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. 2025 Nov 14.
doi: 10.1002/ksa.70182. Online ahead of print.

Impact of change in contralateral knee extensor strength on achieving limb symmetry index targets following anterior cruciate ligament reconstruction

Nicholas Whitworth  1 , Kate E Webster  2 , Haydn J Klemm  1   2 , Jodie A McClelland  2 , Lachlan M Batty  1   2 , Julia C Kirby  1 , Timothy S Whitehead  1 , Julian A Feller  1   2
Affiliations

Impact of change in contralateral knee extensor strength on achieving limb symmetry index targets following anterior cruciate ligament reconstruction

Nicholas Whitworth et al. Knee Surg Sports Traumatol Arthrosc. .

Abstract

Purpose: To determine how changes in contralateral limb strength over time influence limb symmetry indices for knee extensor strength after anterior cruciate ligament (ACL) reconstruction.

Methods: From a prospective longitudinal study, 381 eligible patients who had a primary ipsilateral ACL reconstruction were included. Isokinetic strength testing was performed at 6- and 12-month post-operative time points. Peak knee extension torque of the operated and the contralateral limbs were measured at 60 degrees per second and normalised to bodyweight. Change in knee extensor torque between 6 and 12 months was calculated for each limb, and the proportion of participants who achieved a limb symmetry index (LSI) of >85 was reported at each time point. To explore the impact of change in contralateral limb strength, the analysis was repeated after dividing patients into three subgroups: those with no change, a greater than 10% increase or a greater than 10% decrease in contralateral knee extensor torque.

Results: Mean scores for the operated and contralateral limb strength increased between 6 and 12 months, with larger gains in the operated limb. Consequently, the likelihood of passing an LSI threshold of 85% improved with time. However, subgroup analysis revealed that despite mean cohort strength gains, a substantial proportion of patients (23.1%) had a greater than 10% decrease in their contralateral strength between 6 and 12 months. Despite recording the lowest operative limb strengths, these patients were most likely to pass an LSI threshold of 85%.

Conclusions: Changes in contralateral knee strength occurred between 6 and 12 months following ACL reconstruction. The strength changes in the contralateral knee impact the LSI, which may result in over- or underestimation of the recovery of strength in the reconstructed knee. As such, caution should be exercised when using LSI thresholds in the assessment of readiness to return to sport following ACL reconstruction.

Level of evidence: Level II, prospective cohort study.

Keywords: ACL reconstruction; hamstring tendon graft; isokinetic strength; return to sport.

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References

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