A novel clinic-friendly test protocol to assess quadriceps strength symmetry after anterior cruciate ligament reconstruction.

OBJECTIVES

To evaluate the reliability and validity of a clinic-friendly protocol using a weight-based knee extension (WBKE) machine to assess quadriceps symmetry after anterior cruciate ligament (ACL) reconstruction, compared to isokinetic dynamometry (IKD).

DESIGN

Cross-sectional reliability and validity study.

SETTING

Orthopedic rehabilitation and sports medicine clinic.

PARTICIPANTS

Seventy-four individuals (aged 16-50 years) between 6 and 14 months post-ACL reconstruction.

MAIN OUTCOME MEASURES: Test-retest reliability (intraclass correlation coefficients, ICC) and validity (limb symmetry index, Pearson's correlation, linear regression, Bland-Altman analysis) of WBKE compared to IKD.

RESULTS

The WBKE test showed excellent test-retest reliability (ICC = 0.94-0.98). The limb symmetry index was 90.6% ± 12.4% for IKD and 87.5% ± 12.5% for WBKE, with a mean difference of -3.16% (95% CI: -4.8 to -1.5, p < 0.001). Bland-Altman analysis indicated 95% limits of agreement from 8.31% to -14.63%. The correlation between WBKE and IKD was strong (r = 0.89, 95% CI: 0.81-0.94, p < 0.001), supported by linear regression (R2 = 0.79, p < 0.001).

CONCLUSIONS

The WBKE test demonstrated excellent reliability and strong validity for assessing quadriceps symmetry post-ACL reconstruction. It offers a practical, accessible alternative to isokinetic testing for monitoring strength recovery in clinical practice.