Equine practitioners can use ultrasound (US) to examine the articular process joints in horse’s necks to detect increases in joint effusion (fluid swelling). However, researchers have recently discovered that this technique underestimates the amount of effusion present. Kathryn Seabaugh, DVM, Dipl. ACVS, ACVSMR, of the Translational Medical Institute at Colorado State University, in Fort Collins, presented their findings at the 2022 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas.

Osteoarthritis (OA) of the articular process joints of the cervical region can cause neck stiffness, muscle atrophy (wasting), poor performance, neuropathies (disorders of the peripheral nervous system), and lameness in affected horses, said Seabaugh, making this condition clinically important.

Radiographs might be the first diagnostic tool veterinarians reach for to assess neck pain, and computer tomography (CT scan) can also be valuable. But ultrasound often provides a more detailed view of the anatomic structures in the neck and of bone margin irregularities, enthesopathy (bone abnormalities), and synovial effusion, she said.

To determine ultrasound’s reliability for detecting increased effusion in the articular process joints, Seabaugh and colleagues used cadaver necks of five Quarter Horses. They conducted CT scans and ultrasound exams on each neck, then injected specific joints with 0, 2, or 4 milliliters of contrast agent before conducting another ultrasound and CT exam.

They gave the cervical facet joint effusion scores for the CT and ultrasound exams both pre- and post-contrast injection.

“Ultrasound evaluation of the articular process joints had significantly lower effusion scores than CT, said Seabaugh. “For both CT and US, scores were greater post-contrast injection.”

“These findings indicate that articular process joint effusion is easily identified on US, but this technique appears to underestimate the amount of effusion present in the joints,” she added. “An equal amount or more effusion is present on the medial (inner) aspect of the articular process joint not visible by ultrasound, and knowing this will help guide treatment.”

If practitioners use ultrasound to examine equine neck vertebral processes, Seabaugh emphasized the importance of knowing the region’s anatomy. Confusing the tendon of the multifidus muscle around the vertebral column with the joint capsule will overestimate joint effusion.