## 4 Discussion  
Highlighting the key findings of this study, one may observe that the CDA protocol may be successfully implemented for the quantification of BMD on the field conventional radiographs of normal and OA-affected equine tarsal joints. Through the CPC protocol, the individual BMD characteristics of the decomposed sub-images, representing the increasing severity of the radiological signs of bone spawin, were obtained. Comparing these characteristics among the groups that represent different OA severities revealed that two out of the ten examined relative density ranges allowed the differentiation of the joints affected by severe OA from the others, while another two ranges allowed the differentiation of the joints affected by moderate and severe OA from the normal ones. Considering the discussed limitations and potential clinical applications of the proposed preliminary protocol, it can be suggested that the color annotation-assisted radiographic image decomposition using the CDA protocol holds promise for advancing research on quantifying OA radiological signs, aiding in the field disease progression monitoring in older horses. Bone spawin stands as a prominent cause of hind limb lam lameness in performance horses [28; 29; 33; 36; 37; 38; 65], with its severity progressively increasing with age [9; 12; 13; 19]. While identifying the tarsal joint as the origin of lameness may be evident in horses with clear clinical signs of tarsal region abnormalities, a comprehensive lameness examination, supported by diagnostic imaging, is advisable in all cases [38]. Typically, the tarsal joint is assessed using ultrasonography, conventional radiography [61], and CT [38], with the latter two modalities enabling qualitative bone assessment. Therefore, advancements in radiological image processing, both in conventional and CT-based modalities, can facilitate the quantitative assessment of bone lesions in the context of bone spawin. Despite the increasing use of equine CT, recent equipment advancements, and modifications allowing for fan-beam CT use in standing sedated horses [66; 67], CT examination is still much more expensive than conventional radiographic examination and requires transporting the horse to a reference clinic, limiting the use of CT for the initial monitoring of disease progression in the field. However, CT-based BMD can be successfully used in future scientific research as a cross-validation method. In the equine tarsal joint, three radiographic rating systems have already been proposed for quantifying OA structural changes [68; 69; 70]. These systems assign scores based  
Figure 5: The %color pixels for each step of the density standard are presented as follows: (**A**) S1, (**B**) S2, (**C**) S3, (**D**) S4, (**E**) S5, (**F**) S6, (**G**) S7, (**H**) S8, (**I**) S9, and (**J**) S10. The data are compared between the groups, representing the severity of tarsal joint osteoarthritis (OA). Group 0 represents the normal tarsal joint, group 1 represents mild tarsal joint OA, group 2 represents moderate tarsal joint OA, and group 3 represents severe tarsal joint OA. The data for each group are presented in the bar graph mean + SD. The lowercase letters indicate the differences between the steps. The black points represent single individuals. The significance level was established as \(p<0.05\). on the appearance and severity of the radiological signs of OA [68; 69] or consider the expert consultation process in the Delphi technique [70]. The latter, the most accurate rating system, qualitatively assesses the total extent of the affected DTJ surface, leading to a subjective quantitative assessment of OA severity [70]. In the recent study, the four-point scale concerning no OA, mild OA, moderate OA, and severe OA [70] was also considered in the current research. However, none of the developed rating systems have quantified the severity of the radiographic signs based on BMD.