"The treatment of tendon lacerations is arguably one of the most difficult endeavors a surgeon is confronted with," Jann suggests.
The veterinary surgeon can sew the ends together, do tenorrhaphy, but returning the animal to full function is another issue.
"Just getting them to recover from the anesthesia, getting the wound to heal, getting a functional animal back, are real challenges,"
says Jann. "If an infection gets going, it's a challenge to resolve. It's similar to human surgery. If you cut your hand badly,
when a tendon is affected it's pretty hard to regain full function."
During the repair process, tendons sometimes heal too well, producing scar tissue that is inelastic. Normal tendon tissue
is elastic. It is what enables kangaroos or deer to jump or a human athlete to dunk a basketball.
It's not so much a function of strength, but rather the spring that the tendons provide. When they tear, whether lacerated
or cut, they tend to fill in with scar tissue that doesn't stretch like normal tendon.
Immobilization of the horse's limb is imperative to prevent further lower-leg damage. Various methods (e.g., the Kimzey Leg
Saver or a self-constructed splint of plastic PVC pipe) can be used to keep the limb from further movement and injury.
Once the limb is immobilized, the next concern is hemorrhage, common with tendon lacerations. A pressure bandage will reduce
active bleeding, and systemic antibiotics are warranted due to usually excessive contamination.
"Most of the wounds that we see in horses are pretty contaminated," Jann says. "Horses usually find the most non-sterile
thing in the environment (to cause) a laceration."
Wound debridement is of critical importance. For tendon injuries "it cannot be overemphasized," Jann says, adding, "It would
be appropriate to say that debridement is the sine qua non for successful repair of traumatic tendon lacerations."
But proper debridement of all infected, contaminated tissue can be a problem.
In the early stage of treatment, the surgeon should focus, not only on the tendon, but on the entire wound, Jann says. The
tissue that most often seems to be most contaminated is the paratenon, which must be meticulously debrided.
Even then microscopic foreign debris remains, and irrigation is essential to removing these remaining sources of infection.
Large volumes (2 to 3 liters) of irrigation solution (0.1 percent providone-iodine and lactated Ringer's) are recommended,
along with active suction.
Suturing tendons usually is indicated.
"The three goals of tendon repair are minimizing gap formation, minimizing adhesion formation and creating a minimal interference
to the intrinsic vasculature of the tendon," Jann explains.
After the deep structures are repaired "every effort should be made to close the wound primarily," particularly the paratenon,
he says. This tissue layer should be closed over the tenorrhaphy site.
"This step is important because the paratenon provides the cells from which the tendon scar is formed," says Jann. And it
prevents tendon tissue from adhering to the subcutaneous tissue and skin. These upper layers are closed separately.
Primary wound healing helps prevent formation of granulation tissue and maximizes overall limb function.
Sheathed flexor zones
Tendon lacerations that occur in the sheathed zones (i.e., digital synovial sheath of the fetlock joint) are more problematic
because of the potential for developing septic tenosynovitis. "This is at best a career-threatening and potentially a life-threatening
sequel to any traumatic wound involving a tendon sheath," Jann says.
In horses, any tendon laceration in the palmar and/or plantar aspect of the fetlock or pastern area automatically invades
the tendon sheath, because the tendons are contained within sheaths in these anatomic zones. In performance horses, these
areas are the ones traumatized most often.
"One recent report lists the digital sheath as the most commonly contaminated and infected synovial structure," Jann says.