title: Higher medially-directed joint reaction forces are a characteristic of dysplastic hips: A comparative study using subject-specific musculoskeletal models.
abstract: Acetabular dysplasia is a known cause of hip osteoarthritis. In addition to abnormal anatomy, changes in kinematics, joint reaction forces (JRFs), and muscle forces could cause tissue damage to the cartilage and labrum, and may contribute to pain and fatigue. The objective of this study was to compare lower extremity joint angles, moments, hip JRFs and muscle forces during gait between patients with symptomatic acetabular dysplasia and healthy controls. Marker trajectories and ground reaction forces were measured in 10 dysplasia patients and 10 typically developing control subjects. A musculoskeletal model was scaled in OpenSim to each subject and subject-specific hip joint centers were determined using reconstructions from CT images. Joint kinematics and moments were calculated using inverse kinematics and inverse dynamics, respectively. Muscle forces and hip JRFs were estimated with static optimization. Inter-group differences were tested for statistical significance (p≤0.05) and large effect sizes (d≥0.8). Results demonstrated that dysplasia patients had higher medially directed JRFs. Joint angles and moments were mostly similar between the groups, but large inter-group effect sizes suggested some restriction in range of motion by patients at the hip and ankle. Higher medially-directed JRFs and inter-group differences in hip muscle forces likely stem from lateralization of the hip joint center in dysplastic patients. Joint force differences, combined with reductions in range of motion at the hip and ankle may also indicate compensatory strategies by patients with dysplasia to maintain joint stability.
authors.affiliation: Program in Physical Therapy, Washington University School of Medicine, St Louis, MO 63108, United States; Department of Orthopaedic Surgery, Washington University School of Medicine, St Louis, MO 63108, United States.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Harris
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT 84108, United States; Shriners Hospitals for Children, Salt Lake City, UT 84103, United States; Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, United States.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: MacWilliams
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT 84108, United States; Department of Physical Therapy, University of Utah, Salt Lake City, UT 84108, United States.
authors.forename: K
authors.initials: K
authors.lastname: Bo Foreman
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT 84108, United States; Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, United States.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Peters
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT 84108, United States; Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, United States; Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT 84112, United States.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Weiss
authors.affiliation: Department of Orthopaedics, University of Utah, Salt Lake City, UT 84108, United States; Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, United States; Department of Physical Therapy, University of Utah, Salt Lake City, UT 84108, United States; Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT 84112, United States. Electronic address: andrew.anderson@hsc.utah.edu.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Anderson
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait / Q000502:physiology; D006617:Hip Dislocation / Q000503:physiopathology*; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology*; D066230:Patient-Specific Modeling; D016059:Range of Motion, Articular / Q000502:physiology; D055815:Young Adult
keywords: Acetabular dysplasia; Biomechanics; Gait; Hip; Musculoskeletal modeling