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Research Papers

Rotational Stiffness of Football Shoes Influences Talus Motion during External Rotation of the Foot

[+] Author and Article Information
Feng Wei

 Orthopaedic Biomechanics Laboratories, Michigan State University, East Lansing, MI, 48824weifeng@msu.edu

Eric G. Meyer

 Experimental Biomechanics Laboratory, Lawrence Technological University, Southfield, MI, 48076emeyer@ltu.edu

Jerrod E. Braman

 Orthopaedic Biomechanics Laboratories, Michigan State University, East Lansing, MI, 48824bramanj1@msu.edu

John W. Powell

Department of Kinesiology,  Michigan State University, East Lansing, MI, 48824powellj4@ath.msu.edu

Roger C. Haut1

 Orthopaedic Biomechanics Laboratories, Michigan State University, East Lansing, M, 48824haut@msu.edu

1

Corresponding Author

J Biomech Eng 134(4), 041002 (Apr 04, 2012) (7 pages) doi:10.1115/1.4005695 History: Received December 02, 2011; Revised December 10, 2011; Posted January 25, 2012; Published April 02, 2012; Online April 04, 2012

Shoe-surface interface characteristics have been implicated in the high incidence of ankle injuries suffered by athletes. Yet, the differences in rotational stiffness among shoes may also influence injury risk. It was hypothesized that shoes with different rotational stiffness will generate different patterns of ankle ligament strain. Four football shoe designs were tested and compared in terms of rotational stiffness. Twelve (six pairs) male cadaveric lower extremity limbs were externally rotated 30 deg using two selected football shoe designs, i.e., a flexible shoe and a rigid shoe. Motion capture was performed to track the movement of the talus with a reflective marker array screwed into the bone. A computational ankle model was utilized to input talus motions for the estimation of ankle ligament strains. At 30 deg of rotation, the rigid shoe generated higher ankle joint torque at 46.2 ± 9.3 Nm than the flexible shoe at 35.4 ± 5.7 Nm. While talus rotation was greater in the rigid shoe (15.9 ± 1.6 deg versus 12.1 ± 1.0 deg), the flexible shoe generated more talus eversion (5.6 ± 1.5 deg versus 1.2± 0.8 deg). While these talus motions resulted in the same level of anterior deltoid ligament strain (approxiamtely 5%) between shoes, there was a significant increase of anterior tibiofibular ligament strain (4.5± 0.4% versus 2.3 ± 0.3%) for the flexible versus more rigid shoe design. The flexible shoe may provide less restraint to the subtalar and transverse tarsal joints, resulting in more eversion but less axial rotation of the talus during foot/shoe rotation. The increase of strain in the anterior tibiofibular ligament may have been largely due to the increased level of talus eversion documented for the flexible shoe. There may be a direct correlation of ankle joint torque with axial talus rotation, and an inverse relationship between torque and talus eversion. The study may provide some insight into relationships between shoe design and ankle ligament strain patterns. In future studies, these data may be useful in characterizing shoe design parameters and balancing potential ankle injury risks with player performance.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Shoe stiffness tests preparation and setup. Surrogate lower extremity (a) and football cleat mold (b) were made of epoxy resin. A surrogate limb was attached to the testing machine through a biaxial load cell (c).

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Figure 2

Cadaver tests preparation and setup. The proximal end of the shank was potted using epoxy resin (a) with two screws placed earlier into the proximal tibia (b). A cadaveric limb with markers was mounted upside down into the testing machine (c).

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Figure 3

Testing setup. Five-camera Vicon motion capture system (showing only four cameras) and one video camera (not shown) were used to track motions of the talus relative to the tibia.

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Figure 4

Torque-rotation curves of the four shoe designs from rotational stiffness tests. Different symbols (‡ # § *) indicate statistically significant differences between shoe designs.

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Figure 5

Rotational stiffness determined from the slopes of torque-rotation curves. Data were averaged across the three cyclic tests and plotted as mean ±1 SD. The Air was the least rigid (most flexible) shoe, while the Flyposite was the most rigid design. Different symbols (‡ # § *) indicate statistically significant differences between shoe designs.

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Figure 6

Torque-rotation curves of cadaveric limbs restrained by the flexible (Air) or the rigid (Flyposite) shoe designs showed a toe region followed by a linear region. Linear regression was performed on the linear portion of the curves between 10° and 30°. The symbol § indicates significant difference between curves. The ‡’s indicate significant differences between limbs at various rotation points.

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Figure 7

Comparisons of temporal profiles of external talus rotations in different shoes with the actual shoe rotation (same in all tests) driven by the rotary actuator. All rotations were relative to the tibia.

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Figure 8

Ankle ligament strains (mean ±1 SD) were estimated from a computational model and compared between different shoes at 30° of external foot rotation. Only two ligaments with the highest strains were reported. ATiFL is the anterior tibiofibular ligament, and ADL is the anterior deltoid ligament. The horizontal bar indicates significant difference between shoes. The strain in the ADL was statistically greater than in the ATiFL for both shoe designs.

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