Biodegradable plate fixation of rabbit femoral shaft osteotomies. A comparative study.

Femoral shaft transverse osteotomies in 58 rabbits were fixed with ultrahigh strength poly-L-lactic acid plates made by a drawing technique. Similar osteotomies in another 35 rabbits were fixed using stainless steel plates. The union rate, the mechanical strength of the united bones, bone mineral content and density in the area beneath the plate using dual energy x-ray absorptiometry, and the cortical thickness beneath and opposite the plate using a digitizer was compared between the poly-L-lactic acid and stainless steel groups after postoperative periods of 8, 25, and 40 weeks. The poly-L-lactic acid and stainless steel groups showed union rates of 67% (39 of 58) and 80% (28 of 35) without displacement, respectively. In the poly-L-lactic acid group, plate failure occurred in 14% (8 of 58). The mechanical strength of the specimen was restored to a level equal to that on the untreated side by 25 weeks, and cortical thickness and bone mineral content and density were maintained almost normal for 40 weeks in the poly-L-lactic acid group. The stainless steel group showed significantly lower mechanical strength and led to osteopenia because of stress shielding after 25 weeks.