Sports medicine for cats (Proceedings)

Similar to dogs, joint disorders of the cat are common. Despite this fact, the reported treatment options for cats with joint disease are limited. The object of this presentation is to describe the clinical findings, surgical / arthroscopic findings and post-operative management of cats with joint disorders including elbow osteoarthritis and medial compartment disease, shoulder osteoarthritis and medial shoulder instability, and cranial cruciate ligament insufficiency.

As in dogs, the radiographic findings of osteoarthritis do not always correlate well with clinical function. In a radiological study involving cats of all ages, 22% showed evidence of radiographic osteoarthritis, and when patient records were consulted, 33% of these cats also had clinical signs. Affected cats were significantly older than the control population. These authors also suggested that there may be little correlation between radiographic and clinical findings or that clinical signs of osteoarthritis in cats are not easily recognized.

In a recent study at a university referral hospital, the prevalence of radiographic signs of DJD was 33.9%, and the prevalence of clinical signs was 16.5%, with most affected cats being 10 years of age or older. These authors further classified their findings into DJD and osteoarthritis, the second being less common. The elbow joint was the most commonly affected joint in some published studies. However, when osteoarthritis (rather than DJD) was specifically described, the hip joint was most frequently affected. Many cats have multiple affected joints, and bilateral involvement is common.

Clinical Signs

Compared with the radiographic features of feline osteoarthritis, the clinical signs of feline osteoarthritis are not well-documented. Unlike in dogs, lameness is not common in cats with DJD or osteoarthritis. Because of cats' small size and their innate agility, they can often cope with severe orthopedic disease. In addition, bilateral involvement is common, which makes lameness difficult to detect. It is also notoriously difficult to elicit pain on clinical examination in some cats.

In one clinical study, 28 cats that had historical or clinical evidence of osteoarthritis, or both, together with radiographic evidence of osteoarthritis were recruited for a prospective study. Their median age was 11 years. In addition to the cats' undergoing a clinical examination by a veterinarian, the owners filled out a questionnaire on their cats' general demeanor, food intake, and lameness. On physical examination, periarticular thickening was a common finding but decreased range of motion was not. Crepitus was not detected, and synovial effusions were seldom present. Cats were treated with oral meloxicam for one month and reevaluated. Most owners thought their cats improved, and the most common clinical sign that improved was the willingness to jump and the height of the jump. Improvement of the stiff gait seen in many cats at the beginning of the study was also significant.

Clinical experience suggests that the behavioral changes that accompany osteoarthritis may be either insidious and easily missed or assumed to be inevitable with advancing age, so the owner does not seek veterinary advice. Because of a pet cat's lifestyle, lameness or exercise intolerance is not a common owner complaint. Changes in behavior such as decreased grooming, a reluctance to jump up on favorite places, an inability to jump as high as before, and soiling outside the litter box should prompt the veterinarian to look for sources of chronic pain. Other changes that owners report are altered sleeping habits (an increase or decrease), withdrawing from human interaction, hiding, and a dislike of being stroked or brushed.

Inactivity, which may result from chronic joint pain, is much more difficult to determine in cats than in dogs since cats naturally sleep a lot and are often solitary. In many cases, the owners are not home all day to monitor their cats' activity levels and may not know whether they have changed. Activity monitors attached to cat collars and harnesses have been used to monitor daily movement in cats, including in cats with osteoarthritis during treatment with oral meloxicam or placebo. In that study, the activity counts increased with five days of nonsteroidal anti-inflammatory drug (NSAID) treatment, suggesting alleviation of musculoskeletal discomfort.

It is common for owners and veterinarians not to realize how affected a cat was until they see dramatic improvements after treatment, emphasizing that analgesic trials may sometimes be the only way to confirm that pain was present.

Elbow Dysplasia

Elbow dysplasia is a devastating disease in dogs and cats. As in dogs, early identification and treatment of elbow disease is essential for the best possible long-term health of the joint. Unfortunately, early identification can be challenging due to the lack of correlation between the severity of clinical signs and radiographic findings. This is a great source of frustration as a delayed diagnosis can have a profoundly negative effect on prognosis. Therefore, a thorough physical examination including gait analysis, good radiographic technique, careful scrutiny of the films by a knowledgeable practitioner and arthroscopic evaluation of the joint if any elbow disease is suspected, provides the greatest opportunity for appropriate diagnosis, treatment and improved prognosis for the cat. Left untreated or treated after the onset of secondary degenerative changes, DJD may progress to cause obvious discomfort and lameness. For these cats, the typical treatment regimens available for dogs (oral medications; intra-articular treatments) and surgical intervention (SHO, OATS, total elbow replacement) are limited.

Unlike in dogs, lameness is not a consistent finding in cats with elbow disease. The most common clinical sign according to owners is unwillingness to jump or decreased jump height. Because of cats' small size and their innate agility, they can often cope with severe elbow disease. In addition, bilateral involvement is common, which makes lameness difficult to detect. It is also notoriously difficult to elicit pain on clinical examination in some cats. On physical examination of the elbow, discomfort may be noted on hyperflexion and extension, however, periarticular thickening, decreased range of motion, crepitus and effusion are not common findings. Increased sensitivity on direct palpation of the medial compartment of the elbow may be noted; however these findings are not as consistent as noted in dogs.

Along with the physical examination, radiographic evaluation is performed to determine the presences and extent of elbow disease. Clues as to the underlying cause may be obtained from the radiographs. Further diagnostics are often recommended and include MRI (magnetic resonance imaging), CT (computerized tomography) or arthroscopy. Arthroscopic exploration and treatment of the elbow is similar to dogs. Cats are placed in dorsal recumbency with standard medial portals and a 1.9 mm arthroscope is recommended. Arthroscopic treatments include excision of the fragment(s)/flap(s), abrasion arthroplasty, subtotal coronoidectomy, and standard microfracture techniques.

Medial Shoulder Instability

Another common forelimb condition of dogs which is rarely reported in cats is medial shoulder instability (MSI). In dogs, MSI may cause subtle signs of performance related issues such as refusing tight turns or be as severe as a weight-bearing lameness. In cats, once again reluctance to jump or decreased jump height appears to be the most common history. Currently, the exact cause of MSI in dogs is unknown, although it is suspected to be related to chronic repetitive activity, or overuse rather than trauma. Overuse of the shoulder support structures leads to degeneration of the tissues, lowering the tensile strength of the tissues predisposing them to fraying, disruption, and eventually complete breakdown. The cause of MSI in cats is also unknown, however a similar etiology may be possible.

Medial shoulder instability (MSI) involves multiple components of the shoulder joint (medial glenohumeral ligament, subscapularis tendon, medial joint capsule) and requires a thorough orthopedic evaluation and diagnostics tests to help confirm the condition. Gait analysis which may be difficult in cats may range from a mildly shortened stride in the affected forelimb at a walk and a significant weight-bearing lameness. Depending on the chronicty, atrophy may be noted in the affected shoulder on physical examination. Forelimb circumference may be decreased in the effected forelimb when compared to the contralateral unaffected forelimb. Unlike in dogs, restrictions and decreased range of motion of the shoulder in extension is not typically noted. When placing the shoulder into abduction spasm and discomfort may be noted, however an increased abduction angle is not always recognized (when compared to the contralateral forelimb).

In addition to history, signalment, gait analysis, physical examination, orthopedic and neurologic examinations, and abduction angle tests, further diagnostic tests used to differentiate causes of shoulder pathology currently consist of arthrocentesis, imaging modalities, and arthroscopy. Current imaging modalities include radiographs, computed tomography (CT), ultrasonography, magnetic resonance imaging (MRI), and arthroscopy and each has limitations. However, arthroscopic evaluation of the shoulder joint of dogs allows for direct observation of all major intra-articular structures with magnification, "dynamic" evaluation of tissues during shoulder range-of-motion stress tests, and "palpation" of intra-articular tissues. Arthroscopic exploration with evaluation of intra-articular structures provides a definitive diagnosis of MSI.

Reported arthroscopic treatments for MSI in dogs include radiofrequency, suture imbrication techniques and stabilization techniques including bone anchors, and the TightRope® technique. There is currently only one report of MSI in cats (Bardet J), however the arthroscopic findings and treatment/technique was not described. Arthroscopic exploration and treatment of the shoulder is similar to dogs. Cats may be placed in lateral or dorsal depending on the desired lateral or craniomedial portal(s). Similar to the elbow, a 1.9 mm arthroscope is recommended. Arthroscopic treatments of the shoulder may include excision of fragment(s)/flap(s), abrasion arthroplasty, radiofrequency treatment, or arthroscopic assisted mini TightRope stabilization.

Cranial Cruciate Ligament Insufficiency

Cranial cruciate ligament (CCL) insufficiency is one of the most common causes of hind limb lameness in dogs. Although reported in cats, the prevalence appears to be less. This may be mainly due to the relative rarity of CCL rupture in the cat, but it is also possibly due to a perceived difference in pathogenesis of the problem between the species. In the dog, the degenerative, as opposed to traumatic, etiology of CCL rupture has caused some to coin the term 'cruciate disease.' In the cat, most published reports describe, or assume, a traumatic etiology (usually falling). However, there is a subset of feline CCL patients that parallels the older, overweight, small-breed canine patients in which degenerative CCL rupture is seen and trauma has not been reported.

Non-traumatic CCL rupture is not encountered as commonly in the cat as in the dog. Several theories have been put forward to explain this. The CCL is larger than the CaCL in the cat, whereas the reverse is true in the dog. The relatively smaller size and weight of most cats when compared to canine CCL rupture patients may also be significant. Degenerative changes in the canine CCL have been shown to be more marked and occur earlier with increasing weight. It is also highly likely that the incidence of CCL rupture in the cat is underreported because some cats may never be examined for a relatively short-term hind limb lameness that resolves spontaneously.

Similar to the findings of the forelimb, lameness is not always appreciated at presentation and most common reported clinical sign by the owner is unwillingness to jump or decreased jump height. On physical examination of the stifle, cranial drawer and effusion are common findings. Diagnostics such as radiography may show signs of effusion and periarticular osteophytosis (based on chronicity). Advanced diagnostics such as MRI and arthroscopy may allow for confirmation of CCL injury and/or meniscal pathology.

The recommendation that conservative treatment should be undertaken for atraumatic feline cruciate ruptures seems to be based on a very small number of published cases. However, it should also be noted that over 80% of these conservatively- treated cats had persistent cranial drawer motion, and evidence of degenerative joint disease upon physical examination and radiography.

Surgical management with extracapsular stabilization provides results that are favorable with an apparent quicker return to function. The tibial plateau leveling osteotomy has also been reported with favorable results in the cat. Similar to the TightRope® technique in dogs, the mini TightRope is another option for cats with CCL insufficiency. Arthroscopic exploration and treatment of the stifle is similar to dogs. Cats may be placed in dorsal recumbency with standard parapatellar portal(s). Similar to the elbow and shoulder, a 1.9 mm arthroscope is recommended. Arthroscopic treatments of the stifle may include debridement of insufficient/ruptured CCL tissues, partial menisectomies, excision of fragment(s)/flap(s), and abrasion arthroplasty.

Post-Operative Care

Rehabilitation therapy

Rehabilitation following elbow, shoulder and stifle arthroscopy follows a sequential and progressive multiphased approach. Rehabilitation therapy typically includes a combination of techniques such as cryotherapy, modalities, manual therapies, hydrotherapy and a home exercise program (which significantly differs from dogs). Rehabilitation therapy is used to help decrease post-operative pain and inflammation, restore range of motion, improve muscle strength and condition, and return to function. Improved muscle strength and range of motion will help to provide long term pain relief as well as better overall function of the limb and improved quality of life.

Joint modifying Agents

Following arthroscopic treatment, cats are commonly prescribed non-steroidal anti-inflammatories (NSAIDs) to help decrease inflammation and discomfort. Adequan® (Novartis Animal Health), an injectable polysulfated glycosaminoglycans (PSGAGs) is recommended at 1mg/kg either SQ or IM twice a week for 4 weeks. In addition, oral joint modifying agents such as, Dasuquin for Cats™ (Nutramax Laboratories Inc.), which contains glucosamine, chondroitin sulfate, and avocado/soybean unsaponifiables (ASU), are recommended to potentially help decrease inflammation and slow the progression of osteoarthritis.

NSAIDs

The mainstay of drug therapy for elbow osteoarthritis in most species is an NSAID. These drugs pose a challenge in cats because of cats' susceptibility to NSAID toxicosis, especially with long-term dosing. Pharmacokinetic data are only readily available for single doses of NSAIDs in cats. *Most NSAIDs have a relatively long half-life in cats, and repeated dosing must be administered and monitored carefully to avoid toxicosis. For example, gastrointestinal toxicosis has been reported with carprofen, and based on clinical experience, toxicosis is generally associated with concurrent disease and prolonged administration of the oral formulation.Problems with repeated dosing are likely a result of individual variation in pharmacokinetics because the half-life of carprofen in cats can vary from nine to more than 40 hours.

One NSAID sometimes used to treat the pain and inflammation associated with osteoarthritis in cats is meloxicam, a COX-2 selective NSAID available as an injectable and oral formulation. The injectable formulation is licensed in the United States for use in cats to treat postoperative pain and inflammation but only as a single 0.3-mg/kg dose administered subcutaneously before surgery. The honey-flavored oral liquid meloxicam marketed for dogs is widely used (extralabel) in cats in the United States because it is palatable and small doses are easily measured. An oral formulation of meloxicam is now labeled for long-term use in cats with musculoskeletal disease in many other countries; the registered dose is 0.05 mg/kg once daily.

One published study evaluated the use of short-term NSAIDs for musculoskeletal pain in cats. Sixty-nine cats with acute or chronic locomotor disorders were randomly assigned to receive oral meloxicam or oral ketoprofen. Both drugs were equally effective based on general attitude, appetite, weight-bearing, lameness, and pain on manipulation, but meloxicam was more palatable and easier to administer. In a prospective study of 28 cats, many cats with osteoarthritis improved within one month with meloxicam intervention; 61% showed a marked improvement, 14% showed a moderate improvement, and 25% showed a slight improvement.

In a recently published study of 40 cats with osteoarthritis that were treated with meloxicam (0.01 to 0.03 mg/kg once daily orally) for 5.8 ± 3.4 months, 85% of owners scored the efficacy of meloxicam as good or excellent and thought that palatability was excellent. The 40 cats with osteoarthritis were paired with 40 control cats of similar age (12 or 13 years). No difference was noted in illness events (type or number) between the two groups. No differences were found in serum creatinine concentrations between enrolled and control cats before and after treatment. Three cats with preexisting renal disease were enrolled in the meloxicam group, and the renal function of these cats did not deteriorate faster than that of the three cats in the control group that had similar blood urea nitrogen and serum creatinine concentrations; however, no statistical analysis was possible because of the small number of cats in this category.

The most common side effect of orally administered meloxicam in cats is gastrointestinal upset. In one study, 18% of cats showed intermittent signs of gastrointestinal upset (vomiting or diarrhea), but the signs were not severe enough to terminate treatment in any cat. In the largest clinical study to date, four out of 46 cats vomited during meloxicam treatment, and two of these cats were withdrawn from the study.

Opioids

Because of their side effects such as euphoria, inappetence, and constipation after long-term use (days or weeks), opioids are best reserved for terminal or hospice care in cats or for occasional breakthrough pain while the cat is receiving other analgesics or undergoing other treatment modalities.

Other Analgesic Drugs

The role of other drugs in alleviating chronic osteoarthritis-related pain has not been well-studied in cats. Several drugs have, however, been suggested.

Tricyclic antidepressants including amitriptyline, clomipramine, and imipramine can provide relief in people with chronic neuropathic pain and are thought to alter the actions of serotonin and norepinephrine both centrally and peripherally. Anecdotal reports suggest that amitriptyline (between 2.5 and 12.5 mg for an adult cat orally once a day) may be effective for chronic pain syndromes in cats including osteoarthritis.

The anticonvulsant gabapentin is clinically effective in relieving some types of chronic pain in people, although the mechanism of action is not clear. Individual case reports demonstrate that gabapentin shows promise in cats, and doses starting at 10 mg/kg given orally twice a day have been suggested. Some animals become sedate and occasionally ataxic when given gabapentin. These signs may decrease as a cat acclimates to the drug or can be managed by decreasing the dose. In my experience, the tablet and capsule formulations of gabapentin are more palatable and easier to administer to cats than the liquid oral formulation, and they don't contain xylitol.

Although not classified as an opioid, tramadol has weak binding affinity at mu-receptors. It is thought to activate monoaminergic spinal inhibition of pain, although this may not apply to nonprimate species. It can be administered by multiple routes, including orally, is effective for relieving moderately severe acute and chronic pain in people, and seems remarkably devoid of the usual undesirable side effects of opioids such as respiratory depression and tolerance. The pharmacokinetics of tramadol and its major metabolite has recently been reported in cats ; doses in cats would likely be less than those in dogs (on a mg/kg basis) and the dosing interval may be longer. As of yet, no published studies have reported tramadol's efficacy for relieving osteoarthritis pain in cats. The chief problem with tramadol is its bitter and unpleasant taste, which makes administering it to cats difficult, even after compounding with fish or chicken flavors.

Intra-Articular Treatments

Currently, there is minimal information regarding the use of intra-articular injections (hyaluronic acid, cortisone, or regenerative stem cell therapy) in cats. These therapies are commonly used in dogs, however the safety and efficacy of these treatments in cats have not been reported in the literature.

References

Clarke SP, Bennett D. Feline osteoarthritis: a prospective study of 28 cases. J Small Anim Pract 2006;47(8):439-445.

Staiger B, Beale B. Use of Arthroscopy for debridement of the elbow joint in cats. JAVMA 2005; 226: 401-403

Bardet J. Diagnosis of Shoulder Instability in Dogs and Cats: A Retrospective Study. JAAHA 1998;34;42-54

Harasen G. Feline Cranial Cruciate Rupture; 17 cases and a review of the literature. Vet Comp Orthop Traumatol 4/2005

Robertson SA, Taylor P. Pain management in cats—past, present and future. Part 2. Treatment of pain—clinical pharmacology, Journal of Feline Medicine & Surgery 2004; 6: 321-333