The Management of Degenerative Lumbar Spine Disease

Definition and Anatomy Sciatica is a misnomer freely used to describe lumbar nerve root pain, rather than specific unilateral leg pain in a radicular distribution corresponding to the sciatic nerve (L4,L5,S1,S2). It is caused by nerve root compression in the lumbar spine due to either disc prolapse, osteophytes or ligamentous hypertrophy. These can all be accentuated by spondylolisthesis. The annual incidence of low back pain is estimated at 5%, but only 1% develops radiculopathy. Lumbar disc prolapse is a disease most common between 30 and 50 years of age, with a male preponderance, as well as an association with repeated mechanical forces and smoking. It may occur at any level, but 95% occur at L4/5 or L5/S1. In the older population, with chronically degenerative discs, compression of the nerve root is more likely to be due to facet joint or ligamentum flavum hypertrophy. Nerve roots exit the spinal canal, below the pedicle of the same numbered vertebrae, but above the disc of the next caudal disc space. Nerve root compression can occur in three locations (Figure 1a and 1b): a. A central disc prolapse compresses the thecal sac and the roots of the cauda equina that are contained within. b. A lateral disc prolapse or lateral recess stenosis compresses the transiting nerve root just after it has bifurcated from the dural sac. For example a lateral L4/5 disc compresses the L5 nerve root. c. A far lateral disc prolapse compresses the nerve root that exits the foramen at the level of the involved disc. For example a far lateral L4/5 disc prolapse can compress the L4 root.