title: Predicting tibiotalar and subtalar joint angles from skin-marker data with dual-fluoroscopy as a reference standard.
abstract: Evidence suggests that the tibiotalar and subtalar joints provide near six degree-of-freedom (DOF) motion. Yet, kinematic models frequently assume one DOF at each of these joints. In this study, we quantified the accuracy of kinematic models to predict joint angles at the tibiotalar and subtalar joints from skin-marker data. Models included 1 or 3 DOF at each joint. Ten asymptomatic subjects, screened for deformities, performed 1.0m/s treadmill walking and a balanced, single-leg heel-rise. Tibiotalar and subtalar joint angles calculated by inverse kinematics for the 1 and 3 DOF models were compared to those measured directly in vivo using dual-fluoroscopy. Results demonstrated that, for each activity, the average error in tibiotalar joint angles predicted by the 1 DOF model were significantly smaller than those predicted by the 3 DOF model for inversion/eversion and internal/external rotation. In contrast, neither model consistently demonstrated smaller errors when predicting subtalar joint angles. Additionally, neither model could accurately predict discrete angles for the tibiotalar and subtalar joints on a per-subject basis. Differences between model predictions and dual-fluoroscopy measurements were highly variable across subjects, with joint angle errors in at least one rotation direction surpassing 10° for 9 out of 10 subjects. Our results suggest that both the 1 and 3 DOF models can predict trends in tibiotalar joint angles on a limited basis. However, as currently implemented, neither model can predict discrete tibiotalar or subtalar joint angles for individual subjects. Inclusion of subject-specific attributes may improve the accuracy of these models.
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA. Electronic address: jen.nichols@utah.edu.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Nichols
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA; Department of Bioengineering, University of Utah, James LeVoy Sorenson Molecular Biotechnology Building, 36S. Wasatch Drive, Rm. 3100, Salt Lake City, UT 84112, USA. Electronic address: koren.roach@utah.edu.
authors.forename: Koren E
authors.initials: KE
authors.lastname: Roach
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA. Electronic address: niccolo.fiorentino@utah.edu.
authors.forename: Niccolo M
authors.initials: NM
authors.lastname: Fiorentino
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA; Department of Bioengineering, University of Utah, James LeVoy Sorenson Molecular Biotechnology Building, 36S. Wasatch Drive, Rm. 3100, Salt Lake City, UT 84112, USA; Department of Physical Therapy, University of Utah, 520 Wakara Way, Suite 240 Salt Lake City, UT 84108, USA; Scientific Computing and Imaging Institute, 72S Central Campus Drive, Room 3750, Salt Lake City, UT 84112, USA. Electronic address: andrew.anderson@hsc.utah.edu.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Anderson
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000000981:diagnostic imaging* / Q000502:physiology*; D001696:Biomechanical Phenomena; D005260:Female; D005471:Fluoroscopy / Q000379:methods*; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D013380:Subtalar Joint / Q000000981:diagnostic imaging*; D013628:Talus / Q000000981:diagnostic imaging*
keywords: Ankle; Dynamic imaging; Hindfoot; Inverse kinematics; Motion capture