Magnetic resonance imaging criteria of successful core decompression in avascular necrosis of the hip.

To identify imaging criteria that determine the outcome of core decompression (CD) in femoral-head avascular necrosis (AVN). Radiographs and magnetic resonance imaging (MRI) of 65 hips with early stage AVN treated by core decompression between January 1990 and December 2000 for AVN were reviewed. All hips were categorized into two groups according to the result of CD using total hip arthroplasty (THA) as an end point. Hips that had no THA at follow-up were allocated to group I; those treated with a THA were allocated to group II. CD results were calculated for each group using THA as an end point. The parameters analyzed were the presence or absence of edema associated with the double-line sign on the preoperative MRI, the type of epiphyseal scar (ES) according to Jing, and the type of necrosis according to Mitchell. On follow-up, 45 hips had no THA (group I); 20 patients had a THA (group II). Patients with a radiographic crescent sign and those with edema associated with the double-line sign progressed to THA significantly more frequently. The extent of the necrosis had less discriminatory effect between the two groups. ES and necrotic tissue types had no prognostic value. In regard to the success of CD, it is important to differentiate on MRI between a double line sign plus bone marrow edema and a double-line sign only.