Lumbar clinical adjacent segment pathology: Predilection for proximal levels

Study Design. Retrospective case series. Objective. To evaluate reoperations for lumbar adjacent segment pathology (ASP) during a 10-year period. Summary of Background Data. ASP after lumbar arthrodesis is an important clinical problem. There remains controversy, however, on the distribution of the most commonly affected levels. Methods. Thirty-one patients undergoing revision operation for ASP in the lumbar spine were included in this study. Patients' charts were evaluated for demographic data including age at index and revision operations, time to revision operation, and index and revision levels fused. Results. L4-L5 was the most commonly instrumented level in both single-level (n = 12), and multilevel (n = 13) index fusions. The mean length of time from the index operation to revision surgery was 81 months (range, 11-570 mo). Kaplan-Meier analysis predicted a disease-free survival rate of 32.3% at 5 years and of 12.9% at 10 years after the index operation. L3-L4 was the most commonly affected level by ASP with 75% (16/20) requiring reoperation. L2-L3 was the next most commonly affected level at 52% (14/27). The L5-S1 disk was relatively protected from ASP, with only 4/17 (24%) disks at risk developing ASP. A subgroup analysis of patients undergoing revision after a single-level L4-L5 arthrodesis revealed ASP at L3-L4 in 83% (10/12) of patients, compared with only 3/12 (25%) at L5-S1 (P < 0.05). Of all cases of ASP, the proximal segments were involved 90% of the time. Conclusion. ASP most commonly affects proximal levels in the lumbar spine. In this cohort of patients undergoing revision fusion for ASP, 90% of affected levels were rostral to the index level(s). In patients undergoing L4-L5 single-level arthrodesis, L3-L4 is at high risk, whereas L5-S1 is somewhat protected. Surgeons should pay particular attention to proximal levels when planning a lumbar arthrodesis, however, motion segments distal to fusion may not be as protected as previously thought.