Fracture Repair: The Ups and Downs
Over the past three decades, equine surgeons have become more adept at repairing even the most devastating fractures. Long gone are the days when horses sustaining fractures were humanely euthanized with a sad shake of the head. Now, horses are largely salvaged--and even return to athletic careers--with a little help from skilled hands, an arthroscope, power drill, plates, wires, and/or screws.
"The equine industry has benefited immensely from the introduction of fracture repair techniques," comments Michael Ross, DVM, Dipl. ACVS, a professor of surgery at the University of Pennsylvania's New Bolton Center. "While we still have a long way to go before we reach the same level as human orthopedic surgeons, we have also come a long way from where we were only a few short decades ago."
Despite the improved success rates in fracture repair, not all equine orthopedic cases end successfully--even the seemingly simple ones.
According to Ross, the prognosis for horses with the most common fractures--the condylar (distal aspect of the cannon bone) fracture--has become quite good, with the majority returning to racing.
Ross summarizes a 1998 study published in the Journal of the American Veterinary Medical Association: "In a large retrospective study from the New Bolton Center, over 90% of horses with nondisplaced (no gap or displacement in the fracture line) lateral condylar fractures of the fore or hind limb raced after injury, most having surgical repair. Horses with fore-limb fractures and those with displaced fractures were less likely to race after injury or surgery.
"The prognosis or expected outcome post-surgically depends on the horse's performance type (racehorse or sport horse), size or weight, temperament, the bone involved, the location, configuration, type of fracture within the bone, and how well the fracture was repaired," says Ross.
Downside: Potential Complications
"Be aware that postoperative complications can and do occur," adds Ross. "The repair of any fracture can rapidly proceed from uncomplicated to complicated at any given point after sustaining the injury, sometimes without any warning."
- Post-fracture complications impacting a horse's chance of survival can happen:
- Preoperatively during transport of the horse to the hospital;
- Intraoperatively, while repairing the fracture; and
- Post-surgically (on recovery from anesthesia or during healing).
In this last instance, the major complications that can develop include--but are certainly not limited to--infection and support limb laminitis.
Implant infections Infection is the most important complication of orthopedic surgery in horses, writes Dean W. Richardson, DVM, Dipl. ACVS, chief of large animal surgery and the Charles W. Raker Professor of Equine Surgery at New Bolton Center's Widener Hospital in his chapter, "Complications of Orthopedic Surgery," published in the December 2008 edition of the journal Veterinary Clinics of North America: Equine Practice.
Infection rates vary based on the type of surgery (open reduction, meaning open surgery to set bones, vs. minimally invasive techniques), degree of comminution (fragmentation) and soft tissue damage, and if the skin was broken at the time of injury.
"For arthroscopic surgery in horses with minor fractures, the expected infection rate is only 0.1-0.5%," Ross says. "In horses with complicated fractures necessitating open reduction and internal fixation, infection rates can reach 10-30%."
Even if "successfully" managed, infections substantially increase the overall treatment costs, and they can negatively affect cosmetic and functional outcomes.
A surgeon's ability to treat infections is largely attributable to his or her capacity to deliver large amounts of the appropriate antibiotic directly to the site of infection. Local delivery of antibiotics is widely thought to be superior to systemic administration in combination with repeatedly draining and lavaging the infection site under general anesthesia. This is because higher doses of antibiotics can be attained with local administration without causing systemwide adverse events, such as kidney or liver damage or gastrointestinal upset/colitis (inflammation of the colon). Further, it is more economical to deliver high doses of antibiotics to the affected region alone rather than to the whole horse.
Support limb laminitis Support limb laminitis is defined as the development of laminitis in the forelimb or hind limb opposite to the injury.
"Support limb laminitis is an important and often devastating complication associated with excessive unilateral weight-bearing in adult horses," explains Gary Baxter, VMD, MS, Dipl. ACVS, a professor in equine surgery at Colorado State University's College of Veterinary Medicine.
"We do not know exactly how frequently support limb laminitis develops in horses with fractures, but I would estimate that it occurs in approximately 10-15% of fracture cases," adds Baxter.
Unlike other causes of laminitis, support limb laminitis appears to be caused by a unique mechanism.
"Support limb laminitis almost exclusively occurs in the limb opposite the lame limb," says Baxter. "With grain overload, endotoxemia, or in horses with Cushing's disease or metabolic syndrome, any foot, and often multiple feet, develop laminitis."
The normal architecture of the foot is designed for constant movement, undergoing "constant cycles of loading and unloading that promote blood flow to the foot for the delivery of oxygen, nutrients, and hydration, and removal of waste products," says Baxter. "Even horses at stance are constantly moving."
Studies have shown that horses shift weight from one forefoot to the other between 70 and 180 times per hour. Thus, horses unable to shift weight, such as fracture patients, are seemingly incapable of achieving this "circulation" in the foot. As a result, tissue fatigue, damage, and necrosis are thought to occur.
It is currently hypothesized, therefore, that support limb laminitis is related to altered biomechanics and blood flow in the limb bearing more weight. Unilateral weight bearing could decrease blood flow to the laminae of the foot (the laminae connect the distal phalanx, or coffin bone, to the hoof wall), which reduces the delivery of oxygen to those sensitive tissues, increasing oxidative stress.
"In addition to reduced blood flow, there is also an increased 'pull' on the distal phalanx due to increased tension on the deep digital flexor tendon during excessive weight bearing," notes Baxter. "Together, these factors are thought to contribute to the separation of the sensitive and insensitive laminae of the foot."
While this theory is attractive, Baxter adds that other theories exist that potentially explain how support limb laminitis develops. Research in this field is ongoing to explain not only how support limb laminitis develops, but also how to treat the condition.
As with all forms of laminitis, the most important treatment is prevention. Since duration of unilateral weight-bearing appears to be the biggest risk factor, all efforts should be taken to promote normal weight bearing as quickly as possible.
Current management strategies include both pharmacologic and mechanical approaches. Anti-inflammatories to manage pain, drugs to improve lamellar blood flow and decrease platelet aggregation (clumping together) and thrombosis (blood clots), and specific enzyme inhibitors are all used to prevent and/or treat support limb laminitis. Veterinarians apply local foot therapy to encourage all parts of the sole and frog to bear weight, redistribute weight-bearing to the least-stressed regions of the hoof wall, and decrease tension on the distal phalanx.
Injury on Recovery from Anesthesia
While not technically considered one of the "big" postoperative complications, recovery from general anesthesia in horses surgically treated for fractures instills anxiety and tension in even the most experienced surgical team. It is currently estimated that two of every 1,000 horses suffer a fractured bone on recovery, typically near the site of the pre-existing injury or adjacent to orthopedic implants (such as bone plates or transfixation pins).
To reduce post-anesthesia deaths, the industry has developed various assisted recovery techniques. These include the tilt table, pools, slings, padded mats, inflatable air cushions, and rope recovery systems.
Published studies have demonstrated that the pool, tilt table, and sling are all useful methods for recovering horses. Potential difficulties of these systems include the added expense and manpower required for building, maintaining, and using the equipment, the time-consuming nature of these recoveries, and the failure of some horses to adapt to the recovery system.
In contrast, Hans Wilderjans DVM, Dipl. ECVS, of the Equine Hospital De Bosdreef in Belgium, devised a rope recovery system (see TheHorse.com/13847) that requires only one handler and can be installed easily and economically in any equine hospital's recovery stall. Wilderjans attests that his one-man rope recovery system is a "valuable and safe way of controlling recovery."
Wilderjans has recovered more than 7,000 horses using this system, including 58 fracture repairs.
Post-Fracture Pain Management
According to Laurie Goodrich, DVM, PhD, Dipl. ACVS, an assistant professor in equine lameness and surgery at Colorado State, pain management advances have progressed far more slowly than corresponding advances in fracture repair.
"There are many reasons why horses continue to be deprived of appropriate analgesia (pain control) post-surgically," says Goodrich. "It is widely thought that a horse will cause additional damage and overuse the affected limb if they do not feel some level of pain."
Goodrich says this mode of thinking is outdated and potentially inhumane.
She suggests that horses receiving appropriate analgesia post-surgically are less depressed, maintain good appetites, and have normal functioning immune systems that promote normal tissue healing. Further, she feels reducing or eliminating chronic pain in horses reduces stress and decreases the risk of gastric ulcer formation, development of colitis, and occurrence of depression.
"One of the greatest benefits of pain control in orthopedic patients is the potential to prevent or reduce the risk of support limb laminitis," adds Goodrich.
Avoiding any or all of these undesirable outcomes by using appropriate pain management will, in many cases, lead to faster fracture repair, earlier discharge from the hospital, and a smaller bill for the client.
"Poorly executed pain management in horses with orthopedic injuries can undermine even the best surgical repair," concludes Goodrich.
Veterinary surgeons continue to make improvements in equine fracture repair, resulting in more successful outcomes. Howev-er, many factors come into play and Ross suggests that important contributors to a surgeon's success include:
- Optimal use of new, strong orthopedic implants, such as the locking compression plate;
- Use of antibiotics and local implantation of antibiotics at the fracture/implant site to help manage infections; and
- Use of slings to reduce postoperative weight-bearing and ward off laminitis.
"Not every horse can be saved, but the veterinary profession has truly made tremendous strides," he concludes.
About the Author
Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.