Abstract
Objective:
Isokinetic strength testing is widely utilized in return-to-sport evaluations after anterior cruciate ligament reconstruction (ACLR). While conventional metrics such as peak torque provide global insights, they may overlook regional deficits. Statistical Parametric Mapping (SPM), a waveform-based analytical technique, offers a more refined evaluation of limb symmetry across the full arc of motion. The purpose of this study was to assess differences in concentric knee flexion and extension strength waveforms between operative and non-operative limbs in late-phase (9–12 months post-op) ACLR patients, and to investigate sex-specific patterns using SPM analysis.
Methods:
Concentric knee extension and flexion torque data were collected using a HUMAC isokinetic dynamometer across 10°–90° of knee flexion. Participants were stratified by sex (female vs male), and limb symmetry was evaluated using SPM. Torque values were normalized to body weight (BW).
Results:
A total of 158 late-phase ACLR patients were included (females: n = 61, age 25.0 ± 8.6 years; males: n = 97, age 24.6 ± 6.2 years). SPM analysis identified significant within-subject differences in both knee extension and flexion torque waveforms between the operative and non-operative limbs. These asymmetries were not uniform across the range of motion and varied by sex. Notably, females demonstrated a significant reduction in knee extension torque near terminal extension (knee flexion 10° to 34°, p < 0.001), a pattern not observed in male participants. In females, extension limb symmetry index (LSI) averaged 82.2 ± 14.5%, and flexion LSI averaged 88.8 ± 12.9%. In comparison, males demonstrated extension and flexion LSI values of 91.9 ± 15.1% and 93.0 ± 16.5%, respectively. Traditional peak torque measures failed to detect these subtleties, particularly in female patients.
Conclusion:
Waveform-based SPM analysis reveals persistent and region-specific strength deficits in late-stage ACLR patients that are not apparent with peak torque assessments. These sex-specific asymmetries during terminal extension in females may be linked to inferior clinical outcomes experienced in this patient cohort. This highlights the importance of range-sensitive strength assessment tools and may inform targeted rehabilitation strategies. SPM represents a valuable method for both clinical assessment and research quantification of limb symmetry post-ACLR.