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0196-601 1/67/0901-001 1$02.00/0 THEJOURNAL ORTHOPAEDIC SPORTS OF AND PHYSICAL THERAPY Copyright (O 1987 by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association

Abnormal Biomechanics of the Foot and Ankle
ROBERT DONATELLI, MA, PT* The biomechanics of the foot and ankle is important to the normal function of the lower extremity. The foot is theterminal joint in the lower kinetic chain that opposes external resistance. Proper arthrokinematic movement within the foot and ankle influences the ability of the lower limb to attenuate the forces of weightbearing. It is important for the lower extremity to distribute and dissipate compressive, tensile, shearing, and rotatory forces during the stance phase of gait. Inadequate distribution of theseforces could lead to abnormal stress and eventual breakdown of connective tissue and muscle. Pathologies such as heel spurs, hallux valgus, neuromas, hallux limitus, shin splints, and nonspecific knee pain result from abnormal mechanics of the foot and ankle. The use of orthotics to re-establish the normal biomechanics of the foot and ankle have profound clinical applications. The combined effectof muscle, bone, ligaments, and normal biomechanics will result in the most efficient force attenuation in the lower limb.

Abnormal mechanics of the foot and ankle is the breakdown of the mechanisms designed to distribute and dissipate the normal forces of weightbearing. Pronation and supination are the arthrokinematic movements within the foot and ankle that are essential for proper attenuationof compressive, tensile, shearing, and rotatory forces during the stance phase of gait. For example, Mann8describes a 150 Ib individual walking at a stride length of two 21/2 ft, for 1 mile, would apply 127 tons of force to his feet. If that same individual ran a mile with a stride length of q1/2 ft, he would increase the amount of force to 220 tons.8 A long distance runner's feet contact theground approximately 5000 times in an hour's run, with 2-3 times the body weight at every heel strike.',' These excessive forces are normally attenuated by the dynamic action of muscle, periarticular tissue strength, flexibility, and proper arthrokinematics. Abnormal pronation and supination are nothing more than hyper or hypomobilities, respectively, within the joints of the foot and ankle.Excessive motion or restricted motion reduces the ability of the foot to act as a shock absorber, torque convertor, mobile adaptor to the terrain, and a rigid
'Assistant Professor. Master Degree Program Orthopaedic and Sports Physical Therapy, Georgia State University, Atlanta, GA 30303.

lever to push off from. As a result of changes in the joint mobility, connective tissue changes occur, in additionto alterations in muscle function. This could result in pathological conditions such as neuromas, hallux valgus, tailors bunions, keratosis, shin splints, nonspecific knee pain, plantar fascitis, heel spurs, metatarsalgia, and achilles tendinitis.',l5

ABNORMAL PRONATION
Abnormal pronation is a compensation for a soft tissue or osseous deformity.15The deformity can be intrinsic or extrinsic tothe foot. In the majority of cases, excessive pronation occurs at the subtalar joint to compensate for the abnormality.3z'5 The compensation is persistent and results in pathology.15 Maximum pronation is achieved at footflat and supination begins at midstance. Excessive pronation means that the foot is pronating beyond 25% of the stance phase.138s14915 Consequently, at midstance the foot does notbegin to resupinate, it remains in maximum pronation. The foot may resupinate late in the stance phase or never resupinates, as seen in a rigid flatfoot. This results in the inability of the foot to effectively absorb the forces of weightbearing. The etiology of abnormal pronation can result from many different factors. Congenital, develop-

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JOSPT Vol. 9, No. 1

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