Radiographs of the stifle in horses are a relatively common procedure. They are used to evaluate for developmental and acquired abnormalities of various structures of the knee joint.

Here are some tips for when to obtain these radiographs, and how to obtain great shots of the equine stifle…

When Are Stifle Radiographs Indicated?

Some of the most common indications for stifle radiographs in a horse include a pre-purchase examination or investigation of any swelling of the joints, lameness localized to the stifle, difficulty bending the joint, or traumatic injuries that could affect the knee.

Some of the conditions of the stifle that radiographs may be used to evaluate include osteochondrosis, osteochondritis dissecans (OCD lesions), subchondral bone cysts, trauma, osteoarthritis, joint effusion, infection, or any other suspected abnormalities.

Ultrasound may also prove useful in evaluating the equine stifle, especially for soft tissue structures such as the joint space, meniscus, and ligaments. 

Additional diagnostics—such as joint fluid analysis, arthroscopy, or CT when available—may also provide valuable information. But radiographs are usually a good diagnostic to start with, as they are fairly routine and provide a lot of information.

Planning for Equine Stifle Radiographs

Prior to doing an x-ray study of the stifle, it’s important to thoroughly understand the anatomy of the stifle.

In addition to a working knowledge of stifle anatomy, it’s important to know how this anatomy can change over time. For example, knowing which ages the physes of the joint close can greatly aid in accurate radiographic interpretation.

A vet team should also know how to obtain standard views at appropriate angles, with correct exposure techniques for each view. Due to thick musculature, cranio-caudal views may require significantly longer exposure times than latero-medial views.

Additionally, having a differential diagnosis list will help a vet determine if any additional views are needed to see specific structures of the stifle joint in more detail.

Sedation can help to reduce motion artifact, which can produce x-ray images that are of higher diagnostic quality.

Bilateral views are recommended. This provides an easy basis for comparison in that individual horse, if lesions are unilateral. Also, some lesions (such as OCD) may be bilateral, even if the horse is only showing symptoms on one side at the moment.

Which Views of the Stifle Should be Obtained?

The most commonly obtained views of the stifle include the following…

• Latero-medial. In this view, the x-ray generator is positioned laterally, facing the femorotibial joint, and slightly (10-20 degrees) in a caudo-cranial direction. The beam is directed horizontally, with the detector placed medially and perpendicular to the beam.

• Caudo-cranial. For this shot, the generator is placed caudally to the joint—with the beam centered at the midline—and the detector cranially and perpendicular to the beam. The generator is raised at a 10 to 20-degree, proximo-distal angle. 

• Caudo-lateral to Cranio-medial Oblique. For this view, also known simply as a “lateral oblique,” the beam is centered over the lateral aspect of the femorotibial joint and then angled at a 30 to 60-degree caudo-lateral to cranio-medial orientation. It is directed horizontally across the joint, or at a slight proximo-distal angle. The detector is placed on the opposing side and perpendicular to the beam. 

These three views make up the majority of routine x-ray studies of the stifle. But additional views may be included if more information is needed, such as the patellar skyline or flexed lateromedial views.

For additional information on obtaining views of the stifle in a horse—including detailed pictures of the anatomy in common x-ray views—this article is highly recommended: RadiographWilson.pdf (aaep.org)

Conclusion

As with any aspect of practicing medicine, having a good reference and proper equipment, and gaining practice/experience over time, will help a veterinarian develop confidence in taking and interpreting radiographs of the equine stifle.

Written by: Dr. Tammy Powell, DVM