Multimodal Analysis of Giant Anteater ( <i>Myrmecophaga tridactyla</i> ) Femorotibiopatellar Joint Anatomy: Macroscopic, Radiographic, and Ultrasonographic Findings

The giant anteater (Myrmecophaga tridactyla) is an endangered species, and further studies on its morphology are essential for conservation efforts. These animals adopt a bipedal posture on their pelvic limbs for defense and foraging. This study aimed to evaluate the femorotibiopatellar joint, that is, the stifle joint (SJ), in M. tridactyla, and to describe its anatomical characteristics using macroscopic, radiographic, and ultrasound approaches. A total of 18 joint evaluations were conducted using five specimens fixed in 10% formalin (six joints) and six thawed carcasses (12 joints). Radiographic examinations, both simple and contrast-enhanced, were performed, alongside joint ultrasound. Anatomical assessments included macroscopic dissection and frozen sectioning using a band saw. Radiographic evaluation was conducted with mediolateral and caudocranial views, focusing on bone elements in simple radiographs and joint capsule distension and meniscal contouring in contrast radiographs. Ultrasound allowed for the evaluation of articular and periarticular soft tissues, including ligaments, tendons, menisci, articular capsule, cartilage, and the infrapatellar fat body. The anatomical assessment revealed several particularities, such as a long medial collateral ligament and patellar ligament, as well as the presence of a supratrochlear fat pad and synovial folds in proximal suprapatellar region. Additionally, the absence of femoropatellar ligaments was noted, along with the presence of a large, rectangular sesamoid bone in the m. popliteus tendon (also known as cyamella). Furthermore, no communication was found between the joint cavity and the tendon sheath of the m. long digital extensor. In conclusion, the anatomical peculiarities of the SJ in M. tridactyla should be considered in the diagnosis, clinical evaluation, and surgical procedures for conditions affecting this species.