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Research Papers

A Robotic Cadaveric Flatfoot Analysis of Stance Phase

[+] Author and Article Information
Lyle T. Jackson1

Department of Veterans Affairs, RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, Seattle, WA; School of Medicine, University of Washington, Seattle, WA

Patrick M. Aubin

Department of Veterans Affairs, RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, Seattle, WA; Department of Electrical Engineering, University of Washington, Seattle, WA

Matthew S. Cowley

Department of Veterans Affairs, RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, Seattle, WA

Bruce J. Sangeorzan

Department of Veterans Affairs, RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, Seattle, WA; Department of Orthopaedics & Sports Medicine, University of Washington, Seattle, WA

William R. Ledoux2

Department of Veterans Affairs, RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, VA Puget Sound Health Care System, Seattle, WA; Department of Orthopaedics & Sports Medicine, and Department of Mechanical Engineering, University of Washington, Seattle, WAwrledoux@u.washington.edu

1

Present address: Department of Orthopaedic Surgery, Greenville Hospital System/University of South Carolina School of Medicine, Greenville, SC.

2

Corresponding author.

J Biomech Eng 133(5), 051005 (Apr 28, 2011) (6 pages) doi:10.1115/1.4003869 History: Received December 29, 2009; Revised February 16, 2011; Posted March 28, 2011; Published April 28, 2011; Online April 28, 2011

The symptomatic flatfoot deformity (pes planus with peri-talar subluxation) can be a debilitating condition. Cadaveric flatfoot models have been employed to study the etiology of the deformity, as well as invasive and noninvasive surgical treatment strategies, by evaluating bone positions. Prior cadaveric flatfoot simulators, however, have not leveraged industrial robotic technologies, which provide several advantages as compared with the previously developed custom fabricated devices. Utilizing a robotic device allows the researcher to experimentally evaluate the flatfoot model at many static instants in the gait cycle, compared with most studies, which model only one to a maximum of three instances. Furthermore, the cadaveric tibia can be statically positioned with more degrees of freedom and with a greater accuracy, and then a custom device typically allows. We created a six degree of freedom robotic cadaveric simulator and used it with a flatfoot model to quantify static bone positions at ten discrete instants over the stance phase of gait. In vivo tibial gait kinematics and ground reaction forces were averaged from ten flatfoot subjects. A fresh frozen cadaveric lower limb was dissected and mounted in the robotic gait simulator (RGS). Biomechanically realistic extrinsic tendon forces, tibial kinematics, and vertical ground reaction forces were applied to the limb. In vitro bone angular position of the tibia, calcaneus, talus, navicular, medial cuneiform, and first metatarsal were recorded between 0% and 90% of stance phase at discrete 10% increments using a retroreflective six-camera motion analysis system. The foot was conditioned flat through ligament attenuation and axial cyclic loading. Post-flat testing was repeated to study the pes planus deformity. Comparison was then made between the pre-flat and post-flat conditions. The RGS was able to recreate ten gait positions of the in vivo pes planus subjects in static increments. The in vitro vertical ground reaction force was within ±1 standard deviation (SD) of the in vivo data. The in vitro sagittal, coronal, and transverse plane tibial kinematics were almost entirely within ±1 SD of the in vivo data. The model showed changes consistent with the flexible flatfoot pathology including the collapse of the medial arch and abduction of the forefoot, despite unexpected hindfoot inversion. Unlike previous static flatfoot models that use simplified tibial degrees of freedom to characterize only the midpoint of the stance phase or at most three gait positions, our simulator represented the stance phase of gait with ten discrete positions and with six tibial degrees of freedom. This system has the potential to replicate foot function to permit both noninvasive and surgical treatment evaluations throughout the stance phase of gait, perhaps eliciting unknown advantages or disadvantages of these treatments at other points in the gait cycle.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Robotic gait simulator schematic with (A) surrounding frame, (B) (inset) R2000 motors, (C) force plate, (D) cadaveric foot, (E) (main image and left inset) mobile platform, (F) (main image and right blow-up) tibia mounting frame, (G) tendon actuation system, (H) motion analysis system, (I) (main image and right blow-up) tendon actuation cables, and (J) custom freeze clamps, PXI National Instruments embedded real-time controller not shown. Retroreflective marker scheme (right inset) with three markers per bone. Note: tibia and ground markers not shown. Tibia markers were placed on the anterior tibia and medial and lateral malleoli. Ground markers were placed on three corners of the force plate. A vector from the first marker to the second marker defined the primary axis. The line connecting the second and third markers defined a dummy vector. The second axis was created as the dummy vector crossed with the primary axis. Finally, the third axis was constructed from the first two to create a right-handed Cartesian coordinate system.

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Figure 2

In vivo compared with in vitro tibia with respect to ground in the sagittal (left), coronal (center), and transverse (right) planes angular positions. Error bars indicate 1 standard deviation of in vivo pes planus gait data. Positive rotation is defined as the proximal tibia moving posteriorly and the distal tibia moving anteriorly (left), or abduction of the tibia (center), or external rotation of the tibia (right).

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Figure 3

In vivo compared with in vitro vertical (left), anterior/posterior shear (center), and medial/lateral shear (right) ground reaction forces normalized to cadaver BW. Error bars indicated the standard deviation of the in vivo data. Positive force is a superior, i.e., compressive, reaction force (left), anterior (central), or medial (right). 1 BW=945 N.

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Figure 4

First metatarsal position with respect to the talus in the sagittal plane. Positive rotation is dorsiflexion of the first metatarsal.

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Figure 5

First metatarsal position with respect to the talus in the transverse plane. Positive rotation is abduction of the first metatarsal.

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Figure 6

Calcaneus position with respect to the tibia in the coronal plane. Positive rotation is eversion of the calcaneus.

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