Subchondral involvement in osteonecrosis of the femoral head: insight on local composition, microstructure and vascularization

Abstract

To determine changes of subchondral bone composition, micro-structure, bone marrow adiposity and micro-vascular perfusion in end-stage osteonecrosis of the femoral head (ONFH) compared to osteoarthritis (OA) using a combined in vivo and ex vivo approach. Male patients up to 70 years old referred for total hip replacement surgery for end-stage ONFH were included (n=14). Fifteen patients with OA were controls. Pre-operative MRI was used to assess bone perfusion (dynamic contrast-enhanced (DCE) sequences) and marrow fat content (chemical shift imaging). Three distinct zones of femoral head subchondral bone - necrotic, sclerotic, distant - were compared between groups. After surgery, plugs were sampled in these zones and Raman spectroscopy was applied to characterize bone mineral and organic components (old and newly-formed), and contrast-enhanced micro-computed tomography (CE-μCT) to determine bone micro-structural parameters and volume of bone marrow adipocytes, using conventional 2D histology as a reference. In the necrotic zone of ONFH patients compared to OA patients: 1) the subchondral plate did not exhibit significant changes in composition nor structure; 2) the volume fraction of subchondral trabecular bone was significantly lower; 3) type-B carbonate substitution was less pronounced, 4) collagen maturity was more pronounced; and 5) bone marrow adipocytes were significantly depleted. The sclerotic zone from the ONFH group showed greater trabecular thickness, and higher DCE-MRI AUC and Ktrans. Volume fraction of subchondral bone, trabecular number, and Kep were significantly lower in the distant zone of the ONFH group. This study demonstrated alterations of subchondral bone microstructure, composition, perfusion and/or adipose content in all zones of the femoral head.