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TECHNICAL PAPERS: Joint/Whole Body

In Vitro Assessment of a Motion-Based Optimization Method for Locating the Talocrural and Subtalar Joint Axes

[+] Author and Article Information
Gregory S. Lewis, H. J. Sommer

Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802

Stephen J. Piazza1

Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802 and Department of Orthopaedics and Rehabilitation, The Pennsylvania State University, Hershey, PA 17033steve-piazza@psu.edu

1

Corresponding author.

J Biomech Eng 128(4), 596-603 (Jan 17, 2006) (8 pages) doi:10.1115/1.2205866 History: Received June 11, 2005; Revised January 17, 2006

The locations of the joint axes of the ankle complex vary considerably between subjects, yet no noninvasive method with demonstrated accuracy exists for locating these axes. The moments of muscle and ground reaction forces about the joint axes are dependent on axis locations, making knowledge of these locations critical to accurate musculoskeletal modeling of the foot and ankle. The accuracy of a computational optimization method that fits a two-revolute model to measured motion was assessed using computer-generated data, a two-revolute mechanical linkage, and three lower-leg cadaver specimens. Motions were applied to cadaver specimens under axial load while bone-mounted markers attached to the tibia, talus, and calcaneus were tracked using a video-based motion analysis system. Estimates of the talocrural and subtalar axis locations were computed from motions of the calcaneus relative to the tibia using the optimization method. These axes were compared to mean helical axes computed directly from tibia, talus, and calcaneus motions. The optimization method performed well when the motions were computer-generated or measured in the mechanical linkage, with angular differences between optimization and mean helical axes ranging from 1deg to 5deg. In the cadaver specimens, however, these differences exceeded 20deg. Optimization methods that locate the anatomical joint axes of the ankle complex by fitting two revolute joints to measured tibia-calcaneus motions may be limited because of problems arising from non-revolute behavior.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Mechanical linkage used for initial assessment of the optimization method. Two revolute joints represent the TC and ST joints, and reflective marker clusters are mounted to the “tibia,” “talus,” and “calcaneus” segments.

Grahic Jump Location
Figure 2

Schematic illustration of apparatus used to apply a constant longitudinal load to the tibia during movements of the ankle complex. The tibia plate is moved by the tester like a joystick, inducing plantarflexion/dorsiflexion, inversion/eversion, and combinations thereof while the foot remains approximately stationary on the nonskid base plate. Marker clusters attached to the tibia, talus, and calcaneus bones are shown. (For the experiments, the calcaneus cluster was attached at the medial side and positioned with a steel arm to face in the lateral-posterior direction.) The positions of anatomical landmarks are shown with asterisks; these points were located during static trials with the foot in a neutral position, and the medial malleolus point is not shown.

Grahic Jump Location
Figure 5

Angular errors between ST axis resulting from optimization (computed from tibia-calcaneus motion) and mean helical ST axis (computed from calcaneus-talus motion), for both the mechanical linkage and cadaver specimens. The averages across trials are shown, with the error bars indicating the maximum and minimum values across trials.

Grahic Jump Location
Figure 4

Angular errors between TC axis resulting from optimization (computed from tibia-calcaneus motion) and mean helical TC axis (computed from tibia-talus motion), for both the mechanical linkage and cadaver specimens. The “total error magnitude” is the angle between the two axes, and the deviation and inclination errors serve to further describe this total error. The averages across trials are shown, with the error bars indicating the maximum and minimum values across trials.

Grahic Jump Location
Figure 3

Deviation and inclination angle definitions for the TC and ST joints, used to relate the joint axes to the calcaneus anatomical planes (dotted lines) with the foot in neutral position. Positive directions for the angles are shown.

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