Absolute knee extensor strength, not limb symmetry, predicts outcomes and defines a rehabilitation threshold after medial opening-wedge high tibial osteotomy.

PURPOSE: To identify a clinically relevant body mass-normalised knee extensor strength threshold after high tibial osteotomy (HTO) and examine how absolute strength and limb symmetry index (LSI) relate to patient-reported outcomes (PROMs), dynamic balance and longitudinal muscle strength recovery.

METHODS: A total of 125 patients undergoing HTO were evaluated preoperatively, 1 year, and mid-term follow-up (mean, 37.2 ± 5.6 months; n = 90). Assessments included isokinetic strength, PROMs and the Y-Balance Test. Patients were stratified by involved-limb extensor strength at 1 year. Multivariable regression analyses determined independent associations between strength and functional outcomes. Receiver operating characteristic analysis identified an extensor strength threshold for a satisfactory International Knee Documentation Committee (IKDC) subjective score.

RESULTS: Extensor strength decreased at 6 months, recovered by 1 year and further improved by mid-term follow-up, whereas flexor strength recovered more rapidly and exceeded preoperative values by 1 year. PROMs differed across extensor-strength quartiles at 1 year (p < 0.01), with the largest separation between the third and fourth quartiles (IKDC, +9.2 points). Body mass-normalised extensor strength independently predicted IKDC score (β = 8.20; p = 0.015), whereas normalised flexor strength (p = 0.832) and extensor LSI (p = 0.074) did not. The optimal threshold was 1.3 N·m/kg (area under the curve, 0.691), above which a satisfactory IKDC score was achieved more frequently (65.5% vs. 20.8%; p < 0.001). For the Y-Balance Test composite LSI, extensor LSI was the strongest predictor (β = 0.124; p < 0.001), followed by flexor LSI (β = 0.091; p = 0.009).

CONCLUSIONS: Despite slower extensor than flexor recovery, achieving an extensor strength threshold of 1.3 N·m/kg was associated with a satisfactory IKDC score after HTO. Absolute extensor strength predicted PROMs, whereas LSI was more closely related to dynamic balance. These findings support combining absolute strength targets with limb symmetry benchmarks in rehabilitation.

LEVEL OF EVIDENCE: Level III.