title: A non-invasive, 3D, dynamic MRI method for measuring muscle moment arms in vivo: demonstration in the human ankle joint and Achilles tendon.
abstract: Muscle moment arms are used widely in biomechanical analyses. Often they are measured in 2D or at a series of static joint positions. In the present study we demonstrate a simple MRI method for measuring muscle moment arms dynamically in 3D from a single range-of-motion cycle. We demonstrate this method in the Achilles tendon for comparison with other methods, and validate the method using a custom apparatus. The method involves registration of high-resolution joint geometry from MRI scans of the stationary joint with low-resolution geometries from ultrafast MRI scans of the slowly moving joint. Tibio-talar helical axes and 3D Achilles tendon moment arms were calculated throughout passive rotation for 10 adult subjects, and compared with recently published data. A simple validation was conducted by comparing MRI measurements with direct physical measurements made on a phantom. The moment arms measured using our method and those of others were similar and there was good agreement between physical measurements (mean 41.0mm) and MRI measurements (mean 39.5mm) made on the phantom. This new method can accurately measure muscle moment arms from a single range-of-motion cycle without the need to control rotation rate or gate the scanning. Supplementary data includes custom software to assist implementation.
authors.affiliation: Sydney Medical School, The University of Sydney, Sydney, Australia; The Kolling Institute of Medical Research, Sydney, Australia. Electronic address: elizabeth.clarke@sydney.edu.au.
authors.forename: E C
authors.initials: EC
authors.lastname: Clarke
authors.affiliation: Sydney Medical School, The University of Sydney, Sydney, Australia; The Kolling Institute of Medical Research, Sydney, Australia.
authors.forename: J H
authors.initials: JH
authors.lastname: Martin
authors.affiliation: Mechanical Engineering, University of British Columbia, Vancouver, Canada; Department of Orthopaedics and Centre for Hip Health and Mobility, University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, Canada.
authors.forename: A G
authors.initials: AG
authors.lastname: d'Entremont
authors.affiliation: Mechanical Engineering, University of Melbourne, Melbourne, Australia.
authors.forename: M G
authors.initials: MG
authors.lastname: Pandy
authors.affiliation: Department of Orthopaedics and Centre for Hip Health and Mobility, University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, Canada.
authors.forename: D R
authors.initials: DR
authors.lastname: Wilson
authors.affiliation: Neuroscience Research Australia, Sydney, Australia; The University of New South Wales, Sydney, Australia.
authors.forename: R D
authors.initials: RD
authors.lastname: Herbert
mesh_terms: D000125:Achilles Tendon / Q000033:anatomy & histology / Q000502:physiology; D000328:Adult; D000818:Animals; D000843:Ankle Joint / Q000033:anatomy & histology / Q000502:physiology; D001696:Biomechanical Phenomena; D004867:Equipment Design; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology; D019047:Phantoms, Imaging; D012399:Rotation; D012756:Sheep; D055815:Young Adult
keywords: Helical joint axis; Joint torque; MRI; Muscle force; Muscle lever arm; Muscle-tendon length; Subtalar joint motion; Tendon excursion