What is the superficial digital flexor tendon?

The superficial digital flexor tendon extends from the back of the bottom of the femur (thigh bone), down the back of the lower leg (as a component of the common calcanean (Achilles) tendon, together with the tendon of the gastrocnemius (calf) msucle and the combined tendon of the biceps femorus, gracilis, and semitendinosis muscles), over the point of the heel (called the tuber calcanei), and down the bottom of the foot to branch and attach to the toes. This structure functions to flex the toes. The tuber calcanei (end of the heel bone) provides a shallow groove where the SDFT runs over it, and also at this position, connective tissue bands extend from the SDFT to either side of the heel, further stabilizing the tendon in its correct location. 

What is superficial digital flexor tendon luxation?

Superficial digital tendon luxation (dislocation) occurs when the SDFT slips out of its groove on the point of the heel (tuber calcanei), usually to the outside (laterally), but sometimes to the inside (medially). This is typically the result of a tear through one of the connective tissue bands (medial and lateral retinaculum) that hold the SDFT centered in its groove. Most commonly, the medial (inner) component tears, allowing the SDFT to slip off the heel bone to the outside. This prevents normal flexion of the toes, and impairs normal limb use. 

What causes SDFT luxation?

Tearing of the medial (inner) retinaculum is usually associated with rotational forces exerted during vigorous activity such as herding or agility work. It is believed that the medial retinaculum is weaker than the lateral retinaculum, and this is why it is more commonly damaged. Frequently, patients who experience a SDFT luxation also are found to have a shallower-than-normal groove, potentially predisposing them to luxation. Shetland Sheepdogs and Collie breeds are most commonly affected, although this condition has been diagnosed in a wide variety of medium and large breed dogs. 

How is SDFT luxation diagnosed?

Patients with SDFT luxation typically present to their veterinarian for a history of intermittent weight-bearing hind limb lameness that occurs as the tendon pops in and out of its groove spontaneously. On physical exam, the tissues at the point of the hock are usually swollen or thickened. The toes may be more extended than normal, with their toenails angling forward and upward rather than contacting the ground. The SDFT can usually be palpated and manually luxated and reduced by the veterinarian, although in chronic cases in which a large amount of scar tissue has formed, the tendon may be fixed in a luxated position. X-rays are useful primarily to rule out other causes of hind limb lameness. Ultrasound is utilized to confirm the diagnosis and determine the severity of the injury. It also enables the evaluation of the associated tendons to identify potential concurrent injuries. 

How is SDFT luxation treated?

The treatment for superficial digital luxation is a surgical procedure in which the torn retinaculum is sutured back together, thereby restoring the tendon to its correct location. If the groove at the point of the heel bone (tuber calcanei) is found to be absent or abnormally shallow, it will be deepened to further increase stability. 

What is the aftercare following this surgery?

Following surgery, a cast or splint is placed on the limb to hold the hock in partial extension, preventing strain on the superficial digital flexor tendon while the retinaculum heals. After two to three weeks, this is replaced with a soft padded bandage, which provides a decreased level of support and allows a small amount of movement, but prevents full range of motion. After one to two weeks, the soft padded bandage is removed, and the patient is gradually returned to full activity over the next few weeks. Even with the protection of the cast or splint, it is essential to restrict physical activity over the first month post-surgery to prevent re-injury as well as bandage irritation and sores. No running, jumping, or playing with other pets should be allowed during this period. Exercise should be limited to short, slow leash walks until the soft bandage is removed. At that point, leash walks should be gradually increased in length over the next two weeks before off-leash activity is permitted. 

What are the potential risks and complications of this surgery?

This procedure is associated with a relatively low risk of complications. Surgical site infection, bandage sores, and re-luxation of the superficial digital flexor tendon may occur. Infections and bandage sores are managed medically with antibiotics and topical dressings. Re-luxation, while rare, may necessitate a second surgery.

What is the prognosis for SDFT following surgery?

The prognosis following surgery is excellent, with most dogs returning to full activity within two to three months. Most dogs have no further problems with their superficial digital flexor tendon, although re-luxation can occur in rare cases.


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