title: Different roles of the medial and lateral hamstrings in unloading the anterior cruciate ligament.
abstract: BACKGROUND
  Anterior cruciate ligament injuries are closely associated with excessive loading and motion about the off axes of the knee, i.e. tibial rotation and knee varus/valgus. However, it is not clear about the 3-D mechanical actions of the lateral and medial hamstring muscles and their differences in loading the ACL. The purpose of this study was to investigate the change in anterior cruciate ligament strain induced by loading the lateral and medial hamstrings individually.
  
  
  METHODS
  Seven cadaveric knees were investigated using a custom testing apparatus allowing for six degree-of-freedom tibiofemoral motion induced by individual muscle loading. With major muscles crossing the knee loaded moderately, the medial and lateral hamstrings were loaded independently to 200N along their lines of actions at 0°, 30°, 60° and 90° of knee flexion. The induced strain of the anterior cruciate ligament was measured using a differential variable reluctance transducer. Tibiofemoral kinematics was monitored using a six degrees-of-freedom knee goniometer.
  
  
  RESULTS
  Loading the lateral hamstrings induced significantly more anterior cruciate ligament strain reduction (mean 0.764 [SD 0.63] %) than loading the medial hamstrings (mean 0.007 [0.2] %), (P=0.001 and effect size=0.837) across the knee flexion angles.
  
  
  CONCLUSIONS
  The lateral and medial hamstrings have significantly different effects on anterior cruciate ligament loadings. More effective rehabilitation and training strategies may be developed to strengthen the lateral and medial hamstrings selectively and differentially to reduce anterior cruciate ligament injury and improve post-injury rehabilitation.
  
  
  CONCLUSIONS
  The lateral and medial hamstrings can potentially be strengthened selectively and differentially as a more focused rehabilitation approach to reduce ACL injury and improve post-injury rehabilitation. Different ACL reconstruction procedures with some of them involving the medial hamstrings can be compared to each other for their effect on ACL loading.
authors.affiliation: Departments of Orthopaedic Surgery, Northwestern University, Chicago, IL, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Guelich
authors.affiliation: Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Dali
authors.initials: D
authors.lastname: Xu
authors.affiliation: Department of Orthopaedic Surgery, Northshore University Healthcare System, Evanston, IL, USA.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Koh
authors.affiliation: Departments of Orthopaedic Surgery, Northwestern University, Chicago, IL, USA; Department of Orthopaedic Surgery, Northshore University Healthcare System, Evanston, IL, USA.
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Nuber
authors.affiliation: Departments of Orthopaedic Surgery, Northwestern University, Chicago, IL, USA; Rehabilitation Institute of Chicago, Chicago, IL, USA; Department of Orthopaedic Surgery, Northshore University Healthcare System, Evanston, IL, USA; Departments of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA; Departments of Biomedical Engineering, Northwestern University, Chicago, IL, USA. Electronic address: l-zhang@northwestern.edu.
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Zhang
mesh_terms: D000368:Aged; D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D002102:Cadaver; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D019637:Orthopedic Procedures / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology*; D013977:Tibia / Q000601:surgery
keywords: ACL; Lateral hamstring; Medial hamstring