Injury-to-surgery interval does not affect the occurrence of osteonecrosis of the femoral head: a prospective study in a canine model of femoral neck fractures.

Background: It is controversial whether an early reduction and internal fixation can reduce the occurrence of femoral neck fracture-induced osteonecrosis of the femoral head (ONFH). This prospective study was designed to reflect the relationship between injury-to-surgery interval (ISI) and traumatic ONFH based on a canine model of femoral neck fractures.

Material/methods: Twenty-four dogs were equally divided randomly into 3 groups. A lateral L-shape approach centered left great trochanter was used for exposure of the femoral neck. A low-speed drill was used for making displaced fractures in the narrow femoral neck, with the femoral head kept in situ with ligamentum teres intact. In Group A, the fracture was immediately reduced and fixed with 3 parallel pins; while the operation was done 3 days later in Group B, and 3 weeks later in Group C. Another 2 dogs had their fractures untreated. Postoperatively, all dogs were fed separately and received regular x-ray examination. Left femoral heads were harvested for histological examination with a postoperative follow-up of 3.5 months.

Results: The canine model of femoral neck fractures could be achieved successfully. Radiological signs of post-fracture ONFH could not be detected at intervals of 2 weeks, 4 weeks, 1 month and 2 months. Histologically, there were 2 cases with ONFH in Group A, 1 case in Group B, and 2 cases in Group C. The difference had no statistical significance. For untreated fractures, obvious ONFH could be found radiologically.

Conclusions: A shorter ISI may not reduce the incidence of fracture-induced ONFH, which suggests that intrinsic factors play an important role in the occurrence of ONFH.