Lumbar Apophyseal Process Excision and Spinal Instability

Thirty-three patients who underwent lumbar nerve root decompression by apophyseal process excision, usually with discectomy, were evaluated clinically and radiologically from two to five years after surgery. A classification is presented of demonstrable spinal instability after one-level, unilateral, or bilateral apophyseal process excision at either the L4–L5 or L5–S1 levels with or without discectomy. Four patients with multiple-level decompressions showed vertebral instability, and two of these were clinically worse.