title: Evaluation of predicted knee-joint muscle forces during gait using an instrumented knee implant.
abstract: Musculoskeletal modeling and optimization theory are often used to determine muscle forces in vivo. However, convincing quantitative evaluation of these predictions has been limited to date. The present study evaluated model predictions of knee muscle forces during walking using in vivo measurements of joint contact loading acquired from an instrumented implant. Joint motion, ground reaction force, and tibial contact force data were recorded simultaneously from a single subject walking at slow, normal, and fast speeds. The body was modeled as an 8-segment, 21-degree-of-freedom articulated linkage, actuated by 58 muscles. Joint moments obtained from inverse dynamics were decomposed into leg-muscle forces by solving an optimization problem that minimized the sum of the squares of the muscle activations. The predicted knee muscle forces were input into a 3D knee implant contact model to calculate tibial contact forces. Calculated and measured tibial contact forces were in good agreement for all three walking speeds. The average RMS errors for the medial, lateral, and total contact forces over the entire gait cycle and across all trials were 140 +/- 40 N, 115 +/- 32 N, and 183 +/- 45 N, respectively. Muscle coordination predicted by the model was also consistent with EMG measurements reported for normal walking. The combined experimental and modeling approach used in this study provides a quantitative framework for evaluating model predictions of muscle forces in human movement.
authors.affiliation: Department of Mechanical Engineering, University of Melbourne, Carlton, Victoria 3010, Australia.
authors.forename: Hyung J
authors.initials: HJ
authors.lastname: Kim
authors.forename: Justin W
authors.initials: JW
authors.lastname: Fernandez
authors.forename: Massoud
authors.initials: M
authors.lastname: Akbarshahi
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Walter
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Fregly
authors.forename: Marcus G
authors.initials: MG
authors.lastname: Pandy
mesh_terms: D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D004576:Electromyography; D005684:Gait / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology*; D009142:Musculoskeletal Physiological Phenomena; D011237:Predictive Value of Tests; D016474:Weight-Bearing / Q000502:physiology