Regeneration of growth plates in the long bones of the neonatal rat hindlimb.

Twenty-seven male albino rats underwent hindlimb amputations through the lower femur or the midshaft of the tibiofibula on the tenth to 12th day of life. Amputation stumps were examined grossly and histologically in order to assess the significance of level and angle of transaction as determinants of subsequent growth and regeneration and to ascertain whether growth plates can regenerate following their complete excision. Amputees survived for 17-73 days. In order to exclude limbs which had been severed at or distal to the level of the growth plate, amputated limb segments either were cleared to transparency and inspected under low magnification or were sectioned serially and examined by using a compound microscope. Following amputations through the femur, the predominant response involved repair of the skeletal defect and healing of adjacent soft tissues (ten of 17 rats). Among five other animals the skeletal terminus was covered with a plate of cartilage which, in three, included areas of growth-plate architecture. Two additional transfemoral amputees regenerated incomplete growth plates, each overlying a single epicondylar surface, and one provided with a regenerated hemiepiphysis. Five of ten transtibiofibular amputees formed cartilage plates which covered the skeletal terminus in whole or in part and one regenerated an entire growth plate restricted to the distal fibula. It is concluded that angle and level of transection are not pivotal modifiers of growth and regeneration processes, and that distal growth plates may regenerate entirely or in part following their complete removal from the hindlimb.