Cross-sectional anatomy and comparative ultrasonography of the equine medial femorotibial joint and its related structures.

Reasons For Performing Study: Injuries of the equine stifle are frequent causes of hindlimb lameness. Ultrasonography is useful for the diagnosis of many soft tissue lesions but, until recently, its application to the equine stifle has been limited to a description of normal and abnormal structures. A comparative study using gross anatomical sections to identify all structures visible on ultrasonographic images of the equine stifle has not previously been reported.

Objectives: To provide a comprehensive comparative cross-sectional atlas of the normal equine medial femorotibial (MFT) joint and its related structures using ultrasonography.

Methods: The stifle joints of 15 cadaver limbs were examined ultrasonographically using a systematic approach. Ten different scanning planes were defined. The lateral and medial femorotibial and the femoropatellar joints were injected with pigments of different colours. Each leg was frozen (10 in extension and 5 in flexion) and cut into slices corresponding to the different scanning planes. According to the different ultrasonographic reference images, 10 representative anatomical images were selected and digitised.

Results: All bony and soft tissue structures were identified on the anatomical sections and subsequently located on the corresponding ultrasonographic images, except the caudal meniscotibial ligaments. Visualisation of the cruciate ligaments was a challenge due to their position and oblique orientation.

Conclusions: Ultrasonography is a very useful technique for imaging both soft tissue and bony structures of the MFT joint and its related structures, although a protocol is required to perform a systematic and standardised ultrasonographic examination. Good anatomical knowledge is mandatory for identification of the different structures.

Potential Relevance: This study should contribute to 1) knowledge of the ultrasonographic anatomy of the equine MFT joint and its related structures, 2) use of a protocol for a standardised ultrasonographic examination and 3) the ability to recognise abnormal structures.