Achilles tendon injury
The Achilles tendon, also called the common calcaneal tendon, is composed of three tendinous structures including the gastrocnemius tendon, the superficial digital flexor tendon, and
the common tendon of the biceps femoris, gracilis, and semitendinosus muscles. This tendon is most frequently injured by laceration
in both dogs and cats.56 Chronic and acute injuries of the Achilles tendon may occur. Acute injuries are most commonly due to lacerations and often
occur within 48 hours before presentation. Subacute injuries have occurred at any time between two and 21 days, and chronic
injuries are older than 21 days.57
Subacute and chronic injury pathogenesis and diagnosis. The pathogenesis of subacute or chronic injuries not associated with laceration of the tendon is not well understood. Progressive
rupture of the Achilles tendon can develop over time, with injury most commonly to the gastrocnemius component affected.56 Suspected initiators of such chronic ruptures have included chronic corticosteroid ingestion and fluoroquinolone (even one
dose in people may cause tendon damage) administration.58,59 Most veterinary cases are in large-breed, active dogs and may be related to chronic repetitive injury during exercise.57
Progressive Achilles tendon rupture is diagnosed on physical examination and confirmed with radiography and ultrasonography.
Examination may reveal changes in posture with hock hyperflexion, with or without excessive digit flexion, and, possibly,
a plantigrade stance. Palpation of the tendon may reveal thickening, thinning, or a normal-sized tendon. Ultrasonographic
findings may include signs of hemorrhage, fiber disruption, and scar tissue formation (Figures 5A & 5B).60,61 Normal tendon diameter as seen on transverse ultrasound images has been established at 2.4 to 3.2 mm.62
5A & 5B. Longitudinal (proximal is to the left, and caudal is across the top) images of ultrasonographic examination of the
distal Achilles tendon in a Labrador retriever: 5A) The tendon without significant abnormalities. 5B) The contralateral tendon
of same dog with marked fiber disruption and fluid present at the former insertion of the tendon to the calcaneal bone.
Treating tendon rupture. Surgical treatment is preferred over conservative medical management in cases of complete gastrocnemius tendon rupture.56,63 In people, dogs, and cats, primary repair of the tendon is performed and most commonly involves one of two different suture
techniques: the three-loop pulley or the locking-loop suture pattern (Figure 6). Both patterns have superior strength compared with other patterns used in the past, but the locking loop may have improved
resistance to gap formation with loading of the tendon.64 A gap between the torn tendon ends or tendon end and calcaneal bone of less than 3 mm allows strength and stiffness to increase,
with a decrease in repair failure during the first six weeks after surgery.65 All sutures involved in the primary repair are recommended to be nonabsorbable monofilament suture in order to allow gliding
motion along the suture, but sustain reapposition of the tendon ends for at least three weeks.56
6. The three-loop pulley (left) and locking-loop (right) suture techniques for tendon anastomosis.
Tendon repair augmentation. Augmentation of the primary repair is controversial. Acute lacerations or injuries of less than 48 hours' duration usually
are not augmented. Subacute or chronic lacerations are most often augmented with various implants or tissues intended to remain
permanently at the repair site.61,63 Biological implants include free fascia lata graft, porcine small intestinal submucosa, or the semitendinosus muscle.66 Injection of the tendon repair with concentrated platelet gel has been advocated to speed healing postoperatively, but, to
my knowledge, no controlled studies have proven its effectiveness in tendon healing in dogs.67 Porcine small intestinal submucosa has been used experimentally in dogs and facilitates complete tendon healing within 90
days of the surgically created Achilles tendon defect.68
Postoperative care and return to function. Protection of the repair early in the healing process is a must. Additional support can be from a cast, external skeletal
fixator, splint, or calcaneal-tibial bone screw. All of these methods provide relief of tension on the repair for three weeks
to three months after surgery.56,69 Many practices support the repaired tendon with an orthotic such as a neoprene brace, hinged splint, or other custom-made
device so that the dog may again begin training as soon as possible.
Immobilization for longer than four weeks will result in deleterious effects on the joints, some of which can be permanent.70 In addition, early mobilization of the joint improves the healing process and augments the tensile strength of the tendon
repair.67,71,72 The average length of time that some form of immobilization is needed is about 10 weeks, but most surgeons decrease the
amount of support incrementally over that time. A dog may achieve a stable functional hindlimb after repair, but return to
competition is less likely than return to function as a pet. A study from New Zealand determined that only seven of 10 dogs
returned to full or substantial levels of work after healing, and 29% of those had moderate persistent lameness.46
New methods to enhance and speed healing of tendon repairs are being investigated. Low energy shock wave therapy may enhance
neovascularization of the bone-tendon junction in dogs.73 Ultrasound therapy may be able to accelerate healing and tendon maturation in dogs as well.74 While no clinical studies exist, future developments and methods of postoperative care may improve the functional outcome
in small animals with Achilles tendon injuries.
This review describes a wide range of causes of lameness in sporting dogs, but many new conditions will be identified as the
popularity of dog sports continues to increase. A thorough physical examination and an investigation of intermittent lameness
in sports dogs early in the course of their disease can prolong their athletic careers and may even improve performance. Diagnosis
of these conditions should involve any appropriate combination of radiography, ultrasonography, nuclear scintigraphy, computed
tomography, MRI, and arthroscopy, among other diagnostic tools. Further research is needed to determine the best treatment
options for these dogs, but new developments continue to be investigated.
Of course, preventing injury in these canine athletes is the primary goal of owners, trainers, and veterinarians. See the
related article "Preventing injury in sporting dogs" for measures you can recommend clients take to help their dogs stay healthy
and injury-free as they participate in sports.
Wendy Baltzer, DVM, PhD, DACVS
Department of Clinical Sciences
College of Veterinary Medicine
Oregon State University
Corvallis, OR 97331