Relationship Between Isokinetic Knee Strength and Single-Leg Drop Jump Performance 9 Months After ACL Reconstruction

N M Nuala Crotty; Katherine A J Daniels; Ciaran McFadden; Niall Cafferkey; Enda King

doi:10.1177/23259671211063800

Relationship Between Isokinetic Knee Strength and Single-Leg Drop Jump Performance 9 Months After ACL Reconstruction

Orthop J Sports Med. 2022 Jan 5;10(1):23259671211063800. doi: 10.1177/23259671211063800. eCollection 2022 Jan.

Authors

N M Nuala Crotty¹, Katherine A J Daniels^{2

3}, Ciaran McFadden^{2

4}, Niall Cafferkey², Enda King^{2

4}

Affiliations

¹ School of Medicine, Trinity College Dublin, Dublin, Ireland.
² Sports Medicine Research Department, Sports Surgery Clinic, Dublin, Ireland.
³ Queen's School of Engineering, University of Bristol, Bristol, UK.
⁴ Department of Life Sciences, University of Roehampton, London, UK.

Abstract

Background: Deficits in knee strength after anterior cruciate ligament reconstruction (ACLR) surgery are common. Deficits in the single-leg drop jump (SLDJ), a test of plyometric ability, are also found.

Purpose: To examine the relationship between isokinetic knee strength, SLDJ performance, and self-reported knee function 9 months after ACLR.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: Knee isokinetic peak torque, SLDJ jump height, contact time, and reactive strength index (RSI), as well as International Knee Documentation Committee (IKDC) scores were assessed in 116 male, field-sport athletes at 9.2 months after ACLR. SLDJ testing took place in a 3-dimensional biomechanics laboratory. Linear regression models were used to analyze the relationship between the variables.

Results: A significant relationship was found between ACLR-limb isokinetic knee extensor strength and SLDJ jump height (P < .001, r ² = 0.29) and RSI (P < .001, r ² = 0.33), and between ACLR-limb isokinetic knee flexor strength and SLDJ jump height (P < .001, r ² = 0.12) and RSI (P < .001, r ² = 0.15). A significant positive relationship was also found between knee extensor asymmetry and SLDJ jump height asymmetry (P < .001, r ² = 0.27) and SLDJ reactive strength asymmetry (P < .001, r ² = 0.18). Combined ACLR-limb jump height and contact time best predicted IKDC scores (P < .001, r ² = 0.12).

Conclusion: Isokinetic knee extension strength explained approximately 30% of SLDJ performance, with a much weaker relationship between knee flexion strength and SLDJ performance. Isokinetic strength and SLDJ performance were weak predictors of variation in IKDC scores.

Keywords: anterior cruciate ligament reconstruction; exercise test; muscle strength; plyometric exercise; return to sport.