title: Young Athletes With Quadriceps Femoris Strength Asymmetry at Return to Sport After Anterior Cruciate Ligament Reconstruction Demonstrate Asymmetric Single-Leg Drop-Landing Mechanics.
abstract: BACKGROUND
  Young athletes who have had anterior cruciate ligament (ACL) reconstruction demonstrate suboptimal rates of return to sport, high rates of second ACL injuries, and persistent movement asymmetries. Therefore, the influence of musculoskeletal impairments on movement mechanics in this population needs to be further evaluated.
  
  
  OBJECTIVE
  The primary hypothesis was that among young athletes who have had ACL reconstruction, those with greater quadriceps strength asymmetry would demonstrate altered single-leg drop-landing mechanics at return to sport compared with individuals with more symmetric quadriceps strength and also compared with healthy controls (ie, those with no ACL reconstruction). A second hypothesis was that quadriceps strength symmetry would predict single-leg drop-landing symmetry in individuals who have undergone ACL reconstruction.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  The study entailed a total of 103 participants (age, 17.4 years) at the time of return to sport after ACL reconstruction and 47 control participants (age, 17.0 years). The quadriceps index (QI) was calculated for isometric quadriceps strength, which was then used to divide the ACL reconstruction participants into high-quadriceps (QI ≥90%; n = 52) and low-quadriceps (QI <85%; n = 41) subgroups. Biomechanical data were collected by use of 3-dimensional motion analysis during a single-leg drop-landing task. The LSI was calculated for kinematic and kinetic sagittal-plane variables of interest during landing. Group differences were compared by use of 1-way analysis of variance and linear regression analyses (α < .05).
  
  
  RESULTS
  Both the low- and high-quadriceps groups demonstrated greater limb asymmetry during landing compared with the control group in knee flexion excursion (mean LSI ± SD: low quadriceps, 85.8% ± 15.5% [P < .001]; high quadriceps, 94.2% ± 15.6% [P = .019]; control, 102.7% ± 14.1%), peak trunk flexion angle (low quadriceps, 129.2% ± 36.6% [P < .001]; high quadriceps, 110.5% ± 22.6% [P = .03]; control, 95.5% ± 26.2%), and peak knee extension moment (low quadriceps, 79.5% ± 25.2% [P < .001]; high quadriceps, 89.9% ± 19.8% [P = .005]; control, 102.2% ± 10.9%). Compared with the high-quadriceps group, the low-quadriceps group also demonstrated greater asymmetry during landing in knee flexion excursion (P = .026), peak trunk flexion angle (P = .006), and peak knee extension moment (P = .034). In the ACL reconstruction group, quadriceps strength symmetry predicted symmetry in knee flexion excursion, peak trunk flexion, and peak knee extension moment (all P < .001) and predicted symmetry in peak trunk flexion angle (P < .001) after controlling for graft type, knee-related pain, function with activities of daily living, and sport function.
  
  
  CONCLUSIONS
  At the time of return to sport, athletes who had undergone ACL reconstruction, including those in both the high- and low-quadriceps groups, demonstrated asymmetry during a single-leg drop-landing task compared with controls. Compensations included increased trunk flexion, decreased knee flexion excursion, and decreased knee extension moments on the involved limb. In addition, individuals in the low-quadriceps group demonstrated greater movement asymmetry compared with individuals in the high-quadriceps group.
  
  
  CONCLUSIONS
  Restoration of symmetric quadriceps strength after ACL reconstruction is associated with more symmetric mechanics during a single-leg drop-landing movement. However, this appears to be multifactorial, as the high-quadriceps group also demonstrated landing asymmetries. Restoration of symmetric quadriceps strength may improve postoperative athletic participation; however, future study is warranted.
authors.affiliation: School of Health and Rehabilitation Sciences, The Ohio State University, Columbus, Ohio, USA Sports Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Ithurburn
authors.affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Division of Occupational Therapy and Physical Therapy, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Department of Pediatrics, College of Medicine, University of Cincinnati, Cincinnati, Ohio, USA.
authors.forename: Mark V
authors.initials: MV
authors.lastname: Paterno
authors.affiliation: Department of Physical Therapy, High Point University, High Point, North Carolina, USA.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Ford
authors.affiliation: Sports Medicine, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Department of Pediatrics, College of Medicine, University of Cincinnati, Cincinnati, Ohio, USA Sports Health & Performance Institute, The Ohio State University, Columbus, Ohio, USA Departments of Physiology and Cell Biology, Orthopaedic Surgery, Family Medicine, Biomedical Engineering, College of Medicine, The Ohio State University, Columbus, Ohio, USA Biomechanics Laboratory and Sports Medicine, Departments of Orthopaedic Surgery, Physical Medicine and Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Hewett
authors.affiliation: School of Health and Rehabilitation Sciences, The Ohio State University, Columbus, Ohio, USA Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Division of Physical Therapy, School of Health and Rehabilitation Sciences, The Ohio State University, Columbus, Ohio, USA laura.schmitt@osumc.edu.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Schmitt
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000534:rehabilitation*; D056352:Athletes; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007717:Knee / Q000601:surgery; D007719:Knee Joint / Q000601:surgery; D008297:Male; D009068:Movement; D052097:Quadriceps Muscle / Q000378:metabolism*; D000068958:Return to Sport; D055815:Young Adult
keywords: ACL; biomechanics; knee; motion analysis