Written by Beau Whitaker, DVM, CERP
Osteoarthritis (OA) is a common performance limiting musculoskeletal condition in our equine athletes, often resulting in poorer performance and early retirement. Equine veterinarians are well versed in the various systemic and intra articular treatments available to decrease or eliminate the pain caused by joint inflammation and osteoarthritis. These therapies are an important part of managing a horse with OA. Sometimes overlooked however are the rehabilitation options that are available to help prolong the functional use of the horse with joint disease.
What exactly are we rehabilitating in the horse with chronic OA? The disruption in the balance between breakdown and repair of the diseased joint is characterized by an inflammatory synovial response, alterations to subchondral bone, and cartilage erosion. Clinical manifestations of synovitis, thickening and fibrosis of the joint capsule, reduced range of motion, muscle atrophy and joint pain may become evident. Chronic joint pain and changes in mechanical function of the joint often results in muscle guarding and altered loading of the limb in an attempt to help protect the diseased joint. Compensatory muscle guarding leads to muscle weakness, further joint instability, and altered loading of the limb. Compensatory lameness may result from the maladaptive use of the limbs due to overloading other joints and soft tissue structures. The adaptive muscle guarding results in delayed and decreased muscle activation and muscle weakness which further destabilizes the joint that the body is trying to protect. With altered limb biomechanics and restricted range of motion, the arthritic joint creates an environment that contributes to its progression and to pathology in other limbs. In this light, the goal of rehabilitation for the horse with OA should address not only the diseased joint but also the compensatory neuromuscular deficits as well.
The management of neuromuscular control is mediated by proprioceptive and mechanoreceptor feedback from the musculoskeletal and integumentary systems. Rehabilitation of the horse with OA needs to address the neurologic and muscular systems in a way that triggers the pathways to correct and strengthen muscle activation and enhance limb biomechanics over time. Current therapies used for neuromuscular conditioning and osteoarthritic rehabilitation in the horse have little research. Much of the support for their use is extrapolated from human studies and from anecdotal results. Research in the field is growing however and several studies have shed some light on therapies that may help the
equine patient with OA.
A recent study performed at the Orthopaedic Research Center at Colorado State University suggests use of the underwater treadmill may be an effective tool for benefiting both the progression of OA in the joint and the associated compensatory mechanisms 1 . A carpal chip model was used to induce OA in one knee on two groups of horses. One group was exercised on a water-supported treadmill and the other group (control) was exercised on dry ground. The control group showed less weight bearing and decreased muscle activation on the OA limb while the water exercised group was balanced in weight bearing and muscle activation. Range of motion of the knee was greatly improved for the water exercised group after one week and was back to pre OA level by the end of the study, in contrast to the control group which did not regain range of motion. The water exercised horses also showed less scarring and inflammation within the knee compared to the controls. Underwater treadmill therapy should be considered for horses following arthroscopic surgery and as part of a maintenance program for horses with OA.
Swimming in a pool is another commonly utilized aquatic therapy for conditioning and rehabilitation. Most of the research on swimming has focused on the cardiovascular and muscular effects related to conditioning. One should be case selective in utilizing swimming for rehabilitation of OA. Horses are not natural swimmers. In order to swim the horse must maintain an elevated neck posture, a lordotic position of the spine, and utilize a violent kicking motion of the rear limbs. Pathologic conditions of the upper rear limbs (stifle and sacroiliac joints) and back may be exasperated by swimming.
The functional taping technique has been widely used in human sports medicine as a way to improve neuromotor function. This technique has been well researched on the human side. You may have seen athletes at the Olympics wearing Kinesio Tex tape. The tape works by applying tension along the kinesthetic fibers of a muscle which aids in neuromuscular control through proprioceptive feedback. Depending on the direction the tape is applied it will either facilitate or inhibit muscle contraction and awareness. If tension is applied from origin to insertion the neuromotor function is facilitated. If the tension is applied in the direction of insertion to origin the neuromotor function is inhibited. The benefit of using functional taping techniques in the horse with OA is to target specific muscles or groups of muscles that have developed adaptive muscle guarding and delayed activation. Hypertensive muscles can also be addressed with the inhibitory technique. The tape is sweat and water resistant and can be
used while the horse is being ridden and in work.
Electrical stimulation is a therapeutic technique that may be used to improve muscular sensory awareness, muscle activation, and decrease pain. Electrodes applied to the skin deliver a low voltage, intermittent electrical current that stimulate sensory and/or motor nerves to improve sensory awareness and facilitate muscle reeducation. Depending on the settings used, electrical stimulation can be utilized to increase strength in targeted muscles. Horses with disuse atrophy may benefit from treatment over the affected muscle or muscles to improve muscle function and potentially increase cross sectional area of the muscle fibers. Treatment should be done 2 to 7 days a week for 10 to 20 minutes a treatment when treating atrophy.
Laser therapy has become a popular treatment in the horse industry over the last decade and has potential for improving function and decreasing inflammation and pain of the arthritic joint. Rigorous studies are lacking and much of our understanding of the effects of laser light on tissue is from in vivo extrapolations. There is however a growing body of evidence. Laser light works through photochemical effects on cells. An analgesic effect is produced through an increase in nitric oxide, serotonin, beta endorphins, and acetylcholine. A decrease in inflammation is achieved through a decrease in inflammatory prostaglandins, enhancement of ATP production and metabolic activity, and a decrease in interleukin 1 activity. An increase in microcirculation is also achieved through the increase in production of nitric oxide and serotonin.
A double blinded, randomized human study on laser therapy was performed on patients with mild to moderate OA of the knee 2 . The group treated with diode laser therapy twice a week for 4 weeks showed significant improvement in pain, knee circumference, pressure sensitivity, and flexion. The control group receiving the placebo treatments showed no significant improvement in any of the categories measured. The study shows some promise for the use of laser therapy for the treatment of OA. Further research is needed to determine the effects on the equine joint and the appropriate dosage (measured in Watts per centimeter squared) needed to achieve clinical results. Anecdotally I have personally seen impressive results from laser therapy in the treatment of capsulitis and synovitis of the fetlock joint and
significant improvement in pain response on flexion from treatment of the lower hock joints. There are claims of positive results with the use of laser therapy in cartilage repair but no research to show the effects on the equine patient.
There are numerous other treatments and therapies that can be utilized to improve compensatory proprioceptive and neuromuscular deficits including chiropractic, acupuncture, massage, muscle specific stretches, and postural conditioning exercises. Passive range of motion joint modulation can be beneficial in maintaining joint movement and periarticular soft tissue elasticity. Cold therapy can be beneficial to temporarily reduce inflammation and pain in the arthritic joint. Vibration therapy claims benefits for patients with OA but no substantial research exists to show the benefits. There are numerous other medical devices that are being utilized that make similar claims but again have little evidence to support their use. Hopefully over time these devices will be vetted and we can sort the wheat from the chafe.
Management of today’s equine athlete with OA requires a comprehensive approach that utilizes appropriate systemic and intra articular medications, an exercise maintenance program that may include aquatic therapy, and numerous other rehabilitation modalities to treat compensatory and primary pathologies.
References
1. King MR, Haussler KK, Kawcak CE, et al. Mechanisms of aquatic therapy and its potential use in managing equine osteoarthritis. Equine Vet Educ 2013; 25:204-209.
2. Bela Hegedus M.D., Laszlo Vihoras, Ph.D., Mihaly Gervain, Ph.D., Marta Gailfi, Ph.D. The Effect of Low-Level Laser in Knee Arthritis: A Double Blinded, Randomized, Placebo Controlled Trial. Photomed Laser Surg. 2009 Aug; 27(4):577-584.
