Microstructural adaptations of the subchondral bone are related to the mechanical axis deviation in end stage varus OA knees

Abstract

Recent studies highlighted the crucial contribution of subchondral bone to OA development. Yet, only limited data have been reported on the relation between alteration to cartilage morphology, structural properties of the subchondral bone plate (SBP) and underlying subchondral trabecular bone (STB). Furthermore, the relationship between the morphometry of the cartilage and bone in the tibial plateau and the OA-induced changes in the joint’s mechanical axis remains unexplored. Therefore, a visualisation and quantification of cartilage and subchondral bone microstructure in the medial tibial plateau was performed. End stage knee-OA patients with varus alignment and scheduled for total knee arthroplasty (TKA) underwent preoperative fulllength radiography to measure the hip-knee-ankle angle (HKA) and the mechanical-axis deviation (MAD). 18 tibial plateaux were μ-CT scanned (20.1 μm/voxel). Cartilage thickness, SBP, and STB microarchitecture were quantified in 10 volumes of interest (VOIs) in each medial tibial plateau. Significant differences (p < 0.001) were found for cartilage thickness, SBP, and STB microarchitecture parameters among the VOIs. Closer to the mechanical axis, cartilage thickness was consistently smaller, while SBP thickness and STB bone volume fraction (BV/TV) were higher. Moreover, trabeculae were also more superior-inferiorly oriented, i.e. perpendicular to the transverse plane of the tibial plateau. As cartilage and subchondral bone changes reflect responses to local mechanical loading patterns in the joint, the results suggested that region-specific subchondral bone adaptations were related to the degree of varus deformity. More specifically, subchondral sclerosis appeared to be most pronounced closer to the mechanical axis of the knee.

Correlation between tibial and femoral bone and cartilage changes in end-stage knee osteoarthritis

“…In our analyses, the VOI was the anterior medial region of the tibia, which we had identified in a previous work as the site exhibiting the most pronounced adaptation. 11 As previous studies did not examine region-specific changes in the tibia plateau, but rather much larger volumes such as the entire medial plateau, they have reported lower BV/TV for tibial plateau than in our study.…”

“…This study represents a follow-up to our previous investigation, where we examined region-specific microstructural adaptations of the subchondral bone in tibial plateaus concerning the mechanical axis deviation (MAD). 11 As demonstrated in our prior research 11 and supported by existing literature, 2 , 3 it has been established that the lateral side of the tibial plateau in end-stage varus OA is less affected. Therefore, in the current study, we aimed to visualize and quantify cartilage and bone microstructure in the medial tibial plateau and medial distal femur in end-stage varus knee OA.…”

“… 15-17 This study used 18 tibial plateau specimens that were obtained from a previous study. 11 A detailed summary of patients’ characteristics for the 28 specimens (11 males, 17 females, 15 right and 13 left knees) is given in Table 1 . The specimens were rinsed and placed in a plastic bag for preservation in a freezer at −20°C.…”

“… 20-22 A cylindrical volume of interests (VOIs) was located at the center of the anterior half of the ellipse; this is the region where most bone adaptation occurs. 11 For the femoral condyle, a cylindrical VOI was defined in the middle of distal part of the medial condyle ( Figure 2 ). The femoral distal cut did not allow for the definition of multiple VOIs with a 10 mm diameter because, to satisfy the continuum assumption, it was necessary to define the VOI with a minimum thickness of 3 mm.…”

“…Therefore, in the current study, we aimed to visualize and quantify cartilage and bone microstructure in the medial tibial plateau and medial distal femur in end-stage varus knee OA. We focused exclusively on the anterior medial tibial plateau, as it was identified in our previous work 11 as the most affected region and the corresponding femoral region.…”