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The Role of Aquatic Therapy in Managing Equine Osteoarthritis

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Aquatic therapy has become increasingly popular for the rehabilitation of equine musculoskeletal injuries; unfortunately, there has been no scientific evaluation of its effectiveness for the treatment of OA and its associated alterations in musculoskeletal function in horses. The purpose of this review is to define the proposed mechanisms of action of aquatic therapy and to determine its efficacy in the treatment of equine OA.


Osteoarthritis (OA) is one of the most debilitating musculoskeletal disorders among equine athletes.1 It is a common cause of poor performance, early retirement, and reduced life expectancy. Medical and surgical management of equine associated lameness disorders cost more than $700 million within the United States in 1998.2 Osteoarthritis is a progressive disease characterized by joint pain, inflammation, synovial effusion, limited range of motion, and a progressive deterioration of articular cartilage.3 The ensuing disease process affects not only the articular cartilage but also the surrounding articular tissues, including subchondral bone, joint capsule, synovial membrane, and periarticular soft tissues.3 As joint disease progresses, characteristic pathologic changes occur including fibrosis and thickening of the joint capsule, articular cartilage fibrillation and erosion, and osteophyte formation, which all lead to functional impairments.3 Unremitting joint pain and inflammation often cause adaptive muscle guarding and altered weight bearing to protect the affected limb from further discomfort and injury.4 Compensatory muscular adaptations are characterized by inefficient muscle activity leading to muscle weakness, joint instability, and altered limb loading.5 Maladaptive musculoskeletal responses may produce additional gait alterations and predispose other articulations to an increased risk of injury (i.e., compensatory lameness).6 In humans, compensatory changes in posture and movement exacerbate the initial joint injury, which cause further alterations in limb biomechanics and contribute to the progression of OA.5 Similar compensatory mechanisms such as delayed muscle activation, muscle weakness, restricted joint range of motion, and a redistribution of limb loading are likely to also occur in horses.
Physical rehabilitation has become an effective treatment option for improving deficiencies and weaknesses associated with primary joint injuries, as well as reducing harmful compensatory gait abnormalities in humans.7 Rehabilitation programs that address OA and musculoskeletal injuries often incorporate some form of aquatic exercise. Therapeutic aquatic interventions can be used to optimize the treatment of sensory and motor disturbances in order to achieve the functional restoration of full athletic performance. Aquatic therapies, such as underwater treadmill exercise have been reported in humans to increase cardiovascular endurance, improve muscle strength and timing, decrease limb edema, improve range of motion, decrease pain, and reduce mechanical stresses applied to the limb.8 Exercising in water provides a medium in which the effects of increased buoyancy, hydrostatic pressure, and the viscosity of water along with the ability to alter both temperature and salinity combine to play an important role in musculoskeletal rehabilitation (Fig. 1). The increased resistance and buoyancy inherent in aquatic exercise increases joint stability and reduces weight bearing stress on muscles and joints.9-11 The immersion of the distal limb in water applies a circumferential compression of equal magnitude that increases with depth below the surface of the water, increasing extravascular hydrostatic pressure, which in turn promotes circulation and reduces edema. Hydrotherapy can also aid in decreasing pain through the application of either cold or warmer water conditions. Warm water causes blood vessels to dilate increasing circulation and decreasing muscle spasms, while colder water acts to reduce inflammation by restricting blood flow. Aquatic conditions with higher solute concentrations provide an osmotic effect, which ultimately reduces edema and decreases pain. Aquatic therapy is a versatile treatment modality, capable of producing a wide variety of therapeutic effects and therefore is an effective method of rehabilitation for individuals with OA that have difficulty with weight bearing associated with land exercise12 (Table 1).
Effectiveness of aquatic therapy in human OA patients
Rehabilitation protocols used to address OA co-morbidities often focus on improving muscle function and joint biomechanics.13-15 Aquatic therapy is frequently prescribed for rehabilitation of orthopaedic injures in humans, with the goal of improving the overall function of the affected limb and preventing further musculoskeletal injury.16 Following aquatic rehabilitation, human patients have demonstrated normalized muscle activation patterns and improved joint stability, joint range of motion, and proprioception.7 Joint replacement and arthroscopic surgery patients are also commonly referred postoperatively for aquatic therapy intervention. Aquatic exercise decreases the weight bearing stresses applied to the operated joint, which allows an earlier and more intensive but less painful rehabilitation program without risk of overloading the injured joint.17 Human patients undergoing surgical reconstruction of their anterior cruciate ligament demonstrate improved knee range of motion and quadriceps strength following aquatic therapy, compared to traditional clinic based rehabilitation programs.18
Aquatic therapy in dogs
Although aquatic therapy is widely used in rehabilitation programs for humans; there are few investigations into the benefits of this form of exercise for equine patients. However, several studies on aquatic therapy have been conducted in dogs that primarily demonstrate significant improvements in joint range of motion following aquatic exercise. Aquatic therapy in dogs post cranial cruciate ligament reconstruction produces significant increases in joint range of motion, not only in the operated stifle, but also in the non-operated stifle.19 A similar canine study demonstrated improved pelvic limb biomechanics, with no difference in peak vertical force or vertical impulse, as measured by force platform analysis between the repaired and contralateral limb at six-months follow up.20 Kinematic analysis of dogs walking in an underwater treadmill demonstrated that joint flexion is maximized when the depth of the water is maintained above the joint of interest.21 Clinical outcome measures of thigh circumference and stifle joint range of motion were assessed in cranial cruciate ligament-deficient dogs after tibial plateau osteotome.22 Underwater treadmill exercise improved stifle passive joint range of motion and increased thigh circumference, compared to cage rest and controlled walking.22 Six weeks after surgery, there was no difference in thigh circumference and joint range of motion between the affected and unaffected limbs in the aquatic therapy group.22 In contrast, the cage rest and controlled walking group demonstrated continued progression in joint stiffness and muscle atrophy.22
Aquatic therapy in horses
Unlike the canine studies, equine investigations into aquatic therapy focus mainly on the horse's cardiovascular and respiratory responses to exercising in water.23-25 Equine swim training programs report an improvement in cardiovascular function, a reduction in locomotor disease, and an increase in the development of fast-twitch, high-oxidative muscle fibers, reflecting improved aerobic capacity.26,27 In addition, fine-wire EMG electrodes have been used to demonstrate the increased muscle intensity of the equine thoracic limbs during a pool swimming exercise program compared to overground walking.28 A recent equine study assessed changes in stride parameters while walking in various depths of water.29 Underwater treadmill walking with water at the level of the ulna resulted in a longer stride length with a reduced stride frequency, compared to walking in water at the level of the pastern joint.29 To date there are no objective studies that have determined the ability of underwater treadmill exercise to improve muscle activation patterns or limb biomechanics in the horse. There are also no studies that have objectively assessed the effects of aquatic therapy on diminishing the progression of equine OA.


Osteoarthritis in horses is typically managed with conventional therapies aimed at reducing inflammation. There are a limited number of therapies that have demonstrated disease-modifying effects however; no one therapeutic agent has effectively eliminated the progression of joint disease. Any form of treatment that can retard the progression of OA is of great importance, both for continued athletic performance and for quality of life. From the human and canine literature and limited equine studies reviewed, aquatic therapy has a beneficial effect on pain reduction and related musculoskeletal outcome measurements. Similar results such as improving joint range of motion, motor control, and joint stability as well as decreasing pain and soft tissue swelling following aquatic therapy are expected to occur in our equine patients.


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Figure 1. Graph illustrating the combined variables involved in aquatic therapy.
Table 1. Summary of the reported therapeutic effects of aquatic therapy.
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