Denis J. Marcellin-Little DEDV, Diplomate ACVS, Diplomate ECVS College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina
Osteoarthritis is a slowly evolving articular disease that affects the underlying bone and surrounding soft tissues and is thought to originate in the cartilage. Osteoarthritis leads to non-inflammatory degeneration of articular cartilage, reactive bone formation, and hypertrophy of the joint capsule. It's the most common joint disorder in people over 65 years of age, affecting an estimated 70 to 85% of people ages 55 and older,1 and it is the second most common cause of disability in the United States.2 Osteoarthritis can affect all diarthrodial joints but most commonly affects the knee (6% of U.S. adults), hip (3% of U.S. adults), and the hand (13% of men and 26% of women over 70 in one study).3,4 In a study involving 740 patients, people who were overweight were 3.5 times more likely to develop osteoarthritis than people at or under their ideal weight.5 The clinical signs of osteoarthritis include decreased range of motion and strength, decreased functional ability, decreased proprioception, and joint pain. Unfortunately, the articular damage of osteoarthritis is irreversible and only minimally influenced by medical or surgical therapy. Therefore, treatment for osteoarthritis is aimed at addressing its secondary effects and improving overall joint function.
OSTEOARTHRITIS IN DOGS AND CATS
Osteoarthritis is also common in companion animals. In a study of German shepherds, 30% of the dogs had osteoarthritis.6 Of 100 mature dogs surveyed at necropsy, osteoarthritis was present in the hip (52%), shoulder (37%), stifle (36%), and elbow joints (5%).7 Osteoarthritis in dogs is most often secondary to hip dysplasia, cranial cruciate ligament injuries, patellar luxation, elbow dysplasia, and osteochondritis dissecans.8 It was also more prevalent in overweight, 8-year-old dogs than among non overweight, age matched siblings. 9,10 Osteoarthritis was identified in 20 to 90% of cats 12 years of age or older in two studies.11,12 In one study of feline osteoarthritic patients, the disease was present in the elbows (64%), shoulders (21%), hip (7%), and tarsus (7%).11 The course, clinical signs, and treatment goals of osteoarthritis are similar in companion animals and people. The physical therapy interventions for management of osteoarthritis generally include therapeutic exercises on land or in water, cold therapy, heat therapy, electrical stimulation, massage, and joint mobilization. A review of these interventions follows.
Therapeutic exercise represents the basis of physical therapy management of osteoarthritis. Several types of exercise are used: isometric, isokinetic, and isotonic (which can be either concentric or eccentric). Isometric exercises consist of muscle contractions without a change in muscle length or joint motion. Isokinetic exercises are dynamic exercises with constant joint velocity that require the use of a machine to control joint velocity. Isotonic exercises are dynamic exercises conducted using a constant load and are the most practical form of exercise for companion animals. Concentric isotonic exercises are based on the production of force through a decrease in muscle length (e.g., a bicep curl). By contrast, eccentric isotonic exercises are based on the production of force through an increase in muscle length (e.g., slowly lowering the arm while holding a weight). Therapeutic exercises may be performed with the extremity fixed on a surface so the proximal portion of the limb moves in relation to the distal portion of the limb (closedchain), or with a free extremity moving in relation to the proximal portion of the limb (open chain). Therapeutic exercises may be conducted on land or in water. A great deal of research has focused on assessing the influence of specific exercises in patients with osteoarthritis. Isometric, isotonic, and stepping exercises were used to strengthen the quadriceps of 191 people with osteoarthritis of the knee.12 Pain scores decreased 23% in treated patients vs. 6% in controls. Functional ability improved by 17% in treated patients and was unchanged in controls. Further, treated patients were less anxious and less depressed, lost weight, and used less analgesic drugs.13 In a study evaluating the benefits of isometric, isotonic, and isokinetic exercises in 132 people with osteoarthritis of the knee, all forms of exercise led to a decrease in pain and disability indexes. Isokinetic exercises were most effective, followed by isotonic, and then isometric. 14 Isokinetic exercises may be most beneficial due to the positive impact on type-II muscle fibers. Isotonic and isometric exercises were compared in another study involving 102 human patients with osteoarthritis of the knee.15 While both forms of exercise decreased pain, only isotonic exercises led to a perceived functional improvement. Combined concentric and eccentric exercises resulted in more functional improvement than concentric exercises alone.16 High-intensity aerobic exercises were as beneficial as low-intensity aerobic exercises with regard to functional status, gait, pain, and aerobic capacity in a study involving 39 patients with osteoarthritis of the knee.17 While both open- and closed-chain exercises may be used with these patients, no study (to our knowledge) has specifically compared the benefits of these two forms of exercise. In a systematic review of 14 randomized, controlled trials involving 1,633 human patients with osteoarthritis, land exercises had immediate, moderate benefits for joint pain, and immediate, small benefits for limb function.18 Long-term adherence to exercise programs was required to maintain the benefits of exercise for osteoarthritis. Regular patient supervision enhanced adherence to these programs. Aquatic exercise includes swimming and walking in water. Compared with land exercise, aquatic exercise has the advantages of decreasing the weight placed on limbs, increasing the resistance to motion, and potentially providing superficial heat to affected joints. Aquatic therapy has been shown to be effective for human patients with osteoarthritis by increasing their aerobic capacity, ambulation distances, and activity levels.19 In a study comparing land and aquatic exercise programs in 46 people with osteoarthritis of the knee, both programs led to improved joint function, but joint pain was less for the patients exercising in water.20 For dogs, walking on an underwater treadmill is a low-intensity isotonic exercise that includes all the benefits of aquatic exercise. Based on these findings and the practical limitations of therapeutic exercise for companion animals, concentric and eccentric isotonic exercises performed at low or high intensity are most appropriate. The following activities would likely benefit dogs with osteoarthritis: walking and trotting, walking with resistance provided by water or elastic bands, sit-to stand exercises, swimming, and walking on an underwater treadmill. Therapeutic exercise is prescribed using different types of exercises, intensity, frequency, and duration. All these parameters vary between patients based on their diseases and fitness levels. Proprioceptive exercises represent another form of therapeutic exercise that may benefit osteoarthritic patients. Joint mechanoreceptors detect small amounts of motion and provide sensory feedback. These proprioceptive receptors promote joint stability by activating agonist and antagonist muscles. Decreased joint proprioception may initiate or contribute to osteoarthritic changes in joints.21 In people, joint proprioception decreases with age and further decreases in the joints of osteoarthritic patients.22 Exercises can be designed to enhance joint proprioception including standing on one foot with eyes closed, standing on wobble boards, walking on soft surfaces, or jumping. To our knowledge, no study has investigated the benefits of these proprioceptive exercises in people or animals with osteoarthritis.
THERAPEUTIC PHYSICAL AGENTS
The physical agents used to treat patients with osteoarthritis include superficial heat, cold therapy, and therapeutic ultrasound. Heat therapy increases blood flow, enzymatic activity, and collagen extensibility and leads to muscle relaxation and temporary pain relief. Cold therapy decreases blood flow, inflammation, muscle spasm, and pain. Cartilage-degrading enzymes are also inhibited below 30°C.23 In osteoarthritic patients, heat therapy can be used to decrease joint stiffness, and ice can be used to decrease intermittent, acute inflammation. Heat and cold therapies are effective in increasing or decreasing joint temperatures. In one study involving people, superficial heat increased skin temperature by 8°C and joint temperature by 2°C. Both temperatures returned to pretreatment levels after three hours.24 Superficial ice decreased skin temperature by 16°C and joint temperature by 6°C. Skin temperature returned to pretreatment levels after three hours.24 Both heat and cold therapies may be beneficial to companion animals with osteoarthritis. Cold would likely benefit patients with acute exacerbations of chronic osteoarthritis. Heat would likely benefit all other osteoarthritic patients. Therapeutic ultrasound does not appear to influence pain relief, range of motion, or functional status of patients with osteoarthritis. Currently, research involving people does not support the use of ultrasound prior to therapeutic exercise for these patients.25 To our knowledge, similar research has not been conducted on animals. Transcutaneous electrical nerve stimulation is the stimulation of the large cutaneous nerve fibers that transmit sensory impulses faster than pain fibers.26 Four types of transcutaneous electrical nerve stimulation are used clinically: high-frequency, low frequency, burst-frequency, and hyperstimulation. While treatments can last from 20 to 60 minutes, the optimal treatment duration appears to be 40 minutes.27 In one study, high frequency and strong-burst mode transcutaneous electrical nerve stimulation were effective in providing pain relief for osteoarthritic human patients when the treatment period was four weeks or longer.26 Transcutaneous electrical nerve stimulation may be delivered by handheld machines purchased through medical supply vendors. Prices range from $150 to $500. Neuromuscular electrical stimulation is the stimulation of muscle fibers for strengthening. Osteoarthritic patients lose muscle mass proximal to affected joints through progressive weakness and disuse.16 While neuromuscular electrical stimulation could be used to strengthen the muscles of affected patients, no study has specifically investigated the clinical benefits of neuromuscular electrical stimulation for osteoarthritic patients. Both transcutaneous electrical nerve stimulation and neuromuscular electrical stimulation may be beneficial to pets with osteoarthritis.
Massage has been shown to decrease myofascial pain and muscle tension.28 Massage may relax tissues, decrease muscle spasms, eliminate myofascial trigger points (hyperirritable palpable nodules in muscles secondary to sustained focal muscular contractions), and increase flexibility and blood flow for patients with osteoarthritis. However, to our knowledge, no studies have documented the specific benefits of massage in human or animal patients with osteoarthritis.
Joint mobilization is the specific, low-velocity manual displacement of one bone to another in their natural plane of movement. Mobilization is aimed at increasing the range of motion and decreasing pain. Joint mobilization has not proved beneficial as the sole therapy for osteoarthritic patients. However, combined joint mobilization and supervised exercises were beneficial in a group of 83 people with osteoarthritis of the knee.
Acupuncture has been used to treat patients with osteoarthritis. While acupuncture can be effective as adjunctive therapy,30 its overall benefits appear equivocal.
Pulse electromagnetic field therapy has been used to treat patients with osteoarthritis. Two studies documented positive effects of pulse electromagnetic field therapy after 18 half-hour treatment periods. These benefits lasted for more than one month in people with osteoarthritis of the knee and cervical spine.33,34 Many nonsurgical, nonpharmacologic options are available to treat patients with osteoarthritis. Exercise appears to be the most effective method to decrease pain and increase functional ability in these patients, but exercise must be sustained over time to maintain these benefits. Other modalities may also be beneficial as adjunctive therapies, mostly by decreasing joint pain and, therefore, facilitating exercise. Few studies have been conducted to assess the specific benefits of exercise and other physical therapies for companion animals with osteoarthritis. Such studies would increase the base of knowledge in this critical area of orthopedics and should be a focus of further research.
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