Sacroiliac (SI, where the pelvis’ sacrum and ilium unite) pain can cause lameness and poor performance in horses. Veterinarians find SI injuries challenging to diagnose and evaluate, however, due to the region’s anatomy and the joint’s many neighboring structures.

So during the 2018 British Equine Veterinary Association Congress, held Sept. 12-15, in Birmingham, U.K., Carolin Gerdes, VetMed, MRCVS, was asked to address the question: How objective can we be when evaluating horses for SI injury? Gerdes is the head of the orthopedics department at Tierklinik Hochmoor, in Germany.

Sacroiliac injuries can be either acute—usually due to trauma—or, more commonly, chronic due to repetitive strain and degenerative changes associated with osteoarthritis. To diagnose these, veterinarians rely on a combination of clinical examination, diagnostic analgesia (nerve blocks), and imaging. Currently, however, we don’t have a repeatable and measurable way to objectively evaluate SI injuries, said Gerdes. She reviewed current diagnostic options to determine what we do know.

The Physical Exam

It’s challenging to physically assess the SI joint, said Gerdes. You can’t palpate it directly, and it has very little range of motion.

“The response to tests provoking pain by pressure applied to certain points of the pelvis varies dramatically from horse to horse,” she said, adding that it’s also difficult to clearly link a horse’s response to pressure in this region to SI disease. Often, it depends on the horse’s temperament.

Other physical signs include:

• Reduced back mobility and flexibility;
• Underdeveloped spinal musculature;
• Muscle spasms;
• Asymmetrical hindquarter muscling; and
• Reluctance to flex or stand on one hind limb.

However, Gerdes said, these signs aren’t always related to SI pain, and practitioners shouldn’t jump to conclusions. She said veterinarians still need to establish “meaningful criteria for pain assessment and an objective system for quantifying these.”

Gait Analysis

Some horses with SI injuries show no obvious signs of lameness, said Gerdes; others only display it when ridden. For this reason, veterinarians should evaluate horses in-hand, on the lunge, on different surfaces, ridden, and going both directions. She recommended they look for signs of a problem, such as a lack of hind impulsion at the trot and bunny-hopping and swapping leads behind at the canter.

“When ridden, the horse might show a variety of unwanted ridden behaviors or lameness,” said Gerdes.

Gait analysis systems that use sensors placed on the horse’s body and/or motion capture cameras might help provide objective and unbiased information, she said. Their limitation, however, is they can only measure hind-limb lameness and asymmetry and must still be used in conjunction with a ridden and visual assessment and diagnostic analgesia.

Diagnostic Imaging

When it comes to imaging the SI area, ultrasound (over the skin or per rectum) is the easiest and most readily available modality for most veterinarians, said Gerdes. However, “it is limited in that only a small part of the SI joint can be viewed using this technique,” she said. Therefore, negative ultrasound results do not rule out SI pathology.

With scintigraphy (bone scan), veterinarians can visualize the entire pelvis and evaluate the SI joint more objectively, said Gerdes. It should be still be used in conjunction with other diagnostic tools, however, since factors associated with the joint’s appearance on bone scan might not be tied to SI pain.

Take-Home Message

Diagnosing SI injuries remains challenging, and a fully objective evaluation is not yet possible, Gerdes concluded.

“There is a large variety of nonspecific clinical signs thought to be associated with SI disease, which often makes definitive diagnosis difficult without applying further diagnostic tests such as diagnostic local anesthesia,” she said, adding that objective gait analysis or quantitative (semi-objective) analysis of scintigraphy images can help increase the degree of objectivity.

Gerdes emphasized the importance of ruling out other causes of pain when making a diagnosis and taking a systemic approach using all available modalities

Alexandra Beckstett, The Horse Managing Editor

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

Pioneering equine surgeon and researcher C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, Dipl. ACVS, a University Distinguished Professor who holds the Barbara Cox Anthony University Chair in Orthopaedics at Colorado State University, received the American Association of Equine Practitioners’ (AAEP) Research Award for his life-long contributions to equine research, specifically in the areas of orthopedics, joint disease, and biologic therapies.

The AAEP Research Award, first presented in 2014, honors an individual who has completed research that has or will make a significant impact on the diagnosis, treatment or prevention of equine disease. McIlwraith received the award at the President’s Luncheon, held on Dec. 4, 2018 during the 2018 AAEP Convention in San Francisco, California.

Colleagues of McIlwraith, who is also founding director of the university’s Orthopaedic Research Center and namesake of its new Translational Medicine Institute, note the honor of nominating him, saying, “His research and educational efforts have improved the health and welfare of virtually thousands of horses worldwide, and we can think of no one more deserving of this award.”

McIlwraith pioneered arthroscopic surgery and joint disease research in the horse, and many of his procedures have been translated into human medicine. He is the co-author of five textbooks, more than 400 textbook chapters and refereed publications, and has given over 600 presentations and workshops.

Previous awards for his research include:

• The John Hickman Award for Orthoaedic Research by the British Equine Veterinary Association (1997);
• Recognition as an Honored Researcher by the Colorado State University Research Foundation (2004);
• Induction into the University of Kentucky Equine Research Hall of Fame (2005);
• Scholarship Impact Award by Colorado State University (2007);
• Elastickon Award for Equine Research by the Grayson Jockey Club Research Foundation (2008);
• Markowitz Award for outstanding contributions to medicine through experimental surgery, by the Academy of Surgical Research (2013); and
• The Marshall R. Urist MD award for Excellence in Tissue Regeneration Research by the Orthopaedic Research Society (2014).

McIlwraith is a graduate of Massey University in his native New Zealand. He holds honorary degrees from universities in Austria, England, Italy, New Zealand, and the United States, and he consults worldwide as a specialist equine surgeon.

Horses show facial expressions that express pain, and researchers have used those expressions to create the horse grimace scale (HGS). While scientists know through the HGS that certain combinations of facial features can suggest pain, they wanted to determine which ones are most related to pain or are most reliable and consistently evaluated among clinicians.

So Emanuela Dalla Costa, DVM, PhD, Dipl. ECAWBM, of the Università degli Studi di Milano Department of Veterinary Medicine, in Milan, Italy, and colleagues set out to fill those knowledge gaps.

“Without an effective tool of assessing pain (a validated scale for pain assessment), we cannot identify when pain occurs, assess its severity, or assess the effectiveness of anything we do to treat the pain (such as analgesic medicines),” she said. “So, in our opinion, it is paramount not only to develop such a tool but also to test its scientific validity in order to be sure that what we are measuring is pain.”

Dalla Costa and her fellow researchers further refined their original HGS research by running statistical analyses on data from 39 horses undergoing routine castration. They reviewed 126 photographs of the facial expressions of these horses before and after surgery and scored them according to the HGS. Then, they ran a subset of those images through more intense analyses to determine which aspects of the facial expressions seemed most associated with pain.

They found that the most reliable indicators—those that their test observers scored consistently in a similar way—were:

• Stiffly backward ears,
• Orbital tightening (squinting),
• Tension above eye area, and
• Prominent strained chewing muscles.

Strained mouths and nostrils scored less consistently.

They also identified criteria that helps clearly distinguish a horse in pain from a horse that’s not in pain. This is not only helpful for current observations in clinics, but it could also lead to software development that would alert caretakers about horses passing a certain threshold of pain, Dalla Costa said.

“The HGS consists of six facial action units (FAU, different parts of the face that change when the horse is in pain),” she said. “This study gives us an idea of the importance of these parts of the face (showing which are more meaningful when assessing pain). This means that we now have the weights (relative value) of each FAU, and we know, for example, that backward ears could be more indicative of pain than strained nostrils. Furthermore, we have a threshold to classify when a horse is in pain compared to a healthy horse.”

Their current study is limited to horses dealing with castration pain, Dalla Costa said. It’s possible that other pain sources might lead to different facial expressions, so those differences need to be kept in mind.

“In future studies, we should focus on other common painful diseases, such as laminitis or colic,” she said.

The study, “Can grimace scales estimate the pain status in horses and mice? A statistical approach to identify a classifier,” was published in PLoS One.

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor’s in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.