مرکز منطقه ای اطلاع رساني علوم و فناوري - The effect of tibial lengthening on gastrosoleus muscle function: an electrophysiological study

Latin Abstract :

Objectives: We evaluated the changes in electrophysiological characteristics of the contraction forces of the gastrosoleus complex due to stretching in experimental tibial lengthening. Methods: Distraction histiogenesis was performed in 22 guin¬ea pigs weighing 600 to 800 g. Following the application of a semicircular external fixator and right tibial osteotomy, dis¬traction was applied at a rate of 0.25 mm two times a day for 15 days without a latency period. The animals were random¬ized to two groups. In the study group, a foot plate preventing ankle plantar flexion was affixed to the external fixator, while ankle motions were unrestricted in the control group. On days 5, 10, and 15, the posterior tibial nerve was stimulated with a nerve stimulator at a constant frequency. Gastrosoleus muscle contractions were measured with a transducer and contraction forces were recorded. Results: On day 5, muscle contraction forces measured in the study group were much higher than the control group (p<0.05). On day 10, however, muscle contraction forces showed a rapid decline in the study group and, at the end of the study, muscle contraction forces decreased by 81% compared to the base¬line values (p<0.05). Yet, throughout the study period, muscle contraction forces were always higher than the control group (p<0.05). In addition, the rate of the decrease in muscle strength slowed down after day 10 in the study group, and gastrosoleus function and strength were much better preserved. Equinus de-formity developed progressively in the ankles of the control ani¬mals whose muscle contraction forces also showed significant decreases during the experiment (p<0.05). Conclusion: In clinical applications of tibial lengthening, the strength of the gastrosoleus complex should be preserved to pre¬vent equines deformity and maintain ankle functions. This can be achieved through gradual stretching of the muscle during dis¬traction. If there is shortening before surgery or muscle stiffness is expected during lengthening, measures should be taken before distraction osteogenesis and muscle length should be preserved.