Both animal and human studies indicate that changes in subchondral bone play an important role in the initiation and progression of osteoarthritis (OA). MRI identified bone marrow lesions (BMLs) in the subchondral bone have been identified as biomarkers of subchondral bone pathology in OA. However, very little is known about the bone microstructure within BML zones. The aim of this study was to evaluate the rod-and-plate microstructure of subchondral trabecular bone in human tibial plateaus with and without tibial BMLs, in comparison to non-OA controls, by applying a novel individual trabecula segmentation (ITS) technique.
Tibial plateaus were collected from 22 OA patients aged 49-79 years undergoing knee arthroplasty and from 11 non-OA cadaver donors aged 44-89 years without bone disease. All specimens were scanned by MRI to identify BMLs and Micro CT was used to characterize the microstructure of the subchondral trabeculae. The specimens were then processed for cartilage histology and OARSI grading.
When compared to controls, the medial compartment from OA subjects without BMLs had a lower rod bone volume fraction (rBV/TV), (p<0.0001) and rod trabecular number (rTb.N), (p=0.002); the plate bone volume fraction (pBV/TV) and plate trabecular number (pTb.N) did not differ. The subchondral bone of OA tibial plateaus containing BMLs was characterized by increased plate bone volume fraction (pBV/TV), (p=0.003), plate trabecular number (pTb.N), (p=0.04), and both rod and plate trabecular thickness (rTb.Th and pTb.Th) (p<0.0001 for both). These differences also associated positively with increased histological OARSI grade within the BML region.
This study shows that in established knee OA, both the extent of cartilage damage and trabecular microstructural alteration in the subchondral bone depended on the presence of a BML. Thus, use of BMLs as MRI image-based biomarkers may inform on the severity of disease in established OA.