More severe microdamage and micromechanical alterations: altered subchondral bone remodeling in varus knee osteoarthritis with osteoporosis

Abstract

Previous studies show osteoporosis causes tibial varus in knee osteoarthritis patients. Our analysis of tibial plateau specimens from osteoarthritic patients reveals that osteoporosis accelerates the deterioration of the subchondral microstructure of the tibial plateau, exacerbating tibial varus.

Introduction: The relationship between osteoporosis (OP) and knee osteoarthritis (OA) has garnered significant clinical interest, particularly regarding the prevalence of tibial varus in patients suffering from both conditions. This study aimed to elucidate the association between OP and knee OA by examining bone remodeling and microstructural parameters of cartilage and subchondral bone.

Methods: We analyzed tibial plateau specimens from 50 patients, with 25 in the OA group and 25 in the OP-OA group. These specimens were further categorized into four subgroups: OA medial plateau, OA lateral plateau, OP-OA medial plateau, and OP-OA lateral plateau. Comprehensive analyses, including cartilage histology, micro-CT, immunohistochemical techniques, basic fuchsin histological analysis, and micro-finite elements, revealed significant microstructural differences and aberrant bone remodeling processes between the groups.

Results: The OARSI cartilage score of the medial tibial plateau was 13.71% higher in the OP-OA group compared to the OA group (P < 0.05), indicating more severe cartilage degeneration. Micro-CT analysis revealed a lower BV/TV in the subchondral bone of the medial tibial plateau in the OP-OA group (0.58 ± 0.02) compared to the OA group (0.68 ± 0.02) (P < 0.05). Additionally, significant decreases were observed in Tb.N and Tb.Th, while Tb.Sp and SMI increased. The number of osteoblasts in the subchondral bone of the medial tibial plateau was lower in the OP-OA group than in the OA group, while the number of osteoclasts was 55.90% higher (P < 0.05). Result of basic fuchsin staining showed that the CrDn in the subchondral bone of the medial tibial plateau was 69.01% higher in the OP-OA group (P < 0.05), with greater microdamage severity. Micro-finite element analysis showed that subchondral bone stresses in the OP-OA group were higher and more localized to the medial side compared to the OA group.

Conclusions: Our findings indicate that osteoporosis significantly intensifies cartilage degeneration in the medial tibial plateau of patients with knee osteoarthritis. It aggravates aberrant subchondral bone remodeling, increases microdamage, impairs mechanical structure, and accelerates tibial varus.

Keywords: Bone remodeling; Knee osteoarthritis; Osteoporosis; Subchondral bone; Tibial varus.