Do Patients Undergoing Unicompartmental Knee Arthroplasty Who Fail to Achieve MCID Have Higher Rates of Conversion to Total Knee Arthroplasty?

Abstract

With an increase in unicompartmental knee arthroplasty (UKA) being performed in the United States, arthroplasty surgeons may benefit from strategies to identify the UKA patients at high risk for conversion to total knee arthroplasty (TKA). These patients may benefit from closer monitoring, targeted physical therapy, and timely interventions. A strategy for monitoring at-risk patients may be the utilization of the minimal clinically important difference (MCID) threshold. The UKA patients who experience unresolved pain, suboptimal biomechanics, or are unable to actively participate in their recovery may not achieve MCID, which may contribute to higher conversion rates. This study investigated the association between MCID achievement following UKA and rate of conversion. This was a retrospective analysis of a prospectively maintained multi-institutional arthroplasty registry. A total of 760 UKAs with a mean five-year follow-up were identified. Patient demographics, baseline characteristics, and the Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function Short-Form 10a (PF-10a) were collected. The PROMIS PF-10a scores were categorized according to a literature-derived MCID threshold of +3.0. Conversion-free survival through five-year follow-up was compared between patients who achieved MCID and those who did not. Following UKA, the MCID was achieved by 528 patients (69.5%). The UKA patients who did not achieve the MCID had higher rates of conversion at three-year (4.8 versus 0.9%; P < 0.01) and five-year (6.9 versus 1.3%; P < 0.01) follow-up. The MCID achievement remained independently associated with increased likelihood of conversion-free survival (odds ratio = 2.5; P = 0.02) after adjusting for demographics and baseline characteristics. The UKA patients who did not achieve the MCID were more likely to undergo conversion to TKA, even after accounting for demographics and baseline characteristics. Utilization of MCID thresholds in the UKA patients may therefore be a strategy to identify patients at higher risk for conversion to TKA, who could benefit from closer postoperative monitoring.