How does the cost effectiveness of posterior spinal fusion compare to arthroplasty for osteoarthritis of the hip or knee?

2012

Background

Healthcare reform has focused attention on the cost effectiveness of medical treatment. The primary metric used to compare treatment outcomes has been Quality-Adjusted Life Years (QALY). A few reports have compared QALY for spinal fusion (generic) to total hip arthroplasty (THA). No one has compared the cost effectiveness of spine surgery of any kind to total knee arthroplasty (TKA), another gold standard along with THA. No comparisons of improvement in QALY have been disease specific for spine surgery. Markov Modeling allows comparisons of different treatments that involve continuous risk over time (e.g. 10 years projected follow-up).

Purpose

The purpose of this study was to compare the long-term cost effectiveness of single-level posterior spinal fusion (PSF) for degenerative spondylolisthesis to total joint arthroplasty of the hip and knee.

Study Design

Cost effectiveness analysis utilizing a Markov model with current outcomes data.

Patient Sample

Three theoretical cohorts of 1000 patients each, averaging 55 years old: Group 1 underwent THA, Group 2 underwent TKA, and Group 3 had PSF at one level for degenerative spondylolisthesis. Group 1 and 2 data come from published reports. Group 3 data from one spine center consecutive series surgical database.

Outcome Measures

Change in QALY per 2011 USD dollars spent.

Methods

A Markov model was constructed for three cohorts of 1000 patients. All cohorts were 55 years old. The three groups consisted of patients with:1) osteoarthritis of the hip treated with total hip arthroplasty, 2) osteoarthritis of the knee treated with total knee arthroplasty, 3) degenerative lumbar spondylolisthesis treated with posterior spinal fusion. Pre-operative and post-operatively Health Related Quality of Life (HRQoL) scores were utilized to model disease states. PSF scores were calculated from Oswestry Disability Index(ODI) in 175 patients with degenerative spondylolisthesis with average 3 year postop follow-up, translated to HR QoL based on the work of Carreon, et al. Cost was estimated utilizing average Medicare DRG re-imbursement for the index procedure in 2011 dollars. Average cost for total hip arthroplasty was $13603.31/case from DRG 470. Average cost for spinal fusion from DRG 460 was $20,900. HR QoL (QALY) was calculated as the average value for each year for the PSF patients, carried forward from year 3. QALY for THA patients was referenced from Rasanen, et al. Revision was assumed to be a sink state for both groups, with a 4% rate per year for the spondylolisthesis group and a 0.3% rate per year for the THA group. The cost of revision surgery was neglected.

Results

Over a 10-year model projection, our Markov THA cohort amassed 496 QALY across 1000 patients while our Markov TKA cohort amassed 229 QALY. Our PSF cohort amassed 613 QALY over the same time frame. The THA group had a cost of $27,450.93 per change in QALY and the TKA group had a cost of $59,165.40 per change in QALY. The PSF group had a cost of $34,110.03 per change in QALY.

Conclusions

Previous studies have assumed larger changes in HRQoL for THA and TKA, with smaller costs for spinal fusion. Our study showed that the cost of the index procedure was more expensive for spinal surgery, however when the results were adjusted for improvement in quality of life, spinal surgery was similarly cost effective to total hip and knee arthroplasty.