Regional variations of bone quantity and quality impact femoral head collapse

Abstract

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.

Fig. 1A–B

H&E stained photomicrographs at (A) ×200 magnification and (B) ×100 magnification show a transverse section of a femoral head trabecula, which contains a trabecular microfracture surrounded by a trabecular microcallus and a cross-section of a trabecular microfracture, which contains a trabecular microcallus only.

Fig. 2

This medial-to-lateral view of the proximal femur diagrams the anterior and posterior hemispheres and the 4-mm-thick bone slices in relation to the rest of the proximal femur. Ant = anterior; Post = posterior.

Fig. 3

This anterior-to-posterior view of the proximal femur diagrams the location of the superior (SQ), inferior (IQ), medial (MQ), and lateral quadrants (LQ) in relation to the rest of the proximal femur.

Fig. 4A–B

Photomicrographs with (A) H&E staining (Original magnification, ×5) and (B) Gomori’s trichrome staining (Original magnification, ×5) show serial histologic sections from paraffin-embedded bone squares of a human femoral head.