Subchondral bone microarchitecture and mineral density in human osteoarthritis and osteoporosis: A regional and compartmental analysis

Abstract

Osteoarthritis (OA) and osteoporosis (OP) are historically considered to be inversely correlated but there may be an overlap between the pathophysiology of the two diseases. This study aimed to investigate the subchondral bone microarchitecture and matrix mineralization, and the association between them in OA and OP in relation to the degree of cartilage degeneration. Fifty-six osteochondral plugs were collected from 16 OA femoral heads. They were graded on a regional basis according to the stages of cartilage degeneration, as evaluated by a new macroscopic and a modified microscopic grading system. Twenty-one plugs were collected from seven femoral heads with OP. Plugs were scanned by microcomputed tomography and the microarchitectural and mineral properties were obtained for both subchondral plate and trabecular bone. Microarchitecture and material and apparent densities of subchondral bone in OP were similar to regions with early cartilage degeneration but different from regions with advanced cartilage degradation in OA femoral heads. Subchondral trabecular bone was more mineralized than subchondral plate in both OP and OA, and this compartmental difference varied by severity of cartilage degradation. Furthermore, the relationship among trabecular bone volume fraction, tissue mineral density, and apparent bone density was similar in OP and different stages of OA. Subchondral bone microarchitecture and mineral properties in OP are different from OA in a regionalized manner in relation to stages of cartilage degeneration. Both regional and compartmental differences at structural, material, and cellular levels need to be studied to understand the transition of OA subchondral bone from being osteoporotic to sclerotic.

Subchondral Bone Microarchitectural and Mineral Properties and Expression of Key Degradative Proteinases by Chondrocytes in Human Hip Osteoarthritis

“…The articular surface of OA femoral heads was regionally divided according to the macroscopic grading system of cartilage degradation reported in a recent publication [10]. Two immediately adjacent osteochondral plugs (50 pairs) with 4 mm diameter and ~10 mm height were collected from each graded region depending on availability using a steel hollow punch (Figure 1).…”

“…One set of the paired plugs was stored at −80 • C, until they were transported to the collaborating lab (University of Sheffield) for microCT scanning. These plugs were a subset of the samples used in a previous study and were scanned by Skyscan 1172 (Kontich, Belgium), as previously described [10]. Briefly, images with an isotropic voxel size of 4.87 µm were acquired using the following scanning parameters: 50 KeV voltage, 179 µA intensity, 1180 ms integration time, and 180 • rotation.…”

“…Segmentation between bone and soft tissue/marrow was based on a global binarization threshold. A preliminary cylindrical region of interest (ROI) with 3.0 mm diameter and 4.0 mm depth was chosen for the subchondral bone of each sample (Figure 1), which was then separated into ROIs of subchondral plate and trabecular bone using a semi-automated protocol, as described previously [10].…”

“…Duplicate sections randomly selected from each plug were subjected to safranin O-fast green staining [27]. Microscopic grading of cartilage degradation was carried out using a modified version [10] of the OARSI grading system [28] by two observers (Y. Li and Y. Liem) in a blinded manner. Scoring was repeated after eight weeks and both inter-and intra-observer intraclass correlation coefficients (ICCs) were above 0.94, demonstrating excellent reliability [29,30].…”

“…Numerous studies on animal OA models have shown that cartilage degradation is accompanied by changes in the microarchitecture and/or mineralization of subchondral bone (reviewed in [8,9]). Several previous studies on human knees and hips have shown that the microarchitectural and mineral parameters of subchondral bone are closely associated with the local severity of cartilage degradation in OA [10][11][12][13][14][15][16]. Cartilage degradation, represented by the loss of matrix macromolecules, especially proteoglycans and type II collagen, is attributable to the proteolytic activities of aggrecanases and collagenases [17].…”