L5-S1 segment survivorship and clinical outcome analysis after L4-L5 isolated fusion

A retrospective investigation of the L5-S1 motion segment after an isolated L4-L5 posterior lumbar fusion.

To determine the survivorship of the L5-S1 segment in patients undergoing L4-L5 fusion and to identify the correlation between radiographic degeneration and clinical outcome at this level.

There is current controversy regarding future degeneration of the L5-S1 segment following single-segment fusion at L4-L5. There are no long-term studies that look at L5-S1 after L4-L5 fusion to assess the rate of degeneration at this adjacent segment and the functional clinical outcome of the patient.

Thirty-two consecutive patients (average age 56.4 years, range 27-77 years) having isolated L4-L5 posterior spinal fusion for instability or stenosis by a single surgeon were included in this study. There were 25 females and 7 males with an average follow-up of 7.3 years (range 2.3-12.4 years). A survivorship analysis was performed to determine the degeneration at the adjacent L5-S1 segment. Radiographs were analyzed for arthritic degeneration at that level. At the time of the L4-L5 index procedure, the L5-S1 disc spaces were graded on a 4-point scale for degeneration. Questionnaires were submitted by mail, and telephone interviews were conducted by one of the authors to determine the current level of patient function.

Of the total 32 patients assessed, 31 (97%) had no evidence of symptomatic degeneration at L5-S1 requiring additional decompression or fusion. One patient had clinical symptoms that required a foraminotomy and laminotomy at L5-S1, but none of the patients required any further fusion. Although there was a trend of progression of the arthritic grade at L5-S1 from preoperative to postoperative examination, there was no correlation between preoperative arthritic grade versus further degeneration. The discs showed progression of degeneration from an average score of 2.28 before surgery to a score of 2.49 after surgery at the last follow-up.

There appears to be no need to routinely include the L5-S1 segment when performing a posterior lumbar fusion for patients with instability or stenosis at L4-L5 if no symptoms are attributed to the lumbosacral level. At an average of 7.3 years, there was neither increased symptomatic disc degeneration nor symptoms necessitating the need for an L5-S1 fusion.