INTRODUCTION: Osteoarthritis (OA) is a multifactorial disease of the whole joint and it is most commonly seen in hip and knee. It is unclear whether osteoarthritis in hip and knee has different aetiologies and if different factors influence progression and degenerative changes characterising this disease in different joints. This study investigated the type and extent of structural changes at tissue and cellular level between hip and knee osteoarthritis.
METHODS: Tibial plateaus were collected from 11 patients (5 females aged 70±8 years) undergoing total knee replacement surgery and 8 femoral heads (4 females aged 64±12 years) from patients undergoing total hip replacement surgery. Upon receiving surgical samples, two bone core biopsies were sampled per subject. From tibial plateau, biopsies were obtained from anterior and posterior aspects of medial condyle, while biopsies from femoral heads were obtained from anterior superior and anterior inferior aspects. Synchrotron micro-CT imaging was performed on each sample to obtain parameters describing bone microstructure, osteocyte-lacunar network and bone matrix vascularity. Osteocyte density, viability and connectivity were obtained histologically.
RESULTS: The sclerotic appearance of bone microstructure is more pronounced adjacent to severe cartilage loss in both hip and knee OA. However, significantly lower osteocyte cell density (p<0.0001), viability (p=0.02) and connectivity (p<0.0001) were found in hip OA when comparing to knee OA, irrespective of disease severity. Also, significantly lower bone matrix vascularity (p=0.03) was found in hip OA when compared to knee OA.
DISCUSSION: This study provides evidence that OA in hip and knee demonstrate different characteristics at the tissue and cellular levels. Importantly, the results from this study suggest that the mechanisms and phenotypes of OA disease differ across joints. In addition, findings from this study may potentially lead to identify potentially effective therapeutic targets and allow more targeted and tailored treatment in patients.