Are the functional outcomes really inferior following unicondylar knee arthroplasty in patients with partial-thickness cartilage loss?

Objective: The main indication for medial Unicondylar Knee Arthroplasty (UKA) is Full-Thickness Cartilage Loss (FTCL) in the isolated medial compartment of the knee. However, controversial outcomes were reported in patients with Partial-Thickness Cartilage Loss (PTCL). The aim of this study is to compare PTCL and FTCL based on intraoperative findings in medial UKA in terms of functional outcomes and complication rates requiring reoperation and revision.

Methods: Two hundred and fifteen knees of 174 patients who underwent mobile-bearing UKA between October 2014 and February 2018 for the diagnosis of symptomatic anteromedial osteoarthritis were evaluated retrospectively. A single senior surgeon evaluated the type of cartilage loss in the medial compartment intraoperatively according to the International Cartilage Repair Society classification system. Clinical outcomes were evaluated using Oxford Knee Score (OKS) and International Knee Documentation Committee (IKDC) score pre- and post-operatively at the last follow-up. Patients with PTCL and FTCL were compared in terms of their pre- and post-operative OKS and IKDC scores, and their improvements, as well as complication rates requiring reoperation and revision.

Results: The mean follow-up time was 33.1 ± 5.3 months. The PTCL (n = 80) and FTCL (n = 135) groups were statistically similar in terms of age (P = 0.41), gender (P = 0.921), body mass index (P = 0.165), bilaterality (P = 0.111), American Society of Anesthesiologists physical status (P = 0.218), Charlson Comorbidity Index (P = 0.74), and post-operative follow-up (P = 0.167). The mean pre-operative OKS and IKDC scores were improved from 24.5 ± 4.1 and 39.9 ± 5 to 40.3 ± 3.6 and 73.9 ± 7.7 at the last follow-up, respectively (P < 0.001). Pre-operative OKS and IKDC scores were superior in favor of the PTCL group. However, no significant difference was found between the groups in terms of post-operative OKS (P = 0.53) and IKDC (P = 0.975) scores, and their improvements (OKS, P = 0.953; IKDC, P = 0.536). The complication rates requiring reoperation was 5% (n = 11) in all patients. Of these, 9% (n = 7) from the PTCL group and 3% (n = 4) from the FTCL group were reoperated. Nevertheless, no significant difference was found between the groups (P = 0.105).

Conclusion: In PTCL, medial UKA is a reliable surgery in terms of functional outcomes, the same as in FTCL; however, its complication rates requiring reoperation is higher without statistical significance.

Level of evidence: Level III, Therapeutic Study.