Summary

This study suggests that phase angle measured by bioelectrical impedance analysis (BIA) may serve as a practical, non-invasive alternative to the costly BIODEX system for assessing postoperative knee muscle strength in ACL reconstruction patients.

Abstract

Introduction

Muscle strength recovery is crucial for return to sport following anterior cruciate ligament (ACL) injury. While BIODEX is commonly used for strength assessment, its clinical utility is limited due to cost and size. Bioelectrical impedance analysis (BIA) estimates body composition by measuring the impedance of low-amplitude electrical currents through the body. Phase angle, reflecting the ratio of extracellular to intracellular resistance, is considered an indicator of muscle cell mass. This study aims to investigate the utility of phase angle evaluation as an indicator of postoperative muscle strength.

Methods

We prospectively evaluated 27 patients (21 males, 6 females; mean age 33.5 years) who underwent arthroscopic ACL reconstruction at our institution between September 2020 and April 2023. Patients with re-injuries or multiple ligament injuries were excluded. Muscle strength and phase angle were assessed at 3, 6, 9, and 12 months postoperatively using the BIODEX system and a BIA device (MC-980A-N plus, Tanita Corp.). Knee extension strength was measured with the BIODEX at an angular velocity of 60°/sec, and the limb symmetry index (LSI) was calculated for both BIODEX and phase angle. Pearson's correlation coefficient was used to analyze the correlation between these measures, with statistical significance set at p<0.05.

Results

The mean LSI for knee extension strength at 3, 6, 9, and 12 months postoperatively were 59.7%, 70.0%, 77.2%, and 79.6%, respectively. Corresponding mean phase angle LSI values were 91.6%, 95.3%, 96.5%, and 97.4%. Correlation coefficients between knee extension strength and phase angle at each time point were 0.528, 0.596, 0.591, and 0.502, all of which demonstrated significant correlations throughout the study period (p<0.05).

Conclusion

The findings of this study suggest that phase angle measurement using BIA may provide a non-invasive and convenient method for evaluating muscle strength following ACL reconstruction.