The Diagnostic Hurdles of Neck Arthritis

Clinicians have been radiographing the equine neck for a long time. In the literature, most of the available information about the cervical vertebrae focuses on horses with neurologic abnormalities such as cervical vertebral stenotic myelopathy, also known as Wobbler syndrome. In horses with osteoarthritic changes, however, the well of knowledge is not quite as deep.

“Neck pain can cause poor performance,” said Elizabeth J. Davidson, DVM, DACVS, DACVSMR, at a recent Purina Equine Veterinary Conference, an invite-only continuing education event for equine veterinarians and technicians hosted annually by Purina Animal Nutrition in St. Louis, Mo.

“The hard thing in horses that have neck pain is that the list of things that can be problematic is enormous. The different and various clinical signs that can happen and the different types of history information from the owner are tremendous.”

For horses with osteoarthritis of the cervical articular process joints (CAPJs), career-altering pain is a distinct possibility. The most common presenting signs are generalized neck stiffness, lack of flexibility during manipulation of the neck, abnormal head carriage and resistance to rein tension. Riders may report that the horse is unwilling to work on the bit or is unable to maintain a “frame” while riding.

CAPJ arthritis is similar to arthritis of other joints, in that it is characterized by articular cartilage loss and associated osteophyte production, which can produce irregular joint margins. As time passes, this chronic, progressive remodeling can result in changes in the shape of the CAPJs (Figure 1).

Although C6 and C7 are the most common sites, any joint within the horse’s cervical vertebral column can develop arthritis, and that arthritis can occur anywhere within that joint.

The challenge lies in differentiating normal anatomic variations from problem-causing conditions. For example, up to 40% of horses have a spinous process associated with the dorsal aspect of the C6-C7 region.

“That’s exactly where we look to see if there’s bony enlargement associated with periarticular degenerative conditions,” said Dr. Davidson, an associate professor of sports medicine at the University of Pennsylvania’s New Bolton Center in Kennett Square, Pa. “That makes it challenging to determine whether it’s a normal anatomic variation or an abnormal degenerative condition.”

Fortunately, advances in diagnostic imaging have enabled clinicians to gain an upper hand in identifying and managing affected horses. Dr. Davidson gave a rundown of available options.

Radiography
While portable radiography equipment has its benefits in the field, lateral-lateral radiographic imaging of the entire neck requires many images from the poll to the withers, and a well-positioned patient. If the image quality is suboptimal, then diagnosis can become exponentially more difficult.

When imaging a horse’s foot, for example, the complex anatomy and superimposition of the bones require multiple views. The neck is no different. “There are things we can do,” she added. “There are additional radiographic techniques that we use today that can help us sort it out.”

An oblique view, she said, can allow the clinician to visualize the difference between the left and right cervical articular process joints.

Nuclear scintigraphy
While nuclear scintigraphy can be valuable for detecting stress fractures, the value of these bone scans in detecting neck lesions is limited.

In normal horses, increased radiopharmaceutical uptake (IRU) commonly is observed in the C5-C6 and C6-C7 joints when compared with the cranial cervical vertebrae. However, Dr. Davidson said that right and left lateral scintigraphy images are easy to obtain and can assist in identifying laterality of radiopharmaceutical uptake (Figure 2). Aside from IRU, the uptake pattern may identify conformational abnormalities such as enlarged CAPJs or changes in the shape and position of the cervical vertebrae.

Computed tomography
Large-bore computed tomography scans and standing cone-beam robotic CT scans allow for 3-dimensional imaging of the equine neck.

“It helps us to discern all of the nooks and crannies, all of the complicated anatomical regions, the right versus left side, and the dorsal vs ventral areas of the CAPJs,” Dr. Davidson said.

CT also excels in critical assessment of the axial aspect of the CAPJ, where asymmetry or enlargement may lead to compression of the spinal cord or foraminal stenosis. It can also help identify underlying fractures associated with the CAPJs and osseous fragments (Figure 3).

With CT, “we can separate all of the things that are superimposed on the lateral-lateral radiographic evaluation,” she said. “We get more information about the potential pathological abnormalities that we see in the necks of horses.”

Putting it all together
In general, horses don’t particularly care what their necks look like on advanced imaging. If a horse has arthritic changes in the neck, that does not automatically mean it will affect the horse’s work or function.
Dr. Davidson explained that as many as 72% of horses have some sort of bone remodeling along the CAPJs.

“That’s almost every horse,” she added. “Does that mean that every horse has a problem? Probably not.”

To put the diagnostic pieces together, a thorough clinical examination and a gait assessment are critical. Exercising maneuvers to exacerbate gait abnormalities, stretching exercises and observation of the horse while lunging all contribute to the big picture.

“With all these advanced imaging abnormalities, it sounds weird to go back to look at the horse and think about physical exam findings, but it’s still so important,” Dr. Davidson said. “I would argue that it’s even more important than all of the radiographic equipment we use today.” MeV