Osteoarthritis (OA), also known as degenerative joint disease (DJD), is a common problem in small animal patients. An estimated 80% of dogs >8 years old and 60% of cats between 6 and 19 years old have OA.
The slow progressive degeneration of the articular cartilage leads to pain and disability. In severe cases, OA can significantly compromise quality of life.
OA may be classified as primary or secondary. Secondary osteoarthritis is due to an identifiable cause and is much more common. Obesity, joint instability (i.e., cranial cruciate ligament rupture, carpal hyperextension), trauma/articular fracture, inflammatory diseases (i.e., septic/non-septic arthritis), and congenital and developmental abnormalities (i.e., elbow and hip dysplasia, osteochondrosis) are some of the conditions that can lead to secondary osteoarthritis.
Many factors may contribute to the manifestation and progression of OA, including genetics, breed, conformation (low muscle mass), age, sex/neuter status, body weight, and activity. In cats, having outdoor access and having had a previous history of trauma are big risk factors for OA development. Successful management often requires a multimodal approach and regular follow-ups.
Analgesia
Non-steroidal anti-inflammatory (NSAID) drugs are the mainstay of analgesic medications, as they help to alleviate pain associated with inflammation. Initially, the dog or cat may need to be on NSAIDs continuously to control the pain. Dosage should not exceed the recommended dosage range and may need to be adjusted to the patient’s lean weight to avoid overdose. The dosage and frequency of administration can further be adjusted as needed once the pain is controlled and the patient has shown improvements through weight loss and increased mobility.
NSAIDs should be used cautiously in patients with renal disease, hepatopathy, gastrointestinal problems, and endocrinopathy. Geriatric dogs may be more prone to gastric ulceration with continuous usage of NSAIDs.
Cannabinoids (CBD) have increasingly become popular among owners seeking alternative analgesia. Endocannabinoid receptors are widely distributed in the central and peripheral nervous system and synovium, and they play a role in the modulation of pain and inflammation.
Although CBD administration resulted in decreased pain and increased activity level (these dogs were also receiving less gabapentin or had discontinued gabapentin) in some studies, a clinical study looking at ground reaction forces showed no significant difference between CBD products and placebo. CBD seems to be safe overall; however, reported adverse effects include elevated alkaline phosphatase (ALP), sedation (likely from the THC contaminant), and vomiting.
Additional pain medications, such as amantadine, gabapentin, and amitriptyline, can be used to help manage chronic pain via different pathways in dogs. Although not as effective in dogs, tramadol could be considered in cats with OA.
Weight Loss
Orthopedic problems and arthritis are exacerbated by having increased weight/force being placed on the already abnormal joint. Unsurprisingly, weight loss is one of the most effective ways to manage OA. Animals with orthopedic conditions and even normal animals greatly benefit from having a normal to slightly low body condition.
It is important to communicate realistic goals with the owners and make sure everyone involved in the animal’s care is on the same page. Complete omission of treats is often not well received; however, the amount of treats should be limited to <10% of the total calorie intake. Clear instructions that include specific daily calorie goals and measured amounts of food can help simplify the process and increase compliance for the family.
In a controlled, life-span study in Labrador retrievers by Purina, puppies on a restricted diet (25% fewer calories) not only had less severe clinical signs of OA over time, but they also had ~2-year delayed onset of clinical signs and lived 2 years longer (increased lifespan by 15%). Prescription foods formulated to contain fewer calories and/or higher protein (i.e., Hill’s r/d, Hill’s Metabolic, Purina OM) may allow owners to feed a larger quantity of food while feeding fewer calories. Weight loss should be intentional at a rate of no more than 1% to 2% body weight per week.
Supplements
Numerous supplements claim to provide OA support, and the options can be overwhelming and costly over time. Among the supplement categories, omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have consistently been shown to result in decreased inflammation in arthritic joints. Studies looking at omega-3 or lower omega-6:omega-3 polyunsaturated fatty acid supplementation revealed less cartilage degeneration and osteophytes, decreased denatured type II collagen, decreased inflammatory markers, improved subchondral bone parameters, and improved performance and lameness.
Aside from the positive effects on arthritic joints, omega-3 fatty acid supplementation can also enhance wound repair, improve skin barrier and hypersensitivity reaction, promote cardiovascular health, and provide neuroprotection of the brain. High dosages are needed to achieve the desired joint benefits, and diarrhea is not uncommon with administration. Therefore, it is beneficial to start at a lower dose and increase the dosage incrementally until the desired dosage is achieved. (See Colorado State University’s Canine Fish Oil Dosing Chart.)
This supplement can alter the coagulation pathway, so it should be avoided in small animals known to have bleeding disorders. Avocado/soybean unsaponifiables and vitamin E may also reduce pro-inflammatory cytokines and improve pain. No strong evidence has been documented to prove the reliable benefit of glucosamine/chondroitin or other supplements (i.e., green-lipped mussel, turmeric-derived polyphenols). Generally, they are safe with minimal adverse effects and have anecdotal benefits.
Physical Therapy
Low-impact regular exercise, as well as specialized rehabilitation therapy, is helpful in long-term management of OA. Heavy pounding or concussive activity on unhealthy cartilage causes accelerated wear of the cartilage and hastens the progression of arthritis. Less concussive exercise promotes cartilage health while still providing exercise.
Physical therapy helps to develop muscle mass, improve range of motion, and enhance mobility. It is important to maintain as much muscle mass as possible, as the muscles can take some of the strain off the joints.
Extracorporeal shockwave therapy (ESWT) can be a useful modality to reduce pain and improve function. With ESWT, high-energy acoustic pressure waves are delivered to the joint and surrounding tissue. Although the mechanism of action is not completely understood, ESWT has been shown to modulate inflammation, promote neovascularization and blood flow, and stimulate cell proliferation and tissue healing. Up to 85% of dogs show improvement with ESWT.
Intra-articular Injections
Orthobiologics, such as platelet-rich plasma (PRP), adipose or bone marrow-derived mesenchymal stem cells (MSC), and hyaluronic acid, can be injected into the joint and/or surrounding soft tissue to provide pain relief. The quality and effect can be heavily dependent on the collection method, source, and patient.
PRP is a portion of the blood that has been processed, usually by centrifuge, to contain a higher concentration of platelets than in the whole blood. The platelets contain many growth factors and signaling molecules in their granules that accelerate healing and reduce pain associated with inflammation when injected directly into the site of injury.
MSC therapy can decrease inflammatory biomarkers (IL-6, TNF-α), potentially promote cartilage regeneration (when given with hyaluronic acid), and promote bone regeneration. There are no consensus guidelines, and although considered generally safe, there is a lack of studies looking at long-term safety and efficacy.
Radiosynoviorthesis is another option that allows for long-lasting targeted therapy with minimal systemic effects. This is a new therapy that will be offered at the University of Illinois Veterinary Teaching Hospital through the orthopedic surgery and radiation oncology services. Radioisotopes, such as Tin-117m (Synovetin OA), injected into the joint are phagocytosed by macrophages and emit low-energy conversion electrons that penetrate just the thickness of the synovium (0.3mm) to alleviate synovial inflammation and associated pain.
Different from other therapies, this directly addresses the etiology of OA. Studies revealed a reduction of monocytes in the joint fluid analysis, and repeated injections have not been shown to result in detrimental effects or progression of OA on radiographs, CT, and MRI 180 days post-injection. The effects can last up to 12 months, with ~90% success rate in OA grade 1 and 2 and ~70% success rate in OA grade 3. Due to its effects being constrained to the joint, this therapy can be used safely in conjunction with other medications/therapies without interference and increased adverse effects.
As a last resort, long-acting depo corticosteroid therapy can also be used to relieve joint pain for weeks to months. Adverse effects, especially with repeated intra-articular steroid injections, include infection/septic arthritis, cartilage degeneration, bone resorption, and refractoriness to therapy.
Alternative Therapies
Monoclonal antibodies targeting anti-nerve growth factor (anti-NGF), such as bedinvetmab (Librela) and frunevetmab (Solensia), have been a trending first-line treatment for osteoarthritis. Early clinical trials with bedinvetmab revealed 40% to 50% improvement in owner-assessed pain over 3 months, and the effect was comparable to daily meloxicam.
In a study looking at a cohort of healthy beagles given monthly injections for 6 months, most dogs had no radiographic progression of OA on post-injection hip radiographs. One dog receiving 3mg/kg bedinvetmab progressed to have moderate OA on one side after having minimal OA bilaterally pretreatment, and this was dismissed as not related to the treatment.
The reported adverse effects are ~1 in 1,000 injections, with the lack of efficacy being the highest. Other adverse effects include polyuria/polydipsia, urinary incontinence, seizures, paresis and ataxia, and death.
Many veterinarians have raised concerns for a spike in musculoskeletal adverse effects (MSAE), including ligament/tendon injury, fracture, polyarthritis, skeletal neoplasm, and septic arthritis. MSAE were reported ~9x more frequently in dogs treated with bedinvetmab than in dogs treated with NSAID.
Over the 4 years bedinvetamab has been on the market, the reported MSAE is more than 20x that reported for the most common NSAID (carprofen) in the past 20 years. Tanezumab, the human equivalent of anti-NGF, has been associated with rapidly progressive OA and was discontinued in 2021. With any new therapy, long-term safety studies in small animals are warranted.
Acupuncture and radiation therapy are options to provide relief for arthritic pain. In dogs with pain refractory to medical management, radiation therapy (3 fractions of 2 Grays each) resulted in 92% clinical improvement for up to a median of 356 days. Salvage procedures, such as joint replacement and arthrodesis, may be warranted. In severe cases where multiple joints are affected, amputation and humane euthanasia may be considered.
By Dr. Monica Chen, DVM, MS, DACVS (Small Animal)
References
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