title: Knee contact force asymmetries in patients who failed return-to-sport readiness criteria 6 months after anterior cruciate ligament reconstruction.
abstract: BACKGROUND
  After anterior cruciate ligament (ACL) injury, contact forces are decreased in the injured knee when compared with the uninjured knee. The persistence of contact force asymmetries after ACL reconstruction may increase the risk of reinjury and may play an important role in the development of knee osteoarthritis in these patients. Functional performance may also be useful in identifying patients who demonstrate potentially harmful joint contact force asymmetries after ACL reconstruction.
  
  
  OBJECTIVE
  Knee joint contact force asymmetries would be present during gait after ACL reconstruction, and performance on a specific set of validated return-to-sport (RTS) readiness criteria would discriminate between those who demonstrated contact force asymmetries and those who did not.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  A total of 29 patients with ACL ruptures participated in gait analysis and RTS readiness testing 6 months after reconstruction. Muscle and joint contact forces were estimated using an electromyography (EMG)-driven musculoskeletal model of the knee. The magnitude of typical limb asymmetry in uninjured controls was used to define limits of meaningful limb asymmetry in patients after ACL reconstruction. The RTS testing included isometric quadriceps strength testing, 4 unilateral hop tests, and 2 self-report questionnaires. Paired t tests were used to assess limb symmetry for peak medial and tibiofemoral contact forces in all patients, and a mixed-design analysis of variance was used to analyze the effect of passing or failing RTS testing on contact force asymmetry.
  
  
  RESULTS
  Among all patients, neither statistically significant nor meaningful contact force asymmetries were identified. However, patients who failed RTS testing exhibited meaningful contact force asymmetries, with tibiofemoral contact force being significantly lower for the involved knee. Conversely, patients who passed RTS testing exhibited neither significant nor meaningful contact force asymmetries.
  
  
  CONCLUSIONS
  Joint contact force asymmetries during gait are present in some patients 6 months after ACL reconstruction. Patients who demonstrated poor functional performance on RTS readiness testing exhibited significant and meaningful contact force asymmetries.
  
  
  CONCLUSIONS
  When assessing all patients together, variability in the functional status obscured significant and meaningful differences in contact force asymmetry in patients 6 months after ACL reconstruction. These specific RTS readiness criteria appear to differentiate between those who demonstrate joint contact force symmetry after ACL reconstruction and those who do not.
authors.affiliation: School of Kinesiology, University of Michigan, Ann Arbor, Michigan, USA egardin@umich.edu.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Gardinier
authors.affiliation: Sports Health and Performance Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA Department of Orthopaedics, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Di Stasi
authors.affiliation: Delaware Rehabilitation Institute, University of Delaware, Newark, Delaware, USA Department of Mechanical Engineering, University of Delaware, Newark, Delaware, USA.
authors.forename: Kurt
authors.initials: K
authors.lastname: Manal
authors.affiliation: Delaware Rehabilitation Institute, University of Delaware, Newark, Delaware, USA Department of Mechanical Engineering, University of Delaware, Newark, Delaware, USA.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Buchanan
authors.affiliation: Delaware Rehabilitation Institute, University of Delaware, Newark, Delaware, USA Department of Physical Therapy, University of Delaware, Newark, Delaware, USA.
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D001265:Athletic Injuries / Q000503:physiopathology / Q000601:surgery; D001696:Biomechanical Phenomena / Q000502:physiology; D016022:Case-Control Studies; D004576:Electromyography; D005080:Exercise Test; D005260:Female; D005684:Gait / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology; D012421:Rupture; D011795:Surveys and Questionnaires
keywords: ACL; contact force; knee; reconstruction