New techniques make amputation more viable for some patients

We have all been there. A client calls to say that she has just found her horse standing in the field unwilling to move.

Intraoperative view of stump preparation. If adequate tissue to fully enclose stump is not available, as is common in distal limb fracture, then a granulation bed growth is encouraged at the distal end of the stump. A second procedure will be performed in 10 days to transfer grafted frog tissue to this granulation bed.

"His leg is just dangling, there may be a kick mark and I...I think it may be broken."

There have been many improvements in anesthesia and in surgical techniques for fracture repair, you tell yourself as you drive onto the farm road. You see the small crowd standing around the horse as you approach and, from the abnormal angle to the leg and that almost nervous way that he tries to place and replace a leg that no longer does what he wants it to do, you know that the leg is indeed broken.

If the fracture can be repaired surgically then the horse has a chance. If the damage is too severe, then you have to break the bad news to the owner.

Open, infected fractures, bad spirals or comminuted breaks with a multitude of small pieces usually mean the end of a horse's life.

"What about amputation?" someone occasionally asks.

If you are like most veterinarians, the question of equine amputation is usually answered emphatically with "been there, tried that, didn't work." In fact the history of attempts at equine amputation and prosthetic repair does not offer much hope, and this technique has been largely discarded.

If the fracture is so severe or of a type that does not allow standard plate and screw repair or casting with transfixation pins, then the horse is usually euthanized.

Not so fast

Fortunately, a group of veterinary surgeons has been thinking and operating "outside the box" and has come up with new techniques and approaches that may make amputation in the horse a very reasonable alternative to the management of a catastrophic fracture.

Even though these veterinarians do not practice together, they have been sharing information and discoveries and have collectively justified a new look at an old procedure.

Stump being prepared for temporary casting. Transfixation pins are shown illustrating the 30-degree diversion angle placement crucial to weight-bearing and successful post-op recovery.

Actual amputation of the distal limb in the horse is not technically difficult and could be reasonably performed by any qualified surgeon. The poor success rate for this procedure in the horse has been due almost entirely to post operative complications.

Fracture upon recovery from anesthesia, wound dehiscence, osteomyelitis of the stump, pressure sores from the prosthesis, contralateral limb failure from laminitis, tendon rupture of fracture and poor patient acceptance are the major problems that have earned amputation in the horse its dismal reputation.

Dr. Ted Vlahos of the Sheridan Animal Medical Center in Sheridan, Wyo., says, "Amputation has been only minimally accepted, and only as a salvage procedure."

"Taking the leg off a horse is not something that most owners can even contemplate," adds Dr. Barrie Grant of the San Luis Rey Equine Clinic in California.

Healed stump prior to fitting for prosthetic.

Yet these two surgeons, along with Dr. Ric Redden of the International Equine Podiatry Center in Versailles, Ky., have modified and improved the amputation and prosthetic procedure to a point where they feel it should be considered as a reasonable treatment option for some injuries and one that allows the horse a good quality of life as opposed to merely "salvage."

All three surgeons have been performing amputations and modifying the technique as they progressed. While they may currently use slightly different steps, the general principles and procedures are similar.

How it's done

Prior to surgery, a temporary prosthesis is constructed using inch-flat aluminum stock. A cup is fabricated from this material and two aluminum straps are welded to the medial and lateral aspect.

The horse is then taken to surgery where two transfixation pins are placed at 30-degree divergent angles through the bones proximal to the site of amputation.

The site of amputation is dependent on the location of the injury. The most common areas of amputation are the proximal and distal interphalangeal joints, and the metatarsophalangeal joint. Amputations of the hind feet seem more common, perhaps because of the increased number of injuries in this area and because these cases do well and as such are attempted more frequently. The hind limbs bear less weight than the forelimbs and tend to do better following amputation.

Four-and-a-half month foal with temporary prosthetic.

Grant has had considerable experience with amputations just distal to the carpas or tarsus and amputations higher up the leg than this are rarely attempted.

The load bending forces on the limbs seem to be much greater if the amputation is above the knee or hock and "though we will eventually get there," says Redden, "we don't have that capability yet."

The placement of these transfixation pins seems like a small detail, but this was the first step in improving the success of the amputation procedure.

Prior to placing them at 30-degree angles, the pins were placed in a parallel arrangement. This design was associated with a significant rate of fracture on recovery from anesthesia. The divergent angle placement did not stress the bone as much and almost totally solved that post-op complication.

Frog tissue grafts

Another innovation that significantly improved long-term results was the incorporation of frog tissue grafts into the stump closure. Traditionally there is little muscle or other tissue to use when constructing a stump following distal limb amputation in the horse.

Grant has had success using flexor tendon incorporation in stump formation in "high leg" amputations, but this is not possible when amputating lower down the limb. Because of the lack of muscle and other tissue for use in stump construction, many horses had poor stump healing and were prone to rubbing and trauma to the stump by the prosthetic device.

Redden has pioneered the use of grafts of frog tissue that are harvested from the amputated limb, if possible. If the injury has damaged this tissue, then very small grafts are taken from the non-affected foot on the same side.

Redden describes the harvesting of this tissue as making a small slit over the frog and taking a strip of sensitive and non-sensitive tissue. This strip is placed in the stump ending or in a granulation bed if done after the stump has been created.

"It grows like crazy," says Redden, "and creates a wonderful, tough, resilient material for the bottom of the stump. It has to be trimmed every month or so, just like regular frog, or the prosthetic will not fit."

Fiberglass cast

A fiberglass cast is constructed next and this cast incorporates both the transfixation pins and the temporary prosthesis.

Horses are recovered using a sling assembly. The use of the sling is crucial to success of this procedure as well since it further reduces post-op trauma. Horses are immediately weight-bearing through the transfixation cast and temporary prosthesis, and this eliminates the "break-down" problems seen on the contralateral limb.

The horse is then monitored closely and the cast changed every 30 days or so. At 10 to 12 weeks, the transfixation pins are removed.

Permanent prosthesis

Once the stump has fully healed, a permanent prosthesis is constructed.

Complete healing usually takes 90 to 180 days. The permanent prosthesis is made of carbon graphite, fiberglass and polyethylene.

A prosthetic sock is applied beneath the device, and it is initially changed daily and monitored for pressure sores. It can eventually be changed weekly and the horse can usually be provided with unrestricted exercise five to six months post-surgery.

Success factors

Drs. Vlahos, Grant and Redden all agree that patient selection is very important in eventual success.

The acutely injured horse is considered the ideal candidate. "Equine amputation and prosthetic repair is clouded by lack of information and communication," according to Grant.

He feels that too few owners and trainers really understand what is available through this procedure and how well these horses actually do. The perception is that even if the amputation works, these poor horses are merely cripples barely able to get around. "Nothing could be further from the truth," says Redden as he relates the antics of a mare that he has who has been an amputee for the last 11 years.

"She lives outside all year long, and bucks, and runs and plays just like a normal horse," says Redden.

This mare has been a successful broodmare and there have been successful breeding stallions that showed little problem with their handicaps. If amputation could be seen as something other than a last resort, then horses may be presented before they have developed problems of infection or breakdown in the opposite leg. These secondary problems make horses less likely to benefit from amputation, and this has only served to make owners question the efficacy of the procedure.

"Give me a healthy mare that breaks down acutely on the track and turning her around with an amputation and prosthetic repair would be relatively easy," says Redden. "She'd be the perfect candidate," he adds.

Owner commitment

Owner commitment is important as well. This is a long-term project and it is unfair to the horse to put it through this procedure if the owners are not willing to see it through.

Grant laments the fact that more funding for amputation research is not available.

He cites the use of articulated prosthesis with electro-muscular implants as an exciting area worthy of more study. He hopes that interested and committed owners may eventually fund some of this needed research that will help further improve the chances for a horse with a catastrophic injury.

Horse's role

The personality of the horse also has a lot to do with the eventual success of an amputation. Some horses learn quickly how to use their temporary prosthesis. They tolerate the sling, learn how to get up and lie down easily and tolerate the eventual prosthetic. Other horses struggle and make healing and rehabilitation harder.

Some of these horses do not make the adjustment and, though their stumps are healed, they refracture limbs or succumb to other trauma.

It is difficult to determine which horses will tolerate the procedure and which will have trouble. Helping train these horses to more easily accept convalescence and rehabilitation is another area of study that needs to be done, according to Grant.

Considerations

The use of transfixation pins, a recovery cast and a sling greatly improved post-surgical success. The temporary prosthesis and frog grafting to produce a stable, healthy stump clearly added to the improvement of equine amputation to the point where it should now be considered as a potential treatment option in some cases. At a cost of $12,000 to $20,000, it is not a decision to be made lightly, but the chance to provide a good quality life to a breeding animal or valued companion should also be considered.

Most insurance companies will accept amputation as a legitimate procedure.

It is difficult to think of removing a horse's leg and even harder to recommend it to clients as an option, but with the new developments in amputation and prosthetic repair and with the dedication of veterinarians like Grant, Redden and Vlahos, we may find that three good legs are all that are needed.