OrthoPets Blog

June 2018 OrthoPets Case Study for the Canine Rehabilitation Institute: Kinley

Kinley is a 12-year-old lab that presents with chronic and severe degenerative changes of the right tarsus. Chronic ligament instability or a previous OCD lesion was ruled out. She has experienced progressive pain and weakness of the stifle and hip joints secondary to the tarsal pathology. A tarsal arthrodesis was not recommended due to the success rate and that she was responding well to the anti-inflammatories. The goals of the orthosis were to return the patient to his 3-mile-a-day walks as well as to avoid further injury or increase of current instabilities of the tarsus and stifle. 

The severity of tarsal instability concurrent with stifle involvement indicated a non-articulating tarsal orthosis with a paw segment coupled to a cranial femoral shell. The femoral shell added global support (multi-plane) to the stifle to reduce the likelihood of a CCL tear. Due to the complexity of the pathomechanics, several custom modifications were added to this unique case to provide Kinley the greatest amount of comfort and support. Kinley adapted to the orthosis quickly and a marked improvement was noted in her gait. With the added support and stability, Kinley was able to return to her 3-mile-a-day walks and was able to experience increased comfort and confidence during gait.

May 2018 OrthoPets Case Study for the Canine Rehabilitation Institute: Cowboy

Cowboy is a 1.5-year-old mixed breed who is a patient through our OrthoPets Michigan Partner Clinic, Pawsitive Steps Rehab and Therapy for Pets. He originally presented in July 2017 as a puppy for a number of issues, but the most severe was his congenital ectrodactyly of both forelimbs. Additionally, he presents with bilateral severe shoulder joint OCD. Cowboy originally saw a number of different specialists around the Midwest who were unable to agree on a suitable surgical intervention or long-term care plan. Chief among these challenges are his age, predicted growth, and numerous deformities and orthopedic issues. Dr. Tari Kern and her staff met him and determined he could benefit from mechanical support to his forelimbs enabling Dr. Kern to focus on his other orthopedic issues. 

During his physical examination, his left forelimb demonstrated increased pain and discomfort. Once he was closer to skeletal maturity, he would be casted for a custom left carpal orthosis. His radiographs and his exam are quite interesting. Just distal to the carpus on the left thoracic limb, the paw is separated into 2 sections featuring the metacarpals separated from each other rather than united as a single structure. The paw is also separated into the 2nd digit and its phalanges and a grouped structure that includes 3rd/4th/5th digits. Cowboy started a rehabilitation program with Dr. Kern in the meantime and was scheduled for arthroscopy of both shoulders to make him as comfortable as possible. 

Top left: Cranial view of forelimb paws. Top right: Left forelimb extremity. Bottom: Left lateral forelimb extremity.

When Cowboy was 1, he returned to Dr. Kern for his V-OP evaluation and fiberglass impression of his left forelimb for his custom orthosis/prosthesis. One of the most important things to discuss with your clients when determining if an orthosis is the right thing for their pet is to review the “goals” for the use of the orthosis. It is very important to inform OrthoPets of the stated therapeutic goals that have been communicated to the client. In some cases, the client goal for the use of the device may not be something that is possible based on the diagnosis and history. In Cowboy’s case the clients and vet had 3 simple goals:

  • Provide support for L FL paw / carpus
  • Reduce discomfort
  • Improve quality of life

Once the goals have been listed and the fiberglass impression and measurements have been received at OrthoPets, Martin Kaufmann (OrthoPets owner/founder) and the OrthoPets case manager are able to take all of those things into consideration and determine the best V-OP plan for the device to meet those goals. OrthoPets utilizes the requested information and data for each patient to perform a comprehensive case review to develop a V-OP fabrication plan that is the most beneficial and useful device for that patient. You can take a look at this process in the video below. 

OrthoPets New Case Checklist

The device that was the best option for Cowboy was one that allowed us to corral the limb into one solid section via the use of a fully removable foam liner. This is one of our hybrid-style devices that is built similar to a prosthesis but has a paw segment and outer shell similar to an orthosis. Due to the severe deformity of the limb and an abnormal carpal joint along with the MCPJs, we were not able to articulate either the paw segment or the carpus segment. The shell of the device was a caudal style non-hinged device. Cowboy was fitted with his device recently and was quite comfortable even at the first fitting, and by the second follow-up visit, he was moving well and really learning to trust his device! 

Great job to Cowboy’s rehab team and his dedicated family for working so hard to keep him happy and healthy from the start!

Left: Standing, lateral view. Right: Cranial view.

April 2018 OrthoPets Case Study for the Canine Rehabilitation Institute: Sampson

Sampson is a 3-year-old Rottweiler who presented to an OrthoPets Partner Clinic for right hind limb lameness. He was diagnosed with a right cranial cruciate ligament tear and severe hip dysplasia. When surgery isn’t an option due to age, health, financial, or other reasons, OrthoPets can offer an alternative solution via a custom-made orthosis. 

Left: Sampson’s hips. Right: Good hips. Image credit: “Hip Dysplasia.” Orthopedic Foundation for Animals, www.ofa.org/diseases/hip-dysplasia.  

Patients with hip issues can be more of a challenge to create the fiberglass impression, as they can be more uncomfortable then other patients when standing for an extended period of time. There are a few options to aid patients to remain standing during the casting. To help make the impression process easier on the pet, we advise using towels or slings to aid in helping stand the patient up or positioning a yoga ball underneath their abdomen allowing the patient to lay over the ball. This position supports the patient while allowing access to the flank and groin areas. 

It was determined that a standard stifle orthosis would be the best option for Sampson due to his weight and therapeutic goals. OrthoPets utilizes a variety of mechanical hinges and chooses the appropriate set of hinges for the patient’s needs. The completed device was shipped to the OrthoPets Partner Clinic to fit the device properly and discuss the recommended wearing schedule with Sampson’s owners. 

Sampson has been wearing the device for a few weeks and has been able to go on walks again. In the beginning stages of device use, speak with your veterinarian about exercise restrictions. As your treatment plan progress, your veterinarian will guide you in how to restore activities safely. 

Left: Sampson, pre stifle device. Right: Sampson, post stifle device.

Sampson’s owner reports: “Sampson has been doing great! He loves the brace and it enables him to do all the things he loves to do! I’m so pleased that he can go for walks again and dispel his nervous energy!”

Veterinary Orthotics and Prosthetics (V-OP) in Small Animal Rehabilitation and Pain Management: Summary

There are many advantages afforded by orthoses and prostheses. Many injuries are amenable to these devices, and subtotal amputation provides a substitute for quality of life, altering total amputation. Simply put, V-OP devices offer treatment options where none existed before. For chronic or catastrophic injuries, they play an important role in pain management, and can significantly improve, comfort, quality of life, and functional independence as well as limit premature decisions to euthanize. In the severe case, these devices serve as safe alternatives to traditional casting and splinting while providing the opportunity to initiate rehabilitation earlier. Many patients can return to an active lifestyle, which can reduce the risk of obesity and its associated comorbidities. Secondary or compensatory pain can be minimized by correcting or improving gait mechanics and re- establishing quadruped locomotion.

With increasing numbers of fabricators and internet suppliers, veterinarians must educate themselves to advocate for their patients and clients. V-OP devices are valuable therapeutic tools. However, paraprofessionals cannot and should not prescribe and treat. In the absence of knowledgeable and supportive veterinarians, this is the risk and reality. Providing these solutions within the primary care practice is possible and appropriate.

Rehabilitation and V-OP: A Team Approach With a Precedent

Human patients receiving a prescription orthosis or prosthesis work with a physical therapist to learn how to use the device properly. There is a common misconception that orthoses are static, causing muscle atrophy, diminished joint range of motion, and dependence on the device. This is not true of modern dynamic orthoses. These devices are hinged and actually promote muscle development, normalize range of motion, and assist in balance and coordination by stabilizing an unstable limb segment. Rehabilitation provides the link between patient and device.

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Rehabilitation for a stifle orthosis includes gait re-education using
cavaletti poles.

Most veterinary patients adapt quickly, and behavioral techniques can facilitate this. Device-specific rehabilitation focuses on specific skills. Skills include transitions (sitting, lying down, and getting up), stairs, getting into and out of vehicles safely, managing on different types of surfaces (ground, carpet, hardwood floor, etc.), and managing dog doors. Orthopedic injury leads to compensatory abnormal movement and associated muscle strain and weakness. Gait re-education focuses on resolving these issues. The best way to ensure the highest level of success with a V-OP device is to follow a rehabilitation plan established by a certified canine rehabilitation professional (CCRT or CCRP). Each patient’s condition and abilities are unique, and as such, an individualized rehabilitation program is needed. Furthermore, although V-OP devices can get wet, water therapy (swimming and underwater treadmill) comprises a small component of the overall rehabilitation plan. Land- based therapeutic exercise is essential. Balance, proprioception, muscle timing (neuromuscular retraining) and coordination lay the foundation for proper device use; these must be mastered on land so that the patient can learn response to normal ground reaction forces and shifts in their total body force vectors. The buoyancy of water complicates such mastery and does not represent the patient’s home environment. Additionally, daily home exercises are an important part of the rehabilitation plan. Most clients do not have daily access to water therapies, thus practical land-based exercises make up the bulk of in home therapy.

As in the past for human physical therapists, OP is creating a new challenge for veterinary rehabilitation therapists: assistive device-specific rehabilitation. Animals are adaptive and will learn ways of ambulating in an orthosis or a prosthesis. This is not always the most efficient, safe, or functional method of ambulating. Therefore, using the human experience as a precedent, it is reasonable to suggest that veterinary patients are more likely to return to highest level function faster with professionally guided assistance. Veterinary patients present a seemingly endless variety of injury types and an exceptional drive to recover. For the creative rehabilitation therapist, this is an exciting area for professional growth.


The V-OP Evaluation, Fitting, and Assessment Processes

A V-OP patient evaluation must be thorough enough to provide a specific device prescription. It must take into account the entire patient from a mechanical and physiological perspective in addition to a clear understanding of the primary injury. The V-OP examination must fully define the presenting deficit, characterize biomechanical implications, identify complicators or comorbidities, and diagnose all primary and secondary pain generators. The examination should include a general wellness assessment in addition to orthopedic, myofascial, biomechanical, and neurologic examinations. Additionally, the case must be understood from the standpoint of lifestyle, environment, family dynamics, sport or activity, goals and intended outcome as defined by client and veterinarian, and alignment of goals with proposed orthotic or prosthetic device. The good news is that with the help of a qualified fabricator as noted previously, the general practitioner can succeed in providing V-OP devices.

Once a plan is developed and the device is designed, the next step in creating a custom orthosis or prosthesis is fiberglass impression molding of the limb. This step is critical for optimal fit and correct function of the device. Creating a precise replica of the limb in a thin layer of fiberglass tape requires a bit of artistic acumen and a clear sense of device purpose. This fiberglass impression is used to create a plaster model from which the custom device will be fabricated. Therefore, the limb must be molded in the properly aligned position. Just as a poorly positioned or exposed radiograph is less than adequate for accurate diagnosis, a poorly molded fiberglass impression is equally useless in fabricating the best device.

Manufacturing requires skilled modification of the model by hand or using computer-assisted design to build reliefs, which accommodate limb topography and create appropriate corrective forces when the completed device is applied to the limb. The modified model is the structure on which a thermoplastic shell is vacuum formed. The shell is then hand cut, trimmed, and ground to the final shape. Materials used to pad and line the shell vary. Hinges, straps, pads, and motion-limiting components complete fabrication. The typical custom V-OP device cost varies with components and materials and averages $600-$1000. This does not include the necessary appointments to ensure proper fit and function along with client education.

An important advantage to veterinarian-guided use of a V-OP device is fit and function assessment and adjustment. Adjustments are expected and are a normal part of the custom process. Reputable custom fabricators strive to accurately fit the device; however, variations in injury severity, gaiting pattern, and level and intensity of activity all affect the accuracy of initial fit and cannot be predicted in all cases. Couple this with a dynamic process such as Achilles tendon therapy and the necessity for adjustability is clear. Pressure and friction irritation are the most common reasons for adjustment followed by the natural progression of the case. Fortunately, with a removable device, such issues are quickly recognized and corrected; this is an advantage over casts and splints that are changed weekly at best.

Orthoses and prostheses are considered “durable medical devices.” This means that proper use is necessary to meet therapeutic goals and to ensure safe application over the lifetime of the patient or the duration of injury healing. Typically, several follow-up assessments are advised in the first few months. Thereafter, annual to twice-annual appointments, depending on injury, age, and activity of the patient, are needed. At these appointments, the orthopedic condition of the patient and the condition or fit of the device should be evaluated. Lastly, short- and long-term plans are adjusted.

V-OP 101: Getting Started

Why V-OP is Important to Your Practice

  1. Benefit to client and patient
    • It provides diagnosis, treatment plan, medical support, and guidance for underserved population.
    • It provides solutions where none existed before.
    • It provides clients from obtaining inaccurate information, medical advice, and medical devices from nonveterinary sources.
    • It provides ongoing professional care for the V-OP patient to ensure continued proper use of device.
  2. Benefit to veterinarian
    • These are extremely rewarding cases from a professional standpoint.
    • It provides innovation and cutting edge therapies to your community.
  3. Benefit to veterinary clinic
    • V-OP clients are deeply grateful and bonded to the clinic providing a solution when there had been none before.
    • These are unique patients who garner MUCH attention in the community as people wonder “what is that device?”
    • There is much opportunity for traditional and social media exposure because these are interesting cases.
    • A new revenue stream is created from a large population of animals who are not surgical candidates or whose surgery requires additional support.
    • An entirely different population of animals that will benefit from prosthetic limbs is created when subtotal amputation is chosen over total amputation.
    • In the case of long-term device use, twice-annual appointments bring the client into the clinic for continued support over years. These appointments are comprehensive and should be scheduled separately. They include evaluation of therapeutic plan, wearing schedule, activity, concerns, skin condition, device condition, and rehabilitation plan if appropriate.

Primary health care veterinarian responsibilities:

  1. Diagnose presenting orthopedic issue
  2. Create therapeutic plan
    • Device prescription with the support of V-OP fabricator; such durable medical devices should never be provided without the prescription and care of a veterinarian with a valid doctor, client, patient relationship.
    • Rehabilitation prescription, implementation, and supervision.
  3. Management of device long-term therapeutic plan as needed.

Finding a V-OP Fabricating Partner

V-OP are custom-made from a fiberglass impression of the patient’s limb after a diagnosis and complete biomechanical evaluation, and therapeutic plan are established. This is in contrast to off-the-shelf support wraps, splints or braces, or wheeled devices, which may or may not provide the proper therapeutic support and do not come with professional veterinary advice. Custom device design is unique based on the individual corrective needs, conformation, abilities, and environment of the patient. Manufacturing requires a firm understanding of quadruped bio-mechanics and skilled modification to accommodate limb top- ography, create appropriate corrective forces, and provide sufficient malleability to adjust as needed. V-OP is a hands-on therapy; each case should be managed carefully from diagnosis to device application to rehabilitation using a cohesive team approach. The ideal team includes the pet owner, the family veterinarian, a certified rehabilitation therapist, and a V-OP specialist skilled in custom design, fabrication, and fitting of devices for the intended species.

The advantages afforded by custom orthoses and prostheses include (1) reduction and immediate management of coaptation- related wounds; (2) management of primary pain generators associated with functional impairments; (3) improvement of biomechanics, allowing for greater activity and a significant decrease in compensatory pain; (4) return to active lifestyle, resulting in decreased obesity and associated comorbidities; (5) improvement in quality of life and functional independence, both of which can prevent premature decision to euthanize; and (6) the availability of treatment options where none existed before.

As of this writing, there are at least 12 companies offering veterinary-specific orthoses, prostheses, or assistive devices listed on the internet. However, there are opportunities to learn about V-OP at local and national veterinary meetings, and a continuing education course is offered through the Canine Rehabilitation Institute. There is as yet no certification for V-OP. Also, there are no regulating bodies and no requirements for V-OP fabricators at this time. H-OP has no practice act limiting scope of practice to which practitioners must adhere. Although human devices require prescription, the same cannot be said for any nonhuman patient. In addition, veterinary practice acts do not specify prescription or a valid doctor, patient, and client relationship for the use of V-OP devices. Keeping in mind veterinary practice acts have only recently addressed acupuncture, chiropractic, and rehabilitation, such clarification is likely forthcoming for V-OP. Until that time, clients can order and use such devices without the guidance of the veterinarian. Likewise, until regulations and limitations exist, the onus rests with the attending veterinarian to advocate for client and patient by ensuring proper, safe, appropriate prescription, and guidance in the use of these devices. Because clients will seek these devices with or without veterinary support, it behooves the veterinarian to participate in this process.

When choosing a fabricator, the following questions should be asked:

(1) What is the qualification of the fabricator? Many companies are founded by H-OP practitioners; this is a good start. The certifying organizations for this profession are the American Board of Certification-OP and the Board of Certification. Currently, these are voluntary certifications and as such not all H-OP practitioners are adequately trained and certified. These certifications are considered a minimum.

(2) What is the fabricator’s veterinary caseload? Do they work with animals exclusively or work with animals as a side business? Working with animal patients is not the same as working with human patients because of the vastly different biomechanics of the quadruped. Just as cats are not small dogs, and chihuahuas are not small greyhounds, quadrupeds are absolutely not small people on all fours. Veterinary species are tremendously diverse and challenging. Therefore, a fabricator should have a great deal of veterinary patient experience before providing a device for any companion animal.

(3) Does the fabricator require a prescription from a veterinarian with a valid doctor, patient, and client relationship?

(4) Does the fabricator have a close working relationship with a veterinarian who can provide consultation and guidance regarding animal health, locomotion, behavior, wound management, and rehabilitation?

(5) Does the collaborating veterinarian have advanced training in sports medicine, rehabilitation, and V-OP? There are several interest groups and specialty boards providing certification and continuing education for veterinarians. These include, but are not limited to, the Veterinary Orthopedic Society, the American College of Veterinary Sports Medicine and Rehabilitation, the American Association of Rehabilitation Veterinarian, the Canine Rehabilitation Institute, and the University of Tennessee. Association with such organizations is ideal for any veterinarian providing consistent consultation to any V-OP fabricator.



Prosthetics Basics and Subtotal Amputation

The current dogma goes something like this: “animals do great on 3 legs.” This position advocates for total limb amputation when catastrophic injury (e.g., crushing and degloving) or pathology (e.g., neoplasia) arises. However, the short- and long-term structural consequences of a missing limb or limb segment are being recognized and defined in part through the efforts of pain management veterinarians (the American College of Veterinary Anesthesia and Analgesia and the International Veterinary Academy of Pain Management) sports medicine specialists (the American College of Veterinary Sports Medicine and Rehabilitation, and rehabilitation therapists (the American Association of Rehabilitation Veterinarians). As we begin to understand the biomechanics of normal quadruped locomotion, the implications when it is lost become clear. In terms of limb absence or total limb amputation, these include limited mobility and endurance, increased metabolic demand, weight gain, support limb break- down, chronic neck and back pain, and premature euthanasia (Figs 10 and 11). Because of these significant consequences, consideration must be made for the re-establishment of quadruped structure whenever possible.

In human medicine, amputation at the hip for a catastrophic ankle injury would be unthinkable. Yet, this is standard of care in veterinary medicine. Why is this? In the past, prosthetics were not available and therefore concern for injury to the remaining limb segment was valid. Fortunately, prosthetics coupled with subtotal amputation, standard of practice in human medicine, are recent and successful developments in veterinary medicine. Given the consequences of limb loss in the short and long term, it seems appropriate to “contemplate before we amputate” an entire limb when only the distal segment is beyond salvage. Examples include neoplasia, trauma, and partial agenesis. Preservation of at least 50% of the radius or ulna or tibia or fibula allows ready application of a socket-based or ITAP prosthetic limb in species including dogs, cats, as well as others. Subtotal amputation is possible at nearly every level of distal joint as well as transtibial and transradial levels. The basic tenet is to preserve as much limb as possible while providing a tension-free closure. The ideal level of amputation for each injury, the best techniques, and the advantages or disadvantages of each level are still being defined. Regardless, the surgical techniques are simple, and complications are few.

The biomechanics of the quadruped make design of prosthetic limbs challenging, but not insurmountable. The end goal is to provide a limb that allows as close to normal ambulation as possible. Angulation of the thoracic limb vs. pelvic limb, breed differences, as well as level of subtotal amputation must all be considered. Furthermore, these considerations are distinctly different from the biped human amputee. Detailed quadruped prosthesis biomechanics are beyond the scope of this article.

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Fig. 10. Severe carpal varus and digital supination secondary to left thoracic limb
total amputation.

Currently there are 2 types of prosthetic limbs available: socket based and ITAP. Socket-based prostheses have been used in humans for centuries and provide a socket within which the residual limb rests; an extension provides contact to the ground via some form of foot or paw. The key for socket-based prostheses is suspension and retention of the device on the residual limb. Improvements in materials, mechanical joints, and microprocessors have revolutionized these devices. ITAP provides an implanted endoprosthesis to which an exoprosthesis is attached. Surgery is required and the endoprosthesis is integrated into the bone and skin similar to the way an antler is attached a deer’s head; no socket is required.

Prosthetic limbs for animals are becoming available albeit with simpler models than those for humans. The advantage of socket- based prosthetic limbs is their relatively low cost, simplicity of application (no additional surgery required), and adaptability to many levels of limb loss from paw to midantebrachium or crus. The clear advantage of ITAP is direct skeletal integration of the exoprosthesis. This means there is no mechanical delay in gaiting because the exoprosthesis directly transmits forces to the skeleton via the endoprosthesis (implant). An additional advantage is less soft tissue trauma, an intermittent vexing although not intractable sequelae of socket prosthesis in humans and animals.

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Fig. 11. The spinal consequences of thoracic limb loss include chronic cervical,
thoracic, and lumbar spine repetitive strain as well as carpal joint collapse.

Rehabilitation is critical for the prosthesis patient human or animal. Control of the limb is reversed; top down rather than ground up control results in delayed feedback. Through rehabilitation, the prosthesis patient relearns proprioception, balance, gaiting at different speeds, and ambulation over varied terrain.

More on OrthoPets Media Process

We’ve just created a new document to help clients and vets with taking and sending photos and videos to us! Check out the full document here.

OrthoPets Media

Whether you are (a) sending in your case to get started, (b) fitting your device for the first time, or you are (c) seeking help to solve fit & function concerns; your media provides OrthoPets the data required to provide you with the service and support your pet deserves.

Camera Positioning Is Critical

  • To capture the required pictures and videos of your pet, it is critical to:
    Hold your camera at the same elevation as your pet’s affected anatomical joint
  • Hold your camera stationary while your pet walks through your field of view
  • OrthoPets has provided a short instructional video demonstrating this technique for you:

3-2- 1: Media Process

Using our simple 3-2- 1 media process, you can quickly and effortlessly provide OrthoPets with the required media we need to assess your pet’s conformation, angulation, and gait pattern.

3 Still Photos of your pet’s affected limb while your pet is standing:

  • Front (cranial) surface of limb
  • Outside (lateral) surface of limb
  • Back (caudal) surface of limb

2 Walking Videos of your pet:

  • Side-to- side: Your pet walks from left to right and right to left in front of
    the camera
  • Front-to- back: Your pet walks towards the camera and away from the

1 Simple Way to send media:

  • OrthoPets utilizes “Filemail” transfer program enabling you to send
    large files from your mobile device, tablet, or desktop computer: https://orthopets.com/my-pets- journey/

Stifle Joint Orthoses

The stifle joint is less complex in that there are fewer bones and ligaments than the tarsus and carpus and only 2 true joints (femoropatellar and femorotibial). However, it is more complex because it is intended to function in more than 1 plane of motion (femorotibial). The stifle is a polycentric joint rather than a monocentric (simple hinge) joint. In addition to sagittal motion, a certain amount of frontal and transverse plane motion provides livelier and more adaptive function. The tibia and femur shear across the articular surfaces as the joint goes through range of motion. Overall, 4 ligaments and 1 tendon (medial and lateral collateral, cranial and caudal cruciate, and the patellar tendon) limit and control motion. Important muscles include the quadriceps group, the hamstring group, the gastrocnemius, and the biceps femoris. Injury to any of these components may be managed surgically or with an orthosis. Rehabilitation is now considered a standard of care in stifle injury.

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Fig. 9. An example of stifle orthosis for canine cranial cruciate insufficiency uses
force coupling to limit tibial thrust and internal rotation. This device uses
metatarsal suspension.

The classic example of transverse and sagittal stifle instability is injury to the cranial cruciate ligament (CCL). The etiology of this injury is beyond the scope of this article; however, knowledge of partial and complete tear is important. Traditionally, partial to complete, all CCL injuries are managed surgically. There are a number of techniques described each with merit, none perfect. Even so, there is a population of dogs for whom surgery is not possible or not appropriate. These include dogs with comorbidities, advanced age, and owners with limited financial means, among others. Until recently, treatment options for these patients were limited to weight management and nonsteroidal anti-inflammatory drugs.

Stifle support devices have been available for at least a decade. They include off-the-shelf and custom design devices. The intent of all is to support the limb. The degree to which they do is not yet known; however, studies are underway. From a mechanical perspective, a CCL orthosis must restrict tibial translation (cranial shear and internal rotation) or it must impel the muscular structures of the limb to do so. Importantly, the mechanical principle here is not the 3-point correction. This technique would fail during stifle articulation because the stifle undergoes rolling and gliding during normal range of motion. This means that the center of rotation changes, which cannot be accommodated by the 3-point corrective technique. The shearing mechanics of the CCL-deficient stifle are in contradistinction to the relatively simple mechanics of tarsal and carpal instability. Therefore a different technique is needed to stabilize. The proper mechanical principle is called force coupling (Fig 9). It uses the action of the major muscle groups to couple the femur and the crus while allowing a polycentric hinge to provide articulation and limit shear.