Mid-term outcomes of medial metal backed and all-polyethylene unicompartmental knee arthroplasty in obese patients: a retrospective propensity-matched analysis.

Background: This retrospective study compares the outcomes of unicompartmental medial fixed-bearing knee arthroplasty (mUKA), involving a cemented metal-backed (MB) or an all-polyethylene (AP) tibial component, performed in obese patients with a body mass index (BMI) > 30 with a follow-up of at least 5 years.

Methods: The institutional database was mined for primary mUKAs involving an MB or an AP tibial component (MB-UKA and AP-UKA groups, respectively) performed from January 2015 to August 2019. Patient demographics and patient-reported outcome measures (PROMs) were compared and a propensity score matching (PSM) analysis (1:1) using multiple variables was conducted.

Results: PSM analysis yielded 37 pairs of obese MB-UKA and AP-UKA patients. At 5 years, the Knee Society Function Score (KSFS) was 75.1 ± 10.6 in MB-UKA and 79.4 ± 9.1 in AP-UKA patients (p = 0.029), and the Oxford Knee Score (OKS) was 38.1 ± 4.4 in MB-UKA and 40.6 ± 5.7 in AP-UKA patients (p = 0.011).

Conclusion: At five-year follow-up, in a matched group of obese MB-UKA and AP-UKA patients, the AP-UKA group achieved better KSFSs and OKSs. Both the AP and the MB tibial components were able to bring about a significant improvement of the most widely used PROMs.