Inside the equine stifle

Inside the equine stifle

Diagnostic technologies can help uncover minor conditions before acute injury
Jun 01, 2006

Horses that jump are at increased risk for meniscal injuries as the forces on the hind legs, and the stifles in particular, are intensified when horses take off and land. Poor riding, poor footing and other factors can also contribute to possible stifle injuries.
The veterinary community is paying close attention to new information being uncovered using Magnetic Resonance Imaging (MRI) techniques. The increased availability of MRI units and the development of the standing MRI scans have made it possible to hone evaluations, and much has been reported of late about soft-tissue injuries in the foot, especially the caudal heel. Many horses that might have been generally classified as having navicular syndrome prior to MRI use are now being diagnosed with impar ligament damage, deep digital flexor attachment injury or any number of other soft-tissue problems occurring within the hoof capsule.

The technical limitations of MRI technology currently prohibit veterinarians from viewing many other areas of the body that would greatly benefit from the detailed observations and information only available with MRI (see related story). Perhaps chief among these hard-to-evaluate areas and a location that experiences considerable problems in the athletic horse is the stifle joint.

"The preferred diagnostic modality for diagnosing soft-tissue injuries in the human knee is MRI," says Troy Trumble DVM, PhD, Dipl. ACVS, an orthopedic surgeon at the University of Florida College of Veterinary Medicine. "This would be the ideal modality for the horse as well. However, until we have a better way to diagnostically image the stifle, the locations and types of soft-tissue injuries will be debated."

This thermography shows increased heat and swelling of the lateral collateral ligament of the stifle joint. The large number of structures all closely associated with this joint makes accurate diagnosis a challenge.
But there is little debate about the volume of injuries that occur in this joint. In humans, more than 9.5-million people visited an orthopedic surgeon because of knee injuries in 2003, making it the most commonly injured joint. Dr. J. Lane Easter of Performance Equine Associates in Texas considers the stifle joint the No. 2 cause of hind-end lameness in the western performance horse (behind proximal suspensory desmitis). Dr. Sue Dyson a lameness referral specialist with The Animal Health Trust in Newmarket, England, says horses that jump solid fences, such as three-day eventers and steeplechase runners, are more likely to experience trauma to the cranial surface of their stifles and therefore exhibit a higher percentage of such problems. Cutting horses, jumpers, racing Thoroughbreds, dressage horses and equine athletes of all disciplines can and do experience significant stifle injuries. But because this joint and its associated structures can be so difficult to evaluate, many stifle injuries still go undiagnosed and overlooked.

The complexity of the stifle lends itself to many different problems. In a study of 86 cases of stifle lameness, Drs. L. Jeffcoat and S. Kolb found 38 percent of the horses had subchondral bone cysts. Many of these were thoroughbreds noted to be developing stifle lameness at, or before, the onset of training. This study showed 15 percent had upward fixation of the patella; 13 percent had osteochondrosis dissecans (OCD) lesions, while a small percentage of horses showed either osteoarthritis (3 percent), fractures (4 percent), epiphysitis (1 percent) or unknown causes (13 percent). Stifle ligament and meniscal damage was noted in 12 percent of the cases, and many clinicians feel that these soft-tissue injuries are the types of stifle problems that are currently most under diagnosed.

Anatomically correct

The major soft-tissue structures of the equine stifle are the medial collateral ligament (MCL), the lateral collateral ligament (LCL), the anterior and posterior cruciate ligaments (ACL and PCL) and the medial and lateral menisci. The most common injury to the human and canine knee is rupture of the anterior or cranial cruciate ligament. But this injury is very uncommon in the horse.

"Part of the reason is a difference in anatomy," Trumble explains. "In humans and dogs, there is one joint and one patella ligament with the cruciate ligaments located within the joint capsule. Horses have three joints, three patellar ligaments, and the cruciate ligaments are extra capsular making the equine stifle inherently more stable."