Persistent extensor strength deficit despite acceptable clinical outcomes after surgical treatment of patella fractures: a mid- to long-term follow-up study

INTRODUCTION: To evaluate mid- to long-term clinical outcomes together with objective isokinetic measurements of knee flexor and extensor muscle strength in patients who underwent surgical treatment for AO/OTA type C patella fractures, and to investigate the relationship between fracture severity, clinical scores, and strength deficits. We hypothesized that significant quadriceps strength deficits would persist despite acceptable clinical outcomes and that these deficits would be associated with worse pain and functional scores. MATERIALS AND METHODS: This retrospective cohort study included 58 patients treated surgically for patella fractures between 2015 and 2024, with a median follow-up duration of 60 months (IQR: 32-94; range: 13.1-132.0 months). The primary outcome was extensor muscle strength deficit measured by isokinetic dynamometry. Secondary outcomes included flexor strength deficit, Lysholm score, visual analog scale (VAS), and knee range of motion. Isokinetic dynamometry at 60°/s was used to measure concentric flexor and extensor peak torque values, and strength deficits were calculated by comparison with the contralateral limb. Outcomes were compared among fracture subtypes (C1, C2, C3), and correlations between strength deficits and clinical scores were analyzed. Non-parametric tests (Kruskal-Wallis) and partial correlation analysis (Pearson, adjusted for age) were used for statistical analysis. RESULTS: At final follow-up, patients demonstrated generally acceptable clinical outcomes (mean Lysholm: 80.12 ± 16.88; mean VAS: 2.19 ± 1.79) with minimal extension deficits. However, the primary outcome, extensor muscle strength deficit, remained substantial a mean extensor strength deficit of 36.31 ± 17.27%, and 84.5% of patients exhibited marked extensor asymmetry (≥ 20%). Flexor strength deficits were less pronounced (19.09 ± 10.75%) but remained clinically relevant. No statistically significant differences were detected in clinical scores, range of motion, or strength deficits were observed among fracture subtypes (p > 0.05). Greater extensor and flexor strength deficits were significantly associated with higher VAS scores and lower Lysholm scores (all p < 0.05). Revision surgery was required in 12% of patients, and implant removal in 38%, indicating a considerable secondary surgical burden. CONCLUSIONS: Despite satisfactory clinical scores and radiographic healing, substantial and persistent quadriceps weakness appears to be common after surgically treated patella fractures. Objective strength deficits are strongly associated with pain and functional outcomes and may not be fully captured by conventional clinical assessments. Long-term management should therefore incorporate objective muscle strength evaluation and targeted rehabilitation strategies to address persistent extensor weakness.