34th Annual Scientific Meeting proceedings

Physiotherapeutic exercises aimed at stimulating motor control, flexibility and stability are regularly employed in human physical therapy programs. Specifically, the use of such exercises have been shown to reduce both pain and re-injury.^1-3  Human athletes that incorporate core, balance exercises into their rehabilitation programs are significantly less likely to suffer re-injury during a 12-month period following injury, compared to those individuals with similar injuries that did not emphasize core strength (7%  re-injury rate in the balance training group versus 29% re-injury rate in the control group).⁴ Strengthening and improving proprioception and balance control following injury remains a central focus of human physical therapy programs, and while standardized investigations have yet to focus on equine applications, there are several mechanisms through which neuromotor control can be recruited. Physical therapy aides such as ground poles, tactile stimulators and incorporation of surface changes offer clinicians passive means of engaging neuromotor control during activities of daily rehabilitation or training. Ground poles when arranged at various distances, heights and configurations can encourage increase in lateral thoracolumbar excursion. Hill work and incorporating backing exercises into hill work can also be used to simultaneously improve muscular strength and challenge proprioceptive acuity.

Proprioceptive facilitation techniques in horses

Mechanism of Action

Recent human research has expanded our understanding of neuromuscular responses to joint pain.⁵  Mechanoreceptors are characterized as sensory receptors within periarticular tissues that respond to changes in joint position and acceleration of movement, as well as playing an important role in regulating and maintaining neuromuscular control of joint stability.⁵ Pain, inflammation and joint effusion associated with OA alters the normal sensory input from articular mechanoreceptors, which may result in decreased  motor neuron excitability and reduced muscle activation.⁶ A common outcome following experimentally-induced knee effusion is the presence of significant quadriceps muscle inhibition.^7-10 A linear relationship exists between increased intra-articular pressure and the level of quadriceps inhibition.⁷ Electromyography studies conducted on the quadriceps muscle of patients with knee osteoarthritis often indicate a decrease in muscle strength and altered muscle timing.¹¹  Typically there is a delay in the onset of quadriceps muscle activation, which results in the inability of the quadriceps to stabilize the joint and attenuate the loading forces properly during locomotion.⁸  The increased joint instability further alters the distribution of weight bearing forces across joint surfaces and increases the recruitment of adjacent muscles to aid in joint stability.¹²  The resulting imbalances in paired agonist–antagonist muscle groups contribute to increased joint instability and altered limb biomechanics, which leads to progressive OA and chronic maladaptive compensatory mechanisms.¹³

Similar results would be expected in horses, the presence of pain may lead to loss of function, diminished neuromotor control, decreased joint range of motion, and muscle atrophy in the hindlimb and pelvic musculature.  The application of various proprioceptive techniques are frequently utilized to increase joint range of motion, reestablish appropriate neuromuscular firing patterns, and improve the strength of targeted muscles that function to move and stabilize the joints.¹⁴ The use of tactile stimulators applied around the hindlimb pastern demonstrated a significantly higher hoof flight arc, with increased flexion of the fetlock, hock and stifle joints.¹⁴ The use of this proprioceptive technique supports the facilitation of enhanced afferent input to indirectly produce and modulate a targeted efferent response for the purpose of reestablishing motor control and improving joint range of motion.   

A multitude of other proprioceptive techniques are utilized from resistive bands and kinesiotape, to ground poles and changes in ground surfaces. Resistance band training is successfully used in human physical therapy programs to improve core strength and stability.^15-16 Commonly referred to as a Theraband[1], the two-piece equine elastic band system is thought to stimulate core abdominal muscles with the abdominal band and engage hindlimb musculature with the hindquarter band. Its use in horses at a trot was recently investigated and found to reduce mediolateral and rotational movement throughout the thoracolumbar region.¹⁷  Further studies investigating more long-term use and potential mechanistic pathways will help refine its use in the rehabilitation setting. Also pertinent to rehabilitation are the use of training lines. Pessoa training aids were demonstrated to increase both lumbosacral angles and thoracolumbar dorsoventral excursion when used in horses being lunged at a jog.¹⁸  While further studies are needed to establish specific recommendations regarding use, initial biomechanic effects for targeted rehabilitation are encouraging.

Clinical Application:

• Ground poles can be used to increase both range of motion and stride length depending on height and distance of spacing.
  • Used in the early phases of rehabilitation during the hand walking sessions
  • Initially height is kept low and increased as the horse progresses through the program
  • 3-5 poles in succession making 2-5 passes through the poles initially
  • As the horse progresses through the program the number of passes, the height and position of the poles can be adjusted.
• Tactile stimulators can be applied to increase range of motion during hand walking sessions
  • Protocol 2-3x a day daily for 5 minutes
  • Can lessen response (degree of flexion) by applying device to opposite hindlimb initially
  • Habituate quickly to device within the same session thus apply for shorter periods of time multiple times a day
  • Due to degree of response (hyperflexion) caution starting too early in the rehabilitation process
• Resistance bands can be used to encourage lumbosacral flexion and increase hindlimb protraction when applied around hind quarters
  • Applied during hand walking sessions
    • Initially kept in place for 5 minutes during a single hand walking session
    • Increase time at weekly increments until able to wear during a full hand walking session
    • Typically used once to twice a day
• Varied ground surfaces
  • Utilize during the hand walking sessions to promote motor control and core stability

Passive joint range of motion and core strengthening exercises

Mechanism of Action

Passive range of motion can be described as passively moving a joint or joints through the normal physiologic range of motion without muscular activity.  The primary goals of passive range of motion exercise are to prevent joint capsule fibrosis, maintain tissue mobility, improve vascular dynamics, allow for synovial fluid diffusion, and decrease pain.  Passive range of motion exercise stretches those muscles whose action would actively move the joint, thus improving their contractile properties.  In addition, the predominant clinical use of passive motion is to target peri-articular tissues in an attempt to prevent joint capsule fibrosis. Human clinical studies assessing passive range of motion exercises in patients following knee arthroplasty showed a significant improvement in range of motion that was still apparent after one year.^19,20 The improvement in range of motion can be supported from results in the rabbit models that demonstrate as healing occurs within the joint capsule, collagen fibers align randomly.  This random, cross-linking pattern causes increased fibrosis and thickening of the capsule.  Passive range of motion exercises are proposed to work at a cellular level by decreasing the random alignment of the collagen fibers through stimulation of physiologic motion enhancing parallel fiber orientation.²¹

Clinical Application

Passive flexion/extension exercises are typically conducted twice a day with 2 sets of 30-50 cycles per joint of interest.  As the horse progresses gradually, increase either the number of sets or the number of reps.  Caution: only increase once portion at a time; do not increase both the number of sets and the number of reps at the same time. If chronic capsulitis is present it may help to heat the tissues first. 

Core strengthening exercises have been recommended to reduce stiffness, enhance soft tissue mobilization, increase muscle activation, lengthen the musculotendinous unit, decrease pain, and improve performance. A recent imaging study assessed the cross sectional area of the thoracolumbar multifidi muscles in horses with clinical signs of back pain.²² Those horses with evidence of osseous pathologic changes demonstrated a measurable asymmetry in the multifidus muscle cross sectional area at the level of the pathology.²²  In a follow up study, regular performance of dynamic mobilization exercises were shown to increase multifidus muscle CSA from T10 to L5.^23,24 Eight clinically-sound horses performed five repetitions of mobilization exercises five days per week, over a three-month period. The exercises consisted of three cervical flexion positions, one cervical extension position and three lateral bending positions to left and right sides.  The results of the study demonstrated that the CSA of the thoracolumbar multifidi muscles increased in size in response to the mobilization exercises.^23,24 The increase in multifidus muscle development following dynamic mobilization is a promising rehabilitative technique for horses in which this muscle has atrophied due to back pain.

Clinical Application

Cervical spinal range of motion exercises are achieved when the horse follows a controlled movement pattern that recruits both the dynamic mobilizing muscles and the deep stabilizing muscles used to round or bend the neck. ^23,24 The horse is taught to follow a controlled movement pattern using bait, such as a piece of carrot, through a specific movement pattern that involves rounding and/or lateral bending of the neck while stabilizing the back and limbs to maintain balance.²³ A series of dynamic mobilization exercises are often used to induce flexion, extension and lateral bending throughout the cervical spine to reduce stiffness and improve range of motion through portions of the thoracolumbar region as well.  These baited, active-assisted range of motion exercises can be divided into three flexed positions: 1) chin to chest targets flexion of the upper cervical spine, 2) chin between carpi increases flexion of mid to caudal cervical spine, and 3) chin between fetlock increases flexion of mid to caudal cervical spine and activation of the rectus abdominus to contract and lift the back.²³ When asking the horse to bend laterally into 3 positions using a baited, active assisted range of motion exercise, the chin to girth demonstrated the greatest degree of lateral flexion occurring at C1.²³ Bending chin to hip and chin to tarsus both increased lateral bending in the caudal cervical spine with the majority of lateral flexion occurring at C6-T1 and induced lateral bending within the thoracolumbar region as well. The optimal time to perform dynamic mobilization is immediately before exercise each day to pre-activate the postural control muscles. The horse is encouraged to hold the position for several seconds and after each exercise allow the muscles to relax for several seconds. Perform 3-5 repetitions of each exercise per day and, for the lateral bending exercises, do an equal number of repetitions to the left and right sides. ^23,24

Conclusion:

Developing a successful rehabilitation protocol involves first reaching an accurate diagnosis followed by establishing clearly defined rehabilitation goals.   Although the general goals of rehabilitation are usually similar—to first decrease pain and inflammation while preventing further injury and then to restore normal function by restoring proprioception, flexibility, strength and endurance—there is often significant variation in rehabilitation protocols.  For example, the protocol may vary based on the duration, type and severity of the injury, the goals and finances of the owner, available rehabilitation equipment and resources, and the intended use of the horse.  Fortunately, there are often many ways to achieve rehabilitation goals.  Some are traditional and well-established, while others are yet to be proven.  They run the gamut in terms of cost, availability and ease of use. 

References

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16. Macedo, L.G., Maher, C.G., Latimer, J. and McAuley, J.H. Motor control exercise for persistent, nonspecific low back pain: a systematic review. Phys. Ther. 2009;89:9-25.

17. Pfau, T., Simons V., Rombach, N., et al. Effect of a 4-week elastic resistance band training regimen on back kinematics in horses trotting in-hand and on the lunge. Equive Vet J 2017;49:829-835.
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19. Salter R, Hamilton H, Wedge J, et al. Clinical application of basic research on continuous passive motion for disorders and injuries of synovial joints:  A preliminary report of a feasibility study. J Orthop Res 1984;1:325-342.
20. Salter S, Simmond D, Malcom B, et al. The biological effect of continuous passive motion of the healing of full - thickness defects in articular cartilage. J Bone Joint Surg 1980;62:1232-1251.
21. Ferretti M, Srinivasan A, Deschner J, et al. Anti-inflammatory effects of continuous passive motion on meniscal fibrocartilage. J Orthop Res 2005;23:1165-1171.
22. Stubbs, N.C., Riggs, C.M., Hodges, P.W., et al. Osseous spinal pathology and epaxial muscle ultrasonography in Thoroughbred racehorses. Eq Vet J. 2010;(42):654-661.
23. Clayton, H.M., Dynamic mobilisations in cervical flexion: Effects on intervertebral angulations. Equine Vet J 2010;42:688-694.
24. Stubbs, N.C., et al., Dynamic mobilisation exercises increase cross sectional area of musculus multifidus. Equine Vet J 2011. 43(5): p. 522-529.