The effect of tibial lengthening on gastrosoleus muscle function: An electrophysiological study

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 guinea pigs weighing 600 to 800 g. Following the application of a semicircular external fixator and right tibial osteotomy, distraction was applied at a rate of 0.25 mm two times a day for 15 days without a latency period. The animals were randomized 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 baseline 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 deformity developed progressively in the ankles of the control animals 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 prevent equities deformity and maintain ankle functions. This can be achieved through gradual stretching of the muscle during distraction. 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.