facet joint lipping).
Back Pain
Back pain is one of the commonest and most troublesome of complaints; its causes are legion and an exact diagnosis is often difficult. The disability with which it is usually associated is often severe and prolonged; therapy is often ineffective, and the anxious, impatient and dissatisfied sufferer often resorts to lines of treatment which are unproven, illogical and irrational. In this difficult area it is not possible to provide a guide to pathology and diagnosis which is simple and at the same time comprehensive and foolproof. Nevertheless, it may be helpful to consider this subject under three headings:
In taking a history, examining and investigating a patient suffering from back pain, possible extraspinal causes should be excluded and an attempt should be made to place the patient in one of the three groups described above. Thereafter, and if possible, a more precise diagnosis may be attempted.
Important points in history-taking:
Note that pain radiating into the legs is not necessarily due to nerve root involvement: it seems that irritation of facet joints, ligaments and muscles may produce dull, aching pain in the buttocks and backs of the thighs. In contrast, pain arising from nerve roots is usually sharp and knife-like, and in addition, in the case of the commonly affected L5 and S1 roots, it often extends below the knee to the ankle or foot. In the common situation where there is involvement of one, or at the most two, nerve roots, the whole limb cannot be affected; instead, the area of sensory disturbance should correspond with the relevant dermatome(s); and it should be noted whether paraesthesia occurs within the same restricted territory.
A positive answer to any of these questions will generally necessitate appropriate further investigation. The possibility of an invasive primary tumour or metastatic lesion must always be kept in mind, and examination of the abdomen, rectum, and common sites of primary tumour is wise if there is any likelihood of malignancy.
The spine should then be examined clinically; if the symptoms have remained unchanged over a 2-week period, radiological examination and estimation of the sedimentation rate should be carried out. At this stage any well defined spinal pathology should be detected (such as spondylolisthesis, ankylosing spondylitis, osteitis of the spine etc.). If conditions such as these have been eliminated, the question as to whether the symptoms are due to a prolapsed intervertebral disc should be considered. The history, clinical findings, and plain radiographs of the spine should be in harmony before it is reasonable to make this diagnosis. By the process of elimination, if a diagnosis has not yet been made the patient is likely to be suffering from mechanical back pain: but note that both the history and findings should be in accord with this. If not, caution must be exercised, close surveillance should be maintained, and further investigation may be indicated.
Scoliosis
Scoliosis is primarily a lateral curvature of the spine, but there is often a degree of associated kyphosis. Mathematical analysis of the curves has revealed several distinct patterns, which are dependent on the relative contributions of these two deformities.
In the management of any case, the first and most important decision to make is whether there is any deformity of the vertebrae (structural scoliosis). If the vertebrae are normal (non-structural scoliosis) the deformity is usually due to one of the following conditions: it may be compensatory, resulting from tilting of the pelvis from real or apparent shortening of one leg. It may be sciatic and due to unilateral protective muscle spasm, especially that accompanying a prolapsed intervertebral disc. Postural scoliosis occurs most commonly in adolescent girls and generally resolves spontaneously.
In structural scoliosis there is alteration in vertebral shape and mobility, and the deformity cannot be corrected by alteration of posture. A careful history and examination is required in an attempt to find a cause and give a prognosis, the two factors on which treatment depends. Structural scoliosis may be congenital, the deformity being due, for example, to a hemivertebra (only half of a single vertebra is fully formed), fused vertebrae, or absent or fused ribs.
In paralytic scoliosis the deformity is secondary to loss of the supportive action of the trunk and spinal muscles, nearly always as a sequel to anterior poliomyelitis.
Neuropathic scoliosis is seen as a complication of neurofibromatosis, cerebral palsy, spina bifida, syringomyelia, Friedreich’s ataxia and neuropathic conditions. Primary disorders of the supportive musculature of the spine are responsible for myopathic scoliosis (e.g. in muscular dystrophy, arthrogryphosis). Metabolic scoliosis is uncommon, but occurs in cystine storage disease, Marfan’s syndrome and rickets.
Idiopathic scoliosis is the commonest and by far the most important of the structural scolioses, and its cause remains obscure. Several vertebrae at one or, less commonly, two distinct levels are affected (primary curve). In the area of the primary curve there is loss of mobility (the fixed curve) and rotational deformity of the vertebrae (the spinous processes rotate into the concavity, and the bodies that carry the ribs in the thoracic region rotate into the convexity). Above and below the fixed primary curves, secondary curves which are mobile develop in an effort to maintain the normal position of the head and pelvis. The spinal deformity is accompanied by shortening of the trunk (which may be assessed by using anthropometric tables of normal values) and there is often impairment of respiratory and cardiac function. In severe cases this may lead to invalidism. Cor pulmonale may feature in cases where the primary curve exceeds 80°.
Once scoliosis has appeared in the growing child the natural tendency is towards deterioration. The prognosis of a given case is dependent on the age of onset, the level of the spine affected, the size and number of the primary curves, and the type of structural scoliosis (e.g. idiopathic or congenital). The maximal rate of deterioration tends to occur between the ages of 11 and 13 in girls, and 13 and 15 in boys, during the growth spurt that takes place around puberty. In assessing or observing any case it is usual to record the height, and the current stage of sexual and skeletal maturity. In many cases deterioration stops when skeletal maturity is reached, but sometimes continues as a result of disc degeneration and vertebral subluxation: 17° deterioration in 70° thoracic curves, and 20° deterioration in 30° lumbar curves have been recorded. Generally speaking, the higher the level of the spine involved in the primary curve, and the younger the patient, the worse the prognosis. There is the notable exception that in some cases occurring in infancy there is spontaneous recovery, which is as remarkable as its mysterious onset. Favourable factors are left-sided curves occurring in the first year of life in males where there is a rib–vertebral angle of less than 20°. Life expectancy may be reduced in congenital and paralytic scolioses, but not in idiopathic scoliosis.
In all cases of structural scoliosis appropriate investigation, radiographic measurement of the curves and careful observation is essential. Note in particular:
Treatment may be advised in the face of a poor prognosis, evidence of rapid deterioration, or for cosmetic purposes. (Curves are not usually considered for correction unless they are in excess of 25–30°.) The methods available are highly specialised, as is the decision regarding their use and timing. Deterioration in a curve may be controlled by use of the Milwaukee brace (a device incorporating moulded supports for the chin, occiput and pelvis, interconnected by vertical metal struts). This support is employed in older children approaching skeletal maturity who have just acceptable curves, or it may be used in the young child until an age suitable for spinal fusion (10 or over) is reached. Other patterns of support are available, although none has been shown to have statistical superiority (and some doubts have been recently cast on their overall effectiveness). Fusion of the entire primary curve is aimed at preventing further deterioration and at allowing braces to be discarded. Prior to fusion it is necessary to correct the primary deformity as much as is possible. Often a hinged plaster spica (Risser jacket) or the surgical insertion of internal apparatus (e.g. Harrington instrumentation) is employed.
Kyphosis
Kyphosis is the term used to describe an increased convexity of the thoracic spine. This is usually obvious when the patient is viewed from the side. (Diminution of the lumbar concave curve is referred to as loss of lumbar lordosis or flattening of the lumbar curvature; in extreme cases there is reversed lordosis, or posterior convexity of the lumbar curve.)
Kyphosis generally affects a major part of the thoracic spine (i.e. several vertebrae are affected), and the increased curvature is then said to be regular. In angular kyphosis, which must be carefully distinguished, there is an abrupt alteration in the thoracic curvature which is usually accompanied by undue prominence of a spinous process (gibbus).
Where mobility is normal in the kyphotic spine, the deformity is most frequently postural in origin; this is often seen (as is postural scoliosis) in adolescent girls. In some cases the deformity is secondary to an increased lumbar lordosis (which in turn may be due to abnormal forward tilting of the pelvis, and sometimes to flexion contracture of the hips or congenital dislocation of the hips). Less commonly, kyphosis may result from muscle weakness secondary to anterior poliomyelitis or muscular dystrophy.
When the thoracic curvature is not mobile but fixed, the most frequent causes are senile kyphosis, Scheuermann’s disease (spinal osteochondrosis), ankylosing spondylitis and Paget’s disease. When there is an angular kyphosis the most common causes are tuberculous or other infections of the spine, fracture (traumatic or pathological, e.g. secondary to osteoporosis), or tumours. In adults the commonest tumour is the metastatic deposit, and in children the eosinophilic granuloma.
Scheuermann’s Disease (Spinal Osteochondrosis)
This condition (whose exact aetiology is unknown, although there is a strong familial tendency), results in a growth disturbance of the thoracic vertebral bodies which in lateral radiographs of the spine are seen to be narrower anteriorly than posteriorly (anterior wedging). There may be associated back pain. The diagnostic protocol for the condition specifies that no fewer than three adjacent vertebrae should have at least 5° of anterior wedging. The epiphyses of the vertebral bodies are often irregular and may be disturbed by herniations of the nucleus pulposus. Nuclear herniation may occur between the epiphyses and bodies anteriorly, or into the centre of the bodies (Schmorl’s nodes), thought to be due to ischaemic necrosis of the cartilaginous end-plates. Mobility is impaired, thoracic kyphosis is regular and often quite marked, and there is a compensatory increase in lumbar lordosis. Secondary osteoarthritic changes may supervene in the thoracic and lumbar spine.
The normal upper limit of the convexity of the thoracic spine (as measured by the Cobb method) is reckoned to be 45°, and cases of Scheuermann’s disease in adolescence with curves of 50° or less should be observed. Where the curve is in excess of this, a Milwaukee brace, worn continuously for not less than 12–18 months (and afterwards till skeletal maturity) may be advised in an attempt to prevent deterioration. (Some question the efficacy of this method of spinal bracing.) If the curve cannot be controlled and reaches 75°, correction by surgical instrumentation should be considered. In the adult with uncontrollable pain and a curve in excess of 60°, surgical fusion may be performed.
Calvé’s Disease
Back pain in children may be accompanied by gross flattening of a single vertebral body. Symptoms usually resolve spontaneously. In many cases the pathology is due to an eosinophilic granuloma.
Ankylosing Spondylitis
In this chronic inflammatory disease there is progressive ossification of the joints of the spine; its aetiology is unknown but there is a hereditary tendency, with the overall risks of children of an affected parent developing the condition being 1 in 6. Unlike rheumatoid arthritis, to which it is often related, it is comparatively rare in women. The male/female ratio varies from 6 : 1 to 2 : 1, depending on the age of onset. The commonest presentation is that of a male during the third and fourth decades.
The joints between T12 and L1 are often first affected, but the rest of the thoracic and lumbar spine is rapidly involved. The costovertebral joints are usually affected, leading to a reduction in chest expansion and vital capacity. Pulmonary tuberculosis, or pulmonary infections with Aspergillus are sometimes found in association, and there may be cardiovascular, renal, gastrointestinal and ocular complications.
Stiffness of the back and pain are the presenting symptoms in the majority of cases, but on occasion involvement of the hip joints, or the knees with effusions, may first attract attention. There may be pain at the insertions of the Achilles tendons or the plantar fascia (enthesopathy). Stiffness is usually worse in the mornings, and may wake the patient from sleep; it tends to improve with activity as the day wears on.
The disease is progressive, and although it sometimes arrests spontaneously at an early stage it usually leads to complete ankylosis of the spine, with characteristic changes in the radiographs (bambooing of the spine). Progressive flexion of the spine may be severe, so that forward vision becomes impossible as the head is flexed on to the chest. The sacroiliac joints are almost invariably involved at an early stage, and there may be fusion of the manubriosternal joint. There may be a history of iritis or its sequelae. The sedimentation rate is high (40–120 mm/h), rheumatoid factor is not present, and estimations of human leucocyte antigen-B27 (HLA-B27) are usually positive. There is often associated anaemia, muscle wasting and weight loss.
As far as treatment is concerned, exercise and physiotherapy are generally regarded as being beneficial. Non-steroidal anti-inflammatory drugs (NSAIDs) are usually helpful, although the risks of cardiovascular toxicity with long term use must be considered. Disease-modifying anti-rheumatic drugs (DMARDs) have not been found to be particularly useful. Deep X-ray therapy is often effective, but carries the risk of aplastic anaemia. Remarkable improvements in disease activity, mobility, function and pain have followed the use of anti-tumour necrosis factor (TNFα) in the form of infliximab or etanercept.
Where deformity of the spine is gross, spinal osteotomy is occasionally undertaken to give the patient a tolerably erect posture. Replacement arthroplasty of the hips or knees is often carried out, even if these joints have progressed to fusion.
Diffuse Idiopathic Skeletal Hyperostosis (Dish)
This comparatively benign condition, also known as Forestier’s disease, is sometimes mistaken for ankylosing spondylitis. It is characterised and diagnosed by the presence of flowing calcification and ossification along the anterolateral borders of at least four contiguous vertebral bodies. The disc spaces are, however, preserved (unlike in ankylosing spondylitis), without loss of height or other degenerative changes, and the sacroiliac and the facet joints do not ankylose. Most cases are asymptomatic, or have mild or moderate restriction of movements in the parts of the spine affected. No treatment is effective.
Senile Kyphosis
In true senile kyphosis the ageing patient becomes progressively stooped and shorter in stature through degenerative thinning of the intervertebral discs. Pain may occur if there is associated osteoarthritis.
In elderly women the kyphosis may be aggravated by senile osteoporosis or osteomalacia, which lead to anterior vertebral wedging and often pathological fractures. There is usually radiographic evidence of decalcification, the serum chemistry may be disturbed, and pain is a feature if there are recent vertebral body fractures.
Treatment is directed towards controlling the underlying osteoporosis or osteomalacia. Thoracic spinal supports are not particularly effective and cannot be tolerated by the elderly, but often a simple lumbar corset is helpful in relieving pain arising from the secondary increase in lumbar lordosis.
Paget’s Disease
Paget’s disease of the spine is comparatively uncommon, and although the diagnosis is made on the radiographic findings, it may be suggested clinically by other stigmata of the disease. Paget’s disease may lead to disturbance of cord function, which may often be successfully treated with bisphosphonates (e.g. etidronate and pamidronate).
Tuberculosis of the Spine
Bone and joint tuberculosis is uncommon in Britain, but the incidence is increasing. The factors responsible include the increase in numbers of immunosuppressed individuals, the development of drug-resistant strains of Mycobacterium tuberculosis, and an ageing population. HIV is the leading risk factor for the reactivation of latent tuberculous infections. The World Health Organization reckons that a third of the global population is infected with the organism, and that it is the commonest cause of death and disability on a worldwide basis. About a fifth of newly diagnosed cases are extrapulmonary, and the spine is involved in 50% of cases of bone and joint tuberculosis.
The onset of spinal tuberculosis is often slow, with aching pain in the back and stiffness of the spine. There may be fever and weight loss. Radiographs taken in the earliest stages of the disease show narrowing of a single disc space; later, as the anterior portions of the vertebral bodies become progressively involved, they collapse, leading to anterior and sometimes lateral wedging of the spine. This may produce angular kyphotic or scoliotic deformities. The local abscess may expand and track distally.
The spinal cord may be compromised extrinsically or intrinsically, and weakness of the limbs or paraplegia may ensue. Extrinsic causes include caseous abscesses, granulation tissue and fluid, sequestered bone or disc material, and spinal angulation leading to kinking of the cord over an internal gibbus. Intrinsic causes include the spread of tuberculous inflammation through the cord and meninges.
Initial investigation should include radiographs of the chest, culture of urine and any sputum, Mantoux testing, brucellosis complement fixation testing and, in the case of the lumbar spine at least, an intravenous pyelogram (IVP) (renal spread being not uncommon). CT and MRI scans of the spine are also invaluable in demonstrating the extent of bone and soft tissue involvement.
The clinical and radiological features of tuberculosis of the spine are mimicked in the early stages by other infections (especially those due to Staphylococcus aureus), and the only certain method of establishing the diagnosis in the majority of cases seen at this stage is by obtaining specimens for histological and bacteriological examination. CT-guided needle aspiration biopsy may be employed if this facility is available. Again, as the abscess is small at first and the early removal of necrotic bone and pus is generally of value from the point of view of accelerating healing, many surgeons combine these procedures. In the later stages, where there is gross bone destruction, minimal new bone formation and the formation of large abscesses, the diagnosis is seldom in doubt.
The aim of treatment is to overcome the infection, eliminate abscesses and sequestra, and promote sound fusion in the affected spinal segment to prevent any recrudescence. The mainstay of treatment is the use of the antituberculous drugs, although the emergence of resistant strains is causing problems. Sensitivity testing is advisable, and drugs should not be used in isolation. Drug therapy for periods up to 2 years was formerly advised, but it has been shown that regimens employing a combination of rifampicin and isoniazid for 6 months only seem equally effective. This is of particular importance where compliance is low. It has been noted that the addition of streptomycin to the drug regimen, bed rest, or a plaster cast do not seem to affect the outcome.
Conservative treatment alone leads to a comparatively low fusion rate, and in about 70% of adult cases there is a deterioration in the kyphosis. In those parts of the world where resources are good, there is at present a trend to early surgical intervention to achieve or accelerate the healing process and assist fusion by early drainage of abscesses and bone grafting. Where paraplegia is due to intrinsic causes, it may resolve following antituberculous therapy, but in many cases the causes are extrinsic, and surgery is indicated to decompress the cord. An MRI scan may give valuable assistance in selecting cases and delineating the scope of the surgery required. If adequately dealt with in the early stages (i.e. within 6–9 months of the onset of paraplegia) complete cure is often achieved. In paraplegia of late onset, where the cord is often acutely angled over an internal gibbus, surgical intervention should always be carried out, but the prognosis here is less good.
Pyogenic Osteitis of the Spine
Pyogenic osteitis of the spine is relatively uncommon. In the early stages of the disease differentiation from tuberculosis of the spine is often extremely difficult, so that the diagnosis may not be clearly established unless material is provided for bacteriological examination. Specimens may be obtained by needle biopsy with the use of an image intensifier, or by exploration. At a later stage (and many cases may delay in their presentation) exuberant new bone formation in the region of the lesion may favour this diagnosis. The presenting features are of pain and stiffness in the back, often insidious in onset, but sometimes occurring quite rapidly. Nearly all cases resolve with prolonged treatment with the appropriate antibiotic (the majority are due to a staphylococcal infection, but Salmonella typhi (syn. Bacillus typhosus) and other organisms are sometimes causal).
Metastatic Lesions of the Spine
Metastatic disease of the spine is seen particularly in the elderly and may be complicated by paraplegia. Back pain at night, pain unaffected by rest or activity, fatigue and weight loss are common features. The diagnosis is made on the radiographic findings. Treatment of the uncomplicated lesion is dependent on the nature of the primary tumour; in some cases deep X-ray therapy and supportive measures may help the local lesion and give relief of pain. Where paraplegia is present, decompression should be undertaken unless the case is terminal. In the patient with some pre-existing cardiovascular disease the possibility of an abdominal aneurysm should be considered; or if the pain is severe at night and there is weight loss, a further search for evidence of malignancy should be made. Primary tumours of the spine are rare; the common types are mentioned in Chapter 3.
Spondylolysis, Spondylolisthesis
In the erect position there is a tendency for the body of the fifth lumbar vertebra (carrying the weight of the trunk) to slide forwards on the corresponding surface of the sacrum, as the plane of the L5–S1 disc is not horizontal but slopes downwards anteriorly. This movement is usually prevented by the downward-projecting inferior articular processes of the fifth lumbar vertebra impinging on the corresponding upward-projecting articular processes of the sacrum. This mechanism may fail if there is a fracture or defect in the part of the fifth lumbar vertebra lying immediately anterior to its inferior articular process. A defect in this region, if unaccompanied by any significant forward movement of the vertebral body, is known as spondylolysis. The defect may be unilateral or bilateral. When forward slip occurs, the condition is known as spondylolisthesis. Less commonly, the fourth lumbar vertebra may be involved, the slip occurring between L4 and L5.
Both congenital and developmental factors have been recognised in the causation of the condition. There is a higher incidence in the families of those affected (30–70%, with dominant transmission), in certain Inuit tribes (where it reaches 54%), and among the Japanese. The lowest incidence is in black females (1.1%), and in white males it is 6.1%. Defects are rare at birth and before the age of 5, but the incidence in the population goes on increasing up to the end of the fourth decade. Fractures due to trauma or fatigue are thought to be the most likely cause, and this explains the high incidence amongst gymnasts, weightlifters, labourers, loggers and backpackers. It may be associated with sacral spina bifida and Scheuermann’s disease.
Both spondylolysis and spondylolisthesis give rise to low back pain which radiates into the buttocks. In adolescents, the majority of whom are active in sports, resolution of symptoms may be achieved in 80% of cases by the avoidance of sports and the use of a corset support. This may lead to the healing of hairline fractures, or to the spine stabilising as a result of degenerative changes occurring at the level of the slip. In more severe cases, where there is significant forward slip, local spinal fusion is the treatment of choice. This may be performed with or without reduction of the deformity.
A number of patients may suffer from neurological disturbances in the lower limbs, either initially or as an uncommon complication of a local fusion. In the cauda equina syndrome there is usually low back pain with radiation into the buttocks, spinal stiffness, hamstring spasm, gait abnormalities, and disturbance of bladder and bowel control. This may be due to an associated disc protrusion, or be caused by the cauda equina and roots of the lumbosacral plexus being stretched over the prominent upper edge of the fifth lumbar vertebra or the sacrum. These complications should be dealt with by an immediate decompression procedure.
Osteoarthritis (Osteoarthrosis)
Primary osteoarthritis of the spine is extremely common, especially in the elderly, and is often asymptomatic. In the majority of cases there are no obvious causes, apart from those associated with the degenerative processes of age. Sometimes obesity and excessive use of the spine by manual workers may be factors. In secondary osteoarthritis, previous pathology in the spine accelerates normal wear and tear processes.
