Are relative contraindications for unicompartmental knee replacements in medial compartment osteoarthritis really contraindications?

Background: Medial unicompartment knee replacement (UKR) is performed for isolated medial compartment osteoarthritis. Understanding the factors influencing functional outcomes helps patient selection and outcomes. We will review the association between pre-operative BMI and patellofemoral articular wear on post operative Oxford Knee Scores at >2 and > 5 years. Methods: A retrospective review of a prospectively collected database was performed. Inclusion criteria were medial UKR for medial compartment OA. The exclusion criteria were age <16, revision procedures and lateral UKR's. Data was collected between 26/6/2014 and 25/8/2022. Statistical analysis was performed using SPSS. Significance was given to variables that reached p < 0.05. Results: 159 UKR procedures were identified in 155 patients. 116 procedures carried out on 111 patients had follow up at > 2 years. At 5 years there were 14 patients had OKS recorded. There was no statistical difference in the ICRS grade I&II vs III&IV groups for >2 year or >5 year OKS with p = 0.408 and p = 0.876. For BMI there was a moderately negative correlation on spearman's rank p(df) = -0.339 (CI 95 % -0.538, -0.104) at >2 years, which was statistically significant with p = 0.004. >5 year data didn't reach significance with p = 0.828. Conclusion: BMI maybe an important patient factor in predicting post operative OKS at 2-5 years. This is beneficial to surgeons for patient selection in medial UKR. Patellofemoral wear doesn't appear to impact on post operative functional outcomes. This supports the theory that patient who suffer from patellofemoral wear, as well as medial compartment wear can benefit from UKR, expanding the current indications.