The purpose of this study was to investigate the effects of growth hormone (GH) on muscle during limb lengthening.

Sixty rats underwent tibial lengthening of approximately 30% using a protocol consisting of a latency period 4 days, a distraction period of 30 days with a rate of 0.25 mm twice per day, and a consolidation period of 27 days. Recombinant GH was administered to 30 of the rats (100 g/kg/day) and the same dose of normal saline to the remaining 30 rats, during the period from operation to sacrifice. Histopathologic, immunohistochemical, and electrophysiologic studies were performed on the tibialis anterior compare the muscle responses of GH treated lengthened limbs (GL), GH treated non-lengthened limbs (GN), saline treated length-ened limbs (CL), and saline treated non-lengthened limbs (CN) at postoperative days 34 and 61.

Histologic injury scores were worst in the CL, in which vimentin expression was also greatest. Cell proliferation, determined by proliferating cell nuclear antigen (PCNA) staining, was greatest in the GL, in which desmin expression was also greatest. Electrophysiologi-cal methods showed better muscle function was retained in the GL than the CL.

These results suggest that GH can reduce muscle damage during limb lengthening by enhancing myogenesis and decreasing fibrogenesis.