COST-EFFECTIVENESS OF INTERSPINOUS SPACER DEVICES IN THE SURGICAL TREATMENT OF LUMBAR SPINAL STENOSIS

Tapp, Stephanie J.

Purpose: There is no universally accepted standard of care for lumbar spinal stenosis. Several studies suggest surgical care results in better outcomes than conservative care, but the type of surgery (decompression vs. fusion) remains controversial. Interspinous spacer devices (“spacers”) have emerged as a new initial treatment alternative. Our objective was to assess the cost-effectiveness of spacers for lumbar stenosis and to identify thresholds for post-spacer health utility that would result in spacers being a cost-effective initial surgery.

Method: A Markov model tracked health utility and costs for a hypothetical 65-year-old cohort followed over a 10-year time horizon under six care strategies: conservative care (C) and five surgical strategies defined by initial and up to two subsequent surgeries involving spacer (S), decompression (D), and/or fusion (F): S-D-D, S-D-F, S-F-F, D-D-F, and D-F-F. Incremental cost-effectiveness ratios (ICER) reported as cost per quality-adjusted life year (QALY) gained included direct medical costs for surgery (initial S: $8,227; D: $5,925; F: $20,101). Medicare claims data were used to estimate costs, complication rates (S: 4.8%; D: 6.6%; F: 9.4%) and reoperation within 3 years (S: 20.1%; D: 10.8%; F: 14%) for each surgery. Utilities were derived from published studies (C:0.71; S: 0.82; D: 0.77; F:0.74). Reoperation rates after 3 years for D and F were obtained from the literature. Spacer failure beyond 3 years is uncertain and was evaluated through sensitivity analyses. In the base-case, the spacer failure rate was held constant for years 4-10 (cumulative: 47%). In subsequent analyses, the 10-year failure rate was increased either moderately (to 56%) or steeply (to 90%). Additionally, since utility following spacer surgery is rarely reported, we performed threshold analyses on post-spacer utility to determine when spacer surgery fails to be cost-effective either because it is dominated or has an ICER> $100,000.

Result: An initial spacer strategy (S-D-D) emerged as the most cost-effective ($14,400 per QALY gained) in base-case analyses. The ICER rose minimally ($16,800) when the failure rate was increased steeply. Spacer surgery remained cost-effective for post-spacer utilities ≥0.7695 in the base case and ≥0.773 under steeply increased failure.

Conclusion: Post-spacer health utilities in the literature to date exceed the identified thresholds, suggesting that interspinous spacer devices are reasonably cost-effective when implemented as a first surgical intervention for patients with spinal stenosis.