Horses’ tendons and ligaments, soft tissues structures connecting muscles to bone and bone to bone, facilitate a variety of athletic feats. Because these structures function close to their load limits, horses—especially racehorses and performance horses under work stress--are at risk for injury, or re-injury after rehabilitation. Veterinarians now have more treatment options than ever for these injuries; however, controversy lies in what current options are best for recovery.
Scott Palmer, VMD, Dipl. ABVP, addressed these challenges in treating and rehabilitating tendon and ligament injuries at the 2013 American Association of Equine Practitioners’ (AAEP) Convention, held Dec. 7-11 in Nashville, Tenn. For the first time, the convention included a session featuring lectures from the organization’s past presidents, who covered controversial horse industry topics. Palmer, who served as AAEP president in 2005, is the hospital director and staff surgeon at the New Jersey Equine Clinic, in Millstone Township, and currently serves on the AAEP Racing Committee.
Palmer opened his presentation by describing three phases of tendon and ligament healing:
- The inflammatory phase, which lasts approximately seven to 10 days occurring immediately after injury and is characterized by heat, swelling, and pain;
- The proliferative phase, which lasts 10 to 21 days: “During this phase, capillary ingrowth occurs, along with the appearance of cells that manufacture ground substance and collagen,” he explained; essentially, cells appropriate for healing tendon and ligament begin to regenerate tissue; and
- The remodeling phase, which begins at 14 to 21 days and lasts up to a year, in which newly generated tissue is remodeled in response to applied load.
In the past, equine veterinarians treated soft-tissue injuries by cold-hosing the affected area and administering phenylbutazone to reduce inflammation, followed by counterirritation (such as chemical blistering or thermal pinfiring) to increase circulation. With limited ability to monitor healing, veterinarians using these treatments often cleared horses for work only to have them succumb to reinjury, Palmer said.
But times have changed. Current tendon and ligament treatments include a sophisticated arsenal of powerful anti-inflammatory medications, intralesional therapies, surgery, and adjunct therapeutic options, as well as well-planned and carefully monitored rehab-fitness programs.
Intralesional therapy involves injecting compounds, a cellular matrix, biological mediators (platelet-rich plasma, or PRP), or stem cells directly into the injured portion of the tendon or ligament. “The criteria for choosing among these therapeutic options often reflect the experience of the veterinarian or trainer and the perceived cost-benefit ratio of the therapy,” Palmer said.
“Ultrasound-guided injection with PRP or stem cells can, in some cases, restore the normal ultrasound appearance of an injured tendon within 30 days of treatment,” Palmer said. “However, as good as the ultrasonographic image may appear, the injury is not healed at that time with adequate matrix to withstand the rigors of training. There is a need to further understand and manipulate the remodeling process in the hope of increasing the strength and elasticity of the healing tissue.”
Surgical options for treating tendon and ligament injuries are designed to reduce the stress applied to the healing structure or to stimulate the healing response to chronic injury, Palmer explained.
Adjunct therapeutic options at veterinarians’ disposal include extracorporeal shock wave therapy, hyperbaric oxygen, cold laser, and magnetic field therapies. “The biological effects of some of these modalities are better documented than others,” Palmer said. For example, he said, Steven Thom, MD, PhD, of the University of Pennsylvania Institute for Environmental Medicine has shown that hyperbaric oxygen therapy mobilizes stem cells and increases the production of growth factors and signal proteins in the bone marrow that stimulate and support the healing process.
Traditional rehab training programs focus on gradual increases in load and stress over long periods of time, while monitoring the lesion with ultrasound, Palmer said. However, he added, veterinarians now know that “one size doesn’t fit all.”
“In some cases, particularly those characterized by limited fiber disruption (the soft tissue makeup is minimally damaged), a more accelerated program may be indicated,” Palmer said.
Combined, these treatments—intralesional, surgical, and adjunctive therapies, as well as controlled exercise—give veterinarians many therapeutic options for their patients. But, said Palmer, Thoroughbred racing's “Holy Grail”—achieving a sustainable racing career following healing and rehabilitation of tendon and ligament injuries—remains an elusive quest, he said.
"Many performance horses return to full athletic function following treatment of tendon injuries, but the uniquely high loads placed upon the tendons and ligaments of racehorses often leads to reinjury at some point after they resume racing," Palmer said.
“In my opinion, combining these therapies offers us the best chance for successful healing and rehabilitation of tendon and ligament injuries,” Palmer said. “The reality check is that healing tendon and ligament injuries takes time—as long as eight to 12 months of therapy and ultrasound-monitored controlled exercise.” Managing the expectations of owners and trainers is key.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.