Protective effects of growth hormone on physeal distraction: an experimental study on rabbits

The objective of this study is to evaluate the effects of growth hormone on physeal distraction. We performed physeal distraction of the proximal tibia physis on 32 immature New Zealand white rabbits. The rabbits were randomly allocated into receiving either saline (test 1) or growth hormone (test 2), injected subcutaneously around the physis. Physeal distraction was performed from day 3 to day 28. The animals were sacrificed on day 42. Average net lengthenings achieved as compared with the non-distracted contralateral tibiae were 4+/-2 mm (test 1) and 6+/-2.8 mm (test 2). The difference was of borderline significance (P=0.07). The difference in bone mineral density (BMD) between test 1 and control 1 was -0.019+/-0.021 g/cm2 (P<0.0001). The difference in BMD between test 2 and control 2 was 0.027+/-0.017 g/cm2 (P<0.0001). Histology revealed good trabecular bone formation in all groups. Physeal fractures were present in four rabbits in the saline group (test 1). All rabbits in the growth hormone group achieved lengthening via increased physeal thickness without fracture. New bone formation could be accelerated during physeal distraction by administration of growth hormone. By enhancing physeal cellular activity, growth hormone facilitates lengthening without fracture and may reduce risk of premature physeal closure. Growth hormone may also reduce osteoporosis of the regenerate bone during physeal distraction.