Last month’s Research Refresh focused on a VOSM-produced paper that highlighted the ultrasonographic findings of Achilles tendinopathies. The paper was so well written and presented, I felt I just had to spend a little more time sharing its contents with you. Last month we focused on the findings of the paper; this week we’ll look at the anatomy of the canine Achilles tendon, and the signs, causes, diagnosis and treatment of Achilles tendinopathies.
The Anatomy of the Achilles Tendon in the Canine
The Achilles tendon is also known as the common calcanean tendon, and is made up of the tendons of five muscles. The tendon of the gastrocnemius muscle and the superficial digital flexor tendon remain distinct from each other and from the third tendinous unit, known as the common tendon. The common tendon is made up of the tendons of the gracilis, semitendinosus and biceps femoris muscles.
The tendon of the gastrocnemius inserts on the proximal surface of the calcaneus and influences tarsal extension. The superficial digital flexor tendon travels through the superficial digital flexor retinaculum at the proximal calcaneus and then continues distally to the second row of phalanges where it will attach. The common tendon will insert on the medial aspect of the calcaneus and plays a minor role in tarsal extension (Evans et al., 2013).
Rupture of the Achilles Tendon in the Canine
Although not an overly common injury in dogs, rupture of the Achilles tendon has been reported and seems to occur more commonly in medium and large breed dogs who are active and mature, and fall into the middle-aged bracket (Gamble et al., 2017). A rupture can be complete, affecting all three tendon units, or partial, leaving the superficial digital flexor tendon intact.
Signs and Symptoms
A complete rupture of the Achilles will present as a non-weightbearing lameness in the acute phases, with swelling over or near the calcaneus. There may be evidence of a skin lesion or a laceration, and careful palpation may reveal the site of disruption within the tendon. As the injury becomes chronic, swelling might no longer be present and the dog will start weightbearing again in some degree of a plantigrade stance, with the stifle hyperextended and the hock hyperflexed, the metatarsals and digits dropping towards the ground. You should be able to palpate fibrous thickening of the tendon in a chronic case, and extension of the digits will be painful.
In a partial tear, the toes will curl downwards into a crab-claw stance, with the digits knuckling. If the lesion affects only the gastrocnemius tendon and the common tendon, the superficial digital flexor tendon will cause the toes to contract, and the tarsus to hyperflex.
Cause of Injury
Traditionally we have associated an Achilles tendon rupture with acute trauma, such as an impact injury leading to avulsion of the tendon, or a cut or laceration to the muscle or tendon. We are now also recognising that chronic degeneration of the tendon plays a role (Morton et al., 2015). It is possible for active or working dogs to experience an acute on chronic rupture, and chronic degeneration may also result secondary to a systemic disease process (Spinella et al., 2010) such as Cushing’s disease and diabetes. It has also been associated with obesity (Harassen, 2006).
Radiographs have traditionally been used to assess for an avulsion or other signs of injury. Radiography does not, however, give us a clear indication of the condition of the soft tissues and is not a useful tool for re-checks of the injured site.
Diagnostic ultrasound has proved invaluable in this regard, as a means to assess the tendon and surrounding soft tissues, allowing accurate grading of the lesion and identification of the structures involved in the lesion. It allows for direct comparison with the contralateral limb, identification of any asymmetries between the tendons, and will reveal whether or not the contralateral Achilles tendon is symptomatic. Further advantages of this imaging modality include the lack of need for sedation and anaesthesia, as well as its greater affordability when compared to a CT or MRI scan. These factors make it the ideal modality for initial evaluation and regular follow up checks.
The treatment will depend on the grade of injury present and the structures that have been involved, as well as the chronicity of the injury. For grade 1 strains, the recommended treatment is rest, NSAIDs, laser therapy and rehabilitation therapy. A support wrap or immobilization may also be indicated in some cases.
A moderate grade 2 strain will need the above treatment with some additional interventions, such as the use of regenerative medicine. A grade 3 tear will require surgical correction.
The healing time after surgery is 16 weeks, and patients should be managed with a splinted bandage for the first six weeks, followed by a hinged brace that can be dynamized over the rest of the recovery period to allow for gradual increases in range of motion and stress placed on the injured site.
Recovery should be augmented with regenerative medicine and physiotherapy to support healing and regeneration of the tendon.