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Research Papers

Rotational Stiffness of American Football Shoes Affects Ankle Biomechanics and Injury Severity

[+] Author and Article Information
Keith D. Button

Orthopaedic Biomechanics Laboratories,
Michigan State University,
East Lansing, MI 48824
e-mail: buttonke@msu.edu

Jerrod E. Braman

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

Mark A. Davison

Orthopaedic Biomechanics Laboratories,
Michigan State University,
East Lansing, MI 48824
e-mail: daviso29@msu.edu

Feng Wei

Assistant Professor
Orthopaedic Biomechanics Laboratories,
Michigan State University,
East Lansing, MI 48824
e-mail: weifeng@msu.edu

Maureen C. Schaeffer

Assistant Professor
College of Human Medicine,
Michigan State University,
East Lansing, MI 48824
e-mail: Maureen.Schaefer@rad.msu.edu

Roger C. Haut

University Distinguished Professor
Orthopaedic Biomechanics Laboratories,
Michigan State University,
East Lansing, MI 48824
e-mail: haut@msu.edu

1Corresponding author.

Manuscript received June 20, 2014; final manuscript received February 20, 2015; published online March 23, 2015. Assoc. Editor: Kenneth Fischer.

J Biomech Eng 137(6), 061004 (Jun 01, 2015) (8 pages) Paper No: BIO-14-1281; doi: 10.1115/1.4029979 History: Received June 20, 2014; Revised February 20, 2015; Online March 23, 2015

While previous studies have investigated the effect of shoe–surface interaction on injury risk, few studies have examined the effect of rotational stiffness of the shoe. The hypothesis of the current study was that ankles externally rotated to failure in shoes with low rotational stiffness would allow more talus eversion than those in shoes with a higher rotational stiffness, resulting in less severe injury. Twelve (six pairs) cadaver lower extremities were externally rotated to gross failure while positioned in 20 deg of pre-eversion and 20 deg of predorsiflexion by fixing the distal end of the foot, axially loading the proximal tibia, and internally rotating the tibia. One ankle in each pair was constrained by an American football shoe with a stiff upper, while the other was constrained by an American football shoe with a flexible upper. Experimental bone motions were input into specimen-specific computational models to examine levels of ligament elongation to help understand mechanisms of ankle joint failure. Ankles in flexible shoes allowed 6.7±2.4 deg of talus eversion during rotation, significantly greater than the 1.7±1.0 deg for ankles in stiff shoes (p = 0.01). The significantly greater eversion in flexible shoes was potentially due to a more natural response of the ankle during rotation, possibly affecting the injuries that were produced. All ankles failed by either medial ankle injury or syndesmotic injury, or a combination of both. Complex (more than one ligament or bone) injuries were noted in 4 of 6 ankles in stiff shoes and 1 of 6 ankles in flexible shoes. Ligament elongations from the computational model validated the experimental injury data. The current study suggested flexibility (or rotational stiffness) of the shoe may play an important role in both the severity of ankle injuries for athletes.

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Figures

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Fig. 1

Posterior view of a neutral (left) and everted foot (right)

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Fig. 2

Football shoes used for the current study: Nike Flyposite (a) and Nike Zoom Air (b)

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Fig. 3

Football cleat mold made of epoxy resin used to fix the shoe to the testing fixture

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Fig. 4

The experiments were performed on a biaxial testing machine with the motions of the talus and tibia tracked by a 5-camera motion capture system. The ankle was placed in 20 deg of pre-eversion and predorsiflexion prior to rotation.

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Fig. 5

An example of the torque data from a subfailure (a) and a failure (b) test. The failure occurs when there is a steep drop in torque, as indicated by the arrow.

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Fig. 6

Lateral (a), posterior (b), and medial (c) views of one of the specimen-specific models in SolidWorks with linear springs representing ligaments

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Fig. 7

Fibular fracture (a), medial malleolus fracture (b), ATiFL avulsion (c), ATiTL avulsion (d), ATiFL tear (e), and ATiTL tear (f)

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Fig. 8

Representative plot of the ATiFL and ATiTL percent elongation versus tibia rotation in a simulation of the combination ATiFL and ATiTL injury scenario (specimen 2, stiff shoe)

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