Methods: A Markov decision model was used to evaluate the cost-effectiveness of UKA, as compared to TKA, by tracking a hypothetical cohort of 78 year old patients to age 100, or death. Revision rates utilized for this model were those reported by the Norwegian Arthroplasty Register. Transition probabilities regarding, infection and peri-operative mortality, and utility and disutility assignments were estimated from the arthroplasty literature. The average Medicare reimbursement for unicompartmental, tricompartmental and revision knee arthroplasty was used to evaluate the costs associated with each strategy. The model tabulates costs and quality adjusted life years (QALY's) over time to evaluate the cost-effectiveness of each treatment strategy.

Results: UKA was a cost effective strategy for this population, so long as the annual probability of revision is less than 4%. This holds true even if the annual probability of revision of TKA is 0%. The cost UKA must be greater than $13,500 or the cost of TKA must decrease to less than $8,500 before TKA becomes more cost-effective. UKA is also more cost effective if the incidence of infection is lower than 2.6% with UKA or greater than 1.45% for TKA, and if the peri-operative mortality is less than 0.34% for UKA or greater than 0.14% with TKA.

Conclusion: Our model suggests that based on currently available cost and outcomes data both the UKA and TKA treatment strategies have similar cost-effectiveness profiles in this patient population. Therefore, UKA should not be rejected as a treatment option based on the assumption that there will be “too many revisions.” However, several important parameters were identified that could alter the cost-effectiveness analysis, including implant survival rates, costs, peri-operative mortality and infection rates, and utility values achieved with each procedure. Although the analysis cannot be generalized to individual patients making decisions about arthroplasty procedures, the thresholds identified in this study may help decision makers evaluate the cost-effectiveness of each strategy as further research characterizes the variables associate with unicompartmental and total knee arthroplasty and may be helpful in designing future appropriate clinical trials.