Cystic lesions in osteoarthritis and osteonecrosis of the femoral head : a comparative analysis of 3D distribution, microstructure, and histology.

Aims: Cystic lesions are strongly associated with the pathogenesis and selection of treatment strategies in osteoarthritis (OA) and osteonecrosis of the femoral head (ONFH). However, the differences in cystic lesions arising from these two diseases are not fully understood. This study aimed to delineate the variations in cyst characteristics in the femoral heads of patients with OA and ONFH. Methods: A total of 45 patients with OA and 105 patients with ONFH who underwent total hip arthroplasty (THA) between September 2014 and December 2021 were recruited in the study. The 3D distribution, microstructure, and histological characteristics of cystic lesions were comprehensively analyzed. Comparative assessments of the microstructural, histomorphometric, and histopathological properties of cystic lesions between OA and ONFH were performed, using micro-CT, decalcified and undecalcified bone histomorphology, and scanning electron microscopy (SEM). Results: In comparison to ONFH, cystic lesions in OA exhibited a smaller volume and a denser distribution. Despite a common prevalence in the anterior hemisphere in both conditions, ONFH cysts were predominantly located laterally, whereas OA cysts were found mainly medially. In OA, the trabecular bone surrounding the cystic lesions exhibited a more sclerotic microarchitecture, with an increase in bone formation and a decrease in bone resorption at the remodelling level. Histologically, cystic lesions in ONFH demonstrated a higher degree of angiogenesis compared to those in OA. Conclusion: While cystic lesions in both OA and ONFH were predominantly located in the anterior hemisphere, they exhibited different distribution and involvement characteristics, microstructure and bone remodelling properties, as well as histopathological features.