Historical Perspective and the Advent of Veterinary Orthotics and Prosthetics

The use of orthotics and prosthetics to assist humans in ambulation and functional independence was first recorded in 2700 BC (Seymour, 2002). In the past century, veterinary medicine has advanced in technology and sophistication co-incident with the increasing value and importance of companion animals. State-of-the-art veterinary health care now includes a new industry called veterinary orthotics and prosthetics (V-OP). The acronym distinguishes it from the human specialty, referred to as Human Orthotics and Prosthetics (H-OP).

The techniques and materials used in H-OP are easily translated into V-OP with specific modifications to account for quadruped ambulation and the significantly greater magnitude of force gen­erated by veterinary patients relative to humans. V-OP applies the use of veterinary specific hinges, vacuum-molded composite high-temperature plas­­tics, titanium, carbon fiber, custom prosthetic paws, and dynamic motion-assist mechanics to the grow­ing understanding of the intricacies of quadruped biomechanics (Adamson et al., 2005). The advantages afforded by custom orthoses and prostheses include prevention of cast-related wounds; management of primary pain generators associated with functional impairments; improvement of biomechanics, allowing for greater activity and a significant decrease in compensatory pain; return to active lifestyle, resulting in decreased obesity and associated comorbidities; improvement in quality of life and functional independence, preventing the premature decision to euthanize; and the availability of treatment options where none existed before.

Biomechanics and Pathomechanics: the Interrelationship Between Rehabilitation and V-OP

The application of mechanical devices is not a panacea and not without challenges. Return to functional independence requires reeducation of the body as a whole, including muscles, nerves, and the mind. Early pioneers of H-OP did not anticipate the need for such rehabilitation. How­ever, in modern practice, it is clear a mechanical device must be coupled with rehabilitation to maximize its use and the patient’s success. The main aim of rehabilitation is to restore and preserve maximum independence of action and functionality (Geertzen et al., 2001). With respect to veterinary patients, an additional aim is to prolong active and comfortable life to prevent premature euthanasia.

Rehabilitation is a medical specialty concerned with the prevention, diagnosis, treatment, and management of disabling diseases, disorders, and injuries typically of a musculoskeletal, cardio­vascular, neuromuscular, or neurological nature by physical means. Biomechanics encompasses anatomy, kinesiology, neurophysiology, mechanics, physics, and mathematics (Bedotto, 2006). Pathomechanics deals with the abnormal effect of static and dynamic forces on the body as a result of neurologic, muscular, and skeletal disorders. Pathomechanics provides understanding of the underlying cause of gait deviation and the implication of forces acting on the injured body during movement: ground reaction force, inertia, and gravity. The specialty of orthotics and prosthetics addresses pathomechanics through the use of corrective forces including alignment of body position, muscular control, and external mechanical systems (Bedotto, 2006). A complete discussion of the physics of V-OP design is beyond the scope of this chapter.

The addition of an orthosis or prosthesis adds additional challenge to rehabilitative manipulation of movement. Comprehensive treatment of a pathomechanical injury requiring use of a device involves marrying the mechanics of the device with the mechanics of the body; the device must become part of the biomechanical system. The rehabilitation therapist plays an integral part in uniting the mechanics of body (muscle and nerve activation, and integration patterns) and device into the complex biomechanics of locomotion. In this paradigm, the therapist provides physical treatment, and the prosthetist/orthotist provides the device or mechanical treatment. The goal of this united effort in human practice is to allow the patient to ambulate in a safe, efficient, and functional manner (Bechtol, 1967).

Modern technology has advanced the sophistication of veterinary orthotics and prosthetics. What is lacking are device-specific rehabilitation programs to enable veterinary patients to fully realize device potential on par with human patients. The veterinary rehabilitation therapist must have a basic understanding of the purpose, mechanics, and limitations of the device. They must recognize complications in a timely manner to prevent injury and limit time out of the device. Likewise, the V-OP professional must understand short- and long-term rehabilitation goals, the biomechanics of therapeutic exercises, and the limitations of rehabilitation. Ultimately, shared information and diverse expertise leads to intervention, device modifications, or rehabilitation strategies that maximize patient comfort, endurance, and overall function (Pomeranz et al., 2006).

Implications of Limb Loss or Dysfunction

Knowledge of the components of normal quadruped gait guides treatment of pathomechanical deficiencies (see Chapter 2). Quadrupeds who suffer loss of limb function or loss of limb are biomechanically distinct from bipeds with similar loss. Asymmetrical loading of the remaining limbs and functional deficiencies such as loss of plantar and palmar flexor power in propulsion have not been quantified in veterinary patients. Conversely, kinetic and kinematic compensations in human amputees have been extensively studied. Am­­putation causes disruption of the human mus­culoskeletal system resulting in asymmetrical biomechanics (Nolan & Lees, 2000; Nolan et al., 2003; Kent & Franklyn-Miller, 2011; Schoeman et al., 2011). Mechanical alterations of amputees have implications for mobility and for the long-term health of joints, muscles, and spine. Both human and veterinary patients develop compensations for functional deficiencies to maintain balance and locomotion (Prinsen et al., 2011). However, such compensatory movements are not necessarily efficient and frequently lead to short- and long-term complications.

The biomechanical implications of limb dysfunction or limb absence include intact limb breakdown and the development of pathology associated with myofascial tissue, joints, and spine by virtue of altered gait and structural support. In veterinary patients these pathologies lead to chronic pain, poor quality of life, and premature euthanasia. With these significant consequences in mind, alternative approaches such as subtotal or elective level amputation coupled with application of prostheses become more appealing. Human medical practice provides perspective: preservation of normal proximal limb segments is paramount and amputation higher than is absolutely necessary is untenable. A comparable example is the Symes’ amputation technique for the human foot (Shurr & Cook, 1990).

The structural consequences of a missing or non-weight-bearing thoracic limb in the veterinary patient have not been adequately characterized. The typical 60:40 weight distribution of the quadruped may significantly increase the severity of these consequences. Importantly, body condition and type become critical factors because obesity and heavy body type affect the thoracic limbs to a greater extent than the pelvic limbs. With loss of a single thoracic limb or limb segment the following compensatory adjustments may be seen during ambulation: ventral displacement of the head and neck during the weight-bearing phase of gait; explosive thrust of the neck, trunk, and remaining thoracic limb for propulsion of the cranial half of the body during the swing phase; medially displaced remaining thoracic limb, disproportionate percentage of body mass supported by this limb (>30%), and absorption of the full concussive force of landing; and kyphosis of the lumbar spine with ventral rotation of the pelvis about the sacrum as body mass is distributed over remaining three limbs (Figure 11.1).

Figure 11.1 Below carpus prosthesis for amelia of the right thoracic limb distal to the radius and ulna. The pathomechanical consequences of thoracic limb loss (A) can be mitigated with the use of a properly fitted prosthesis (B).

(Lower figure is derived from video.)

A missing or non-weight-bearing pelvic limb may have similar consequences with some unique aspects. During ambulation, the propulsive thrust of the caudal half of the body is dependent on a single pelvic limb and increased reliance on the spinal and core muscles to propel the body forward. Tail movement is altered for balance, the head is ventrally displaced altering the center of gravity, and body mass is shifted onto the forelimbs (>60%) (Figure 11.2). In many cases the pelvis is tilted to the side of the missing limb with concomitant rotation of the lumbar spine. Pelvic asymmetry alters spinal alignment and lumbar epaxial muscle tension. Hypermobility of the lumbar spine in the sagittal, frontal, and transverse planes may increase the potential for altered kinematics and back pain (Landman et al., 2004; Gomez-Alvarez et al., 2008).

Figure 11.2 Below tarsus prosthesis for traumatic tarso-metatarsal amputation. The pathomechanical consequences of pelvic limb loss (upper) can be mitigated with the use of a properly fitted prosthesis (lower).

(Figures are derived from videos.)

Orthoses

Splinting and bracing are described as passive immobilization to rest a limb segment in a fixed position (Heijnen et al., 1997). In contrast, an orthosis is any medical device attached to the body to support, align, position, prevent or correct deformity, assist weak muscles, or improve function (Deshales, 2002). These dynamic devices provide protected motion within a controlled range, prevent or reduce severity of injury, prevent or relieve contracture, allow lax ligaments and joint capsules to shorten and approach normal distensibilty, and provide functional stability for an unstable limb segment (American Academy of Orthopaedic Surgeons, 1987; Prokop, 2006) (Figure 11.3).

Figure 11.3 Bilateral double articulating carpus/paw orthoses stabilize biplanar carpal instability (hyper-extension of the radiocarpal joint and valgus due to medial collateral ligament injury). With proper rehabilitation a normal trot can be achieved.

Surgical management of many orthopedic conditions in veterinary species remains the standard of care and the preferred therapeutic choice. The term coaptation refers to approximation and involves transmitting compressive or corrective forces through skin to the boney structures beneath. Custom external coaptation can be used to provide security before surgical repair and help prevent wounds or surgical failures caused by splinting, wet bandages, splint material fatigue/breakdown, and lack of patient tolerance of a splint. As a general rule, molded external coaptation devices (custom) are more efficient stabilizers of bones and joints than are premade devices (Piermattei et al., 2006). In closely approximating the patient’s individual topography and dispersing corrective forces over a larger surface area fewer soft tissue problems arise, and custom devices are better tolerated (Piermattei et al., 2006).

At the same time and for a variety reasons including financial, personal preference, advanced patient age, perceived increased anesthetic risk, comorbidities, or circumstances requiring a delay of surgery, a number of patients are not surgical candidates. Until recently, veterinarians had no viable option for these patients. V-OP provides choices using customized, articulated (as needed), external coaptation in the pre- or postoperative periods, as well as in lieu of surgical intervention (Table 11.1). Rehabilitation for these nonsurgical patients is as critical to successful outcomes as it is for surgical patients (Figure 11.4 and Figure 11.5).

Table 11.1 Orthopedic conditions amenable to veterinary orthotic devices

Figure 11.4 Use of the physioball to encourage stretch, balance, and proper weight bearing in a dog with moderate carpo-metacarpal hyperextension.

Figure 11.5 Orthosis for stabilization of the cranial cruciate deficient stifle. Rehabilitation is similar to that required for post surgical patients. This dog demonstrates proper weight bearing and balance at the walk.

Prosthetics

In general, it is advantageous to reestablish a normal quadruped structure whenever possible. Fortunately, veterinary patients are amenable to prosthetic limbs and adapt readily especially when coupled with prosthetic-specific rehabilitation (Figure 11.6). Congenital defects and traumatic injuries can be successfully managed with custom prostheses. In the case of distal limb pathology such as neoplasia, necrosis, or nonunion fractures, careful surgical planning provides the opportunity to preserve the functional proximal limb segments. So-called elective level or subtotal amputation is preferable therapy to traditional total limb amputation.

Figure 11.6 Dogs acclimate well to prosthetics as seen in this quad-prosthetic patient whose limbs were severely damaged by frostbite-induced vasculitis and necrosis at 6 weeks of age.

At the time of this writing, to suspend a prosthetic on the thoracic limb, preservation of 40% of the radius and ulna is required; for the pelvic limb the medial and lateral malleoli must be preserved at minimum. Technological advances such as osteointegration and implantable bone topographical segments may alter these level limits in the future. The tremendous variability in veterinary patients requires adaptability in socket design, components, and mechanics to accommodate differences in injury level, body type and condition, species, breed, size, lifestyle, sport/activity, and terrain (Table 11.2).

Table 11.2 Orthopedic conditions amenable to veterinary prosthetic devices

The use of prosthetics and prosthetic-specific rehabilitation can improve functional outcomes and quality of life by guiding intact and prosthetic limb use. Rehabilitation goals include acclimatization to the device, balance and proprioception training, core and appendicular strengthening, gait reeducation, and overcoming compensatory pathomechanics.

V-OP Evaluation, Objectives, and Goal Setting

V-OP patient evaluation is comprehensive including five distinct examinations: general wellness, orthopedic (skeletal/joint), myofascial (muscle), biomechanical (how joints and muscles work together), and neurologic. The purpose of the evaluation is to fully define

• Injury or deficit
  
• Functional and mechanical impairment and implications
  
• Comorbidities or complicators
  
• Lifestyle, environment, family dynamic, sport or activity.

Steps taken during assessment include

Specific therapeutic goals (mechanical and physical) must be established based on client goals and evaluation findings. Goals must be aligned with device functionality, purpose, and intended outcome (i.e., short- or long-term device use). Device design is predicated on the evaluation and these goals. Therefore, this information must be clearly communicated to the V-OP fabrication lab. Custom devices are fabricated from a cast mold of the affected limb. Proper casting and device design are beyond the scope of this chapter. However, it should be noted that the quality of the mold along with clear information regarding the case as noted above dictate the fit and functionality of the device. The best outcomes are achieved with close communication between the owner, the referring veterinarian, the V-OP specialist, and a certified rehabilitation professional.

Device delivery and follow-up appointments are needed to ensure proper fit and function and should include

Rehabilitation of the V-OP patient requires diagnosis; assessment; prognosis; a goal-oriented, device-specific treatment plan; and outcomes measurement to determine efficacy of the plan. Veterinary orthoses and prostheses are considered durable medical devices. As such they should never be prescribed or dispensed without client training and a comprehensive follow-up plan. V-OP patients should be assessed at least annually. Device adjustment and refurbishment are expected in order to continue meeting therapeutic goals.

Improving Independent Functional Performance Through the Use of Braces, Splints, Assistive Devices, and Environmental Modifications

Measuring Functional Independence

For an injured or otherwise compromised pet, limited functional independence may be restored with the use of braces, splints, assistive aids, and/or environmental modifications. To determine which device or modification will yield the great­­est success, functional outcomes can be mea­­sured in various ways. Several scales have been adapted from human rehabilitative medicine to assess a pet’s functional gains and prognosis. One such scale is the Functional Independence Measure (FIM^®; Uniform Data System for Medical Rehabilitation).

The FIM is the most widely utilized functional performance assessment tool in human reha­bilitation settings (Jensen et al., 2005). The FIM measures the patient’s ability to independently perform everyday tasks—Activities of Daily Living (ADLs)—and purposeful activities—Instrumental Activities of Daily Living (IADLs). In dogs, ADLs include basic transitions (e.g., sit-to-stand), ambulation, toileting, and eating, while IADLs include purposeful tasks such as stair-climbing, transitioning to and from a vehicle, play, and those related to service, sport, and work.

The FIM and its supplements, rate ADLs and IADLs on a 7-point scale ranging from “fully dependent” (1) to “independent with no aids” (7) (Table 11.3). These scales help to determine the level of assistance the animal requires and they help define the roles of the caretaker. Braces, splints, assistive aids, and environmental modifications can graduate a fully dependent animal to one that that needs only minimal assistance (e.g., with orthosis, patient bears weight > 75% time with minimal tactile cues) or is independent with modifications (e.g., with ramp, patient can access the home independently).

Table 11.3 Functional Independence Measure (FIM) 7-point scale rating system

Uniform Data System for Medical Rehabilitation (UDSMR) (1993). Guide for the uniform data set for medical rehabilitation. Buffalo, NY: UB Foundation Activities.

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