Myostatic Contracture and Other Changes in the Extensibility of Skeletal Muscle.

Abstract

By myostatic contracture we mean to designate a condition of permanent shortening in resting muscle, which is maintained in the entire absence of nerve impulses, the muscle having acquired, usually as the result of prolonged immobility, a new and shorter than normal resting length. Familiar examples are the contractures which limit the movement of joints after prolonged immobilization in plaster casts, the permanent shortening of muscles after division of their tendons, the paretic contractures due to the unequal paralysis of antagonistic muscle groups in anterior poliomyelitis and multiple neuritis and the rigidity seen in the latter stages of local tetanus.

Muscles in myostatic contracture have approximately normal elasticity, but their ductility, i. e., their tendency to undergo permanent elongation when stretched, is greatly reduced.

The muscle tested was the gastrocnemius of the white rat with sciatic nerve cut but circulation intact. The muscle was stretched with loads increasing by 10 gm. intervals with 2 minute cycles of stretching and rest. A weight of 10 gm. was applied for 1 minute and removed for 1 minute, then 20 gm. was applied for 1 minute and removed for 1 minute and so on up to 100 gm.

In the first set of experiments the muscles were exposed to the air at room temperature while being stretched. Under these conditions a series of 10 normal muscles gave an average permanent elongation of 3.08 mm.; 10 muscles in contracture 15 days after section of the tendo achillis gave an average permanent elongation of 1.33 mm.; and 9 muscles in tetanus contracture gave an average permanent elongation of 1.28 mm. This marked decrease in ductility is not due to fibrosis. Histological sections of these muscles show no increase in connective tissue and only slight changes in the muscle fibers, such as a blurring of the cross striations.