0196-601 1 /85/0703-0096$02.00/0 THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAPY Copyright O 1985 by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association Biomechanical Analysis of the Foot and Ankle for Predisposition to Developing Stress Fractures LAUREN Y. HUGHES, BS, MPT* Forty-seven subjects were studied to discover predisposing factors for their radiologically diagnosed metatarsal stress fractures. Biomechanics of the foot and ankle were introduced to help explain forefoot varus, abnormal rearfoot valgus, and dorsiflexion as intervening variables in metatarsal stress fracture development. Results concluded that subjects with forefoot varus and decreased dorsiflexion had 8.3: 1 and 4.6: 1, respectively, odds of developing a metatarsal stress fracture. Abnormal rearfoot valgus had no significant effect on predisposing the subjects to develop a stress fracture. Stress fractures are seen daily in soldiers in the Army undergoing basic and advanced individual training and account for many hours of lost train- ing time. Most of the literature on stress fractures is oriented to signs and symptoms but does not delve into the etiological factors surrounding the development of stress frac- t~re~.1~2~6~7~15~ 16.'9,20.25.29 This consid- ered three common biomechanical deviations of the foot and ankle and evaluated the potential for each to be a predisposing factor to the develop- ment of stress fractures in the soldier undergoing basic or advanced individual training. Identification of such predisposing factors with subsequent screening during inprocessing could potentially yield a significant decrease in lost time due to stress fractures. A stress reaction is a weakening and, second- arily, a periosteal reaction in bone undergoing large amounts of stress. This results from a cul- mination of repeated submaximal stresses rather than a specific traumatic experience.18 The bone reacts to these repetitive forces with increased osteoclastic activity while the osteoblasts attempt to simultaneously repair the damaged bone. If the stresses encountered are too great, the weak- ened cortex may crack due to an increase in CPT Hughes is Chief, physical therapist at Weed Army Community Hospitalat Ft. Irwin, CA. The views in this paper are those of the author and not those of the Department of the Army. osteoclastic resorption of bony tissue, thus cre- ating a stress fracture. The forces leading to increasing bone resorp- tion can be divided into three basic types: tensile, compressive, and shearing. A tensile force at- tempts to pull apart. ~ompressivh forces shorten or push together. Shearing forces cause relative displacement of parallel planes within an ~ b j e c t . ~ During the gait cycle these forces are dynamically loading and imparting energy into weightbearing bony tissue, causing deformation. The ability of the tissue to absorb this energy without incurring structural damage is dependent on the stress amplitude, temperature, density, and microstruc- ture of the If the osteoblasts are unable to effectively counter osteoclastic activity, which has been accelerated through absorption of ten- sile, compressive, and shearing forces, the result may be a linear fracture in the long bones.12 The ability of the bones and joints in the rear and midfoot to absorb and disperse forces will have a direct bearing on the forces imparted to the long bones in the forefoot.23 The foot and ankle have two major roles during ambulation: adaptation to uneven terrain and pro- pulsion of the body through space. One of the mechanisms by which the human foot can change from a mobile adaptor to a rigid lever for propul- sion is the subtalar joint.8923 The subtalar joint is triplanar and allows for the motions of pronation and supination. Pronation with weightbearing con- 96 Journal of Orthopaedic & Sports Physical Therapy® Downloaded from www.jospt.org at on June 9, 2023. For personal use only. No other uses without permission. Copyright © 1985 Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.
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