Lowri Davies
The equine rehabilitation therapist must consider numerous factors when designing a treatment plan. The majority of horses presented for rehabilitation are athletes of some type; thus, owner expectation for a full return of function is very high. Because of the close interaction between horse and rider, any attempt to rehabilitate the horse without paying attention to farriery, saddle fit, and the role of the rider in creating or amplifying the lameness may result in treatment failure. The rider may be required to undergo a personal rehabilitation regimen because it may be impossible to rehabilitate the horse in the face of ongoing issues with the rider’s posture and balance.
Little formal research exists regarding the benefit of various ther-apeutic techniques and exercise regimens in horses. Accurate diag-nosis remains essential, coupled with an understanding of asso-ciated tissue changes and appropriate choice of techniques for restoring function. Restoration of movement requires a combina-tion of techniques, but the importance of restoring dynamic stabil-ity through enhanced neuroregulation cannot be overemphasized (see previous chapter). Veterinarian, physical therapist, master sad-dler, farrier, and owner will have to work as a team to achieve the desired goal.
RISK FACTORS FOR EQUINE LAMENESS
Risk factors that have been identified as predisposing to muscu-loskeletal injury include exercise frequency, stabling, body condi-tion score, and breed, though controversy exists as to whether an individual’s conformation has a significant role to play (Van Weeren et al., 2006).
Lameness from limb and back disorders accounts for a signifi-cant percentage of health problems in the domestic horse (Ross &
Kaneene, 1996). The link between lameness and back pain is often ignored, even though problems within the axial skeleton will lead to asymmetrical limb loading and subsequent lameness in the distal limbs (Landmann et al., 2004).
Although it is well established in humans that movement assists healing and pain management (Salter, 1982; Jones & Amendola, 2007), equine athletes are frequently prescribed arbitrary periods of stall rest. The absence of loading within the musculoskeletal sys-tem may result in maladaptive responses within its components
(Enneking & Horowitz, 1972; Fitts & Brimmer, 1985; Appell, 1986). Postural feedback, proprioception, and overall tonus are inhibited by stall or stable rest, which has a significant impact on how a horse moves when it is finally led out of the box (McGreevy et al., 2011). Uncoordinated movements will increase the pressure or load on joints, tendons, and ligaments while muscle atrophy inhibits its inherent ability to absorb shock and protect these struc-tures from the impact of movement. Care must be taken to restore neuromotor control prior to embarking on any form of strenuous activity.
In the wild, horses spend a significant proportion of time with the head and cervical spine lowered while grazing, a posture which may facilitate stretching of the soft tissues along the dorsum, including the longissimus dorsi and scalenus muscles (McGreevy et al., 2011).
Flexion and lowering of the cervical spine also generates tension in the nuchal and supraspinous ligaments, elevating and separating the thoracolumbar spinous processes (Denoix & Pailloux, 2004).
Stabled horses, particularly when fed from hayracks or nets, do not utilize this “natural” stretching action, and this may increase the risk of injury (Goodship & Birch, 2001).
Tack and Lameness
During motion, the saddle should support the rider’s weight and distribute it evenly over as large an area as possible in order to reduce pressure. It should also facilitate normal spinal motion through flexion, extension, rotation, and lateroflexion. de Cocq et al. (2004) examined the effect of tack and weight on the equine back. They concluded that both caused overall extension of the thoracolumbar spine without any reduction in spinal range of motion (ROM). Limb kinematics was affected at the walk and trot due to increased limb retraction.
A poorly fitting saddle will cause pain and inhibit movement and lead to local (under the saddle) and general (distal limb) mus-cle atrophy and impairment of cybernetic musmus-cle function. Cyber-netic muscles are mainly composed of Type I muscle fibers, and their main function is to sense motion and produce adaptive postu-ral responses. In contrast to gymnastic (i.e., movement-generating) muscles, cybernetic muscles are richly innervated, which allows for very precise control of movement (Denoix & Pailloux, 2004). They are present in the upper lip, around the eye, around the vertebral column, and next to joints. Cybernetic muscles are extremely
Pain Management in Veterinary Practice, First Edition. Edited by Christine M. Egger, Lydia Love and Tom Doherty.
C2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc.
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148 Section 3 / Nonpharmacological Pain Therapy important in controlling posture and fine tuning movement in
response to the rider’s commands. The function of these muscles may be impaired if the horse is stressed, in pain, or if movement is mechanically hampered, for example, by the saddle.
Devices that force a horse into an outline, such as draw reins and standing martingales, decrease the horse’s ability to hold itself in position while inhibiting normal head and neck motion at the walk and canter. Such abnormal positioning has an adverse effect on balance and coordination and will alter locomotion and may result in pain (McGreevy et al., 2011).
Training and Exercise
Overexercising may predispose to back pain and injury when horses are poorly prepared for competition. Poor training, both in hand and under saddle, can result in distress and anxiety that, if prolonged, can lead to confusion, bad behavior, flight responses, and mus-culoskeletal degeneration. Overtraining can be a significant risk factor for the development of degenerative joint disease in elite ath-letes (Taylor et al., 2002), and may be associated with weight loss, reduced exercise tolerance, reduced red blood cell volume (PCV), altered immune function and an increase in muscle enzyme activity (McGowan & Whitworth, 2008).
PATIENT ASSESSMENT
The horse and the horse and rider unit should be assessed prior to embarking on a rehabilitation program. During anamnesis, an attempt should be made to establish the pattern of lameness and what, if any, activities provoke the lameness; for example, a horse with mild to moderate back pain can demonstrate normal or subtly altered behavior and gait patterns when ridden on the flat, but may demonstrate significant discomfort and move with a markedly altered gait when faced with a decline.
Pain Assessment
Behavioral changes that are associated with pain in the horse include kicking or biting when the tender area is touched, gen-eralized restlessness, sweating, frequent movement of the painful limb, or continuous shifting of weight from one limb to another.
Changes associated with back pain, such as poor performance, poor appetite, and slight changes in demeanor may be very subtle ini-tially. These may progress to tail swishing or holding the tail to one side, bruxism, head shaking, resistance to saddling and grooming, loss of flexibility, stumbling, bucking, and rearing (Marks, 2000;
Haussler & Paulekas, 2009). The horse may become withdrawn in nature, and tension in the abdominal muscles may lead to a
“herring-gutted” or tucked appearance. Breed and an individual’s temperament must be taken into consideration when trying to assess pain in horses.
Objective measurements of pain in the horse that may assist in diagnosing and treating pain include heart rate (not con-sistently increased in pain), pressure algometry, thermography (Figure 12.1), kinematic gait analysis, and response to analgesia (e.g., nerve blocks). Response to analgesic therapy is often quoted as an objective measure of pain. Frequently, however, only non-steroidal anti-inflammatory drugs (NSAIDs) have been adminis-tered, and other classes of analgesics or multimodal pain man-agement techniques have not been tried. The author has regularly
Figure 12.1. The use of thermal imagery to detect subtle alterations in regional blood flow, which determines tissue temperature.
encountered horses deemed to “not be in pain” when their behav-ior did not alter in response to an NSAID. Such horses are often subject to progressively harsher riding and controlling techniques in an attempt to counter what is deemed as bad behavior rather than a normal response to pain.
Assessment of Conformation, Muscle Tone, and Posture A horse’s posture should be assessed from both sides, cranial and caudal and from above. Limb alignment and weight distribution should be evaluated along with any irregularities in hoof or shoe wear and discrepancies in hoof size. Lordosis or kyphosis should be noted along with any conformational anomalies, as these often predispose to lameness (Kirkendall & Garrett, 1999).
Evaluation of muscle tone can give valuable information regard-ing an animal’s psychological and physical well-beregard-ing. Basic tonus is the light contractile tension in every skeletal muscle, which allows maintenance of posture at rest and changes in response to internal and external influences. External influences can increase (e.g., perceived threat) or decrease (e.g., calm and familiar envi-ronment) tonus. Internal influences, such as pain and anxiety, will generally increase tonus while fatigue will reduce it (Denoix &
Pailloux, 2004). Although an increase in tonus through mild anx-iety and stress may serve to enhance a horse’s athletic ability, it can lead to muscle rigidity and poor performance if poorly managed.
Palpation
Systematic palpation of the whole body should be undertaken.
This should serve to identify distention in the tendon sheaths and joint capsules, along with focal areas of pain and heat. Hoof testers should be used to assist with localizing pain in the foot.
12 / Equine Rehabilitation 149 An internal pelvic examination may be required to identify any
pelvic and lumbosacral abnormalities as well as patency of the iliac arteries.
Manipulation of each joint should establish ROM and whether discomfort is associated with that movement (Chapter 11). These findings provide a benchmark against which to measure either improvement or exacerbation of clinical signs.
Gait Evaluation
Gait evaluation should identify the lame limb(s) as well as any subsequent compensatory changes. The horse should be observed at walk and trot on a straight line and on a left and right circle.
The arc of flight should be noted along with limb placement (i.e., adducted or abducted). An attempt should also be made to identify any increase or decrease in an individual joint’s ROM. The overall character of the movement should be evaluated for its fluidity and coordination, which may be affected by spinal stiffness or lordosis.
The horse should then be examined under tack and, finally, a ridden assessment should be carried out in order to evaluate how the gait is modified in response to external influences. Video assessment at each stage can be useful, both as an aid to diagnosis and as a way of monitoring progress.
Neurological Assessment
A neurological examination should be part of the assessment to help differentiate between neurological cases exhibiting gross cen-tral pathological change or vertebral malformation, and those that merely have impaired neuromotor control.
Neuromotor Control Assessment
Motor control relies on intact sensory and proprioceptive afferent input, well-developed central control of coordination and motor output, adequate motor neuron recruitment of muscle fibers, and
Table 12.1. Stages of tissue healing
Stage of tissue healing Rehabilitation Objective Techniques
Phase 1: Immediate postinjury period
Pain management
Minimize tissue swelling and promote tissue perfusion
Reduce movement at the trauma site
NSAID and centrally acting analgesics Cryotherapy, light compressive bandage Rest and external support if appropriate Phase 2: Subacute phase Ongoing pain management
Minimize tissue swelling, promote tissue perfusion and healing
Maintain range of motion (ROM)
Promote functional neuromotor recruitment with controlled movement or loading Early reintroduction of exercise
NSAID & centrally acting analgesic, acupuncture
Cryotherapy, massage, therapeutic ultrasound, low level laser therapy
Gentle active and passive ROM exercises Regular short periods (5 minutes; 4–6 times
daily) of in-hand walking to include proprioceptive stimulation such as proprioceptive track or weight shifting Aquatic treadmill therapy (Herzog & Longino,
2007) Phase 3: Repair Promote tissue healing
Promote correct alignment of collagen fibers along the lines of stress and minimize adhesions
Neuromotor recruitment Enhance proprioception Maintain joint ROM
Develop core strength and improve posture Correct for compensatory changes; e.g.,
abnormal hoof wear, back and neck pain, contralateral limb loading
Acupuncture, ultrasound, massage, local heat, low-level laser therapy
Controlled exercise gradually increasing in duration and intensity; e.g., introduce poles on proprioceptive track.
Turn out in confined area.
Gentle stretches 1–2 times daily. Cross-fiber massage over the scar.
Therapeutic exercises
Active ROM and stretching exercises Various therapeutic exercises Corrective farriery, physical therapy,
acupuncture Phase 4: Remodeling Ongoing neuromotor training and
proprioceptive enhancement
Improve muscle strength and endurance Improve cardiovascular fitness
Discipline-specific training
Stretching, increase in level of difficulty and duration of therapeutic exercises
Introduction of short periods of fast work during the latter stages.
Reintroduce specific tasks such as jumping or dressage
150 Section 3 / Nonpharmacological Pain Therapy Table 12.2. Techniques to improve mobility and reduce
pain in patients with osteoarthritis
Focus Treatment option
Joint inflammation Cryotherapy; low-grade joint mobilization; NSAIDs;
chondroprotectants;
nutraceuticals; weight management
Stiffness and pain: joint and associated soft tissue structures
Heat (infrared lamp, heat pack, rugs and wraps); therapeutic ultrasound; low-level laser therapy; massage, ROM, and stretching exercises;
acupuncture Muscle atrophy Therapeutic exercises Altered proprioception and
neuromotor recruitment
Therapeutic exercises
the ability of the muscle fibers to respond to an electrical stim-ulus. Subsequent to injury, the sensory receptors within the joint capsule, ligaments, and tendons, as well as the muscle spindles, exhibit altered function. Inadequate proprioceptive input changes the frequency and rate of muscle fiber recruitment and adversely affects balance and coordination leading to clumsy, erratic move-ment that persists in the absence of nociceptive signals. Neuromotor control can be tested by watching a horse walk up and down slopes,
Table 12.3. Techniques to treat back pain in horses
Focus Treatment option
Management Increase time at pasture to encourage natural stretching of the longissimus dorsi;
feed from the floor rather than hay nets
Reduce stress Promote interaction with other horses; adopt a relaxed manner when handling and riding; increase time at pasture; acupuncture Reduce pain Analgesics; acupuncture;
physical therapy; local heat;
osteopathy; chiropractic;
massage Increase flexibility Stretching exercises Improve abdominal muscle
tone
Therapeutic exercises Improve iliopsoas function Therapeutic exercises Improve balance and
proprioception
Therapeutic exercises Improve core stability Therapeutic exercises
turning tightly, or navigating obstacles. It can also be tested through assessing the horse’s ability to maintain its trajectory in the face of external forces, such as tail pulling. Adequate time must be given during rehabilitation to allow for proprioceptive re-education and restoration of balanced, controlled movement.
Core Stability Assessment
When the abdominal muscles contract against the resistance of the diaphragm, hydrostatic pressure inside the abdominopelvic cavity increases and the pressure generated counters the pressure from the back, the rider, and gravity. In well-conditioned muscle with appropriate tonus, the abdominal muscles function as a system of stays supporting the intervertebral joints (Denoix & Pailloux, 2004).
Reinforcement of this support is a critical part of any therapeutic exercise program. Assessment of abdominal muscle mass and tone should be an integral part of a lameness evaluation.
REHABILITATION FOR MUSCULOSKELETAL DISEASE AND INJURY
As outlined in the section on canine rehabilitation, the design of any treatment program should be influenced by the degree of inflamma-tion and the rate of progress through the different stages of tissue healing. Table 12.1 describes the phases of healing, the rehabilita-tion goals, and techniques used to achieve them for acute injuries in horses.
Osteoarthritis and back pain are the most commonly encountered musculoskeletal diseases in horses. Frequently, the two are inter-linked and should be addressed simultaneously. Osteoarthritis is not merely a problem of cartilage degradation within the joint; it is the end result of abnormal mechanical wear and tear. Local changes in muscle function may well be a precursor to its development (White et al., 2007). Joint instability due to ligament laxity and loss of functional control through altered proprioception and neuromo-tor function are also important predisposing facneuromo-tors. A multimodal approach to managing osteoarthritis in the equine is likely to have
Figure 12.2. Stretching may provide pain relief through central mechanisms.
12 / Equine Rehabilitation 151
Table 12.4. Therapeutic exercises for horses
Exercise Therapeutic effect
In-hand walking on a proprioceptive road (3–6 m lengths of alternating surfaces)
5 minutes sessions repeated twice daily
Proprioceptive re-education, rapid neuroreceptor adaptation
Tail pulling—axial traction: Grasp the end of the tail and gently apply caudoventral traction in line with the sacrum Wait for the horse to pull against you and hold for 1 minute,
repeat twice daily
Reduces tension in the lumbar epaxial and gluteal musculature
Lateral tail pulls:
Apply gentle tail traction on both the left and right sides 1 minute, repeat twice daily (Figure 12.5)
Rhythmic movement stimulates activation of the spinal stabilizers (cybernetic muscles) and core musculature Activates joint mechanoreceptors and assists development of
neuromuscular coupling at the lumbosacral junction Improves balance and triggers a stabilizing response in the fore
and hind limb muscle groups Rocking:
Stand parallel to the horse and place your hands over the withers or sacrum
Rock the horse gently from side to side Move around to the other side and repeat 1 minute twice daily
As above
Serpentine, figure of eight, and labyrinth work:
Start with large, wide turns and tighten them progressively to increase the level of difficulty
1 minute twice daily (Figure 12.3)
Promotes side bending, enhances proprioception, strengthens limb adductors and abductors
Introduces nonlinear motion and increases the load on individual joints
Labyrinth work teaches the horse to step medially across the midline
Promotes concentration and requires the horse to drop his head Ground pole work:
Place at intervals equal to the horse’s stride length 1 minute repeated twice daily; duration increased as horse
progresses (Figure 12.4)
Increases ROM, promotes abdominal muscle recruitment, improves balance and coordination, improves proprioception and motor control
Promotes limb flexion and pelvic limb protraction
Walking over a low bridge Novel proprioceptive and auditory stimulus
Promotes cervical flexion
Stimulates abdominal muscle contraction Walking uphill:
Use a short slope
The severity of the incline can be increased as rehabilitation progresses
Similarly, start with short sessions (2–3 minutes) and increase the duration (up to 10–15 minutes)
Stimulates abdominal and iliopsoas muscle contraction and lifts the back
Strengthens the gymnastic muscles of the pelvic limb Increases flexion and protraction of the pelvic limb Improves shock absorbing capacity of pelvic limb Walking uphill over poles:
Increases the difficulty of the exercise
Enhances concentration, coordination and proprioception Encourages a caudal shift in the horse’s center of gravity and
increases the load on the hind limbs while reducing the load on the forelimbs
Walking downhill:
Use a short slope; the severity of the decline can be increased as rehabilitation progresses
Similarly start with short sessions (2–3 minutes) and increase the duration (up to 10–15 minutes)
Eccentrically strengthens the pelvic limb as the limb is placed under the body in descent
Improves abdominal muscle function Improves balance and coordination
Walking downhill over poles Enhances concentration, coordination, and proprioception Improves abdominal muscle function
Improves balance
(continued)
152 Section 3 / Nonpharmacological Pain Therapy
Table 12.4. (Continued)
Exercise Therapeutic effect
Backing uphill:
Start with short sessions of 30–60 seconds repeated twice daily
Enhanced proprioceptive stimulation Strengthens the pelvic limb
Trotting over ground poles and Cavaletti rails
Start on the ground and progress to ridden work, 2–3 minutes repeated twice daily
The height of the rail and duration of the exercise can be increased as the horse progresses
Increase ROM
Promote abdominal muscle recruitment Improve balance and inter limb coordination Improve proprioception and motor control Elevates the forehand
Encourages poll flexion
the best outcome. Such an approach should include appropriate surgical intervention, pain management through traditional phar-macological means, acupuncture (Deyle et al., 2000), physical ther-apy (Frick, 2010), therapeutic exercises to enhance proprioception and neuromuscular activation, weight loss and nutritional manage-ment, and nutraceuticals and chondroprotectants. Techniques that can improve mobility and reduce pain in the osteoarthritic patient are listed in Table 12.2.
Back Pain
Any condition which induces a change in a horse’s normal pattern of movement, whether through changes in management (enforced stabling), introduction of tack and rider, or disease and injury, may well predispose to back pain.
The longissimus dorsi muscle, under normal circumstances, should be able to control lateral and dorsoventral movements of the spine through sequential relaxation and contraction. However, if the muscle is permanently shortened or in a state of increased tonus, the horse will be unable to carry out these maneuvers or support the weight of the rider. Another contributing factor in the recovering athlete or in young horses is the lack of ability to contract the abdominal muscles, iliopsoas, or the cervical flexors.
An inability to flex the spine results, and passive support mecha-nisms are altered. Factors that should be considered when design-ing a program to strengthen the back and reduce pain are listed in Table 12.3. Initially, therapeutic exercises should focus on ground-work, with ridden work only being reintroduced when the horse is capable of elevating the back and keeping the longissimus muscles relaxed.
Stretching
Some studies have demonstrated that stretching (Figure 12.2) assists with pain relief through centrally mediated effects (Frick, 2010).
As stretch tolerance increases, the application of a constant force produces less pain, and it is hypothesized that this is due to an antinociceptive effect mediated by the stretch of the muscle (Shrier, 2002).
Stretching improves flexibility, which relieves pain, prevents injury, and enhances performance (Marko, 1979; Taylor et al., 1990;
Thacker et al., 2004). These exercises also improve balance, body awareness, and proprioception. By increasing tissue compliance and reducing the viscoelasticity of resting muscle, stretching can enhance the ROM in a single joint or a system of joints. Com-pliance represents the ability of tissues to lengthen under minimal
force, and poor compliance during active muscle contraction is a significant factor in tissue injury (Shrier, 2002; Krivikas, 2006).
Spinal reflexes mediated by motor muscle spindles and the Golgi tendon organs influence flexibility. The muscle spindle responds to an absolute change in length of muscle fibers and the rate of change in fiber length. When activated during rapid muscle contraction, the muscle spindle stimulates the primary afferent fibers and promotes muscle shortening and an increase in tension. The Golgi tendon organ, on the other hand, is located at the muscle–tendon interface and senses muscle tension. It relays information to the spinal cord that results in inhibition of the agonist muscle and contraction of the antagonist, thus enhancing the ability of the muscles to stretch.
Thus, the aim of any stretching exercise should be to activate the Golgi tendon organ and inhibit the spindle reflex (Marko, 1979).
Other factors that influence flexibility include myofascial com-pliance, local skin elasticity, the presence of adhesions and scar tissue, hydration status, local joint and tissue temperature, and the type of joint.
Tissues should be warmed prior to stretching to minimize the risk of further injury. This can be achieved through the application of heat packs, the use of infrared radiation, massaging the tissues, or by gently walking the patient. Heat increases the firing rate of the Golgi tendon organ while inhibiting muscle spindle activity, and increases tissue elasticity. In general, it is recommended that stretching be carried out prior to exercise to improve flexibility and help prevent injury. It is also effective during the cooling down period, as it helps reduce postexercise muscle stiffness, fatigue, and shortening (Thacker et al., 2004).
Any performance horse will benefit from a regular stretching routine. This becomes particularly important in stabled horses that undergo very little “natural” stretching through grazing activity.
Stretching should initially be introduced at a basic level, with the intensity or level of difficulty only being increased when the horse has demonstrated adequate improvement. It is essential that the horse is relaxed before starting, and has been adequately warmed up, as previously outlined. When teaching owners to perform a stretch, it is imperative that the purpose of the stretch be explained, and that clear written and pictorial instructions are issued for them to follow. The number and frequency of repetitions should be clarified as well as instructions on the duration of the stretch. Although some immediate improvement can be seen, it may take as long as 6 weeks for the full benefit to be witnessed. For more detailed information the reader is referred to the textbook entitled Physical Therapy and Massage for the Horse (Denoix & Pailloux, 2004).