title: The influence of task complexity on knee joint kinetics following ACL reconstruction.
abstract: BACKGROUND
  Previous research indicates that subjects with anterior cruciate ligament reconstruction exhibit abnormal knee joint movement patterns during functional activities like walking. While the sagittal plane mechanics have been studied extensively, less is known about the secondary planes, specifically with regard to more demanding tasks. This study explored the influence of task complexity on functional joint mechanics in the context of graft-specific surgeries.
  
  
  METHODS
  In 25 participants (10 hamstring tendon graft, 6 patellar tendon graft, 9 matched controls), three-dimensional joint torques were calculated using a standard inverse dynamics approach during level walking and stair descent. The stair descent task was separated into two functionally different sub-tasks-step-to-floor and step-to-step. The differences in external knee moment profiles were compared between groups; paired differences between the reconstructed and non-reconstructed knees were also assessed.
  
  
  RESULTS
  The reconstructed knees, irrespective of graft type, typically exhibited significantly lower peak knee flexion moments compared to control knees during stair descent, with the differences more pronounced in the step-to-step task. Frontal plane adduction torque deficits were graft specific and limited to the hamstring tendon knees during the step-to-step task. Internal rotation torque deficits were also primarily limited to the hamstring tendon graft group during stair descent. Collectively, these results suggest that task complexity was a primary driver of differences in joint mechanics between anterior cruciate ligament reconstructed individuals and controls, and such differences were more pronounced in individuals with hamstring tendon grafts.
  
  
  CONCLUSIONS
  The mechanical environment experienced in the cartilage during repetitive, cyclical tasks such as walking and other activities of daily living has been argued to contribute to the development of degenerative changes to the joint and ultimately osteoarthritis. Given the task-specific and graft-specific differences in joint mechanics detected in this study, care should be taken during the rehabilitation process to mitigate these changes.
authors.affiliation: Department of Biomedical Engineering, McCormick School of Engineering and Applied Science, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, IL 60611, USA. Electronic address: megan.schroeder@u.northwestern.edu.
authors.forename: Megan J
authors.initials: MJ
authors.lastname: Schroeder
authors.affiliation: Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, 710 North Lake Shore Drive, Chicago, IL 60611, USA; Department of Physical Medicine and Rehabilitation, University of Michigan, 325 East Eisenhower Parkway, Ann Arbor, MI 48108, USA.
authors.forename: Chandramouli
authors.initials: C
authors.lastname: Krishnan
authors.affiliation: Department of Biomedical Engineering, McCormick School of Engineering and Applied Science, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, IL 60611, USA; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, 710 North Lake Shore Drive, Chicago, IL 60611, USA.
authors.forename: Yasin Y
authors.initials: YY
authors.lastname: Dhaher
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D018482:Muscle, Skeletal / Q000601:surgery*; D010329:Patella / Q000601:surgery*; D017847:Patellar Ligament / Q000601:surgery*; D011795:Surveys and Questionnaires; D013710:Tendons / Q000601:surgery*; D019415:Torque; D016138:Walking
keywords: ACL reconstruction; Gait; Joint torques; Knee; Motion analysis; Stair descent