As surgeons gain more experience at repairing challenging fractures, new techniques and devices emerge

by Kenneth L. Marcella, D.V.M.

THE UNPRECEDENTED media coverage of Kentucky Derby (G1) winner Barbaro's injury, surgical repair, and recovery at the University of Pennsylvania's New Bolton Center has turned casual horse enthusiasts into quasi-medical interns. Countless numbers of people have downloaded the images of Barbaro's fractured leg and its repair, and they have followed the daily media updates through cast changes, implant removal and replacement, laminitis, and suspected osteomyelitis (bone infection).

At each step of the way, ordinary people--carpenters, secretaries, truck drivers, and cooks--have been exposed to the methods used to repair equine fractures and the medical care necessary following such procedures. They have followed Barbaro's assisted recovery in New Bolton's surgical recovery tank, read about the titanium plate and screws in his injured limb, and seen pictures of him standing in a supportive sling.

Daily conversations around the water coolers may have included comments on vital signs, medication, and rehabilitation as matters of general discourse. Through the struggles of this one equine athlete, many horse owners and horse enthusiasts have been able to learn about the special problems associated with fracture repair in the horse and with the many innovations currently in use to help heal these athletes.

As educational as these articles and Barbaro updates have been, there is still more to learn about equine fracture repair. Newer techniques and innovations currently are being researched and implemented experimentally. Newer types of plates, more advanced and innovative screws and implants, and novel techniques and therapies will make up the next chapter in bone repair in the horse.

New techniques

As recently as 30 years ago, most horses experiencing a severe fracture were simply euthanized or, at best, retired. Advances in anesthesiology have enabled safer, more reliable induction that provides surgeons with ample time for proper surgical repair.

Advances in recovery techniques now reduce the risk of the patient developing new fractures coming out of anesthesia or refracturing a newly repaired bone. The use of plates and screws and the eventual development of full internal fixation techniques allow for a strong, stable fracture repair that enables the horse to stand and bear weight on repaired legs almost immediately.

Because these monumental developments occurred, the field of equine fracture repair has focused on continuing innovations in two main areas:

•Better, stronger implants and less traumatic fixation techniques; and

•Medical therapies to improve and accelerate bone healing.

As seen in discussions of Barbaro's complications, infection of a traumatic fracture is a significant problem for horses. In fact, Dean Richardson, D.V.M., chief surgeon on Barbaro's team, prophetically wrote prior to Barbaro's injury: "Complications of osteosynthesis [bone formation], including deep and superficial infection, continue to adversely affect the outcome in surgery of the equine lower limb." Richardson made this comment in an article that looked at the use of minimal-contact repair plates.

Bone plates currently used are made of stainless steel or titanium. These plates are made with relatively flat surfaces and are placed along the shattered bone so that they can bridge the fracture gap.

In the past, surgeons tried to make the plate contact as much of the bone surface as possible so that, with screw placement, the plate made the bone sturdy. Studies began to show, however, that with the pressure of the plate on the bone and the tightness created by screw fixation, these compression plates damaged the periosteum or the thin covering of the bone. Damage to the periosteum reduced the bone's ability to heal.

Researchers tried to solve this dilemma by creating minimal-contact plates. These plates, made of the same materials, have a half-diamond, staggered array pattern that provides limited contact between the plate and the bone but still provides stability. Limiting the interface of the bone plate decreases damage to the bone surface or periosteum, which can then increase healing of some fractures. Other researchers and clinicians feel that this reduced contact will weaken repair and that the minimal-contact plate, while great for some types of fracture repair where there is inherent stability, may not work for other types of equine fractures.

Another technique that veterinary surgeons and researchers are currently testing and applying to cases is minimally invasive plate fixation. Older methods required that large incisions be made to allow the equine surgeon to expose the fractured bones and repair them. Large, open incisions always increase the chances of infection. And if a muscle, ligament, or tendon needed to be moved to expose the surgery site, it usually had to be cut or, at the very least, stretched. This older approach to fracture repair resulted in sore, lame horses following surgery, and these horses took longer to heal and to return to athletic function.

Minimally invasive plate fixation attempts to place the implant (plate) on the damaged bone by tunneling under tissue, using arthroscopic viewing whenever possible and generally trying to do very little damage to the fracture site. Screws are placed with individual small incisions exactly where they need to be to go into the plate. Reducing trauma at the fracture site increases healing, gets the horse up and moving quickly (because it is not sore and waiting for a tendon to heal), and more efficiently brings horses back from a serious fracture.

As more and more ways are documented to get repair plates gently and accurately to where they are needed, minimally invasive plate-fixation surgery will become much more commonly practiced.

New hardware

Hardware advances will continue to be made in equine fracture repair. Larger and stronger plates currently are being made. New types of screws that provide support, pull fracture pieces together in several specific ways, and do minimal trauma to the bones in which they are placed are being developed. Long nails or metal rods are being placed within the intramedullary canal or the hollow space within bones. These nails are then held in place by special screws so that there is minimal slipping and no rotation of the bone. These interlocking nails offer potential for some types of repair.

With all the specific plates and the numerous lengths, sizes, and types of screws and nails that are needed for various fracture repairs, equine clinics will come to resemble Home Depot hardware aisles.

Andy Parks, Vet. M.B., head of equine surgery at the University of Georgia, offered this warning: "The sheer economics of stocking proper inventory will become a challenge since it becomes prohibitively expensive to keep on hand all types of fracture implants that may be used for specific cases only once or twice each year."

If private hospitals and smaller equine clinics reduce their inventory and limit the types of fracture cases that they can handle properly, some horses with serious fractures may have to be trailered longer distances for surgery. Transporting a horse with one or more broken bones can adversely affect the success of fracture repair.

Accelerated bone healing

The second major area of research in equine fracture repair involves numerous ways to accelerate and strengthen bone healing. Many fractures that are successfully repaired surgically fail to heal because of poor bone growth. Several research groups are investigating certain drugs and therapies that may allow clinicians to switch on bone production following fracture repair.

Bone marrow has long been known to contain a population of unique cells capable of differentiating into bone, cartilage, muscle, tendon, and other connective tissues. These cells are called mesenchymal stem cells, which can be isolated from bone marrow, grown in culture, and loaded into porous ceramic cylinders. These cylinders then have been implanted into fractures in long bones of experimental animals ranging from rats to dogs to sheep.

The research is very promising and has demonstrated that MSCs can heal clinically significant bone and cartilage defects in animal models. Other groups are looking into gene therapy where specific recombinant peptides are produced that stimulate bone growth. Currently, the bulk of this work has been done in humans, but certain human gene products have been shown to be active in horses as well.

Investigators at the Comparative Orthopedic Research Laboratory at the University of Wisconsin School of Veterinary Medicine have been working with BMP-2. This human bone morphogenic protein has been combined with various matrix products and applied to normally healing fractures, developing unions, and to non-unions (cases where the ends of the fractured bones fail to grow together). BMP-2 has been shown to promote faster and healthier bone growth. These biologics are felt to be part of the future in fracture repair,

Lisa Fortier, D.V.M., Ph.D., assistant professor of large-animal surgery at Cornell University, pointed out the current pros and cons of these products.

"Researchers can select the specific gene product they wish to use, place it in the cassette virus [a carrier virus that can infect tissue and implant the gene protein without causing any disease], and infect their tissue of choice," said Fortier, whose work focuses on tendon and cartilage repair.  One of the biggest problems with this technology is that it is still difficult to control.

"If you try to stimulate bone growth in a fracture repair, for instance, you may not be able to turn off the bone production, and a large callous of bone may result," Fortier said.

More research needs to be done, but BMP-2, stem cells, platelet-rich plasma, and other biologicals are certainly on the horizon for use in equine fracture repair. "If I could only have one thing on the shelf for use in fracture repair, these products would be it," Fortier said.

Barbaro's legacy

It is too early to be sure about Barbaro's legacy. As the Kentucky Derby winner continues to battle complications associated with repair of his right hind leg, it is premature to speculate how Barbaro will be viewed in years to come. Will he be thought of as a gifted athlete that excited and thrilled the world of horse racing? Will he be remembered for his ability in the breeding shed? Will he be forever linked to his struggle to recover from a devastating injury? One thing is certain so far: Barbaro may well be best remembered for providing the public with an education in the advances and possibilities available through veterinary medicine.

Kenneth L. Marcella, D.V.M., is a practicing veterinarian in Canton, Georgia.