The long digital extensor tendon attaches onto the bottom of the thigh bone (femur), runs through the knee joint and then forms a muscle located along the side of the shin bone (tibia).
Cause of long digital tendon avulsion
Generally this type of condition occurs in very young large breed dogs. At this early age the bones are very soft; thus the long digital extensor tendon can tear out of the bone with minimal trauma. The avulsed end of the tendon always has a small bone fragment that has broken out of the femur bone.
Breeds most commonly affected include great Danes, golden retrievers, and Labrador retrievers. Dogs develop this problem when they are typically under one year of age; however, two reports have cited great Danes that were 14 and 16 months of age. Clinical signs of this condition include lameness and swelling on the outer side of the knee over the region of the avulsed tendon.
X-rays and physical examination findings support the diagnosis of a long digital extensor avulsion. Uncommonly, CT scan or MRI of the knee is needed to arrive at a diagnosis. Exploratory surgery is the most definitive way to diagnose and treat the problem. In preparation for surgery, preoperative blood work including a complete blood count, chemistry profile and urine testing are recommended to ensure that your pet is healthy enough to undergo anesthesia and surgery.
Surgery is the recommended treatment option for an avulsed long digital extensor tendon in the knee joint. An incision is made on the side of the knee over the affected tendon. If the avulsion fracture is fresh (occurred within one week), the bone may be reattached to the femur bone with a screw. Because most avulsion fractures are chronic, the typical treatment involves suturing the long digital extensor tendon to the side of the joint capsule following removal of the bone fragment.
Excellent results are achieved with surgery; however, full resolution of lameness may take one to two months. Uncommon complications that may be seen include swelling, infection and arthritis.
For more information on this subject, speak to the veterinarian who is treating your pet.