Regional variations of bone quantity and quality impact femoral head collapse.

Osteonecrosis (ON) of the femoral head causes the bone to deteriorate, buckle, and collapse. As the vasculature is reportedly uniform in the femoral head, one would expect uniform susceptibility to ON; however, collapse typically occurs in the anterior region. We asked whether regional variations in bone quantity and/or quality could explain the bone's anterior susceptibility despite uniform vascularity. We examined seven femoral heads resected for primary osteoarthritis and three removed after femoral neck fracture. Each was cut into 4-mm-thick, 1.5 cm x 1.5-cm bone squares, processed for light microscopy, and sectioned twice. One section was stained with Gomori's trichrome and assessed by a computer-assisted microscope, which calculated trabecular area, a measure of bone quantity. The other was stained with hematoxylin and eosin and assessed by light microscopy to identify trabecular microfractures, a measure of bone quality. Bone quantity and quality were reduced in the fracture group as a whole; bone quantity was uniform in each femoral head, but the quality was reduced in the anterior portion. The quality was further reduced in the superior region of arthritic bone and in the lateral-inferior regions of the fractured bones. Our findings suggest the anterior susceptibility is the result of bone loading and, as such, reinforcement of the femoral head in ON should focus on the anterior hemisphere.