I wrote a research article on prosthetic devices for companion animals (particularly cats and dogs), and discussed my findings. The topics include the biomechanics of movement and prosthetic treatment options. Below is the paper, as well as references at the end:

Prosthetic Limbs in Companion Animals

Jacqueline Chang

Simple Summary: In veterinary medicine, the use of prosthetic devices are a relatively new alternative to total limb amputations in companion animals. Some of the most common reasons for limb amputation include trauma and neoplasia. Limb amputation in companion animals remains a controversial topic between veterinarians and owners as some believe that quadrupeds can adapt well to tripedal life, while others argue that there can be negative long-term effects resulting from the loss of a limb due to the difference in body weight distribution across the cranial and caudal aspects of an animal (with approximately 60% of their body weight on the forelimbs and 40% on their hindlimbs). The consequences of limb loss are presented as changes in ground reaction forces. Though initially reluctant to pursue limb amputation and prosthesis use, most owners reported that their pet’s recovery and acceptance of the device were better than they expected. This review discusses the use of socket-based prostheses and intraosseous transcutaneous amputation prostheses in companion animals, including the advantages and disadvantages, associated costs, success of the procedure and device, and return to baseline functions.

Abstract: The use of prosthetic devices in companion animals can reduce the negative consequences of long-term tripedal ambulation, improving the quality of life of these animals. The loss of a limb or limb segment can lead to a number of issues, such as limited mobility and endurance, weight gain, breakdown of the support limb, and premature euthanasia. Despite the potential concerns, owners were hesitant to pursue limb amputation surgery because they were worried about reduced mobility, reduced quality of life, and pain associated with the surgery, among other reasons. However, owner-based surveys showed that their pets recovered quickly following surgery and adapted well to the use of a prosthetic device, reporting a high quality of life in the animals. This review examines the currently available information on veterinary socket-based prostheses and intraosseous transcutaneous amputation prostheses and the success of its use in companion animals.

Keywords: amputation, artificial limb, prosthesis, osseointegration, dogs, cats

1. Introduction

Consequences of a lost limb or limb segment can include limited mobility and endurance, increase in metabolic demand, weight gain, breakdown of the support limb, chronic neck and back pain, and premature euthanasia [1]. There are many reasons for why an animal may require a limb amputation, but owners can be hesitant to pursue the surgery due to their concern for the well-being of their pet following the procedure (i.e. adapting to tripedal locomotion) [2, 3]. A custom prosthetic device can be used to replace the missing limb and re-establish a normal quadruped structure in these animals. Veterinary prosthetics and orthotics is still a relatively new technology; as such, there is a limited amount of information available regarding socket-based prostheses and intraosseous transcutaneous amputation prostheses in companion animals.

It has been suggested that the use of a prosthesis improves the quality of life by preventing the development of secondary musculoskeletal diseases that could have arisen from continual tripedal locomotion by restoring the lost limb segment [4]. While there are concerns regarding acceptance and habituation of the device in companion animals, Wendland et al (2019) found success in dogs adapting to the use of a prosthetic leg, with these dogs spending up to 15-18 hours per day for a median of 7 days a week in their prostheses. Jarrell et al (2018) observed prosthesis use in cats for standing, walking, and jumping. Eighty three percent of owners in a study reported a good to excellent quality of life for their pet following the use of a prosthetic device compared to their quality of life prior to receipt of a prosthesis [4].

An underreported aspect of prostheses is on associated costs. Mich (2014) claimed that the typical veterinary prosthetic device costs $600-$1000 on average (not including appointments for fitting and modifications). Walfield et al (2017) believes that intraosseous transcutaneous amputation prostheses can be a more expensive option due to their complexity. However, differences in the materials and design of the prosthesis can affect the price of the device. With advancements in medical technologies, the cost of producing a prosthesis may decrease with time.

2. Biomechanics of Movement

It is currently unknown whether the mechanisms used for compensation of the lost limb in tripedalism will contribute to the incidence of later musculoskeletal or joint complications [7, 8], though it is thought that the resulting change in gait from the amputation of a limb may cause an increased incidence of orthopaedic diseases in the remaining intact limbs [9]. Recent kinetic and kinematic analyses of dogs with total forelimb or hindlimb amputations were shown to have significant changes in the biomechanics of their gait as compared to normal dogs, suggesting negative effects on long-term musculoskeletal health and other aspects of quality of life [10]. It is to the animal’s advantage to re-establish quadrupedal structure whenever possible [11]. Amputation of more than one limb has been shown to result in diminishing quality of life, and thus, is not often performed [12].

2.1. Body Weight Distribution

The body weight of a dog is not equally distributed between its forelimbs and hindlimbs; the forelimbs support approximately 60% of their body weight and 40% on the hindlimbs (or 63:37, respectively, according to Griffin et al and 59.8:40.2, respectively, according to Kano et al) when standing and walking [3, 6, 9, 11, 15, 16, 17, 18]. Theoretically, this means that the dog’s center of gravity is three fifths of the distance between the forelimbs and hindlimbs [9]. Dogs compensate for the loss of a limb by shifting their weight to the remaining limbs [9, 17].

2.2. Functions of Digits and Limbs

Digits three and four are the primary weight bearing digits of the paw [19, 20]. Loss of one of these digits is tolerated but results in a functional disturbance in ambulation due to splaying of the second and fifth digits (causing increased weight bearing stress on the interposing tissues) and can cause long-term complications [19, 20]. Digits one, two, and five bear only small amounts of weight [19, 20]. Amputation of one of these digits result in less severe complications than amputation of the primary weight bearing digits [19, 20]. Loss of more than one digit (particularly if the loss includes digits three or four) causes more functional disturbance than the loss of a single digit [20]. In cases where the second and third or fourth and fifth digits are amputated, the paw rolls towards the site of the amputation, causing an increase in weight bearing stress, ulceration, and pain [19].

The forelimbs of cats and dogs function differently in weight-bearing and locomotion as compared to the hindlimbs [3, 15, 21]. The forelimbs have a greater contribution towards braking (e.g. shock absorbance, slowing of the animal), whereas the hindlimbs contribute highly towards propulsion (e.g. maintaining momentum, propelling the animal forward) [3, 6, 15, 17, 21]. Ground reaction forces between cats and dogs are similar [21]. According to Corbee et al (2014), the forelimbs of cats spent 57% of the stance phase braking and 43% of the stance phase in propulsive phase. Similarly, in dogs, the braking phase is longer in the forelimbs and the propulsive phase is longer in the hindlimbs; the forelimbs spent 55% of their ground contact time braking as compared to 40% for the hindlimbs and generated a greater peak braking force (~75% of the total braking impulse), as well as a greater peak propulsive force (50% of the total propulsive impulse) compared to the hindlimbs [13, 21]. Compared with dogs, cats were found to have a higher peak vertical force during the propulsion phase (cat 3.89 N/kg; dog 3.03 N/kg) and a higher hindlimb propulsive force (cat -1.08 N/kg; dog -0.87 N/kg) and hindlimb impulse (cat -0.18 N/kg; dog -0.14 N/kg) [21]. As well, cats had medially directed motion (whereas dogs did not) and cats had less laterally directed motion [21]. Dogs walk in straight lines (putting their hind paw behind the ipsilateral forepaw), starting supination during the swing phase, whereas cats have a stilted gait (more flexion of the stifle and tibio-tarsal joints) and ended their stance phase by beginning supination, just starting to pronate prior to the stance phase [21]. Corbee et al (2014) noted pronation and supination in the cat to be minimal in the hindlimbs. This crouched gait of cats requires more propulsive force than that of dogs, particularly in the hindlimbs [21]. Due to the constant changes in the body’s acceleration throughout the gait cycle, maintaining balance, speed, and the trajectory of the body requires an equilibrium of the external work done on the center of mass by the limbs during a stride [17]. In normal dogs, the diagonal limb pairs exert forces in unison during trotting, meaning that the forelimb and hindimb of the supporting pair can exert forces to rotate the body or prevent the rotation of the body [17]. In amputees, however, the opposing force of one support pair is lost and must be compensated through altering the force exerted by the remaining limb of the support pair, altering the forces exerted by the unaffected pair of limbs, or a combination of these two strategies [17].

Forelimb amputations can lead to difficulties associated with walking and running, climbing inclines (e.g. stairs), difficulties urinating and defecating, and can result in a seroma (an accumulation of fluid at the surgical site), causing tissue infection and possibly tissue necrosis, preventing proper healing and the potential need for a follow-up surgery [6]. Amputation of a forelimb results in greater changes in the remaining contralateral limb compared to a hindlimb amputation as it results in the remaining forelimb bearing a larger load than prior to amputation [2, 9, 10, 11, 16, 22]. Kaufman and Mich (2014) found that the remaining forelimb supported >30% of the body weight. In a study of large breed dogs, it was found that 46.9% of the bodyweight was carried on the remaining forelimb and 53.1% (combined) was carried on the hindlimbs (compared to a normal distribution of approximately 60:40, respectively) [9, 14]. The total stance time was significantly decreased and the contact times for braking and propulsion were drastically changed in the remaining forelimb [9]. Jarvis et al (2013) found a 14% increase in weight distribution on the remaining forelimb and 17% (total) increase on the hindlimbs. As well, the remaining forelimb and hindlimb ipsilateral to the lost limb had a significantly increased braking ground force, whereas the ipsilateral hindlimb had a significantly increased propulsive ground reaction force [23]. In order to compensate for the loss of a forelimb, dogs take longer braking with the remaining forelimb [9]. The tarsal joint of the remaining pelvic limb had a significantly increased range of motion, which may have relation to clinical findings of abnormalities in the remaining stifle or hip joints in the hindlimbs in order to reduce discomfort [18]. Dogs with forelimb amputations changed the pattern of their walk more than dogs with hindlimb amputations [9]. Kaufman and Mich (2014) reported ventral displacement of the head and neck during the weight-bearing phase of the gait cycle, and propulsion of the cranial half of the body during the swing phase. Kirpensteijn et al (2000) noted that these dogs significantly decreased the time they loaded the limbs without increasing their velocity of the leg movement, resulting in an increase in the rhythm of the leg movement. Unlike normal dogs, forelimb amputees did not find a significant increase in peak vertical force or vertical impulse, however, the peak braking forces and impulses of the hindlimbs decrease significantly [9]. It is suggested that these dogs are not using their hindlimbs to compensate in braking force and impulse from the loss of a forelimb; the propulsive forces on both the contralateral limbs decreased to be similar in total to the forces on the remaining ipsilateral hindlimb [5, 9].

The loss of a hindlimb is thought to have a negative effect on balance and locomotion due to increased weight bearing on the remaining hindlimb and increased vertebral range of motion to support balance and propulsion of the remaining hindlimb, though hindlimb amputations often have less impact than forelimb amputations as the animal can more easily shift the hindlimb towards the center of the body [6, 18]. Kirpensteijn et al (2000) determined that the remaining hindlimb supported 26% of the body weight and 37% in each forelimb [18], while Fuchs et al (2014) found that the forelimbs and the remaining hindlimb supported an average of 33% body weight each. Dogs will bend the vertebral column laterally to shift the placement of the remaining hindlimb closer to the ipsilateral forelimb [11, 18]. This results in a greater proportion of the body weight (>60%) shifted onto the forelimbs and may increase the chances of altered kinematics and back pain [11]. The time it took to reach the maximum braking force was significantly shorter for the remaining hindlimb and significantly longer for both forelimbs as compared to normal dogs, but the braking and propulsive times did not differ significantly between hindlimb amputees and normal dogs [9]. As the remaining hindlimb now has to support a greater proportion of the body weight, knee extensors such as the M. vastus lateralis significantly increase their activity to prevent excessive knee flexion and to compensate for losses in propulsive forces [24]. With the loss of a hindlimb, contralateral limb support for one of the thoracic limbs is lost, therefore, there needs to be sufficient compensation in the limb or spine to maintain balance and core stability [11, 18]. Hogy et al (2013) noted that dogs with a hindlimb amputation move their head upwards during propulsion of the contralateral forelimb to elevate the body’s center of mass, then move their head downwards near the end of the swing phase and the start of the stance phase [17], while limiting the range of motion of the tail to maintain balance [11]. These trotting results from Hogy et al (2013) are similar to those of walking amputee dogs of another study wherein there was an increase in weight bearing of approximately 6% per limb. Though a decrease in stance duration is associated with increased velocity in normal dogs, the decreased stance duration in hindlimb amputees is a result of an increase in strides and not an increase in velocity [17, 18]. There was also a significant decrease in stride duration and an increase in relative stance times [17, 25]. The only significant change in limb kinematics was an increase in the range of motion of the tarsal joint of the remaining hindlimb, likely as a means to compensate for the increased weight bearing through maximizing the elastic recoil within the calcaneal tendon and other contributing muscles (e.g. the gastrocnemius muscle) [18]. Since other limb kinematics did not differ much, it is likely that dogs with a hindlimb amputation did not compensate for the loss of a limb through reliance on alterations in joint angular kinetic mechanisms, rather, they did so through changes in ground reaction forces and vertebral kinematics [18]. Fuchs et al (2014) found that vertical and craniocaudal forces were significantly different in the remaining hindlimb, whereas the propulsive force increased in the contralateral forelimb and decreased in the ipsilateral forelimb (with unchanged vertical forces). Compared to normal dogs (with comparable vertical forces of the two forelimbs and two hindlimbs), hindlimb amputees had significant increases in all vertical force parameters in the contralateral hindlimb [17]. The peak braking force was significantly increased in the ipsilateral forelimb but all propulsive forces decreased significantly [17]. In the contralateral forelimb, the peak and mean propulsive force significantly increased [17]. In both forelimbs, the time to peak braking force was significantly shorter [17]. In the contralateral hindlimb, all braking forces increased and the propulsive force was approximately double the propulsive force of quadrupedal trotting [17]. With the loss of a limb, alterations in the ground reaction forces, contact times of the remaining limbs, center of gravity, weight distribution, range of motion of joints, stance duration, and forces on the remaining limbs can be noted [7]. The changes to ground reaction forces and contact times of the remaining limbs suggest that there may be an increased degeneration of the remaining joints due to the change in weight bearing [8].

3. Causes of Limb Injury

In current veterinary medicine, the principle is to amputate the whole limb if a distal segment cannot be saved, leading to limited mobility, weight gain, break-down of an otherwise sound limb, chronic neck and back pain, and potentially premature euthanasia [5]. Amputation is a commonly performed and often well-tolerated procedure in small animal practice [7, 8, 12, 16, 22, 26]. The most common reasons for amputations in small animals include trauma and neoplasia (65% and 35%, respectively, by Adamson et al) [2, 4, 26]. In Kirpensteijn et al’s (1999) study, the main reasons for amputation were neoplasia, fractures, trauma-related causes, post-surgical infections, followed by other reasons. Other reasons include peripheral neuropathies, incomplete limb development, infection, deformities, neurological injury, vascular compromise, disabilities from degenerative or congenital processes, arthritis, ischaemic necrosis, and irrevocable discomfort [2, 3, 4, 7, 8, 12, 16, 22, 25, 26, 27]. Osteosarcomas from the medullary bone are the most common form of skeletal neoplasia in dogs, cats, and humans [28]. Turrel (1982) reported that osteosarcoma affected the hindlimbs of cats 1.6 times more often that the forelimbs, whereas in dogs, osteosarcoma affects the forelimbs more frequently. In both cats and dogs, osteosarcoma had a higher incidence in males [28]. Limb amputation is the most promising method to treat primary bone and joint tumors in cats and dogs [27, 28]. The decision to amputate a limb may also take into account a poor prognosis or financial limitations [2]. In Forster et al’s (2010) study, the most common reasons for amputations in cats were broken bones (59.3%), nerve damage (24%), and other traumatic causes (12.7%). There was no significant difference in the reasons for amputation in male cats compared to female cats, but nerve damage was significantly more common in younger cats compared to older cats, masses and tumours were significantly more common in older cats, and the incidence of neoplasia was more common with an increase in age [2]. Unsupervised free-roaming outdoor access to cats increases the risk of vehicular collisions that can lead to traumatic injury (e.g. lesions, rupture or displacement of internal organs, hemorrhaging, broken bones causing discomfort, pain, and consequences in the long term) or death [29]. In the United Kingdom, a study on the impact of automobile accidents showed that 27 out of 127 (21.3%) cats were dead on arrival at the hospital or died subsequently to the hospital visit, and 25 of the 127 (19.7%) cats developed severe injuries that resulted in long-term issues (e.g. limb amputations, ongoing bladder problems, ruptured diaphragms) [29]. Automobile accidents resulted in three times more injuries to the hindlimbs than the forelimbs; it was noted by Forster et al (2010) that the amount of trauma necessary to cause fracture in a limb was associated with significant forelimb trauma in 22% of cats with forelimb fractures as compared to 13% in cats with hindlimb fractures. Other reasons for paw and limb wounds include tumour removal, snake and insect bites, leg hold trap injuries, burns, gunshot wounds, and wounds resulting from interactions with other animals [19]. Full or partial amputation of the paw are common secondary to degloving, strangulation, crushing, bandaging, or gunshot injuries [19].

4. Prosthetic Treatment

4.1. Socket-Based Prostheses

Socket-based prostheses (also called external prostheses or prostheses) are external devices used in most instances to replace the loss of a limb segment in order to enable locomotion [30, 31]. The residual limb rests within a socket of the prosthesis and contacts the ground through a shank and foot or paw [1]. The device is fabricated using casts of the affected limb and limb contralateral to the affected limb [4, 32]. The socket or contact layer (layer of the prosthesis that contacts the skin) often consists of a silicone liner, urethane, or foam adhering to the shell and can be secured to the shell with locking pins or simply through friction within the shell [10, 32]. The suspension and retention of the device through suction of the residual limb, or a harness, dictates the success of socket-based prostheses [1, 10, 27]. The shell of the pylon or shank provides structural support to the prosthesis [10]. The shell of most prostheses are made of thermomoldable plastic, fiberglass, or carbon fiber [32]. Thermoplastics are the cheapest of the materials but fiberglass or carbon fiber may be more suitable for large patients as they are stronger and stiffer in comparison [32]. The component of the prosthesis that contacts the ground is called the ground contact device [10]. Often, this surface is rounded and made of a lightweight, wear-resistant, non-skid rubber with varying stiffness, specific to the patient’s needs [31, 32]. Hook and loop fasteners are used most frequently for the fixation of a prosthetic device [31]. The straps need to be wide enough and the prosthesis should have multiple straps (at the upper and lower antebrachium, and across the manus) to avoid “buckling” of the limb [31].

Stability when using a prosthetic device is key in the success of a prosthesis [31]. It is likely that the longer the residual limb is, the better the stability of the prosthesis will be and the less likely there will be skin breakdown [32]. Ideally, patients should have a functioning shoulder and elbow joint or hip and stifle joint [31]. The stability of a prosthesis can be defined as axial, angular and torsional [31, 32]. According to Marcellin-Little et al (2015), stability should be axial in traction and compression; angular in medial, lateral, cranio, and caudal bending; and rotational in internal and external rotations. Axial stability is the displacement of the prosthesis along the long axis of the limb, dictated by the shape of the bone and surrounding soft tissues, as well as skin mobility relevant to underlying soft tissues [32]. Axial stability relies on the success of locking the prosthesis in place through the presence of bony prominences, creating suspension [32]. Companion animals generally have a more difficult time creating the locking mechanism due to having more discrete bony prominences than humans [32]. Angular stability is defined by the lack of movement of the prosthetic device relative to the residual limb when mediolateral and craniocaudal forces are applied [32]. Often, the longer the residual limb is, the better the angular stability is [1, 4, 32]. As such, preservation of at least 50% of the limb for the application of a prosthesis is recommended [1]. Kaufman and Mich (2014) required a 40% preservation of the forelimb (radius and ulna) or hindlimb (tibia and fibula) in order to successfully suspend a prosthetic device on the stump. Torsional stability is defined as the lack of movement of the prosthesis relative to the residual limb when internal or external torsion is applied to it [32]. A limb segment with a smaller diameter and rounder shape can decrease the torsional stability, particularly in the antebrachium [32]. The axial and torsional stability of prostheses are drastically improved when the prosthetic device passes over a joint (i.e. the hock, stifle, or elbow joint) and can be accomplished by adding hinges over the center of rotation of the joint [31, 32]. Passive hinges are often made of nylon with varying sizes and stiffness with softer passive hinges being more suitable for smaller patients and stiffer passive hinges for larger patients [31]. While the addition of hinges will make the device more costly and complex, it can also greatly enhance limb function of the patient [32].

An advantage to socket-based prostheses is the relative affordability, simplicity of application (no requirement for additional surgery), and adaptability to different levels of limb losses [1, 8]. The use of these devices may improve the quality of life of the animal [30]. Though animals were originally believed to adapt well to a tripedal gait [10], socket-based prostheses are a growing aspect of companion animal medicine and can be considered as an alternative to full-limb amputation or euthanasia [4, 30, 31].

4.2. Intraosseous Transcutaneous Amputation Prostheses

Intraosseous transcutaneous amputation prostheses (ITAP, also called osseointragration or osteointegration) requires the surgical implantation of a (metallic) prosthetic device into the bone and allowing for ingrowth into or outgrowth onto the prosthesis over the span of three to six months [1, 10, 12]. It is recommended by Mich (2014) that at least 50% of the limb is preserved, but ITAP can be performed in nearly every level of distal joint as well as transtibial and transradial levels. Kaufman and Mich (2014) required 40% of the limb to be preserved for socket-based prosthetic devices but noted that the limits of these levels could be altered with technological advancements in ITAP. The implant is attached to the marrow cavity and protrudes through the skin [12, 33]. Afterwards, an exoprosthesis is attached to the implant [1]. The metallic implant is often made of a titanium and a porous collar [12, 33]. Drygas et al’s (2008) study used a porous tantalum collar which is 80% porous and has been proven to be both osteoconductive and a conductor for soft tissue ingrowth. The high strength to width ratio and low elasticity of porous tantalum metal encourages bone ingrowth and the porosity decreases infection as compared to a denser material [12]. The pore size has an association with the strength of the attachment of implant to soft tissue, with an increase in strength seen with increasing pore size [12].

With direct skeletal integration of the implant, there is no mechanical delay in gait as the forces are directly transmitted from the exoprosthesis to the implant [1, 5, 8, 27]. ITAP has potential benefits for small animals with bilateral amputations, or in patients with unsuitable skin conditions for socket-based prostheses [10]. ITAP is also reported to be more comfortable with less stump-socket interface issues, have greater range of motion, and results in less soft tissue trauma [1, 5, 8, 34]. However, some of the issues noted with ITAP include fracture, infection, skin breakdown, and aseptic loosening, as well as prolonged recovery from the implant surgery [8].

4.3. Costs

The costs associated with prosthetic devices in companion animals is underreported. Fitzpatrick et al (2011) reported that single-limb amputations in dogs are inexpensive and can be completed without specialized training or instruments. Pre-anesthetic medications (i.e. 0.1 mg/kg intramuscular diazepam and 0.05 mg/kg subcutaneous hydromorphone) were given and anesthesia was given intravenously (i.e. 0.1 mg/kg diazepam and 4 mg/kg propofol), maintained with isoflurane and oxygen [12]. In Farrell et al’s (2014) study, the pre-anesthetic medication given subcutaneously included 60-80 µg/kg dexmedetomidine, 10 mg/kg ketamine, and 10 mg/kg xylazine, and anesthesia was maintained with isoflurane inhalation (1-3%). During anesthetization, electrocardiogram, capnography, pulse oximetry, and indirect blood pressure was monitored [12]. For ITAP, postoperative radiographs were taken to ensure the proper position and alignment of the implant [12]. Animals received 48 hours of intensive care following the surgery [12]. Postoperative medications included 0.5 mg/kg hydromorphone for 24 hours (as needed), 2 µg/kg fentanyl patch, and 0.5 mg/kg oral carprofen twice a day for 14 days [12]. In Forster et al’s (2010) study, 89.1% of the responses from owners reported that analgesia was provided to their cat at home (postoperatively). Most of the cats were given a pain relief or anti-inflammatory drug, whereas very few of the cats were given an antidepressant or sedative drug [2]. Pain relief reported by Straw and Withrow (1996) included epidural morphine, systemic opioids, and fentanyl patches. Custom orthotic and prosthetic devices for animals varies by component and material choices, but average approximately $600-$1000, not including appointments to ensure the fit and function of the device [1]. The cost of ITAP can be more expensive as it is, as a whole, more complicated and requires more resources and manpower than a socket-based prosthesis [6]. Because the control of a limb with a prosthetic device is reversed (resulting in delayed feedback), rehabilitation for prosthesis patients is highly recommended to re-learn balance, different gaiting speeds, and ambulation over various terrains through increasing forelimb and hindlimb strength, increasing the range of motion and circulation, improve coordination, prevention and correction of contractures, and reduction of edema [1, 30]. Rehabilitation promotes the use of the device for ambulation and helps integrate the use of a prosthesis into the daily life of both the patient and the client [30].

Recently, the use of three-dimensional printers has been growing in veterinary medicine and will likely increase in use with experience and availability of the technology [36]. With three-dimensional printing, prosthetic devices are modeled on computer-aided design software applications [36]. Depending on the model of the printer, materials such as plastic, nylon, and metals can be used [36]. The printer model will also dictate the maximum size of the model that can be printed, time required to complete the print, and amount of detail that can be produced without processing [36]. Three-dimensional printing has also been used to help assess complications in the fit of intraosseous transcutaneous amputation prostheses [36]. With advancements in three-dimensional printing in a veterinary medical setting, prosthetic devices can be printed at a lower cost [6].

With the number of companion animals steadily increasing, and the bond between people and their pets ever-growing, owners are willing to spend more on the health and well-being of their animals. In 2015, over 1.6 million companion animals in the U.S. were covered by health insurance (by the North American Pet Health Insurance Association) [37]. The American Pet Products Association (2018) reported that approximately 68% of the U.S. households reported owning a companion animal with dogs and cats making up the largest percentage (roughly 44% of households containing dogs and 35% containing cats) [37, 38]. Since the year 1998, companion animal ownership has risen by 56%, and only continues to increase [37]. In 2011, 63.2% of pet owners reported that they consider their pets a member of the family [37, 38]. People are willing to spend money on their pet’s health care if they are closely bonded; according to AVMA, the average annual cost of veterinary care was $375 per household in 2011 [37].

4.4. Success of the Procedure

Although most veterinarians believe that animals adapt quickly to a limb amputation, many owners are still reluctant to pursue the surgery [7, 16, 17, 26].  Limb amputation is often the safest, least demanding, and most cost-effective treatment option for issues regarding limbs [16]. The most common concerns regarding limb amputation from owners include reduced mobility, cosmetic appearance, perceptions of reduced quality of life, owners’ guilt associated with limb amputation, and pain associated with the surgery [3, 16, 26]. Owners’ concerns may be amplified due to diseases such as osteosarcoma which are associated with a short survival time following amputation surgery [16]. As well, owner concerns could be linked to emotional, social, and financial aspects [17]. Many owners reject the amputation as an alternative to euthanasia or will only accept limb amputation surgery after other grueling surgical or medical treatments [26]. Results of surveys evaluating owner satisfaction after limb amputation showed that pet owners were very satisfied with the outcome of the surgery [3, 16, 25]. More than three quarters of owners in Dickerson et al’s (2015) study reported that their dog’s surgical recovery and adaptation to tripedal ambulation were better than they expected [3], and 75% of the owners reported that their dog adapted to tripedal ambulation better than they had expected in Forster et al’s (2010) study.

Forster et al (2010) reported that although 93% of dogs that underwent limb amputation surgery adapted well, owners noticed behavioural changes (e.g. 32% dogs showed increased aggression, submissiveness or nervousness in the presence of other dogs). Dickerson et al (2015) and Kirpensteijn et al (1999) reported signs of aggression, anxiety, decrease in dominance, and decreased interest in other dogs. As well, a third of the cats were thought to be in pain following discharge [2]. However, almost all owners still reported that they would make the same decision (to pursue limb amputation surgery) again given similar circumstances [2]. Some owners expressed that they would have preferred to have limb amputation surgery earlier in their cat had they known how well their cat would have adapted, as opposed to attempting to repair the fracture [2].

Age and size of the animal were determined to be factors that were not associated with delayed recovery in limb amputation surgeries, nor did it have an effect whether the amputation was on a forelimb or hindlimb [16]. Contraindications to limb amputations include extreme obesity and coexisting orthopedic or neurologic diseases [16]. The reason most frequently reported for lack of a full recovery from limb amputation surgery were difficulty with mobility and decreased stamina [16]. Forster et al (2010) reported that 10% of the cats were reported by the owners to have not returned to a “normal” quality of life. Lower quality of life scores were significantly correlated with higher body weight which was correlated with a higher body condition score [16]. There was no correlation found between quality of life scores and the age at which the surgery was performed [16]. Common complications that may arise from prosthesis use include a poor fit, pressure necrosis, pain, ulceration, and loss of mechanical integrity, all of which can lead to prosthesis failure and disease in the remaining limb [12]. These issues can result in the inability to ambulate until they are resolved, decreasing the quality of life of the patient [12].

4.5. Acceptance of the Device

It was reported in an owner-survey based study that 87.5% of patients had the same or improved quality of life following the receipt of a prosthetic device, and owners in another study reported that 83.3% of the animals had a good to excellent quality of life following the use of a prosthesis [4]. On a scale of one to five (with one being very poor quality of life and five being full recovery to pre-amputation quality of life), 67% of owners in Dickerson et al’s (2015) study reported a score of 5, 20% reported a score of 4, 8% reported a score of 3, 2% reported a score of 2, and 3% reported a score of 1. The three dogs of owners that reported a score of 1 and 2 were euthanized within three months following the surgery due to metastatic neoplasia (in two of the dogs) and unspecified reasons (in one of the dogs) [16].

Two cats in Farrell et al’s (2014) study received ITAP and it was noted that the animals loaded the prosthesis less than the intact right hindlimb prior to implantation (and other intact limbs after surgery). Both cats were able to walk stably at normal speeds with the prosthetic limb [33]. While walking, the peak vertical force on the hindlimb was 43% and 52% (of the body weight of cat 1 and cat 2, respectively) whereas it decreased to 33% and 20% on the prosthesis after surgery (or 78% and 38% on the same hindlimb prior to surgery) [33]. The loads on the prosthetic limb during walking decreased by 22% and 62% respectively (4 months after implantation) [33]. The vertical loading of the left contralateral pair of limbs increased above forces in normal animals, whereas the vertical loading of the right ipsilateral forelimb remained similar [33]. The left hindlimb increased in peak vertical loading (13% and 17% body weight in cat 1 and cat 2, respectively) [33]. There was an increase in the propulsive force of the left hindlimb and decrease in breaking forces of the other two intact limbs for both cats, helping them both maintain normal walking speeds; these load analyses suggest that the cats shifted their body weight to the contralateral side [33].

4.6. Return to Normal Function and Walking

In Dickerson et al’s (2015) study, the median time from surgery to discharge from the hospital was three days (ranging from one to 17 days). This was not significantly impacted by whether the dog underwent forelimb versus hindlimb amputation [16]. Seventy three percent of the owners reported that their dogs were able to walk without any support at the time of discharge from the hospital, with the remaining dogs requiring up to three weeks after discharge [16]. There were no significant differences in age, body weight, or body condition score between the dogs that were able to walk without assistance at discharge and those that were not able to, and there was no significant difference in dogs that had a forelimb versus hindlimb amputation [16]. Sixty nine percent of the owners reported that their dog walked unchanged on or off a leash following amputation, as compared to prior to surgery [16]. This was not significantly affected by whether the amputated limb was a forelimb or hindlimb [16]. Forty seven percent of owners reported that their dog was able to enjoy their regular recreational activities (e.g. swimming, agility training, flyball, hiking, and playing in the park) [16]. Sixty one percent of the owners reported that there was no change to the dog’s stamina during exercise, and 38% reported only a slight decrease in stamina [16]. Fifty eight percent of owners reported that their dog had no change in the ability to maneuver stairs, and 33% reported only a slight decrease [16]. Seventy seven percent of owners reported being able to return to normal walking routines following amputation [16].

5. Conclusion

Prosthetic devices are a novel innovation that can be considered when limb amputation is required in an animal. Proper design and use of a prosthesis can improve the quality of the lives of these animals, and can potentially prevent further consequences of tripedal ambulation relating to altered weight distribution. As with any medical procedure, there are risks associated with limb amputation surgery and prosthesis use in contraindicated patients. However, it currently seems as though the majority of animals benefit from this technology. Recently, three-dimensional printing technology has been growing in the veterinary medical field and has been used to produce prosthetic devices for companion animals. The materials available are lightweight but strong (e.g. ABS plastic, carbon fiber, or fiberglass). These devices are often lower in cost and require less manpower for production. In addition, they allow for customization and modifications to be made simply through computer aided design software programs. However, further studies need to be conducted to assess the durability of these devices over time, and whether three-dimensional printing is an acceptable method for producing these devices. Further research is needed to determine whether socket-based prostheses and intraosseous transcutaneous amputation prostheses are suitable for general use in veterinary medicine as an alternative to total limb amputation.

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