A look inside: Using digital radiography to confirm feline osteoarthritis

Cats experiencing OA pain are often unable to signal discomfort, so radiography is often the best way to diagnose the condition

Feline osteoarthritis is a degenerative joint disease common in middle age to older feline patients and can have significant impacts on a cat’s quality of lifeFeline osteoarthritis is a degenerative joint disease common in middle age to older feline patients and can have significant impacts on a cat’s quality of life. Reduction in articular cartilage, formation of osteophytes and periarticular fibrosis are associated with pain as joints progressively degenerate over time, resulting in decreased mobility. This leads to a decrease in a cat’s ability to reach resources such as food, water, and litterbox.

These deficits can also impact both a cat’s ability to interact and socialize with family members, as well as feeling comfortable during day-to-day activities. Affected cats will frequently experience a decrease in grooming behavior, socialization, and litterbox use. All of these symptoms are likely due to pain experienced when jumping and performing normal movement behaviors. In more serious presentations, osteoarthritis may cause weight loss due to decreased food intake, irritation, or even aggression with other patients.

Given the range of impacts from a quality-of-life standpoint, it is best when there is recognition of osteoarthritis early in the disease process. This allows for interventions that help maintain mobility and muscle mass.

Yet, due to subtle cat behaviors that often do not signal owners to feline distress, along with diagnostic challenges with physical exams in the veterinary practice setting, diagnostic investigation of feline osteoarthritis is often delayed. After owner observations and a physical exam, digital radiography can provide an accurate and definitive diagnosis of feline osteoarthritis.

Subtleties that delay diagnosis

Cats are solitary hunters. It is generally presumed this impacts how they manifest pain and discomfort from conditions like osteoarthritis. From an evolutionary standpoint, it does not seem that social cueing to demonstrate pain has evolved in cats and they have likely adapted to conceal pain except in extreme circumstances.

It is presumed this prevents the hunter from becoming the hunted. Unfortunately, it also presents challenges diagnostically. Since cats tend to not show obvious signs of pain or discomfort, it is often overlooked by owners who do not appreciate the subtle changes in behavior that accompany the initial onset of feline osteoarthritis. As a result, diagnostic investigation based on owner observations are frequently delayed until the disease has progressed to a significant degree.

As owners generally do not recognize signs of osteoarthritis in cats, it is incumbent upon the veterinarian to diagnose its presence based on other forms of evidence. Unfortunately, cats are not amenable to complete orthopedic exams in the veterinary office.

One diagnostic method is to observe the animal moving independently to determine if there are obvious changes in its stride. However, in a clinical setting, cats often freeze and cannot be induced to move—or will not ambulate normally. In these cases, the veterinarian does not have a chance to appreciate subtle gait changes that would be apparent in a different setting. The method of using force plate gait analysis suffers similarly from atypical feline behavior in a veterinary practice setting and is not a commonly available piece of equipment.

Orthopedic exam clues

Orthopedic examination, where the joints and long bone are physically palpated and manipulated, is the most easily accessible tool available to veterinarians. Signs of osteoarthritis in cats and other animals—such as canines—can include reduced range of motion and pain in one or more affected joints, as well as detectable crepitus during manipulation.

Feline elbow radiograph showing mild degenerative joint disease (DJD) apparent on the cranial caudal view.
Photos courtesy MinXray

Range of motion can be utilized by moving the joint until pain is observed and utilized quantitatively with the use of a goniometer to determine the maximum angles of flexion and extension. Because cats tend not to demonstrate obvious markers for pain, and are generally fearful and anxious in the veterinary setting, it is difficult to determine if a cat is resisting movement of a joint due to pain versus anxiety.

The lack of obvious pain in a single joint can complicate a veterinarian’s ability to detect and diagnose osteoarthritis during a typical exam. Crepitus manifests as a feeling or sound of friction within a joint as it is being manipulated. However, crepitus is not always observed and correlates poorly with the actual presence of osteoarthritis in many cases.

Indeed, a feline osteoarthritis case study performed by Clarke and Bennett and published in the Journal of Small Animal Practice showed no cats in the sample showed crepitus, and only a small portion of the examined joints even showed a reduction in range of motion. Furthermore, feline patients often have bilateral changes in joints leading to an overall decrease in painful activities such as jumping and running. This is less common in canine patients, where arthritis is frequently unilateral, leading to a more easily observable lameness of a leg.

The difficulty of appreciating these subtle changes in behavior have led to the recommendation to administer owner surveys and pain questionnaires. This provides a route for pertinent information gathering about a cat’s behavior at home and can focus the owner on making observations regarding changes in behavior that may have developed slowly over time.

Radiography for the ‘big picture’

Given the difficulties in obtaining complete information through physical exam alone, it is easy to see why radiography is such an important primary diagnostic test for feline osteoarthritis. Lascelles et al completed a prospective observational study that was published by BMC Veterinary Research. The study concluded palpation and goniometry had a significant correlation with negative findings and thus, could be used as a diagnostic screening tool to determine that osteoarthritis is unlikely
to be present.

A stifle view of a cat showing arthritic symptoms. The radiograph was negative for DJD.
A stifle view of a cat showing arthritic symptoms. The radiograph was negative for DJD.

However, there was no reliable method of orthopedic examination that correlated significantly with the presence of radiographic evidence of feline osteoarthritis. Another study, performed by Freire et al and published in Veterinary Radiology and Ultrasound, established that radiographic evidence of degenerative joint disease in cats correlated significantly with the presence of osteophytes, mineralization, and cartilage damage in post-mortem macroscopic analysis.

Frequently, treatment trials are incorporated into the plan to diagnose osteoarthritis in feline patients. However, there are, indeed, advantages to obtaining radiographic evidence of a likely diagnosis of osteoarthritis before treatment. Among these is the opacity of cat behavior to many owners.

If a patient’s pain is not immediately obvious from the owner’s standpoint, then it is helpful to demonstrate the presence of degenerative joint disease in a concrete way through radiography.

Medicating the feline patient for pain is often difficult for owners, stressful for patients, and in the case of NSAIDs, still controversial in the veterinary community at large. Giving an owner the additional evidence of radiographic change can help in communicating the severity of disease and ideally, give additional motivation to follow through on initial treatment long enough to appreciate a positive impact.

Confirming a diagnosis of feline osteoarthritis with radiographs is merited when owner reporting and/or physical exam suggests pain and limited range of motion in cats. Sedation is often needed to capture the highest quality images of limbs and joints. Multiple pharmacologic options are available, including opioids (butorphanol, buprenorphine), benzodiazepines alone or in combination with ketamine, alfaxan, alpha-2 agonists, and oral gabapentin.

Sedation can be safe and effective with proper drug selection. This should be based on patient signalment and behavior in-clinic, any pre-existing conditions and level of pain, as well as proper monitoring from administration through recovery. In a geriatric patient, significant sedation may be obtained using butorphanol with a benzodiazepine. Younger and more reactive patients may need the addition of ketamine or an alpha-2 agonist.

Areas for radiographic focus

Orthogonal views are essential to obtaining a complete radiographic assessment. With the limbs, a straight true craniocaudal (or dorsopalmar) view in combination with the lateral are needed. Obliqued or stressed views are needed in some instances. Imaging the contralateral leg can be helpful, especially when trauma or other causes of lameness like neoplasia are a concern.

A cat exhibiting arthritic symptoms is positioned by veterinary technicians for proper image capture.
A cat exhibiting arthritic symptoms is positioned by veterinary technicians for proper image capture.

Further, adequate sedation and analgesics cannot be overlooked when obtaining images as extension or manipulation of a diseased joint can be very painful. When imaging the spine, it is important to avoid rotation, so it is recommended to use foam wedges or even towels as needed to help with positioning.

The spine should also be imaged in separate cervical, thoracic, or lumbar segments instead of trying to consolidate multiple regions in one image. Compact digital radiography systems designed specifically for veterinary practices, while offering exceptional imaging capabilities, are often preferred.

According to Jeanne Walter, CVT, vice president of sales and marketing at digital radiography systems manufacturer, MinXray, “the lack of variability in the size and conformation of the feline patient allows for radiographs of diagnostic quality to be rapidly obtained once the operator is familiar with the positioning and specifics of the unit being used to obtain the images. Wireless units that provide the functionality of a larger station but exist in a portable, compact package are an added benefit for obtaining images in-clinic or even during mobile visits.”

Feline patients are frequently affected by osteoarthritis of both the appendicular joints and axial skeleton. The joints most frequently affected by osteoarthritis include the elbow, hip, stifle, and shoulder. In a cross-sectional study, 91 percent of 100 randomly selected cats showed at least one appendicular joint with radiographic signs of degenerative joint disease (DJD), and 55 percent of cats had DJD of the axial spine (DJD of Cats—What the Radiographic Signs Mean, B. Duncan X. Lascelles, 2010). An additional resource for veterinarians treating felines and other companion animals is the Journal of Feline Medicine and Surgery (Volume 14, Issue 1, January 2014), which presents an extensive review of the radiographic signs of osteoarthritis in the appendicular skeleton (Bennett et al).

While radiographs are key to diagnosis, they are not generally used to monitor progression of osteoarthritis. However, if there is an acute change in patient comfort or mobility, the joint should be reassessed radiographically.

Because cats experiencing osteoarthritis pain are often unable to signal discomfort and are not typically cooperative or consistent in their presentation of osteoarthritis signs in a clinic setting, radiography is often the best way to obtain a feline’s osteoarthritis status—especially when utilizing high-quality diagnostic imaging and proper positioning is implemented.

Mary Ubatuba, DVM, practices at the Abbeywood Cat Hospital in Westmont, Ill. A feline-focused doctor with special interest in diagnostics and dental surgery, she has earned a Feline Friendly certification and is a member of the American Association of Feline Practitioners.

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