A meta-analysis of unicompartmental knee arthroplasty revised to total knee arthroplasty versus primary total knee arthroplasty

Background: This study was performed to compare the clinical outcomes of unicompartmental knee arthroplasty (UKA) revised to total knee arthroplasty (TKA) versus primary TKA. Methods: Relevant trials were identified via a search of the Cochrane Central Register of Controlled Trials and PubMed from inception to 17 June 2017. A meta-analysis was performed to compare postoperative outcomes between revised UKA and primary TKA with respect to the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Knee Society Score (KSS), mean polyethylene thickness, hospital stay, revision rate, range of motion (ROM), and complications. Results: Five of 233 studies involving 536 adult patients (revised UKA group, n = 209; primary TKA group, n = 327) were eligible for inclusion in the meta-analysis. The primary TKA group had better WOMAC scores, KSS, and ROM than the revised UKA group (P < 0.05). Compared with primary TKA, revision of UKA to TKA required more augments, stems, and bone grafts and a thicker polyethylene component (P < 0.05). There were no significant differences between the two groups in the revision rate, hospital stay, or complications (P > 0.05). Conclusion: Conversion of UKA to TKA is associated with poorer clinical outcomes than primary TKA. Furthermore, we believe that conversion of UKA to TKA is more complicated than performing primary TKA. Revision UKA often requires more augments, stems, and bone grafts and thicker polyethylene components than primary TKA. However, patients who undergo conversion of UKA to TKA have similar hospital stay, complications, and revision rate as patients who undergo primary TKA.