Objective:​ Subchondral bone plays an important role in the pathological mechanisms of knee osteoarthritis (OA). High-resolution peripheral quantitative computed tomography (HR-pQCT) is an imaging modality allowing noninvasive microstructural analysis of human bone, and the second generation enables scanning of the knee. The purpose of this study was to perform in vivo analysis of subchondral trabecular bone in patients with medial knee OA, to elucidate features of bone microstructure in medial knee OA, and to investigate relationships between bone microstructure and both stage of disease and lower limb alignment.

Methods:​ Subjects were 20 women, including both patients with medial knee OA (Kellgren-Lawrence (KL) grade 2, n = 5, KL grade 3, n = 7, and KL grade 4, n = 4;​ mean age:​ 63.0 years;​ body mass index (BMI):​ 23.8 kg/m²) and volunteers without knee OA (KL grade 1, n = 4, mean age:​ 66.0 years;​ BMI:​ 23.8 kg/m²). The proximal tibia (20-mm length) was scanned by second-generation HR-pQCT at a voxel size of 60.7 μm. A subchondral trabecular bone volume of 5 mm length was extracted from the medial and lateral plateaus. They were then divided into 4 regions:​ anterior, central, medial or lateral, and posterior. Finally, subchondral bone microstructure parameters were analyzed and compared, between each plateau and region. Relationships between microstructural parameters and disease stage (KL grade, minimum joint space width), and between those parameters and lower limb alignment (femorotibial angle:​ FTA, mechanical axis deviation:​ MAD) were also investigated.

Results:​ In the medial plateau, volumetric bone mineral density (vBMD), bone volume fraction (BV/TV), and trabecular thickness were significantly higher and structure model index (SMI) was significantly lower than in the lateral plateau, particularly in the anterior, central, and medial regions (p < .01 each). In the anterior region of the medial plateau, vBMD, BV/TV, and connectivity density showed strong positive correlations with KL grade, FTA, and MAD (r-range:​ 0.61 to 0.83), while trabecular separation and SMI exhibited strong negative correlations with KL grade, FTA, and MAD (r-range:​ −0.60 to −0.83).

Conclusions:​ Higher bone volume, trabecular thickness, and a more plate-like structure were observed in the medial tibial plateau than in the lateral. Subchondral bone microstructure at the anterior region in the medial plateau showed strong relationships with KL grade and lower limb alignment. These results indicate that subchondral bone microstructure in this region may provide representative indices, particularly in medial knee OA. Although this study involved a specifically Asian cohort with a lower BMI distribution than other ethnic groups, the technique presented may be useful in studying the pathogenesis of OA or evaluating treatment effects.