Magnetic resonance imaging and histology of repair in femoral head osteonecrosis

Different repair processes affect the clinical course of nontraumatic avasc ular femoral head osteonecrosis, not just necrotic lesion size and location , Fourteen femoral heads were retrieved at total hip arthroplasty after cor e decompression treatment, or after conservative treatment was done on 13 m ale patients diagnosed with different stages of femoral head osteonecrosis. To determine repair types, features of coronal magnetic resonance images w ere correlated with light microscopy findings on corresponding coronal unde calcified sections and microradiographs of the retrieved femoral heads. In five femoral heads, repair of necrotic bone and marrow remained restrict ed to the reactive interface for as many as 63 months, producing the diagno stic osteosclerotic rim with adjacent hypervascularity (limited repair). Ni ne femoral heads showed extension of the repair process into the necrosis, In five femoral heads, predominant resorption of necrotic bone led to femor al head breakdown within 2 to 50 months (destructive repair). In four femor al heads, reparative bone formation had started from subchondral fractures and/or the reactive interface, definitely reducing the size of the necrotic area (reconstructive repair). In the latter, the disease progressed slowly or stopped for as many as 45 months, irrespective of treatments, but elimi nation of risk factors seemed beneficial. Although core decompression did n ot always reach the necrotic area and improve repair, it reduced accompanyi ng bone marrow edema and could delay the disease progress. Osteonecrosis wi th limited repair can be identified on magnetic resonance images obtained a t followup, but the similar signal changes of destructive and reconstructiv e repair cannot be distinguished on magnetic resonance images alone, The ev idence of reconstructive repair in nontraumatic osteonecrosis, however, giv es hope for treatments that can improve repair to a sufficient creeping sub stitution of the affected femoral head.