The prevalence and clinicopathological appearance of extension of osteonecrosis in the femoral head

In about 50% of cases, osteonecrosis of the femoral head is known to occupy more than one site. These is controversy as to whether a single focus may increase in size. We have reviewed 606 consecutive femoral heads which had been surgically removed for osteonecrosis, Extension of osteonecrosis was o bserved in only two (0.3%) and was confirmed histopathologically by the enl argement of the necrotic segment beyond the repair zone formed for the prim ary necrosis into the adjacent, previously uninvolved bone. In both cases, the necrotic regions were wedge-shaped and occupied over 80% of the femoral head. It appears that an increase in size is extremely rare and that osteonecrosi s is due to a single event, Our findings may be of value in assessing the u se of joint-salvage procedures for osteonecrosis of the femoral head.