The present study provides unprecedented information regarding sonographic findings of the articular and periarticular structures of the hip joint in canine patients with and without canine hip dysplasia (CHD) evaluated using the joint distraction method and OFA. In addition, the established ultrasound evaluation protocol may contribute to the investigation of dysplasia in puppies and adults due to the diagnostic characteristics established by changes in joint capsule thickness.
Although the gold standard of CHD diagnosis in dogs is radiographic examination [8, 10], the results of this study demonstrated that ultrasonographic evaluation can be used as a screening and diagnostic aid for CHD and that the association of both imaging methods can bring greater accuracy in disease investigation.
In medicine, ultrasonography of the hip joint is used to guide the diagnosis of developmental dysplasia of the hip (DDH) in newborn babies [26]. Until now, the authors are unaware of studies that provided diagnostic information for CHD in puppies and adults using the ultrasound approach. In this study, capsule thickness was associated with diseased animals, making it possible to determine its diagnostic value when correlated with radiographic evaluation by DI and OFA. This association can be explained by the fact that CHD generates joint laxity [3], intensifying the stress suffered by the joint capsule over time, which is consistent with the degeneration of joint structures.
A report suggested that capsule thickening is progressive, as inflammatory factors are still present in the diseased joint [27], which contributes to changes in joint structures. Furthermore, the cut-off point for young dogs was lower than that for adults, with a positive correlation between the variables.
Some studies have demonstrated that OFA grading underestimates osteoarthritis in adult dogs compared to the distraction index method [10, 28]. The interpretation of capsule findings and bone alterations is important because alterations in these structures may be correlated with animals with less joint laxity in adult life, which attests to the utility of ultrasound diagnosis by distraction index. Thus, we believe that ultrasonography can be implemented as an auxiliary method in the diagnosis of hip dysplasia, especially in borderline patients or in cases that cannot establish interrater agreement on the OFA scale. Moreover, it eliminates the need for new radiographic examinations; thus mitigating radiation exposure and anesthetic risk to patients.
Although a statistical analysis of the echotexture and echogenicity evaluations was not carried out due to the subjectivity of the evaluation and the limited sample size, the ultrasonographic evaluation of the pectineus muscle is important for the therapeutic approach, as there is a positive correlation between the presence of muscular fibrosis and patients [29]. This musculature plays a fundamental role in the biomechanics of the hip [15], justifying the change in the pattern of the identified fibers seen via B mode ultrasound in some patients in this study.
ARFI elastography has provided important information about the morphostructural behavior of tissues, making it possible to differentiate healthy structures from diseased ones in dogs through variations in tissue stiffness [18–20]. Although this study failed to obtain diagnostic results with elastography for CHD in joint and periarticular structures, it was possible to identify changes in the elasticity of the pectineus musculature between healthy and sick young animals. The change in the rigidity of the pectineus in dogs has already been correlated with dysplasia in adult dogs [25], but based on our findings, we believe that the pectineus is not the main structure of the hip that is compromised by CHD, but rather the joint capsule, as it is the main structure responsible for the stabilization and movement of the hip joint [30].
In this study, no difference was found in the elasticity of the joint capsule using the ARFI method between healthy and diseased animals. The authors believe that this may be related to the size of the caliper used to obtain the shear wave velocity (SWV) results, since the capsule is a small structure, and the area of interest may have approached structures adjacent to the capsular evaluation, overestimating or underestimating authe results. Therefore, histopathological studies of the joint capsule should be encouraged to assess structural changes in sick dogs, in order to provide more concrete information about the interference of CHD in the capsular structure.
In this study, we demonstrated the importance of evaluating the articular and periarticular structures in dogs, proving that ultrasonography can help in the screening and diagnosis of CHD and allowing for the prompt treatment of sick animals. In addition, ultrasound examination is a painless, non-invasive procedure that does not require sedation, which provides greater safety to patients.
This study has limitations, among which is the difficulty we encountered in performing homogeneous sampling (weight, sex, race, and age) between the groups, which could have changed the characteristics of the joint and periarticular structures and may have interfered with the elastography values. In addition, some elastography values may have overlapped, such as the pectineus elasticity findings in young animals, which may be related to the study’s inability to diagnose changes in tissue elasticity using the ARFI method in patients with hip dysplasia.