Introduction: The purpose of this study was to investigate the effects of combination treatments with anticoagulant (warfarin) and a lipid-lowering agent (probucol) on the prevention of steroid-associated osteonecrosis (ON) in rabbits.

Materials and Methods: Male adult Japanese white rabbits were intramuscularly injected once with 20mg/kg body weight of methylprednisolone acetate into the right gluteus medius muscle. These rabbits were divided into three groups: a warfarin plus probucol treatment group (WP Group, n=25), a probucol treatment group (PR Group, n=30), and a non-prophylactic treatment group (NP Group, n=20). Two weeks after the cortico-steroid injection, both femora and humeri were histopathologically examined for the presence of ON, and the sizes of bone marrow fat cells were morphologically examined.

Results: The incidence of ON in the WP Group (5%) was significantly lower than that in the NP Group (70%) (p < 0.0001). The incidence of ON in the PR Group (37%) was significantly lower than that in the NP Group (p < 0.05), but it was significantly higher than that in the WP Group (p < 0.01). The mean size of the bone marrow fat cells was significantly smaller in the WP Group (53.5 ± 4.1μm) than that in the NP Group (60.0 ± 4.0μm) (p < 0.0001). There were no significant differences in the size of bone marrow fat cells between the WP and the PR Groups (52.0 ± 5.0μm).

Discussion: This study experimentally confirmed that anticoagulant plus lipid-lowering agent treatment has a preventative effect on steroid-associated ON in rabbits.

We have studied the correlation between the prevention of progressive collapse and the ratio of the intact articular surface of the femoral head, after transtrochanteric rotational osteotomy for osteonecrosis. We used probit analysis on 125 hips in order to assess the ratio necessary to prevent progressive radiological collapse over a ten-year period. The results show that a minimum postoperative intact ratio of 34% was required. This critical ratio may be useful for surgical planning and in assessing the natural history of the condition.