The stifle (or knee) of the dog is situated between the large thigh bone (femur) and the 2 lower shin bones (tibia and fibula). A ligament is a dense fibrous band that connects one bone to another. The stifle joint is kept stable by a series of ligaments, the collateral ligaments that prevent the joint moving sideways and the cruciate ligaments which cross in the the centre of the joint, and prevent rotation and backwards and forwards movement of the joint.
Cranial cruciate rupture is the tearing of the ligament leading to instability of the stifle joint. It is the most common cause of hind leg lameness in the dog and a major cause of arthritis. Rupture may be acute or chronic in nature. An acute injury to the ligament is usually related to a traumatic event causing the limb to rotate – such as sudden twisting, stepping into a hole or jumping. Chronic cruciate injury is generally related to age related deterioration, obesity, or conformation abnormalities. Large breed dogs with straight hind limbs are more predisposed as more force is placed on the cruciate ligament. In cases of chronic cruciate degeneration up to 50% of dogs will rupture the cruciate ligament in the opposite hind leg within 2 years. Risk factors for cruciate injury are large active dogs, obesity and intermittent excessive activity by inactive dogs.
Signs will vary depending on the nature of the injury. An acute complete rupture of the cruciate ligament often presents with a non-weight bearing lameness of the affected hind leg of sudden onset – often related to exercise/play. Dogs with a more chronic injury or only a partial tear to their cruciate ligament, may only present with a mild lameness associated with exercise that often improves with rest. Often as the ligament degenerates the stifle becomes increasingly unstable and the lameness gradually gets worse. On examination by your veterinary surgeon they may be able to detect pain and swelling of the affected joint. With more chronic injuries there may be swelling on the inside of the joint related to scar formation. With some dogs they may be able to detect instability (called the cranial drawer sign) of the joint – meaning the joint can move backwards and forwards. Often though, your dog will need to be sedated to check for instability as pain and nerves will cause them to tense their muscles so the instability cannot be appreciated in the consult.
With small breed dogs under 10kg of weight, conservative therapy may be sufficient. This involves 6-8 weeks of rest, anti-inflammatory medication followed by gradual return to exercise and weight loss if indicated. Ligaments have a limited blood supply so are unable to heal, however with time the body can stabilize the stifle joint using scar tissue. Approximately 65% of dogs will recover by 6 months. With large dogs however, continual instability of the stifle joint leads to progressive arthritis and ongoing lameness and pain. In view of this it is preferable to surgically stabilise the joint.
There are many surgical options used these include:
Extra-articular method – this involves the placement of a large suture outside the joint in the approximate plane of the ligament, to tether the femur to the tibia. This procedure relies on scar tissue to ultimately cause stability of the joint. Post operative rest is crucial to the success of the surgery. Most dogs will return to 75% of their normal function.
Tibial Plateau Levelling Osteotomy (TPLO) and Tibial Tuberosity Advancement (TTA) are specialised surgical techniques that need to be performed by a surgeon trained in these techniques. It is beyond the scope of this article to explain them in depth, however the outcome of these surgeries is to level the surface of the tibia to eliminate the need for a cranial cruciate ligament. Both the TPLO and the TTA procedures are more recommended for large breed dogs with very straight hind limb conformation.
Regardless of the surgical technique complications following surgery can include infection, surgical wound problems, implant breaking (suture/plate), fracture (TPLO/TTA) or failure to return to exercise.
With all procedures a controlled exercise program will be required to gradually return your dog back to work after a number of weeks.
Regardless of the method of treatment, unfortunately osteoarthritis will progress over time. Your dog may gradually become less active especially in the cold weather and may become stiff after a period of rest. Controlling your dog’s weight and moderate daily exercise may help to ameliorate these signs.
Animal Care Vets is actively involved in our local community. We support a number of charities, including the SPCA. We also care for the Hawkes Bay Police dogs. Our customers know by experience that they can rely on us for sound advice on treatment options and that their pet is in the very best hands with our team.
