Mylène Jansen

388 Chapter 18 a partial normalization. This, in combination with the fact that KJD has shown anabolic and catabolic changes in joint homeostasis as well (measured with synovial fluid biomarkers and mesenchymal stem cells), indicates KJD results in modification of the whole-joint including not only cartilage but also bone and synovial tissue activity that could lead to long-term joint repair. 20,21 As the subchondral cortical bone plate is thicker in advanced OA, especially in the tibia, it was anticipated that at baseline the most affected compartment showed a higher cortical bone thickness compared to the less affected compartment (LAC) of the joint. 3,22 Throughout the entire subchondral bone, but most evidently in the most affected compartment, KJD appears to result in a decrease in thickness at the subchondral bone plate that is sustained at 2 years. Between 1 and 2 years after treatment, the cortical thickness around the joint margins seemed to increase, which might be related to formation of osteophytes in those regions, as previously shown using this same analysis technique in the hip. 16 This exploratory study is hampered by the absence of a matched healthy control group with CT images available. As such it is difficult to say what a normal subchondral cortical bone thickness is, particularly given the novelty of this analysis technique. The fact that the most affected compartment of the OA joint seems to become more similar to the less affected compartment, point towards (at least partial) normalization of subchondral cortical bone plate thickness. Effects appeared greater in patients with a higher age and Kellgren-Lawrence grade (data not shown), indicating more severe OA, which is consistent with previous bone-related results measured on radiographs and KJD treatment effects in general. 9,10,23 The subchondral trabecular bone density showedhigher values in themost affected compartment as well. The density decreased throughout the entire joint in the first year after treatment, likely the result of the 6-week unloading, and remained decreased at 2 years compared to baseline despite the small increase between 1 and 2 years after treatment. Also, values in the most affected compartment shifted towards values observed in the least affected compartment, with the largest and most significant changes occurring in the most affected compartment, again indicating a shift towards (partial) subchondral bone normalization. CT analyses in patients treated with ankle distraction showed subchondral bone density normalization was well, as the overall density decreased while density in low-density (cystic) areas increased. 24 Previous radiographic evaluations showed a significant subchondral bone density decrease 1 year after KJD treatment as well, and this decrease was significantly larger in patients who 9 years after treatment still did not receive a TKA compared to patients who did. 9 In these studies, no differentiation between cortical plate thickness and trabecular density was made. In the present study for the first time we show that these observed density changes on ankle CTs and on plain knee radiographs could be the result of a combination of both a decrease in cortical plate thickness and a decrease in trabecular density. Also, as with cortical