To analyze the BMD of lengthened bone in rabbit with steroid induced osteoporosis.

Rabbits of both sexes weighing 2,500 gm were divided into five groups (five rabbits in each group) according to steroid dose and injection period: no injection (Group I); 0.4 mg/kg/day for 2 weeks (Group II) and 4 weeks (Group III); 0.8 mg/kg/day for 2 weeks (Group IV) and 4 weeks (Group V). Unilateral external fixators (E/Fs) were applied to femurs and osteotomies performed. Distraction was started at the rate of 0.35 mm twice daily, from the eighth operative day. We evaluated 1) radiographs 2) %BMD and 3)performed a microscopic study.

After the steroid injection, the BMD decreased in Group II by 22.2%, Group III by 30.7%, Group IV by 23.4%, and Group V by 32.7%. Fractures in all rabbits in Groups III and V were observed in week 1. Upon observing the average %BMD in the distraction area of Groups II and IV 7 days after distraction, it was noted that when the %BMD was above 30, the E/Fs were well maintained and that length-ened bone formation was satisfactory. On microscopic study, demineralization was evident and the thickness of the bony trabeculae in compact bones decreased.

BMD was changed uniformly in a steroid dose and time dependent manner. Rabbits with steroid induced osteoporosis can be used as models for the study of complications in humans, such as insufficient bone formation and the loosening of E/F in the distraction osteogenesis of elderly patients.