Manipulation under Anesthesia: Does Polyethylene Thickness Matter?

Total knee arthroplasty (TKA) has been established as the most effective treatment for end-stage, symptomatic osteoarthritis of the knee. However, improper polyethylene size selection has been proposed to predispose patients to postoperative stiffness following TKA. The aim of this study is to evaluate if there is a correlation between the use of the thinnest tibial implant thickness and implant manufacturer with the likelihood of undergoing manipulation under anesthesia (MUA). A retrospective review of unilateral TKAs performed between January 2012 and November 2015 was performed. Each knee implant system was normalized by total tibial component thickness for each individual implant system (metal back plus polyethylene) and reaggregated to assess the difference in MUA rates when comparing the thinnest tibial component thickness against the next two sizes. Subset analysis was performed comparing the thinnest tibial component thickness for each individual implant system versus (1) all other tibial component sizes and (2) tibial components one and two sizes larger. A total of 2,728 patients were retrospectively evaluated, of which 71 (2.60%) underwent MUA. Combined tibial component thickness ranged from 8 to 21 mm. When aggregated together to compare the MUA rate between the thinnest liner and the next two sizes, no statistically significant difference was observed (p = 1). Subset analysis demonstrated inconsistent significant differences in MUA rates. Our results suggest that the polyethylene liner thickness alone is not a predictor of postoperative knee stiffness necessitating MUA. When selecting a polyethylene liner, a proper fit maximizing flexion/extension stability is the most crucial factor.