An antalgic posture, referred to as sciatic scoliosis, is maintained by reflex contraction of the paraspinal muscles, which can be both seen and palpated. In walking, the knee is slightly flexed, and weight bearing on the painful leg is brief and cautious on the ball of the foot, giving a limp. It is particularly painful for the patient to go up and down stairs.
The signs of more severe spinal root compression are impairment of sensation, loss or diminution of tendon reflexes, and muscle weakness, as summarized in
Table 10-1.
Generally, disc herniation compresses the root of the level just below the herniation (see below). Hypotonia may be evident on inspection and palpation of the buttock and calf. In only a few patients is a foot drop (L5 root) or weakness of plantar flexion (S1 root) the main feature of disc protrusion, but it is notable that some patients have little pain with disc rupture. The reflex changes noted below have little relationship to the severity of the pain or sensory loss. Furthermore, compression of the fourth, or sometimes fifth, lumbar root may occur without any change in the tendon reflexes. Bilaterality of symptoms and signs is rare, as is sphincteric paralysis, but they occur with large central protrusions that compress the cauda equina. The cerebrospinal fluid (CSF) protein is then slightly elevated, usually in the range of 55 to 85 mg/dL, sometimes higher.
As emphasized earlier, herniations of the intervertebral lumbar discs occur most often between the fifth lumbar and first sacral vertebrae (compressing the S1 root;
Fig. 10-3) and between the fourth and fifth lumbar vertebrae (compressing the L5 root). Lesions of the fifth lumbar root (L5) produce pain in the region of the hip and posterolateral thigh (i.e., sciatica) and, in more than half such cases, lateral calf (to the lateral malleolus), and less often, the dorsal surface of the foot and the first or second and third toes. Pain is elicited by the straight-leg raising test or one of its variants, and protective nocifensive reflexes come into play, limiting further elevation of the leg. Paresthesia may be felt in the entire territory or only in its distal parts. The tenderness is in the lateral gluteal region and near the head of the femur. Weakness, if present, involves the extensors of the big toe and foot and the foot invertors (a distinguishing feature of foot drop originating from peroneal nerve damage, which spares inversion because it is a tibial nerve function). The ankle jerk may be diminished (more often it is normal), but the knee jerk is hardly ever altered.
With lesions of the first sacral root (S1), the pain is felt in the midgluteal region, mid-posterior part of the thigh, posterior region of the calf to the heel, outer plantar surface of the foot, and fourth and fifth toes. Tenderness is most pronounced over the midgluteal region. Paresthesia and sensory loss are mainly in the lower part of the leg and outer toes, and weakness, if present, involves the plantar flexor muscles of the foot and toes, abductors of the toes, and hamstring muscles. The Achilles reflex is diminished or absent in the majority of cases. In fact, loss of the Achilles reflex may be the only objective sign. Walking on the toes is more difficult and uncomfortable than walking on the heels because of weakness of the plantar flexors.