Which unicondylar prosthesis is better in the mid- term in obese patients: fixed or mobile?

Abstract

As it is mentioned in the literature, rates of complications and revision are higher in the obese compared to non-obese patients, although obesity does not a contraindication for unicompartmental knee arthroplasty and successful outcomes are achieved. However, there is not any study in the literature comparing the outcomes of fixed and mobile unicompartmental prostheses which are applied in the obese patients. Objective of this study was to compare outcomes of our obese patients who we applied fixed or mobile unicompartmental arthroplasty and followed up for 8 years and over.

Of 293 patients in whom we performed unicompartmental knee prosthesis due to medial gonarthrosis between 2003 and 2014, 239 patients who were regularly followed-up at least for 18 months were included in this study. Total 248 knees with 193 (77.8%) fixed including bilateral prosthesis in 9 patients and 55 (22.2%) mobile prostheses were retrospectively assessed. The study included 57 patients having BMI >30 kg/ m2 who were regularly followed-up.

In the final controls; mean flexion was found as 107° (100-128°)(p < 0.05), mean extension as 3° (0-5°) and mean tibio femoral angle as 4° (1-5°) (p < 0.05) valgus. Postoperative mean WOMAC value was found as 91.23 ± 3.02 (92-96) (p < 0.05) and mean KSS score as 88.3 ± 3.94 (85-100) (p < 0.05). In the final controls, respective knee flexions were seen to be 105° (100-125°) and 108°(105-128°) in the fixed and mobile insert subgroups (p > 0.05).

Unicompartmental knee prosthesis is a good treatment option which can be applied also in obese patients and has high survival rates. No significant difference was found between the prostheses with fixed and mobile insert in terms of function and knee scores. However, fixed unicompartmental prosthesis should primarily be preferred in obese patients because of the challenging surgical technique, difficult learning curve and insert dislocation that we encounter with mobile prostheses.