Archives of Orthopaedic and Trauma Surgery - 2026-07-10 - Journal Article; Comparative Study
Unicompartmental knee arthroplasty and total knee arthroplasty in patients with 15 or more degrees of varus deformity: age- and gender-matched comparative study of radiographic and clinical outcomes.
Mullaji A, Chopperla S, George GK, Kazi R
Topics
Key Takeaway
In 52 age- and gender-matched pairs with ≥15° varus deformity, UKA and TKA produced equivalent OKS, SF-12, and FJS scores at mean 3.7 and 5.5 years respectively, with 98% vs 94% achieving good-to-excellent outcomes despite UKA correcting 5.7° less deformity (ΔHKA 10.6° vs 16.3°, p<0.001).
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Summary
This study compared radiographic and clinical outcomes of UKA versus TKA in patients with ≥15° varus deformity using 52 age- and gender-matched pairs from a single institution (2016–2021). TKA achieved significantly greater deformity correction (ΔHKA 16.3° vs 10.6°, p<0.001) with changes in both mLDFA and MPTA, while UKA left 68% of patients in a postoperative HKA range of 171.2°–175.7° (residual varus). Despite radiographic differences, no statistically significant differences were found in OKS, SF-12, or FJS between groups, and neither preoperative deformity severity nor residual postoperative varus correlated with outcomes.
Key Limitation
The study is underpowered and not designed to establish equivalence, meaning the absence of statistically significant PROM differences cannot be interpreted as non-inferiority of UKA in this deformity range.
Original Abstract
INTRODUCTION
To date, few studies have directly compared matched cohorts of patients with severe varus deformity undergoing UKA versus TKA. The current study seeks to address this gap. The hypothesis was that, in patients with deformity of > 15°, postoperative PROMs following UKA would be inferior to those achieved with TKA.
METHODS
Records of patients operated for UKA and TKA from January 2016 to December 2021 were evaluated, and the data for patients with deformity of ≥ 15° were selected. The UKA patients were then matched for age and gender with TKA patients. 52 matched pairs of patients were obtained. The HKA, mLDFA, MPTA were measured. OKS, SF12, and FJS were collected. The magnitude of change in the mLDFA and MPTA was assessed using the Estimated Marginal Means.
RESULTS
The mean follow-up times for UKA and TKA were 3.7 years and 5.5 years, respectively. The mean deformity correction (ΔHKA) was significantly greater in TKA (16.3° ± 4.5°) than UKA (10.6° ± 3.1°) (p < 0.001), with significant changes in mLDFA and MPTA (p < 0.001). In UKAs, 68% of patients demonstrated a postoperative HKA between 171.2° and 175.7°, whereas in TKAs, values clustered between 174.5° and 179.8°. Mann-Whitney U test demonstrated no statistically significant differences between the UKA and TKA cohorts across all assessed PROMs, including OKS, SF-12, and FJS (p > 0.05 in all). 98% of the UKA and 94% of the TKA cohort achieved excellent or good outcomes.
CONCLUSION
UKA performed in carefully selected patients with large varus deformities (> 15°) can provide satisfactory short- to mid-term outcomes. Although no statistically significant differences were observed in postoperative PROMs between the UKA and TKA groups, the current study was not designed or sufficiently powered to establish equivalence or detect subtle clinically meaningful differences between procedures. Greater deformity correction was achieved with TKA; however, UKA also resulted in substantial correction despite persistence of some residual varus in certain patients with severe preoperative deformity. Neither the severity of preoperative deformity nor the degree of postoperative residual varus demonstrated a statistically significant correlation with postoperative outcomes in this cohort.