A ruptured cruciate ligament is amongst the most frequently seen clinical conditions of the knee joint in dogs. It is characterized by complete severing of a fibrous ligament connecting thigh bone and shinbone, thus acting as an important structure of stabilization.
In normal condition the cruciate ligament prevents that the shinbone opposite to the femur slides forward. When the ligament ruptures this function is no longer given and the knee becomes instable in itself. The animal feels pain with every step. In order to avoid these pains, the dog relieves the affected leg with slightly bended knee joint and is lame.
The cruciate ligament can rupture due to an accident where the dog, for example when jumping, gets caught with the hind legs on an object. In such cases the cause is clear. The cruciate ligament may however rupture also without evident reason, what often happens with older animals. In those cases the reason is unclear; it is however assumed that a previous damage of the ligament is the reason, which makes the ligament brittle so that a minimal stress may result in the rupture. Frequently, the ligament of the other knee also ruptures in near future, what confirms the assumption. Above all overweight and little moving dogs are endangered.
The veterinarian diagnoses with the cruciate ligament rupture by means of a special test (drawer phenomena). Here it is tested whether the shinbone in front of the thigh can be pushed forward. If that is possible, the rupture is diagnosed. X-ray photographs can also support the diagnosis. The treatment of a cruciate ligament rupture does not always need to be realized surgically. With smaller, lighter dogs, a six to eight weeks immobilization of the knee may effect stabilization. The animal is then free of pain and does no longer lame. A healing of the rupture does not happen in this case. If the immobilization does not bring any improvement, an operation will be required. Heavier dogs (> 15 kg) should always be operated since the knee may not stabilize on its own. Additionally, in case of non-treatment arthrosis may appear which will damage the joint permanently. Both limping of the dog and immobilization for stabilization of the knee may have negative consequences. Amyotrophia, muscle tensions and inappropriate mechanical stresses are possible which may also adversely affect the joints.
A cruciate ligament rupture is not an emergency and does normally not require immediate consultation with the veterinarian. At the next opportunity, agree upon a date at the veterinarian's. If the dog hast strong pain or in case limping handicaps the dog, then the veterinarian should more urgently be consulted. The risk for the dog to suffer cruciate ligament rupture which is not based on an injury can be reduced. Experiences show that slim, active animals are less frequently affected by cruciate ligament ruptures than overweight inactive dogs. Movement and a good, balanced nutrition are appropriate to this effect.