Do Outcomes Differ After Medial Unicompartmental Knee Arthroplasty Based on Indications? A Prospective Cohort Study

Unicompartmental knee arthroplasty (UKA) has grown recently, highlighted by shorter recovery periods and positive clinical outcomes. This study's purpose was to determine whether clinical outcomes differ after medial UKA between patients indicated with strict versus liberal criteria as defined by established literature.

We prospectively enrolled 94 patients (110 knees) undergoing UKA by a single surgeon. Patients were categorized preoperatively as strictly or liberally based on published criteria. Patients were recategorized based on intraoperative findings. Patient-reported outcome measures, reoperation, and complications were recorded. The mean length of follow-up within the cohort was 3.3 years (range, 1.7 to 5.3). Preoperatively, 58 patients (53%) met strict criteria and 52 (47%) met liberal criteria. There were 26 strict patients (45%) recategorized intraoperatively to the liberal group due to patello-femoral changes. There were seven patients (four strict and three liberal) excluded as they underwent total knee arthroplasty based on intraoperative findings. The final postoperative group categorization was 28 strict and 75 liberal patients. A two-sample t-test power analysis determined that 45 patients per group were required to identify a Knee Society Score difference of six with 80% power.

Preoperative liberal patients had greater improvements in Veterans Rank-12 item mental scores compared to preoperative strict patients at final follow-up (8.67 versus 4.30, P = 0.02). Postoperative liberal patients had greater improvements in University of California, Los Angeles Activity Scale scores compared to postoperative strict patients (2.16 versus 1.11, P = 0.03). Overall survivorship was 98.1%, with no difference between preoperative strict and liberal patients (P = 0.3). There were two preoperative liberal patients revised to a total knee arthroplasty: one for a periprosthetic fracture of the tibia and one for unexplained pain.

Stricter indications potentially lead to underutilization of UKA, as demonstrated by similar short-term patient-reported outcomes and survivorship between groups.