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Single leg hop for distance symmetry masks lower limb biomechanics: time to discuss hop distance as decision criterion for return to sport after ACL reconstruction?
  1. Argyro Kotsifaki1,2,
  2. Rod Whiteley1,3,
  3. Sam Van Rossom2,
  4. Vasileios Korakakis1,
  5. Roald Bahr4,5,
  6. Vasileios Sideris1,
  7. Philip Graham-Smith6,
  8. Ilse Jonkers2
  1. 1Rehabilitation Department, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
  2. 2Department of Movement Sciences, Human Movement Biomechanics Research Group, KU Leuven, Leuven, Belgium
  3. 3School of Human Movement & Nutrition Sciences, The University of Queensland, Brisbane, Queensland, Australia
  4. 4Aspetar Sports Injury and Illness Prevention Programme (ASPREV), Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
  5. 5Department of Sports Medicine, Norwegian School of Sports Sciences, Oslo, Norway
  6. 6Sports Science Department, Aspire Academy, Doha, Qatar
  1. Correspondence to Argyro Kotsifaki, Aspetar Orthopaedic and Sports Medicine Hospital, Doha 29222, Qatar; argyro.kotsifaki{at}


Background We evaluated the lower limb status of athletes after anterior cruciate ligament reconstruction (ACLR) during the propulsion and landing phases of a single leg hop for distance (SLHD) task after they had been cleared to return to sport. We wanted to evaluate the biomechanical components of the involved (operated) and uninvolved legs of athletes with ACLR and compare these legs with those of uninjured athletes (controls).

Methods We captured standard video-based three-dimensional motion and electromyography (EMG) in 26 athletes after ACLR and 23 healthy controls during SLHD and calculated lower limb and trunk kinematics. We calculated lower limb joint moments and work using inverse dynamics and computed lower limb muscle forces using an EMG-constrained musculoskeletal modelling approach. Between-limb (within ACLR athletes) and between-group differences (between ACLR athletes and controls) were evaluated using paired and independent sample t-tests, respectively.

Results Significant differences in kinematics (effect sizes ranging from 0.42 to 1.56), moments (0.39 to 1.08), and joint work contribution (0.55 to 1.04) were seen between the involved and uninvolved legs, as well as between groups. Athletes after ACLR achieved a 97%±4% limb symmetry index in hop distance but the symmetry in work done by the knee during propulsion was only 69%. During landing, the involved knee absorbed less work than the uninvolved, while the uninvolved knee absorbed more work than the control group. Athletes after ACLR compensated for lower knee work with greater hip work contribution and by landing with more hip flexion, anterior pelvis tilt, and trunk flexion.

Conclusion Symmetry in performance on a SLHD test does not ensure symmetry in lower limb biomechanics. The distance hopped is a poor measure of knee function, and largely reflects hip and ankle function. Male athletes after ACLR selectively unload the involved limb but outperform controls on the uninvolved knee.

  • ACL
  • biomechanics
  • sporting injuries
  • knee injuries
  • injury prevention

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  • Twitter @RoulaKotsifaki, @RodWhiteley, @SamVanRossom, @KorakakisV, @RoaldBahr, @vasilisbme, @PhilipGrahamSm2, @IJonkers

  • Correction notice This article has been corrected since it published Online First. Table 2 has been corrected.

  • Contributors AK, RW, SVR and IJ participated in the design and conception of the study. AK, VS and PG-S were responsible for data collection. AK, RW and VK performed the data analysis and table designs and all the authors contributed to the interpretation. AK drafted the manuscript and all the authors revised it critically and gave their approval of the final version.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval Ethics approval was granted from the Anti-Doping Lab Qatar Institutional Review Board (F2017000227).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available on reasonable request. All publicly available data are included in the article or uploaded as online supplemental information.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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