Spinal Instrumentation

The main disadvantage of pedicle screw systems is the possibility of direct injury to the nerve root in the intervertebral foramen. Universal transpedicular instrumentation systems are the most versatile because they employ a series of devices connected with rods that can be molded in three dimensions. Systems that fit these criteria are many in the market.

Spinal instrumentation for direct repair of spondylolysis should be considered in symptomatic young patients with Meyerding grade I isthmic spondylolisthesis. Stainless steel 18-gauge wire looped around each transverse process and tied below the spinous process of the same vertebral segment, or screws placed through the lamina, across the isthmic defect, and into the pedicle have been used for this purpose in the past. The fibrous tissue within the spondylolytic defect which may be compressing the nerve root is removed prior to instrumentation, Bone graft can be harvested from the spinous processes. Clinical results are similar for each of these methods, and more than 80 percent of properly selected patients will have an acceptable result and a permanent fusion at the defect. Results tend to be worse in older patients and in patients with greater displacements. This procedure should not be expected to relieve symptoms derived from other etiologies, and, therefore, is contraindicated in patients with evidence of degenerative disc disease. Success with these procedures may be predicted by pain relief after lidocaine infiltration of the spondylolytic defect. The main advantage of this approach in eligible patients is the maintenance of all mobile disc segments.

Instrumentation can also be used to reduce and to maintain a reduction of a high grade spondylolisthesis. The goal of reduction is to normalize the biomechanical alignment of the spine. This is designed to make stabilization easier, to decrease the pseudoarthrosis rate, to reduce progression of the deformity, and to correct the cosmetic deformity. Although reduction procedures are the only way that meaningful correction of the severe deformity associated with high degree slips can occur, most of these patients when treated with intertransverse fusion alone will have resolution of pain and neurological symptoms. In addition, the risk of permanent motor weakness secondary to a reduction procedure, which usually was involving the L5 nerve root, approached 20 %. Therefore, the increased risk of reduction, in old fashion treatment modalities, was often difficult to justify and was not advised without careful attention to the relatively high risk of neurological injury.