Medially congruent total knee arthroplasty in valgus knee deformities yields satisfactory outcomes: a multicenter, international study

Purpose: Postoperative instability represents one of the most common complications following primary total knee arthroplasty (TKA). To prevent this outcome, valgus deformities have been historically treated using more constrained implants. The purpose of this study was to evaluate the outcome of treating a moderate valgus deformity by combining a surgical technique used to release the postero-lateral soft tissue envelope with the use of a medially congruent (MC) TKA design without using classical, semi-constrained inserts. Methods: Seventy-nine MC TKAs were performed by three surgeons at three institutions between 2016 and 2018 as part of a multicenter, international study. Inclusion criteria were: radiographic late-stage osteoarthritic knees with Ranawat's type 1 or 2 classification of valgus deformity and integrity of the medial capsular-ligament complex (less than 10 mm of medial opening during valgus stress test at 10° of knee flexion). Exclusion criteria were: BMI > 40; neuromuscular, metabolic, or immunologic disorders; or the inability to complete outcome measures or radiographic assessment. Results: Seventy-seven patients (79 knees), 59 males and 18 females, were evaluated at 2-year minimum follow-up according to the Knee Society Score (KSS) and Forgotten Joint Score (FJS). Mean age at surgery was 70 years (range 48-91). The mean range of motion (ROM) improved from 110° (range 85°-130°) preoperatively to 121° (range 105°-135°) (p < 0.001) at the time of the last follow-up. Preoperative knee extension significantly improved from 3° (range - 15° to 20°) to 1° (range - 5° to 5°) of flexion at the last follow-up in all the patients. KSS and KSS Functional scores were 89 (range 65-100) and 82 points (range 55-100), respectively. The FJS obtained at the last follow-up was 72 (range 49-88). Two patients (2.5%) had major postoperative complications (one periprosthetic joint infection; one postoperative patellar fracture) requiring surgical interventions. Conclusions: In different surgeon's hands, the use of a modern medially congruent TKA design yielded good clinical outcomes at 2 years in a consecutive series of TKA in valgus arthritic knees. Postoperative instability was not recorded in this series and this finding was related to the high conformity design of the MC polyethylene insert, which significantly differs from classical posterior-stabilized (PS) designs. Level of evidence: IV.