The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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28 TheHorse.com THE HORSE September 2016 Identifying Stifle Injuries "Although the stifle is a large joint, and swelling of one or more of the compart- ments of the stifle joint is usually obvious to veterinarians, the proximal location often doesn't make the outward observa- tion of swelling obvious," says Kawcak, referring to the close proximity of the stifle to the bulk of the horse's body. This is in contrast to the knee or fetlock, where swellings are more obvious to many owners. A physical examination, including a lameness examination, as well as diagnos- tic anesthesia (i.e., nerve blocks, or inject- ing a local anesthetic such as lidocaine into the joint to confirm the suspected source of lameness) certainly serve as diagnostic mainstays. But to pinpoint the exact cause, nature, and severity of the injury, veterinarians typically recommend one of the following diagnostics: radiog- raphy, ultrasonography, and arthroscopy. "Compared to other joints in the limb, such as the knee and fetlocks, the bulky muscles surrounding the horse's stifle and the close, complex anatomy often makes diagnosis of the injured structures chal- lenging," Kawcak says. Radiographs are typically a go-to di- agnostic tool in many cases, helping rule out fractures and other bony changes, such as osteoarthritis, subchondral (un- der the cartilage) bone damage, and ex- cessive bone growth where the ligament should attach (enthesophytes). Ultrasonography is the next noninva- sive and readily available diagnostic op- tion. It allows the veterinarian to examine the soft tissues (specifically, the patellar and collateral ligaments) around the joint as well as in the joint, such as the menisci and meniscal ligaments. He or she can also assess the joint capsules, bone mar- gins, and articular cartilage. Like radiographs, however, ultrasound cannot be used to diagnose all stifle inju- ries, says Myra Barrett, DVM, MS, Dipl. ACVR, an assistant professor of radiology at CSU. "Ultrasound can fall short in detecting articular cartilage damage in the absence of subchondral bone injury," she says. "Evaluation of the cruciate ligament is very limited with ultrasound because they are located deep within the joint." Kawcak concurs, adding, "Owners need to remember that ultrasonography only provides a window into the joint, not a complete picture, and a combination of imaging techniques is usually required to get the best characterization of the dam- aged tissues." In some cases veterinarians perform ultrasonography in conjunction with arthroscopy (inserting a slender arthro- scope into a small incision to view the joint) to get a more detailed picture of the stifle joint's overall health. "Arthroscopy can identify some of the injuries to the menisci, avulsion injuries (fragments pulled loose from the bone), as well as cranial medial meniscotibial ligament tearing, among others," says Goodrich. But again, it's not useful for diagnosing all of these injuries, and she recommends using multiple imaging modalities, such as radiographs and ultrasound, to get a global assessment of the stifle. One alternative to traditional arthros- copy is needle arthroscopy, originally described by Frisbie in 2015. With this method the practitioner uses a dispos- able 18-gauge needle measuring only 1.2 mm in diameter and 100 mm in length. A camera attaches to the arthroscope at one end and projects the image on a monitor, while the other end probes the stifle joint. The needle arthroscope's small size and maneuverability allow veterinarians to see all the major structures of the stifle, especially the menisci and collateral ligaments that other approaches, such as ultrasonography, allow them to only partially visualize. "The utility of this minimally invasive technique is becoming popular, partly because of the short downtime associated with the procedure," says Frisbie. "Horses are back to work in as little as 48 hours, depending what is found at arthroscopy. Further, more and more veterinarians are learning how to perform the procedure." For the last four years Frisbie has taught a course at CSU for veterinarians to become proficient at needle arthros- copy. He has also traveled internationally to share this technique. "Horses that have pain localized to the stifle, but other diagnostics such as X ray or ultrasound don't provide answers to why there is pain, turn out to be the perfect indication for this technique," says Frisbie. "When I am in my private practice I am performing this procedure weekly." In human medicine, magnetic resonance imaging (MRI) and computed tomography (CT) are invaluable for Stifling THE PAIN Radiographs help rule out fractures and other bony changes such as enthesophytes. SHELLEY PAULSON Owners need to remember that ultrasonography only provides a window into the joint, not a com- plete picture." DR. CHRIS KAWCAK