JOA - 2026-03-13 - Journal Article
Do Patients Undergoing Unicompartmental Knee Arthroplasty Who Fail to Achieve Minimal Clinically Important Difference Have Higher Rates of Conversion to Total Knee Arthroplasty?
Singh R, Narravula R, Williams DL, Sauder N, Booth M, Lim PL, Melnic CM, Bedair HS
Topics
Key Takeaway
UKA patients failing to achieve MCID on PROMIS-PF10a have a 5-year conversion rate to TKA of 6.9% versus 1.3% in MCID achievers (OR 2.5, p=0.02).
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Summary
This study asked whether failure to achieve MCID on PROMIS-PF10a after UKA predicts conversion to TKA, using a prospectively maintained multi-institutional registry of 760 UKAs with mean 5-year follow-up. MCID (threshold +3.0) was achieved by 528 patients (69.5%); non-achievers had significantly higher conversion rates at both 3 years (4.8% vs 0.9%) and 5 years (6.9% vs 1.3%). On multivariable analysis, MCID achievement remained independently associated with conversion-free survival (OR 2.5, p=0.02) after adjusting for demographics and baseline characteristics.
Key Limitation
Conversion to TKA reflects surgeon and patient decision-making thresholds that vary by institution, meaning conversion rate is a surrogate for failure rather than a standardized, objective endpoint.
Original Abstract
BACKGROUND
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.
METHODS
This was a retrospective analysis of a prospectively maintained multi-institutional arthroplasty registry. A total of 760 UKAs with a mean 5-year follow-up were identified. Patient demographics, baseline characteristics, and the Patient-Reported Outcomes Measurement Information System Physical Function Short-Form 10a were collected. The Patient-Reported Outcomes Measurement Information System Physical Function Short-Form 10a scores were categorized according to a literature-derived MCID threshold of +3.0. Conversion-free survival through 5-year follow-up was compared between patients who achieved MCID and those who did not.
RESULTS
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 3-year (4.8 versus 0.9%; P < 0.01) and 5-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.
CONCLUSIONS
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.