Unicompartmental knee arthroplasty possibly more cost-effective than TKA, study suggests

Compared to TKA, unicompartmental arthroplasty was associated with more quality-adjusted life-years and a lower accumulated cost.

Both total knee arthroplasty and unicompartmental knee arthroplasty are similarly cost-effective for treating unicompartmental arthritis in elderly low-demand patients, a cost analysis shows. However, unicompartmental arthroplasty may be more cost-effective when considering additional factors, such as revision rates, the authors said.

James Slover, MD, MS, and colleagues at Dartmouth-Hitchcock Medical Center in Lebanon, N.H., used a Markov decision model to compare the cost effectiveness of the two procedures in a theoretical group of 78-year-old patients. Their analysis included data for 9,278 TKAs and 770 unicompartmental arthroplasties contained in the Norwegian Arthroplasty Register.

The researchers measured all outcomes or "utilities" in quality-adjusted life-years and measured all costs in 2005 U.S dollars, according to the study, published in the American edition of the Journal of Bone and Joint Surgery.

The researchers found that unicompartmental arthroplasty was associated with a greater number of quality-adjusted life-years and lower accumulated costs. "However, the average difference in cost was only $200, and the average difference in quality-adjusted life-years gained was only 0.05," the authors said.

In the sensitivity analysis, the researchers found that unicompartmental arthroplasty would have to have an annual probability of revision over 1.5% for TKA to be the less costly procedure. But unicompartmental arthroplasty remained cost-efficient up to a 4% annual probability of revision, the authors noted.

"If the probability of revision of unicompartmental arthroplasty is held constant, TKA does not become less costly unless the annual probability of revision ... is <0.5%," they said.

"In fact, even if the annual revision rate following [TKA] is 0%, the cost of each additional quality-adjusted life-year gained ... is greater than $50,000, which is the commonly accepted threshold for cost-effective interventions. This suggests that, under the assumptions of our model, total knee arthroplasty may not be more cost-effective regardless of revision rates," the authors said.

Unicompartmental arthroplasty would have to cost $10,900 for TKA to become the less costly of the two procedures. Also, it would have to increase to $13,500 to be more cost-effective in terms of gains in quality-adjusted life-years. Conversely, the cost of TKA would have to decrease to less than $11,000 before unicompartmental arthroplasty becomes the more expensive surgical intervention, according to the study.

In addition, mortality and infection rates associated with unicompartmental arthroplasty would have to be higher than those associated with TKA for TKA to become the more cost-effective option, according to the study.

"The fact that unicompartmental knee arthroplasty remains more cost-effective even when the annual probability of revision of [TKA] is zero is important. It reflects the fact that this elderly population is unlikely to need a high number of revisions of any prosthesis ... because of their limited life expectancy, and therefore the associated decreased disutility of unicompartmental knee arthroplasty offsets the poorer implant survival rate for the population modeled," the authors said.

"Thus, unicompartmental knee arthroplasty should not be rejected as a treatment option on the basis of the assumption that it will be more prone to revision," they said.

For more information:
Slover J, Espehaug B, Havelini LI, et al. Cost-effectiveness of unicompartmental and total knee arthroplasty in elderly low-demand patients. J Bone Joint Surg Am. 2006;88-A:2348-2355.