Microstructural transition and mechanical incompetence of trabecular bone around subchondral cyst in knee osteoarthritis

Abstract

Introduction: Subchondral bone cysts (SBCs) were associated with greater loss of articular cartilage and increased risk of joint replacement. This study aimed to characterise subchondral bone disturbance with SBC formation in knee osteoarthritis (OA). Materials and Methods: Tibial specimens were collected during surgeries for a total of 70 patients (age range, 52-86 years) with late-stage knee OA. The specimens were then divided into the SBC+ and SBC- groups according to the presence or absence of SBCs under microcomputed tomographic evaluations. They were processed for the compressive mechanical testing and nanoindentation sequentially. Comparisons of microstructural and mechanical properties of trabecular bone were performed between 2 groups using Student’s t test. Results: The SBCs were present in the majority of tibial specimens (55/70, 78.5%). Their diameter ranged from 1.5 to 14 mm. A greater increase in mean (± standard deviation) trabecular bone volume fraction (BV/TV) was found in OA specimens with SBC+ group (24 ± 9%) compared with SBC- group (18 ± 5%, p = 0.035). It was prominent when the SBC was < 5 mm. The mean compressive modulus of trabecular bone of SBC+ group (47 ± 23 MPa) did not statistically differ from SBC- group (53 ± 33 MPa, p = 0.646) although the former presented higher BV/TV. The mean nano-stiffness of trabeculae in SBC+ group (7.73 ± 1.29 GPa) was significantly lower than SBC-group (12.03 ± 1.98 MPa, p < 0.001). Discussion and Conclusion: The presence of SBC could be an indicator for the poor quality of subchondral bone in the pathophysiology of knee OA.