Vasculature deprivation-induced osteonecrosis of rats' femoral heads associated with the formation of deep surface depressions.

Background: Shallow or deep bowl-shaped depressions often develop after drilling an intraosseous conduit in the necrotic, avascular femoral head of rats. The etiopathogenesis of tissue loss at the articulation surface after a drilling procedure was elaborated in the authors' previous reports.

Goals: To scrutinize a large collection of femoral heads of rats in order to search for similar changes in cases in which no drilling procedure was carried out.

Study: This retrospective study comprised the specimens of 386 rats with vessels-deprived osteonecrosis of the femoral heads, none of the animals having undergone a drilling procedure.

Results: Shallow or deep bowl-shaped depressions were encountered at an incidence as low as 2.8% of the femoral heads of the above mentioned 386 rats. It is not feasible to distinguish histologically the "spontaneously" arising from and drilling-related depressions.

Conclusions: No assured explanation can be offered for the evolving depressions of the surface of femoral heads of rats, which have not undergone a drilling procedure. It is hypothesized that the synovial fluid forces its way via slits in the articulation surface and bores cavities in the substance of femoral heads, which display a postosteonecrotic osteoarthritis-like disorder. The rising pressure in the arthritic joints results, firstly, in an enlargement of these cavities and, secondly, loss of fibro-cartilaginous tissue such that the cavities come to communicate with the articular space.