Subchondral bone histology and grading in osteoarthritis.
OBJECTIVE
Osteoarthritis (OA) has often regarded as a disease of articular cartilage only. New evidence has shifted the paradigm towards a system biology approach, where also the surrounding tissue, especially bone is studied more vigorously. However, the histological features of subchondral bone are only poorly characterized in current histological grading scales of OA. The aim of this study is to specifically characterize histological changes occurring in subchondral bone at different stages of OA and propose a simple grading system for them.


METHODS
20 patients undergoing total knee replacement surgery were randomly selected for the study and series of osteochondral samples were harvested from the tibial plateaus for histological analysis. Cartilage degeneration was assessed using the standardized OARSI grading system, while a novel four-stage grading system was developed to illustrate the changes in subchondral bone. Subchondral bone histology was further quantitatively analyzed by measuring the thickness of uncalcified and calcified cartilage as well as subchondral bone plate. Furthermore, internal structure of calcified cartilage-bone interface was characterized utilizing local binary patterns (LBP) based method.


RESULTS
The histological appearance of subchondral bone changed drastically in correlation with the OARSI grading of cartilage degeneration. As the cartilage layer thickness decreases the subchondral plate thickness and disorientation, as measured with LBP, increases. Calcified cartilage thickness was highest in samples with moderate OA.


CONCLUSIONS
The proposed grading system for subchondral bone has significant relationship with the corresponding OARSI grading for cartilage. Our results suggest that subchondral bone remodeling is a fundamental factor already in early stages of cartilage degeneration.
Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, Oulu, Finland.
Olli-Matti
OM
Aho
Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.
Mikko
M
Finnilä
Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.
Jerome
J
Thevenot
Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.|Department of Diagnostic Radiology, Medical Research Center, Oulu University Hospital, Oulu, Finland.
Simo
S
Saarakkala
Department of Anatomy and Cell Biology, Institute of Biomedicine, University of Oulu, Oulu, Finland.|Division of Orthopaedic and Trauma Surgery, Department of Surgery, Medical Research Center, Oulu University Hospital, Oulu, Finland.
Petri
P
Lehenkari
D000368:Aged; D000369:Aged, 80 and over; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging; D010003:Osteoarthritis / Q000000981:diagnostic imaging / Q000473:pathology*; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology*