The Effect of Muscle Length and Excursion on Myostatic Contracture : A Study in Rabbit Soleus Muscles

Gong, Hyun Sik; Baek, Goo Hyun; Oh, Joo Han; Lee, Young Ho; Kim, Sae Hoon; Choi, Jin Man; Chung, Moon Sang

Abstract

PURPOSE
The purpose of this study was to determine the effect of preserving muscle length or excursion on the progression of myostatic contracture after tendon injury in a rabbit soleus tenotomy model.
MATERIALS AND METHODS
Forty rabbits underwent tenotomy of the soleus muscles bilaterally and the tendons were managed according to the five experimental groups (N=40). Group A was a tendon-lengthening group maintaining a half of the excursion. In group B, maximal muscle length was maintained and in group C, resting muscle length was maintained. In group D, the tendon was allowed to undergo myostatic contracture and in group E, the tendon was partially transected and repaired. Four and eight weeks postoperatively, soleus muscles were harvested from each hindlimb and histomorphometric evaluations were performed to measure the connective tissue and fiber cross-sectional areas. Electrophysiologic studies were carried out to measure the compound muscle action potential to assess the number of functioning muscle fibers.
RESULTS
The results showed that maximal muscle length preservation (Group B) was the most protective in preventing muscle contracture within 4 weeks of tenotomy, but this protective effect was gradually offset by prolonged immobilization, and 8 weeks after tenotomy, maintenance of excursion (Group A) was the most protective.
CONCLUSION
These observations can be useful in the intraoperative evaluation of myostatic contracture in neglected tendon ruptures, and be applied to the management of acute tendon injuries to prevent myostatic contracture when immediate anatomical reconstruction cannot be performed.