Survival analysis of the Wallis interspinous spacer used as an augment to lumbar decompression

The Wallis fixed interspinous spacer may augment traditional decompression in the treatment of lumbar spinal stenosis. The aim of this study was to determine factors influencing survival of the Wallis interspinous spacer and to identify specific modes and predictors of failure.

We performed a retrospective cohort study of 244 Wallis interspinous spacers implanted in 195 consecutive patients with a mean age of 56 years (range 21-87) to augment single or multi-level decompression. We examined patient demographics, indications for surgery, surgical techniques and pathology on magnetic resonance imaging (MRI). A Kaplan-Meier survival analysis was performed.

Median follow-up was 4.5 years (range 2-8). Sixteen patients were lost to follow-up. Repeat MRI was performed in 98 patients (50%). A recurrent stenosis was found in 21% of patients (41/195) and occurred at a similar incidence at the level of the spacer and at adjacent spinal levels. Revision decompression was performed in 19 patients (10%) at 2.8 ± 1.8 years (range 6 months-6 years) with implant removal in 15 and conversion to fusion in 4 patients. No specific patient factors or pre-operative MRI findings predicted failure. Five-year survival was 91% (95% CI: 79-96%).

The Wallis implant is generally implanted without complication when used as an adjunct to decompression with a good medium term survival. Though disc heights were maintained, the Wallis spacer did not however appear to reduce the incidence of recurrent spinal or foraminal stenosis from that expected from decompression alone.