Description
Objectives: Unicompartmental kneearthroplasty (UKA) is a procedure that couldbe done in near 50% of knee replacements, but it is known to be less reproducible thantotal knee arthroplasty. Avoidingovercorrection is the golden rule in theimplementation of medial unicompartmentalarthroplasty (UKA) and restoring theprimitive alignment is one of the mainobjectives. The aim of this study was todevelop a strategy to detect the postoperativerisk of overcorrection when implanting a medial UKA using preoperative radiographicdata based on long leg films, valgus stress views and the joint line convergence angle (JLCA). Additionally, the study aimed toidentify intraoperative protective factors thatcould help prevent overcorrection.
Methods: This retrospective study involvedradiographic measurements of consecutive patients who underwent image-assistedrobotic medial UKA between February 2022 and February 2023 at a single high-volumecenter. Postoperative overcorrection wasdefined as an HKA angle more or similar to180°. Receiver Operating Characteristic(ROC) curves were constructed to evaluatethe predictive ability of three parameters: "preoperative HKA" (preHKA) measured onlong-leg films, "preoperative stress HKA" (sHKA) (HKA measured on preoperative valgus stress x-rays), and the "estimatedHKA" (eHKA) (HKA + JLCA). The areaunder the curve (AUC) was calculated todetermine the best parameter for predictingthe risk of overcorrection. Cut-off points, along with their respective sensitivity (Se) and specificity (Sp), were determined usingthe Youden method. Subsequently, a subgroup analysis was performed on patientsat risk to determine if any specific cut-off value of residual laxity (sHKA - postoperative HKA) measuredintraoperatively could be identified as a protective factor against overcorrection.
Results: The study included ninety-fivepatients, of whom eight cases ofovercorrection (8.4%, 8/95) were recordedwith a mean postoperative HKA of 180.6° +- 0.5 [180.1-181.3]. The best predictor ofovercorrection was preHKA (AUC=0.96) with a cut-off point of 176° (Se=100%, Sp=86%). This was followed by eHKA(AUC=0.94) with a cut-off point of 179.7° (Se=100%, Sp=86%), and sHKA(AUC=0.81) with a cut-off point of 181.1° (Se=100%, Sp=85%). In the subgroup of 20 patients with preHKA ≥176°, maintaining a residual laxity >2.6° was found to be aprotective factor against overcorrection (0/8 in the overcorrected group versus 6/12 in thecontrol group, p<.04).
Conclusions: PreHKA ≥176° was the bestpredictor of overcorrection. In thispopulation, maintaining a residual laxity>2.6° was identified as a protective factor against overcorrection. SHKA and eHKAwere also significative predictive factors, with a cut-off point >181,3o and 179,7o respectively. It represents a very valuablecontribution to the understanding of UKA principles, which can serve to extend itsindications, and increase reproducibility ofthe surgical technique
