To the Editor.—
Standing is almost a completely passive act. The line of gravity must fall behind the center of rotation of the hips, in front of the knees and ankles, and within the base of support. Stability of the hips is normally accomplished by balancing the force of gravity posteriorly, against the iliofemoral ligament anteriorly. The gravitational force is restrained by the posterior ligaments and capsule at the knee and by some contraction of triceps surae at the ankle.1Walking requires coordinated lower extremity muscle activity. Patterns of substitution in diseases with selective muscle loss can occur. This has been observed in conditions such as poliomyelitis. Duchenne's muscular dystrophy (DMD) is characterized by loss of hip and knee extensor power, accompanied by hip flexion and abduction contracture and ankle equinus. By age 7 years, the majority of such patients show discernible quadriceps weakness, and most stop walking between
Siegel IM, Weiss LA. Postural Substitution in Duchenne's Muscular Dystrophy. JAMA. 1982;247(5):584. doi:10.1001/jama.1982.03320300014014
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