The axial skeleton is formed from the skull, vertebral column, ribs and sternum. The vertebral column provides protection for the spinal cord, and a firm strong bilaterally symmetrical central axis for supporting muscular activity. It is formed of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccygeal. The vertebral canal extends from the foramen magnum to the sacral hiatus. It is formed by the vertebral arches and intervening ligaments laterally and posteriorly, and anteriorly by the vertebral bodies and intervertebral discs. It houses the spinal cord, its meningeal coverings and the emerging spinal nerves. The number of nerves corresponds to that of the vertebrae, except in the cervical region, where there are eight: the first emerges above the axis, the remainder below each of the seven cervical vertebrae (but the nerve number is one greater than that of the related vertebra). The thoracic and lumbar spinal nerves pass beneath the pedicles of the same numbered vertebra. The sacral nerves pass through the sacral foramina, the dorsal roots posteriorly and the ventral anteriorly. The coccygeal nerves pass through the sacral hiatus.
The spinal cord ends opposite the first lumbar vertebra (third in children), and the collection of descending nerves below this level is termed the cauda equina. The dural sac descends to the level of the second sacral vertebra, this means that the lower dural sac contains the cauda equina and lower spinal nerves, but not the spinal cord. This fact is made use of clinically, as a needle can be introduced into the sac to inject substances, or sample cerebrospinal fluid, without risk of damage to the spinal cord.
The surface marking for this insertion is the supracristal plane (the uppermost level of the iliac crests – figure 5), this passes through the fourth lumbar spine. A needle is inserted above or below this spine, which is palpable (lumbar puncture). The needle passes through the skin and supraspinous ligaments and into the extradural space (containing fat and a venous plexus). Local anesthetic can be introduced at this level (epidural anesthesia), or the needle advanced through the meninges into the dural sac to deliver anesthetic (spinal anesthesia). Local anesthetic may also be introduced into the sacral hiatus (caudal block) to anesthetise the perineum, this technique is used to suppress pain in vaginal childbirth.
In utero, the spine is curved in C fashion, with a primary thoracic kyphosis. After birth, a secondary cervical lordosis develops in relation to raising the head and the lumbar lordosis in relation to walking. In the upright position the vertebral column supports the weight of the head, trunk and upper limbs and transmits it through the pelvic girdle to the lower limbs. The segmental nature of the vertebral column adds flexibility without reducing its strength. Movement between individual vertebrae is not marked but collectively there is extensive movement across the whole vertebral column. Flexion is most marked in the cervical region, rotation in the thoracic, and extension and lateral flexion in the lumbar region.
Everyone suffers from backache at some time in their life, but fortunately the vast majority of these problems are self-limiting and only challenge the difficulties of diagnosis when they are persistent, recurrent or disabling. Figure 6a–f shows some normal and abnormal radiological features.
Backache is usually musculoskeletal in origin. However, always consider the possibility of referred pain and look for other diagnostic features. Acute severe thorocolumbar and abdominal back pain can be produced by acute aortic lesions (both dissection and rupture), and the pain of myocardial infarction may pass between the scapulae; gallbladder disease often presents with pain below the right scapula. Pancreatic pain is typically in the upper lumbar region and other retroperitoneal lesions, such as neoplasms, hemorrhage and renal disease, may present in similar fashion. Pain of gynecological origin typically presents with low back pain; it is an important differential diagnosis.
Backache in the skeletally immature should always be considered organic and investigated, as should neurological signs, such as muscle wasting, and bladder and bowel dysfunction. Deformities may be congenital, these include all forms of spinal bifida, ranging from spina bifida occulta, involving only a local skin abnormality, through vertebral arch defects to myeloceles and meningomyeloceles: in the latter the cord presents as a surface neurological plaque. Severe forms are commonly associated with hydrocephallus, in relation to the Arnold Chiari malformation (where the cerebellar hemispheres cone into the foramen magnum, and obstruct the flow of cerebrospinal fluid).
Vertebral deformities include hemivertebrae, spondylolisthesis and sacral agenesis. Increased thoracic kyphosis is an ageing phenomenon and is accentuated in osteoporosis, Scheuermann’s disease, ankylosing spondylitis, and Parkinson’s and Paget’s diseases. Acute angulation of the spine, with prominent abnormal spinous processes (gibbus), may be due to congenitally abnormal vertebrae, trauma and destructive infections, such as tuberculosis. The lumbar lordosis may be accentuated in protrusion of an intervertebral disc, osteomyelitis and spondylolisthesis.
Scoliosis (lateral curvature of the spine) may be postural (this is common in adolescent girls and corrected in flexion), compensatory (secondary to previous thoracic surgery, hip pathology or leg length discrepancy), in the latter the curve corrects on sitting down, or sciatic scoliosis (list – due to muscle spasm – the convexity is usually directed to the side of the offending intervertebral disc protrusion). Structural scoliosis indicates a fixed bony abnormality; it is usually accompanied by rotation and a prominent rib hump deformity. It may be related to the ageing process, including osteoporosis associated with a crush vertebral fracture.
Spinal stenosis may be related to osteoarthritic changes, particularly involving the lumbar region, and compressing the spinal cord and emerging spinal nerves. Vertebral osteomyelitis usually commences in the disc, and progresses to end plate destruction and paravertebral abscess formation. There may be collapse of the infected vertebra with severe angular kyphosis. A psoas abscess tract, secondary to vertebral infection, passes along the psoas sheath, to present as a lump below the inguinal ligament, it is a feature of tuberculous disease.
Spinal tumors may originate in the spinal cord, particularly meningiomas and peripheral nerve neuromas, or they may be benign or malignant bone tumors. Benign tumors include osteoid osteomas, giant cell tumors and osteochondromas. Malignant tumors are predominantly metastases: common primary sites are the lung, breast, prostate, kidney, thyroid and, less commonly, lymphomas and from the gastrointestinal tract. Biopsy is frequently necessary to reach a diagnosis.
Spinal fractures may be divided into compression, burst, flexion- distraction injuries and fracture dislocations. In the latter the spinal cord is subject to injury, with initially flaccidity and areflexia below the level of the injury.
When taking a history of back or spinal pain, try to differentiate between pain limited to the lower back and leg pain. In deformity, note the age of onset and the rate of progression, together with precipitating factors and the general state of the patient’s health. Note whether the pain is related to coughing and movement, and its relieving factors. Determine whether any medicolegal claims are outstanding from injury, and the mental and psychological state of the patient.
Observe the patient throughout the consultation, including the history taking and when undressing: note body proportions, congenital syndromes, deformities, evidence of endocrine or metabolic disease, and gait. An antalgic gait is when the patient spends more time on one leg, indicating pain related to the other, it is particularly suggestive of hip and knee pathology. A flexed gait is suggestive of spinal stenosis (there may also be a simian stance with flexion of the spine, hips and knees). A shuffling gait often indicates a neurological abnormality, while spacticity may produce a hemiplegic (unilateral) or scissors (bilateral) gait. A short gait (shoulder dipping on the short side) becomes a Trendelenburg gait (sideway dipping of the shoulder) when there is weak adduction: the latter becomes a waddling gait when the abnormality is bilateral.