Hypoechoic ultrasonographic findings in the patellar ligaments are common in riding and trotting horses in training (116 cases).

Patellar ligament (PL) injuries are increasingly being reported in horses, but few studies have described the normal PL ultrasonographic appearance in horses. The aims of this prospective observational study were to describe the ultrasonographic appearance of the PLs and infrapatellar fat pad in a population of horses in training and to relate the ultrasonographic findings to objectively measured movement asymmetry. B-mode and color Doppler ultrasonographic examination of the PLs and infrapatellar fat pad in both hind limbs and objective gait analyses were performed on the 116 riding and trotting horses included in the study. The association between ultrasonographic findings, horse age, and movement asymmetry during the trot was then investigated. Distinct or diffuse hypoechoic regions were commonly found in the intermediate PL (24/116; 20.7%), especially in the caudal aspect of the mid-third of the ligament. The infrapatellar fat pad had a hypoechoic striated appearance in all horses except one, in which it was hyperechoic. No association was found between ultrasonographic findings in the PLs and infrapatellar fat pad and lameness. It is important to recognize that there is biological variation in PL appearance, which may or may not be associated with pain in this area, therefore emphasizing the use of local analgesia to determine the location of the lameness.