Effect of tension on force of contraction of muscle and nerve conduction velocity of the repaired nerve in a rat model Pramod Devkota, 1 Wang Lei, 2 Zeng Bing-fang, 2 Tang Jian-fei 2 and Fan Cun-yi 2 1 Department of Orthopaedic Surgery, Patan Hospital, Lagankhel, Lalitpur, Nepal 2 Department of Orthopaedic Surgery, Shanghai Sixth People's Hospital, Shanghai 200233, P R China Corresponding address: Dr. Pramod Devkota, Department of Orthopaedic Surgery, Patan Hospital, Lagankhel, Lalitpur, Nepal. ABSTRACT To investigate the effect of tension on the contractive force of muscle and nerve conduction velocity of the repaired nerve, this study was designed. Fifty-four Sprague-Dawley (SD) rats were randomly divided into 3 groups. The left gastrocnemius muscles of the rats were dissected with the neurovascular pedicles intact; the tibial nerves were cut and immediately repaired by epineurial suture. Then the Achilles tendons were isolated and treated accordingly; the Achilles tendon was lengthened by 0.5 cm in lengthened group, shortened by 0.5 cm in shortened group and left alone in normal (control) group. In the 2nd, 4th and 8th weeks after operation, the isometric twitch contractive force of both the right and the left gastrocnemius muscles and the nerve conduction velocity (NCV) of the tibial nerve were measured. The shortened group showed greater isometric twitch contractive strength of the bilateral gastrocnemius muscles than those in the normal and lengthened groups in all the postoperative periods. The nerve conduction velocity (NCV) in the shortened group showed greater than other groups. A proper high tension of the muscle can increase the contraction of the muscle and may improve the nerve conduction velocity of the repaired nerve. Keywords: Muscle tension Isometric twitch contractive force nerve conduction velocity (NCV). INTRODUCTION A neurovascularized free muscle transfer is an ideal solution to the reconstruction of a devastated skeletal muscle or a paralyzed extremity, 1,2 But, there are lots of factors that govern the functional outcome of free muscle transfer and the reconstructive surgeons emphasized the need of placing the transferred muscle in an optimal tension. It remains unknown how a skeletal muscle responds towards the tension in terms of contraction and how muscle tension responds towards nerve conduction velocity of the repaired nerve. Further research is therefore needed to give an answer to this question and this study is thus designed. MATERIALS AND METHODS Fifty-four Sprague-Dawley (SD) rats were used in the experiment. The left gastrocnemius muscles of the rats were dissected with only the neurovascular pedicles intact; the tibial nerves were cut and immediately repaired by epineurial suture. Then the Achilles tendons were isolated and treated accordingly. The rats were randomly divided into 3 groups with 18 rats in each, based on the manner of the Achilles tendon treatment. In group A (the normal group), the Achilles tendons were just isolated without cut, in group B (the shortened group), the Achilles tendons were cut and sutured back with a shortening of 0.5 cm, and in group C (the lengthened group), the Achilles tendons were divided with stair cut and sutured back with their length increased by 0.5 cm. The wounds were then closed and the rats allowed to move freely. (Fig 1 shows the animal model) At 2 nd , 4th and 8 th weeks after operation, 6 rats from each group underwent measurement of isometric twist contraction of both right and left gastrocnemius muscles and nerve conduction velocity (NCV) of the tibial nerve. When measured, the rats were anaesthetized by injecting ketamine into the abdomen and put in prone position. The left and right gastrocnemius muscles were exposed and connected to the tension transducer with 5-0 suture. The tension of suture was adjusted to keep the muscle in its initial length. Multipurpose physiological stimulator device (voltage 15v, frequency 90Hz, wave length 2ms) was used to stimulate the gastrocnemius muscle and the isometric twitch contraction of gastrocnemius was recorded with a two-channel physiological recorder (sensitivity 10 mv/cm, time constant 0.25, filtered frequency 100 Hz). The ratios of isometric twitch contraction of the bilateral gastrocnemius were calculated (as shown on Fig 2). In