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- The sonographic appearance of the normal intermediate patellar ligament
The sonographic appearance of the normal intermediate patellar ligament
VRU 2023 - 64(3):530-536
Obi Veterinary Education
December 12, 2023
Background: The intermediate patellar ligament is a soft tissue structure in the equine stifle that is often injured. It has striations on ultrasound that can be confused with tears. This study aimed to describe the striation patterns in Warmbloods and Quarter Horses, and compare them between breeds and limbs.
Study: This was a prospective, observational study that included 12 client-owned horses (6 Warmbloods and 6 Quarter Horses) that were free of clinical signs of hindlimb lameness and stifle pathology. The intermediate patellar ligaments of both hindlimbs were examined ultrasonographically and the striation number, pattern, width, and cross-sectional area were recorded and analyzed.
Methods: The horses were evaluated for lameness and then underwent ultrasound examination of the intermediate patellar ligaments in the transverse plane at three locations: proximal, mid-portion, and distal. The number and pattern of striations were determined by visual inspection, and the width of the widest striation and the cross-sectional area of the ligament were measured using the ultrasound software. Statistical tests were used to compare the variables between breeds and limbs.
Results: No significant breed differences were found in striation number, width, pattern, or cross-sectional area, except for the mid-portion of the ligament where Quarter Horses had more striations than Warmbloods. The prevalence of striations was greatest in the distal aspect of the ligament for both breeds. The most common striation pattern was parallel, followed by arborizing. Two-thirds of the horses had bilaterally symmetrical striation patterns, while one-third were asymmetric.
Limitations: The main limitations of this study were the small sample size, the lack of histopathology to confirm normality of the ligaments, the inclusion of mildly lame horses, and the potential bias of a single, unblinded observer.
Conclusions: This study showed that multiple variations of striation patterns are present within the distal aspect of the intermediate patellar ligament and that there are no significant differences between Quarter Horses and Warmbloods, apart from striation number at the mid-portion of the ligament. Comparison to the contralateral limb may not be reliable to differentiate normal striations from pathologic changes in one-third of horses. Other signs of pathology on ultrasound should be used instead.
Transverse-sectional ultrasound image of the distal aspect of the intermediate patellar ligament demonstrating normal appearance of striations. Lateral is to the left of the image, images were acquired with a variable frequency linear transducer set at 8–12 MHz in B mode. The horses were standing square on a flat level surface and weightbearing equally on both hindlimbs. The cranial aspect of the stifles was clipped, isopropyl alcohol was used to clean the area and ultrasound coupling gel was applied. Machine parameters were adjusted as needed to improve image quality. A stand-off pad was not used. White asterisks indicate normal hypoechoic striations present
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