Microstructural analysis of subchondral bone in knee osteoarthritis

Summary: The results of this study show increased formation of bone in the subchondral areas in advanced stages of osteoarthritis of the knee. These changes seem to be influenced by mechanical factors. Introduction: Subchondral bone changes seem to contribute to the progression of knee osteoarthritis (OA). This study aimed to analyze subchondral bone microstructure in specimens of late-stage knee OA in respect to articular cartilage damage, meniscus integrity, and knee joint alignment. Methods: Thirty proximal tibiae of 30 patients (20 female and 10 male) with late-stage OA retrieved during total knee arthroplasty were scanned using a high-resolution micro-computed tomography. The scans were semi-automatically segmented into five volumes of interest. The volumes of interest were then further analyzed using commercially available software. The degree of articular cartilage damage was assessed semi-quantitatively by magnetic resonance imaging before surgery. Results: The mean bone fraction volume (bone volume/total volume (BV/TV)) in all weight-bearing locations was significantly higher compared to the non-weight-bearing reference point below the anterior cruciate ligament (p = 0.000). The mean BV/TV in the medial compartment was significantly higher compared to the lateral compartment (p = 0.007). As for the BV/TV in intact menisci, there was a significantly lower subchondral bone fraction volume compared to subluxated or luxated menisci in the medial (p = 0.020) and lateral compartment (p = 0.005). Varus alignment had a significantly higher subchondral BV/TV in the medial compartment, whereas valgus alignment had a significantly higher subchondral BV/TV in the lateral compartment (p = 0.011). Conclusions: The results show significant differences of subchondral bone microstructural parameters in respect to cartilage damage, meniscus’ structural integrity, and knee joint alignment. Therefore, subchondral bone changes seem to be a secondary process in the late-stage OA of the knee caused by mechanical changes.