Callus development after bored and unbored femoral interlocking nailing. An experimental study

This was a prospective randomized baboon animal study, the study protocol was approved by the ethical committee according to the international guidelines for animal research projects. In 8 animals a midschaft femoral osteotomy was stabilized with reamed femoral interlocking nailing and in 8 animals by unreamed locked femoral nailing. Polychrome sequence bone labeling was done 5 weeks postop. with calcein-green, 8 weeks postop. with xylenol-orange and 10 weeks postop. with oxytetracycline. 10 weeks postop. the animals were sacrificed, the femurs explanted and planimetric and epifluorescence histomorphometric evaluation of serial transverse sections were done. In planimetric histomorphometric evaluation in unreamed femoral nailing a mean endostal callus formation was recorded with 28.0 +/- 9.9 mm2 per section and in reamed femoral nailing with 11.5 +/- 5.0 mm2 (p < 0.001). Periostal callus formation was recorded in the unreamed group with 238.7 +/- 87.1 mm2 per section and in the reamed group with 142.1 +/- 71.9 mm2 (p < 0.001). In epifluorescence histological evaluation endostal as well as periostal callus formation was more extensive and earlier after unreamed than reamed femoral nailing. Endostal callus formation was found in all animals after unreamed femoral nailing, and was present in 2 out of 8 specimen in the reamed group. Also 1 out of 8 animals in the reamed group developed a non-union. Unreamed femoral nailing with low diameter interlocking nails proved to be safe regarding bone healing in this experimental model with obvious advantages both in amount and time course of callus formation compared to reamed femoral nailing. Based on this results unreamed femoral nailing techniques can be recommended for femoral fractures.