Some information may be gained by inspection of the back, buttocks, and lower limbs in various positions. The normal spine shows a thoracic kyphosis and lumbar lordosis in the sagittal plane, which in some individuals may be exaggerated. In the coronal plane, the spine is normally straight or shows a slight curvature, particularly in women. One should observe the spine for excessive curvature, a list, flattening of the normal lumbar lordosis, presence of a gibbus (a sharp, kyphotic angulation usually indicative of a fracture), pelvic tilt or obliquity (Trendelenburg sign), and asymmetry of the paravertebral or gluteal musculature. A sagging gluteal fold suggests involvement of the S1 root. In sciatica one may observe a flexed posture of the affected leg, presumably to reduce tension on the irritated nerve. Or, patients in whom a free fragment of lumbar disc material has migrated posterolaterally may be unable to lie down and extend the spine.
The next step in the examination is observation of the spine, hips, and legs during certain motions. No advantage accrues from determining how much pain the patient can tolerate. More important is to determine when and under what conditions the pain begins or worsens. Observation of the patient’s gait may disclose a subtle limp, a pelvic tilt, a shortening of step, or a stiffness of bearing—indicative of a disinclination to bear weight on a painful leg. One looks for limitation of motion while the patient is standing, sitting, and reclining. When standing, the motion of forward bending normally produces flattening and reversal of the lumbar lordotic curve and exaggeration of the thoracic curve. With lesions of the lumbosacral region that involve the posterior ligaments, articular facets, or sacrospinalis muscles and with ruptured lumbar discs, protective reflexes prevent flexion, which stretches these structures (“splinting”). As a consequence, the sacrospinalis muscles remain taut and prevent motion in the lumbar part of the spine. Forward bending then occurs at the hips and at the thoracolumbar junction; also, the patient bends in such a way as to avoid tensing the hamstring muscles and putting undue leverage on the pelvis. In the presence of degenerative disc disease, straightening up from a flexed position is performed with difficulty.
Lateral bending is usually less instructive than forward bending but, in unilateral ligamentous or muscular strain, bending to the opposite side aggravates the pain by stretching the damaged tissues. With unilateral sciatica, the patient lists to one side and strongly resists bending to the opposite side, and the preferred posture in standing is with the leg slightly flexed at the hip and knee. When the herniated disc lies lateral to the nerve root and displaces it medially, tension on the root is reduced and pain is relieved by bending the trunk to the side opposite the lesion; with herniation medial to the root, tension is reduced by inclining the trunk to the side of the lesion.
In the sitting position, flexion of the spine can be performed more easily, even to the point of bringing the knees in contact with the chest. The reason for this is that knee flexion relaxes tightened hamstring muscles and relieves the stretch on the sciatic nerve.
Examination with the patient in the reclining position yields much the same information as in the standing and sitting positions. With lumbosacral disc lesions and sciatica, passive lumbar flexion causes little pain and is not limited as long as the hamstrings are relaxed and there is no stretching of the sciatic nerve. Thus, with the knees flexed to 90 degrees, sitting up from the reclining position is unimpeded and not painful; with knees extended, there is pain and limited motion (Kraus-Weber test). With vertebral disease, passive flexion of the hips is free, whereas flexion of the lumbar spine may be impeded and painful.