Indepth Equine Podiatry Symposium Notes Written and presented January 2009 by R.F. (Ric) Redden, DVM
Amputation can be an option for horses that have suffered irreversible, catastrophic loss of blood supply to the foot, pastern, fetlock, cannon bone, hock or knee due to injury or disease. Typical cases may include acute and chronic debilitating deformities in young horses, explosive fractures involving the pastern, distal cannon, combination suspensory apparatus failure, extensive irreversible damage due to joint sepsis and extreme lacerations that destroy major arterial supply to the digits. Fractures of this nature can occur at high speed, be the result of paddock injuries and occur while in a stall or being worked on a lunge line.
When determining whether or not amputation is a viable option many things must be taken into consideration. The personality of the animal is very important to consider. Aggressive, high strung, unruly or unbroken animals pose serious risk of injury for those attending to frequent surgeries and aftercare. Financial commitment can also be a determining factor, as a great deal of expense can be involved, especially if complications arise. The location of the injury (below or above the knee or hock) can also affect whether or not amputation should be attempted. Adequate surgical and aftercare facilities must be available and should include a 12 foot high beam system compatible with using an electric one ton hoist and sling, as after care is performed in a sling for the first 4-5 months until the horse learns to stand quietly without the sling for support. Aftercare personnel with good horsemanship skills will be necessary as well as a qualified farrier who enjoys mechanical challenges. The farrier should be open minded with the energy and optimism to make it happen, and willing to work closely with a veterinarian who also thrives on challenges.
Athletes who suffer an acute, catastrophic injury are good candidates for amputation as they are otherwise very fit and healthy and the opposite foot is most likely very healthy at the time of injury. Hind limb injuries at or below the fetlock would be the very best candidates; the second choice would be a mid to upper cannon amputation site on a hind limb, which would require a full limb prosthesis.
Ponies and miniature horses (200-300 pounds) have a very good prognosis simply due to their light body weight. I have had several cases, and all have been receptive to the prosthesis. Prosthesis and stump management have been uneventful.
Hind limb cases have a better prognosis than front limb cases due to less weight distribution on the hind end. Lower leg injuries have a better prognosis and lower maintenance requirements than mid-cannon amputations. Pastern or hind limb fetlocks require a short limb prosthesis (below the hock or knee). Mid-cannon, carpal or hock amputations and some front limb fetlock amputations require a prosthesis with an above the knee or hock extension. This can be hinged for select cases in front but a stiff, full limb works best for behind.
Breeds that naturally have exceptionally good quality feet (thick and tough walls, 20+mm of sole with natural cup, 3-5 degree PA and strong digital cushion) can be reasonably good candidates even when contra limb laminitis affects the good foot. However, the laminitis must be manageable regardless of the degree of vascular damage and should always be the prime focus, as the good foot can deteriorate very quickly when laminitis is present. Standardbreds top the list of tough footed horses, followed closely by Tennessee Walking Horses. I often say you can't hurt these breeds with a running chain saw, as they are very durable with no limit to their pain threshold.
Front limb injuries or disease that involves both limbs are not good candidates for amputation. Note that I classify these cases as poor candidates, not impossible. There is enough clinical evidence to suggest that bilateral amputation is possible and could be a viable option for select cases.
Young horses with chronically painful injuries or disease that bow the opposite limb at the knee or hock are poor candidates as the opposite limb deformity remains a threat. As a rule it will continue to worsen with age and weight gain, which precludes all efforts to offer them a quality life even when the amputation and acceptance of the prosthesis are uneventful.
Contra limb laminitis certainly diminishes the prognosis considerably when injury or disease has precipitated this frequently occurring problem. Laminitis in the opposing foot can be a major problem following surgical repair of catastrophic injury. Fortunately this common complication can be prevented in a large majority of high risk cases and can be treated successfully in most cases provided irreversible vascular damage has not occurred. Detection and timely realignment followed by a mid-cannon DDF tenotomy guided by evidence from comparative venograms can have very gratifying results even when it looks like all is lost to this devastating disease. This is where an ounce of prevention is worth a pound of cure.
Cases that are initially treated surgically but deteriorate due to sepsis or major blood loss to the healthy tissue are poor candidates for amputation. Due to new, ongoing surgical developments many catastrophic injuries are now considered potential surgery candidates. Their ability to heal is based on adequate vascular supply, efficiency of fixation, temperament of the animal and uneventful aftercare. However, cases that are borderline for surgery due to the extent of the injury become far better candidates for an amputation than surgery, provided the decision is made at the time of injury and not weeks after it is obvious that the surgical approach failed to meet the criteria for returning the limb to a healthy, useful state. Contra limb laminitis is imminent in cases that heal slowly and have ongoing complications. Performing the amputation at the time of injury instead of attempting a very high risk surgery can offer much better long term results and bypass the risk of contra limb laminitis. Amputee pin cast cases are much sounder immediately following surgery than those with implants and cast.
The problem with slow healing or complicated surgical cases is that they will show no signs of contra limb laminitis until the good foot becomes more painful than the surgical leg. By this time laminitis has been present for several weeks and tremendous vascular damage has occurred. However, if the initially injured limb is 80-90% healed when laminitis is detected good results can be obtained by realigning the palmar surface with the natural load zone (derotation) followed by a DDF tenotomy. When performed in a timely fashion, most hind limb contra limb laminitis cases have a reasonably good prognosis.
Financial Obligations: In my practice the average surgical procedure with fitted temporary prosthesis runs between $6,500 and $10,000. Hospitalization may average $150-200 per day with up to five months of hospitalization. During the five month recovery period at least two additional surgical procedures are indicated. The first is a frog graft performed within the first two weeks of the initial surgery or when the granulation bed is most receptive and the second is pin removal and re-casting. Each requires general anesthesia and can cost between $1000 and $1500. All subsequent cast changes are performed in the sling (when the patient is cooperative) every 2-4 weeks depending on stump response. A permanent prosthesis can be fabricated approximately 5 months post op, and runs between $1,500 and $10,000, depending on the level of detail involved. Complications can incur additional expense and can include pin failures, premature bone failure around the pins, spiral fractures, septic stump and long bone fracture above the prosthesis. All are low risk, but possible.
It is extremely important to discuss the financial commitment, both immediate and long term, with the owner before electing the procedure. Many cases can go on to be low maintenance and the projected budget held in check, but the possibility of complication and unexpected costs should be clearly communicated so that everyone can be on the same page and prepared to meet financial obligations.
The procedure can differ greatly depending on the level of amputation, therefore it is extremely important to have a good plan in place that has been well established and well rehearsed with all participants before proceeding. A good back up plan is also important as there is no time to think about plan B if it has not been rehearsed. Several surgeries are involved, including the initial amputation and pin cast, followed by a frog graft surgery 2-3 weeks later and pin removal 4-6 weeks post op. Complications could require additional surgeries. Thorough preparation, necessary equipment, and an adequate temporary prosthesis with necessary tools to quickly modify it should all be in place before the surgery is attempted.
It is best to use general anesthesia for the initial surgical procedure. Not to say it can't be done in a sling, because it has, and has been quite successful. I assisted an orthopedic surgeon in 1974 on a standing amputation. We made it happen, but we almost lost the surgeon a couple of times. A standing amputation in a sling can be a bit hairy to say the least.
Necessary equipment: A sling setup is extremely valuable for optimum success. A support sling that can be used for induction and recovery and for follow up temporary cast changes is imperative as this optimally protects the bone at the pin sites. Ceiling height should be a minimum of 10 feet, preferably 12, with an adequate overhead beam that will support well over 1 ton. An electric 1 ton hoist (preferably with lift rate of 16 feet per minute or faster) is also standard required equipment.
Creating a temporary prosthetic: The size of the stump may change periodically for the first five months post op, therefore a temporary prosthetic is necessary until the stump heals. Very economical temporary prosthetics can be fabricated in a matter of minutes using a 1/4 inch aluminum plate, cast material and an aluminum pipe. Qualified, experienced farrier services are a very helpful adjunct to therapy, as farriers have a natural, mechanical thought process that can greatly assist the creation of a temporary prosthetic.
PIII and PII removal: When the heel bulb, frog or even part of them remains viable I use them as an autogenous graft, removing the diseased tissue, hoof capsule, PII and PIII. This has worked well several times.
Fetlock removal: Front limbs present a problem as the limb becomes very round and the shape of a baseball bat. All prostheses need to have a bulb or large distal end to prevent it from falling off. However, in front the prosthesis will rotate around the stump. If at all possible I retain a section of PI that can be used at an angle to prevent rotation of the prosthesis. Hind limbs do not pose this problem as the cannon bone is quite flat, which prevents the rotation when fitted properly.
Mid-cannon or higher removal: Hind limbs require a full limb to prevent it from falling off and twisting. A rigid prosthetic works better behind than a hinged one, but on front limbs a hinged prosthetic can have advantages over a stiff limb.
Pin cast: Pin placement is like a lot of other procedures. Surgeons choose sites based on past experience. I personally like to place the first one just above the distal condoyle and the second one at an angle to the first, one inch above and tipped slightly out of the parallel plane.
I prefer to use Procel Cast Liner padding directly on the skin followed by a close fit cast over the protruding pins. I routinely fill the cap from a 3cc syringe