Lowri Davies
The cornerstone of rehabilitation is the ability to simultaneously manage pain and restore function. A successful therapist will be an individual who is well-versed in acute and chronic pain man-agement, has an understanding of the biomechanics of movement and how tissues respond to stress and strain patterns, is familiar with the principles of exercise physiology, and is able to apply these principles to the treatment of patients with neurological or musculoskeletal injuries.
A comprehensive approach requires a multidisciplinary team, as it is unlikely that one individual will possess all the skills required of a rehabilitation practitioner. Such a team may consist of a vet-erinary neurologist or orthopedic surgeon, a veterinarian skilled in rehabilitation, a certified physical therapist with further training in animal physical therapy, and appropriately trained technicians or assistants. Furthermore, a compliant owner and patient are funda-mental to the success of the program.
The World Health Organization’s (1992) definitions for impair-ment and disability are pertinent to veterinary patients. Impairimpair-ment is defined as “Any loss or abnormality of psychological, physio-logical, or anatomic structure or function.” Disability is defined as
“Any restriction (resulting from impairment) of ability to perform an activity in the manner or within the range considered normal for the species.” To restore function it is essential to understand the motor adaptations of the patient in response to pain. If altered function was merely a response to nociception then the adminis-tration of analgesics should resolve the problem. This is often not the case, however, and many aspects of motor adaptation persist despite resolution of pain (Hodges & Richardson, 1996).
This chapter outlines some of the adaptive changes in movement that arise as a consequence of pain and how these changes may provide treatment guidelines for the rehabilitation practitioner. It will consider clinical examination of the patient from a rehabili-tation perspective and examine some of the most commonly used modalities in a rehabilitation program and how to develop a safe framework for their use. The reader is referred to texts on veterinary physical therapy for further information (McGowan et al., 2007).
UNDERSTANDING PAIN IN REHABILITATION PATIENTS
Musculoskeletal pain is a consequence of repetitive strain and overuse. These injuries include a variety of disorders that cause
pain in bones, joints, muscle, or surrounding structures. Muscle pain may also be referred to other deep somatic and visceral structures.
The causes of musculoskeletal pain are not fully understood but likely involve inflammation, fibrosis, tissue degradation, and neuro-transmitter and neurosensory disturbances, and may include central and peripheral hypersensitivity and impairment of descending inhi-bition of incoming nociceptive impulses (IASP, 2009).
Restoring or improving the neuromotor control of skeletal move-ment is fundamove-mental for managing pain associated with the muscu-loskeletal system.
Why is Movement Different with Pain?
The fact that animals move differently when in pain cannot be disputed; however, the physiological basis for why this occurs is poorly understood. A recent theory (Hodges, 2011; Hodges &
Tucker, 2011) (Figure 11.1) examines the concept that excitatory and inhibitory activity is redistributed in response to pain, and this modification of mechanical behavior is designed to protect tissues from injury. Hodges (2011) has concluded that muscle adaptation to pain involves redistribution of activity within and between muscles;
modification of mechanical behavior, including decreased variabil-ity of movement and increased stiffness; and protection from further pain or injury through reduced voluntary activity, increased muscle splinting, and redistribution of load. These changes are mediated at multiple levels, centrally and peripherally, and while they provide short-term antinociception, they result in long-term negative conse-quences due to increased load, decreased movement, and decreased variability of movement.
Mounting evidence suggests that pain also affects postural func-tion by altering balance (Mok et al., 2004) and causing changes in anticipatory and reactive postural mechanisms (MacDonald et al., 2009). Thus, the ability of the body to make subtle adjustments in posture and balance is hampered, and dynamic stability is lost (Hodges, 2011).
ASSESSMENT OF THE REHABILITATION PATIENT Anamnesis
The reported history should identify the primary problem, for example, fracture, lameness, or poor performance. It should note
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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134 Section 3 / Nonpharmacological Pain Therapy
New theory for adaptation to pain
Rehabilitation Rehabilitation
Reduce pain to reduce impact on control and
motor learning
Pain/injury or threat of pain/injury
Changes at multiple levels of the nervous system
Redistribution of activity within and between muscles
Changes the mechanical behavior
Modified direction/load distribution
↑ Stiffness
Short-term benefit
Protection of the injured/painful part
Long-term consequences Reduce unnecessary components of adaptation
Optimize load with balance between useful (compensation for
injury) and unnecessary adaptation Identify and train relevant aspects of redistributed activity
high-quality training
↑ Load
↓ Movement
↓ Variability Multiple techniques
likely to be required to influence motor adaptation at different
levels of the motor system including exercise, psychological treatments, and other
modalities
Enhance helpful components of adaptation
Figure 11.1. New theory of motor adaptation to pain and its implication for rehabilitation. The central column postulates that pain and injury or the potential threat of pain and injury lead to changes at multiple levels of the nervous system. The resultant changes lead to the redistribution of activity within and between muscle groups and altered mechanical behavior.
Although an increase in stiffness can confer short-term benefit through the protection of the injured part, in the long term it leads to increased load on individual components of the musculoskeletal system, reduced movement, and loss of
variability of movement. This model necessitates high quality rehabilitation through precise neuromotor training targeting multiple sites within the nervous system, e.g., cortical, spinal, and motor end plate. Reproduced with permission, Hodges, P.W. (2011) Pain and motor control: from the laboratory to rehabilitation.Journal of electromyography and Kinesiology 21, 220–228.
past surgical procedures, if any, and how satisfied the surgeon was with the result; that is, is the repair stable and have joint biome-chanics been altered? Other factors to consider when evaluating a candidate for physical rehabilitation include the time post surgery or injury, tissues involved, duration of dysfunction, age, body con-dition, preinjury activity level of the patient, and desired outcome.
A detailed history should also include correct identification of the animal’s degree of pain and disability. By identifying how the patient copes with the activities of daily living, a true picture of the animal’s disability can be constructed. Information regarding the following should be gathered:
r Ability to ascend and descend stairs r Ability to enter and exit vehicles
r Ability to cope with difficult surfaces such as wooden or tiled floors
r Ability to remain standing while eating r Willingness to exercise and exercise tolerance r Ability to remain squatting while defecating r Ability to posture for urination
r Inappropriate elimination
r Willingness to play r Change in demeanor r Response to grooming
r Response or lack thereof to medication r Effect of exercise on the lameness r Effect of rest on the lameness
r Duration and intensity of the lameness r Changes in sleep patterns
It is important to understand how pain developed in each patient and how the patient is coping. Some owners will report a gradual decline in their pet’s mobility where the pet chooses to exercise less as pain progresses. Secondary issues, such as weight gain and mood changes, can develop. These patients often appear to have a depressed demeanor and are termed “passive” copers. “Active”
copers are patients who bounce into the consulting room on three legs, dragging their owners behind them. These individuals are always keen to exercise, in spite of pain and lameness, and appear to be less susceptible to mood changes (Butler & Mosely, 2003). From a musculoskeletal perspective active copers can be challenging to treat as they often have weight shifting, compensatory movement,
11 / Canine Rehabilitation 135 and novel neuromotor recruitment patterns that are well established
in order to facilitate exercise. In contrast, chronic musculoskeletal and nervous system changes may not have occurred in passive copers, but they may have more immune and endocrine system dysfunction. They benefit from stress reduction, may require more coaxing through the therapeutic exercise regimen, and take longer to respond to treatment than would be expected in view of the degree of dysfunction observed. This is referred to as a disability-dysfunction mismatch (Butler & Mosely, 2003).
Questionnaires, such as the acute pain questionnaire (Thomas et al., 1996) or the Helsinki Chronic Pain Index (Eskelinen et al., 2012) (Chapter 22), can be given to owners to complete during anamnesis and at various points during treatment to help evaluate the patient’s progress. Good communication will improve outcome, and recent studies have shown that the relationship between the clinician and the patient and owner is of primary importance in successful management of chronic pain (Jamison, 2011).
Assessment of the Patient for Pain
Diagnosis of altered pain states in animals can prove extremely challenging. Relying on lameness alone is inadequate, particularly after the acute period has passed, and signs may include tenderness, weakness, limited motion, and stiffness (IASP, 2009).
Identifying Movement Adaptations to Pain
Once discomfort has been identified, the next challenge in the design of a rehabilitation plan is to detect the movement adaptations that led to the changes in gait pattern and altered biomechanics of limb and trunk movement.
Much of conventional veterinary medicine emphasizes a reduc-tionist approach, but a systems-based approach is required. The systems-based approach considers the joint to be an organ system in which all tissues comprising the joint work together, biomechan-ically and biologbiomechan-ically, to maintain joint health and allow full, pain-free function. Thus, successful treatment should consider, for exam-ple, not only the cranial cruciate ligament but also the synovium, joint capsule, articular cartilage, menisci, and subchondral bone (Cook, 2010). Consideration should also be given to the neuromus-cular consequences of injury, such as alterations in somatosensory and proprioceptive function (Ingersoll et al., 2008). Any rehabil-itation program should consider how changes within the affected joint influence the system as a whole, including the back, trunk, and other limbs. For example, if the diagnosis is simply “torn cru-ciate ligament” and the treatment is simply “surgical correction of instability”, it will be difficult to develop a safe and effective reha-bilitation protocol. Instead, the diagnosis should be lameness, pain, and dysfunction due to inflammation, changes within the passive stabilizers of the joint, changes within the dynamic stabilizers of the joint, and altered neuromotor, somatosensory, and propriocep-tive function. This provides a better understanding of the patient’s impairment and dysfunction as well as the underlying causes, and can inform an effective rehabilitation plan (Panjabi, 1992).
Clinical Examination Static Assessment
Static assessment includes assessment of muscle hypertrophy or atrophy, head and tail position, abdominal muscle tone, scarring or
swelling, symmetry of the axial and appendicular skeleton, devia-tion in the sagittal plane of the thoracic and lumbar spine or lordosis or kyphosis, distribution of body weight among all four limbs, and any adduction or abduction of the limbs in the animal at rest. Note the limb alignment (including joint angles or goniometry), angular deformities (valgus and varus), and internal and external rotation of limbs. Determine if the deformity is bony in nature and thus, not correctable by rehabilitation alone, or whether it is functional in nature. If the deformity is functional, a neutral alignment is restored when the limb is elevated; thus, therapy is directed at maintaining this alignment during weight bearing.
Dynamic Assessment
Dynamic assessment involves moving the limbs and noting reac-tions and resistance in the muscles as joints are flexed and extended or limbs are advanced and retracted, observing the patient as it moves from standing to sitting and vice versa, and assessing qual-ity and control of movement. Symmetry of the animal when sitting, and any tendency to lean or to brace with the forelimbs, is assessed.
Observation should be made of the spinal column and of the inter-action between the neck and back during flexion and extension.
Gait Assessment
This portion of the assessment allows grading of the severity of the lameness, localization of the lameness, and description of the gait in terms of cranial and caudal phases, arc of flight, and linearity of the movement. Assess gait at the walk and trot, in a straight line and in a circle, on a flat, nonslippery surface, and then on a variety of surfaces. Observe the movement of the pelvis, lumbar, thoracic, and cervical spine, observing for bilateral symmetry. Observe how the patient positions the limbs and curves the trunk when walked or trotted in a right and left circle. Observe the animal on the left and right sides of body and note any differences. Observe the animal as it walks over low poles or up and down stairs.
Neurological Examination
A neurological examination should be part of the assessment to help differentiate poor balance due to stiffness and pain from ataxia due to a neurological lesion, as each has different rehabilitation requirements and prognosis.
Palpation and Range of Motion
Palpation and manipulation should occur with the patient during standing and in lateral recumbency. It is best to develop a systematic approach: palpate muscles for their overall symmetry, texture, and tone, presence of edema, trigger point formation, and the presence of lactic acid, which confers a feeling of crackling tissue paper within the muscle.
During palpation of joints, subtle effusion and temperature changes should be identified. Any remodeling in response to stress, for example, the formation of a medial stifle buttress in response to instability, should be noted. The stability of a joint should be deter-mined through its full range of motion (ROM) while remembering that associated changes, such as muscle atrophy, may increase joint laxity without direct involvement of the joint. The quality of move-ment should be established as well as the total and pain-free ROM and the nature of the end stop (see below). Note pain on extension and flexion and internal and external rotation and assess medial and lateral instability of each joint.
136 Section 3 / Nonpharmacological Pain Therapy
Figure 11.2. Using a hand-held goniometer to measure range of motion in the elbow joint.
The axial skeleton should be examined as a system and on an individual vertebral basis. Ventrodorsal and lateral motion should be evaluated and any restriction noted. Active and passive ROM should be established.
Range of Motion and End Stop Assessment of Joints
Range of motion within a joint is the degree of motion that joint is capable of undergoing from full flexion to full extension in the sagittal plane. It can also be used to describe the degree of abduction and adduction afforded to an individual joint.
A more useful measure to assess joint function may be the func-tional ROM. This is the degree of motion required within a joint to allow for normal motion to take place, that is, for an individual to move normally and comfortably. For many individuals, pain within the extreme ROM is not limiting to function; however, for the canine athlete, pain within the outer ranges of motion will become limiting to performance.
Range of motion is measured with a manual or laser goniometer (Figure 11.2). Studies with a group of Labrador Retrievers have demonstrated repeatable measures for the joints of the distal limbs (Jaegger et al., 2002). To increase accuracy, a mean of three mea-surements should be taken with the dog placed in lateral recum-bency. The joint should be measured in both limbs, and it is often easier to start with the “normal” joint. Interbreed variation occurs and factors such as emaciation, obesity, and muscle atrophy may also affect values.
End stop, or feel, is a term used to describe the normal end point of motion within a joint, and each joint has a typical end stop. For example, the elbow joint will exhibit a soft end stop when flexed, as the biceps brachii limits further flexion. This type of end stop feels very different from the capsular or firm end stop felt in elbow extension. This stop has a firm feel but with a slight give to the end point, and it is abnormal if it occurs too early in the motion, as may occur in an osteoarthritic stifle joint. In a bony end stop, the stopping motion is abrupt and hard, and this may be observed in a joint affected by severe bony remodeling. A springy end stop is felt when the joint rebounds from the limit of motion, and it indicates the presence of a loose fragment within the joint. An empty end stop is one where no end point is reached, for example, with a fracture.
A painful end stop is one whereby the end point is never reached, as pain becomes a limiting factor to movement early on in flexion or extension.
Goniometry and measurement of a joint’s ROM can be useful outcome measures when assessing the rehabilitation patient. Even small increases in joint motion, particularly within the functional range, can significantly improve mobility. End stop evaluation is important when assessing how much improvement in joint ROM is possible. A bony end stop is unlikely to change, and may contribute to a mechanical lameness that will be refractory to any rehabilitation technique. Such a gait may not necessarily be painful, provided the compensatory pattern adopted during motion is not too severe. On the other hand, an abnormal capsular, soft, or painful end stop to a joint’s motion may well benefit significantly from rehabilitation.
For further information on detailed examination of the canine the reader is referred to McGowan et al., (2005).
TREATMENT OF MUSCULOSKELETAL PAIN
Many of the modalities used in rehabilitation medicine are appro-priate for treating musculoskeletal pain (Table 11.1). The act of standing can be considered an exercise, and even 1 minute of stand-ing in the correct position can be difficult for a dog that has been lying down for most of the day over a period of several months.
The degree of pain and level of dysfunction are not necessarily lin-early related, and an animal showing the greatest dysfunction is not necessarily in the most pain. Progression is essential and, once a baseline therapeutic exercise regimen is established, the aim should be to gradually increase the complexity and duration of the regimen over the subsequent weeks. This will vary from patient to patient, so each animal should be carefully assessed throughout therapy.
A helpful strategy is to ask the owner to keep a diary of the pet’s progress, and to repeat the pain questionnaire at regular intervals.
Movement and Exercise
Continued movement is beneficial as it improves joint nutrition and soft tissue function and facilitates fine motor control (Bennel et al., 2009). A challenge in treatment is establishing an appropriate level of exercise that does not further damage tissues. “No pain, no gain”
is not a viable management strategy for the rehabilitation patient.
Table 11.1. Treatment options for musculoskeletal pain Anti-inflammatory and centrally acting analgesics
Acupuncture
Transcutaneous electrical nerve stimulation
Improve biomechanics of movement and redistribute load Therapeutic exercises
Massage
Hot and cold therapy
Therapeutic modalities—ultrasound, cold laser, neuromuscular electrostimulation
Osteopathy Chiropractic
Environmental enrichment and play Weight loss/dietary modification Nutraceuticals/supplements
11 / Canine Rehabilitation 137 The aim should always be to reduce pain, although some discomfort
may be required for the rehabilitation program to progress, particu-larly with therapeutic exercise. Pain management techniques, such as acupuncture and ice therapy and the judicious use of analgesics, may be required, especially early in the course of treatment.
Stress Distribution within the Joint
The load across a joint is not simply a reflection of the patient’s body weight. Rather, it is a vector summation of body weight, the forces of acceleration and deceleration of the segment or moving part, and the muscular forces required to stabilize the joint and move the limb (Radin et al., 1979). Joints are configured to maximize the surface area for load distribution and, as the joint is loaded, cartilage and cancellous bone deform to further increase the surface area. Carti-lage deforms under stress through the outflow of water and small solutes. Under a constant load this outflow occurs rapidly in the early stages, but as the material compresses it becomes more diffi-cult for particles to escape; thus deformation is nonlinear. Another unique behavior of cartilage is that deformation is closely related to the rate at which external force is applied. The faster it is squeezed the harder it is for the particles to exit, and the harder it is for the cartilage to deform. This type of nonlinear deformation is termed viscoelastic, and has implications for the rehabilitation practitioner.
By slowing or controlling joint motion there is both increased com-pliance of the cartilage, and reduced load across the joint. Exercises to improve neuromotor control of joint motion and enhance each joint’s postural support will serve to reduce the load acting on a joint.
Mechanical Factors and Erosion of Articular Cartilage Although the yield strength of articular cartilage is reduced by chemical, enzymatic, and metabolic factors, the actual wearing away of cartilage from weight-bearing surfaces requires mechani-cal forces. Cracks and tears beginning in the superficial tangential fiber layer are initiated by tensile stress—that is, the cartilage is pulled apart. If articular cartilage were compressed evenly across its entire surface, no tensile stresses would exist. In whole joints this is probably never the case, and only part of the joint is bearing the load at any given time. If one part of the cartilage surface is compressed and another is not, tensile stresses are created at the margins of loaded areas. Repetitive loading results in crack forma-tion (Radin et al., 1979). Cartilage “wear” occurs when its ultimate tensile strength is exceeded. Failure to heal may be due to persistent high levels of stress in the joint. If these stresses can be decreased, a degree of functional healing of both bone and load-bearing surfaces can take place.
Stresses within a joint are reduced by increasing the surface area over which the load is distributed and reducing the overall load.
By taking a broad view of the patient, it should be possible to determine what, if any, global changes in trunk and limb position-ing have occurred to result in increased loadposition-ing of an individual limb. Furthermore, load distribution within the limb should also be considered; that is, how the limb is positioned under the body will determine whether more weight is sent through the cranial or caudal, lateral or medial aspect of the joint, which again will lead to stress concentrations within the joint, and cause further remodeling in the diaphysis and associated connective tissue along the lines of stress. Thus, prior to carrying out even the simplest of weight-shifting exercises, the clinician must assess limb positioning and
how this affects the distribution of load through its constituent parts.
Repeating an exercise on a poorly positioned limb will only serve to accentuate the pain and dysfunction and serve no therapeutic pur-pose. In contrast, positioning the limb correctly and subsequently loading it should serve to stress the tissues in a functional manner and promote appropriate neuromotor adaptations.
Dynamic Stability
During rehabilitation, exercise regimens are often used to target specific areas of the body. In the face of a nociceptive stimulus the initial response is to attempt to reduce motion in the painful area through increased muscle activation and localized splinting and stiffening (Hodges, 2010). While decreasing localized motion is an effective short-term strategy, it becomes self-defeating in the long term and often results in a loss of dynamic stability, increas-ing movement on a global scale. Dynamic stability represents the ability to continue moving in the desired trajectory in the face of external forces, as it allows the patient to absorb these forces, remain stable, and not be thrown off course. However, as tissues stiffen, stability is reduced and the animal becomes incapable of absorbing external forces and, consequently, stumbles or alters the course of movement.
The concept of increasing muscle mass without any thought to how that muscle actually functions is not the aim of rehabilitation.
Excessive muscle mass will increase static stability but impede per-formance through increasing stiffness, restricted ROM, and reduced dynamic stability, resulting in little predictability of movement. In contrast, a training regimen that develops strength without stiffness will achieve a high error tolerance and predictability during move-ment. The ultimate goal for any rehabilitation therapist should be to develop dynamic stability through improving muscle function and creating sufficient muscle mass to support the athletic requirements of that individual. Only in this way can controlled movement pat-terns that minimize the load placed on the musculoskeletal system during movement be generated.
Formulating a Treatment Plan and Ongoing Assessment Treatment goals include correction of posture, movement, and mus-cle activation. When correcting posture, every attempt must be made to avoid reinforcing the maladaptive posture. Thus, when carrying out weight-shifting exercises not only must the limb be aligned squarely but also the whole body must be aligned squarely and maintained in such a position during the exercise. When correct-ing for movement, ensure that poor gait patterns are not reinforced.
For example, during rehabilitation of the spinal patient a treadmill can be used to develop a functional neuromotor recruitment pattern by actively moving the patient’s limbs (Figure 11.3). The animal should not be allowed to move freely at other times if this uncon-trolled movement re-enforces poor or nonfunctional neuromotor recruitment patterns.
A rehabilitation program should aim to restore the injured tissue to preinjury levels of activity by promoting healing of the injured tissue and minimizing further tissue damage. As a result of the injury systemic changes in cardiovascular and neuromotor function will have occurred and the rehabilitation program must take this into account. The rehabilitation plan should also feature techniques to improve core stability, proprioception, muscle strength, muscle endurance, and cardiovascular function.