The less-frequent lesions of the third (L3) and fourth (L4) lumbar roots give rise to pain in the anterior part of the thigh and knee and anteromedial part of the leg (fourth lumbar), with corresponding sensory impairment in these dermatomal distributions. The knee jerk is diminished or abolished. Third lumbar (L3) motor root lesions may weaken the quadriceps, thigh adductor, and iliopsoas and reduce the knee jerk; L4 root lesions weaken the anterior tibial innervated muscles, sometimes with a mild foot drop and variably affect the knee jerk. First lumbar (L1) root pain is projected to the groin, and L2, to the lateral hip.
Much has been made of a distinctive syndrome associated with extreme lateral disc protrusions, particularly those situated within the proximal portion of the intervertebral spinal foramina. Unremitting radicular pain without back pain and a tendency to worsen with extension of the back and torsion toward the side of the herniation are characteristic. Also, in rare instances of lumbar intradural disc rupture, there may not be sciatic pain because the free fragment in the subarachnoid space does not impinge on the roots of the cauda equina. Both of these configurations may confound clinical and radiologic diagnosis and make surgery more difficult.
Rarer still, and often clinically obscure, are protrusions of thoracic intervertebral discs (0.5 percent of all surgically verified disc protrusions, according to Love and Schorn). The four lowermost thoracic interspaces are the most frequently involved. Trauma, particularly hard falls on the heels or buttocks, is an important causative factor. Deep boring spine pain; root pain circling the body or projected to the abdomen or thorax (sometimes simulating visceral disease); paresthesia below the level of the lesion; loss of sensation; both deep and superficial; and paraparesis or paraplegia are the usual clinical manifestations.
A herniated lumbar disc at one interspace may compress more than one root (see Fig. 10-3), and it follows that the symptoms reflect this. Furthermore, the above descriptions of single root compression refer mainly to signs and symptoms of typical posterolateral disc protrusion. Very large central disc protrusions may compress the entire cauda equina with a dramatic syndrome that includes intense low back and bilateral sciatic pain, incomplete paraparesis, loss of both ankle jerks, and, most characteristic, varying degrees of urinary retention and incontinence. This circumstance usually demands surgical attention.
Anomalies of the lumbosacral roots may lead to errors in localization (see descriptions by Postacchini et al). The combined rupture of two or more discs occurs occasionally and complicates the clinical picture. When both the L5 and S1 roots are compressed by a large herniated disc, the signs of the S1 lesion usually predominate.
Herniation may occur directly into the adjacent vertebral body, giving rise to a Schmorl nodule. In such cases there are no signs of nerve root involvement although back pain may be present, sometimes recurrent and referred to the thigh. Most often, these circular radiographic densities adjacent to the endplate of the vertebral body are found incidentally on CT or MRI.