The effects of drilling on revascularization and new bone formation in canine femoral heads with avascular necrosis: an initial study.

In this study, the effects of drilling on revascularization and new bone formation were evaluated in nine dogs with surgically induced avascular necrosis (AVN) of the femoral head. Six animals had holes drilled from the greater trochanter into the femoral head at the time of vascular interruption. Vital fluorescent bone stains were injected immediately postoperatively (calcein green). 6 weeks postoperatively (xylenol orange), and 12 weeks postoperatively (oxytetracycline). In the operative femoral heads, a relative absence of calcein green indicated successful production of AVN. All of the specimens had uptake of oxytetracycline, indicating complete revascularization by 12 weeks postoperatively. Xylenol orange was found throughout the femoral head in the six drilled heads, indicating complete revascularization by 6 weeks postoperatively. Two of the three undrilled dogs failed to show distribution of xylenol orange throughout the femoral head, which indicated incomplete revascularization by 6 weeks postoperatively. In the drill tracts that were identified, calcein green was observed along the full length of the tract, indicating very early new bone deposition in the drill tracts following surgery. These results suggest that a drill hole provides a path for rapid vascular invasion and quickly results in new bone formation in and around the drill tracts. In addition, revascularization takes place more rapidly in canine femoral heads that have been drilled.