KBD mainly damages epiphyseal cartilage, epiphyseal plate cartilage and articular cartilage of developing children, seriously affecting the development of children [1, 2]. By improving diet, living environment and other strategies to block the transmission chain of etiology [5, 6], there are almost no new cases [7, 8]. However, there are still millions of patients with KBD, predominantly among the middle-aged and elderly, for whom diagnosis and treatment continue to pose significant challenges [20]. KBD is a systemic disease, which mainly affect the joints of the limbs. Previous studies mostly focused on the hands and knees, but there are few reports about the lesions of the ankle joint of KBD. The purpose of this study is to explore the classification of ankle X-ray imaging in adult KBD patients, and to study the correlation between the degree of ankle disease and the clinical classification of KBD.
First of all, we found a statistically significant difference in talar trochlear angle between adult KBD patients and the control group, suggesting that compared with the normal population, adult KBD patients had significant lesions in the ankle, which was consistent with previous studies that the ankle joint was the main site of KBD damage [12, 13]. Ankle CT and MRI studies of KBD in middle-aged and elderly patients also suggest significant differences between patients with KBD and the normal population [21, 22]. This disparity may be attributed to the limited blood supply and substantial load-bearing capacity of the talus bone [23], resulting in a higher prevalence of chondrocyte necrosis and apoptosis over time, leading to talus depression and ischemic necrosis [24]. As a result, ankle joint damage is a common and serious issue in adult KBD patients.
Secondly, we explored the X-ray image classification of ankle joint in adult KBD patients using the K-L grading. In the imaging study of ankle joint, Ficta divides talus necrosis into I-IV (grade I: normal; grade II: cystic and / or sclerotic lesions, normal talus contour; grade III: crescent sign, talus subchondral collapse; grade IV: joint space stenosis, secondary tibial cyst, osteophyte, arthritis changes.). However, it's worth noting that 75% of talus necrosis classified by the Ficta system results from trauma [25], with 90% being due to talus neck fractures [26].. Howere, the ankle joint lesion of KBD patients is mainly caused by environmental and other risk factors, which lead to joint hyaline cartilage necrosis during the development of children [24], and affects the entire ankle joint and multiple joints throughout the body from the beginning. Therefore, we believe that the reference K-L classification is more suitable for adult KBD ankle disease. In this study, the X-ray findings of adult KBD patients' ankle were divided into 0-IV levels. Because adult KBD ankle arthritis is often accompanied by typical talus lesions, which are more obvious than OA, such as talus trochlear sclerosis, flattening, collapse and even deformity [24], especially grade IV talus shows different degrees of collapse, straightness and even depression. To improve our imaging grading, we further subdivided grade IV into subtypes a, b, c, and d based on talus trochlear angle. We believe that this classification can provide some reference for the treatment of ankle arthritis in adult KBD patients. For instance, grade IV-C indicates a flat talus joint surface, mirroring a flat lower tibial joint surface. The force distribution in such an ankle joint is relatively uniform over a wide flat area, resulting in less pressure per unit area. The patient's ankle joint may have no pain or only mild pain, Similar to the effect of ankle fusion, the ankle of such adult KBD patients may not require further special treatment. Collapse of the talus fornix may lead to degenerative changes, pain and disability of the ankle and subtalar joints, as well as shortening of the affected leg [27]. However, Adelaar et al [28, 29] pointed out that the presence of talar changes does not necessarily mean that the patient will have arthropathy; Many patients with talar osteonecrosis continue to have functional ankles without significant ankle discomfort. We also observed that ankle pain was not obvious in many adult KBD patients with flat talus collapse. Nevertheless, our findings revealed a significant correlation between the Visual Analog Scale (VAS) score for ankle pain and the X-ray imaging grading of the ankle joint in the KBD group (r = 0.601, r = 0.621, r = 0.610). Finally, based on the above ankle imaging grading of adult KBD patients, we further analyzed the correlation between ankle imaging grading of adult KBD patients and clinical grading of hand. The results indicated that there was no correlation between the total sample grade and the clinical grading of hand. Similarly, we observed no meaningful correlation between the left and right ankle grades and the clinical hand grading (r = 0.232, r = 0.184, r = 0.208). Further study found that there was no correlation between VAS score of ankle pain and hand clinical grade in KBD group (r = 0.110, r = 0.093, r = 0.101). These results suggest that the extent of ankle joint lesions in adult KBD patients does not align with the clinical grading of hand involvement.. Previous studies have also found that there is no consistency between the range and degree of KBD involvement of large joints such as hip, knee, ankle and the clinical grading of KBD hand [30]. Therefore, the clinical grading of KBD hand may not accurately reflect the severity of ankle joint lesions in adult KBD patients. This may be due to the anatomical characteristics of the talus, the blood supply status, and the weight-bearing of the acquired ankle [23]. Which is prone to serious lesions, while the relative load of the hand is small, resulting in the degree of ankle lesions in adult KBD is not related to the clinical graduation of the hand. Therefore, the comprehensive evaluation of the diagnosis and clinical grading of adult KBD patients should consider not only the hand but also the ankle joint. This area warrants further discussion and investigation..
In conclusion, our exploration of ankle X-ray imaging grading in adult KBD patients and analysis of its correlation with clinical grading of KBD hand provide a new perspective for the study of adult KBD ankle. However, we acknowledge certain limitations in our study, such as the limited geographical scope of our survey and the relatively small sample size. In future studies, it is necessary to further expand the sample size, multi-region, and collect more clinical data related to ankle pain degree, activity function and quality of life and so on for in-depth research.