SI injuries in horses

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.