title: Limited benefit of hamstrings forces for the anterior cruciate ligament-deficient knee: an in vitro study.
abstract: The hamstrings are considered stabilizers of the anterior cruciate ligament-deficient knee; however, anterior cruciate ligament injury primarily influences tibiofemoral kinematics near full extension, where the hamstrings have the least influence on kinematics. Ten knees were tested at multiple flexion angles in vitro to directly compare the influence of anterior cruciate ligament injury and hamstrings activation on tibiofemoral kinematics. Tibiofemoral kinematics were measured for three testing conditions: (1) anterior cruciate ligament intact, with forces applied through the quadriceps muscles (596 N), (2) anterior cruciate ligament cut, with forces applied through the quadriceps, and (3) anterior cruciate ligament cut, with forces applied through the quadriceps and hamstrings (200 N). Based on repeated measures comparisons performed at each flexion angle, cutting the anterior cruciate ligament significantly (p < 0.05) increased tibial anterior translation, medial translation, and internal rotation at 0 degrees and 15 degrees of flexion by approximately 2.5 mm, 1 mm, and 2 degrees, respectively. Internal rotation also increased significantly at 30 degrees. With the anterior cruciate ligament cut, loading the hamstrings significantly decreased anterior translation, medial translation, and internal rotation at 45 degrees, by approximately 2 mm, 2 mm, and 4 degrees, respectively. Loading the hamstrings caused kinematic changes in the opposite direction of the anterior cruciate ligament injury, but the changes occurred at deeper flexion angles than those at which anterior cruciate ligament injury influenced tibiofemoral kinematics.
authors.affiliation: Department of Orthopaedic Surgery, Akron General Medical Center, OH 44307, USA. john.elias@akrongeneral.org
authors.forename: John J
authors.initials: JJ
authors.lastname: Elias
authors.forename: Marcus S
authors.initials: MS
authors.lastname: Kirkpatrick
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Stonestreet
authors.forename: Kushal S
authors.initials: KS
authors.lastname: Shah
authors.forename: Caroline E
authors.initials: CE
authors.lastname: Frampton
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Morscher
authors.forename: Kerwyn C
authors.initials: KC
authors.lastname: Jones
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016118:Anterior Cruciate Ligament / Q000503:physiopathology*; D000070598:Anterior Cruciate Ligament Injuries; D006801:Humans; D007718:Knee Injuries / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D004856:Postural Balance; D016059:Range of Motion, Articular