Causes of a ruptured anterior cruciate ligament in dogs
Biomechanically, dogs and humans are not comparable. In contrast to humans, whose cruciate ligament can be torn due to trauma or mechanical overuse with no prior injury, the same injury in a dog displays characteristic symptoms.
In histopatholological tests it can be shown that in nearly all cases, parts of the ligaments were degenerated or ruptured before the tearing occurred.
A once-off overuse of the ligament seems to usually not be a main cause of a tear in dogs. This is also evidenced as in many "fresh" cruciate ligament tears, there were radiologically proven osteoarthritic changes of the bones that existed prior to the injury. Recent studies have suggested bacterial infections as a contributory cause of ligament degeneration.
The breed and weight of the individual dog seem to be deciding factors in whether a dog will sustain a ligament tear. Certain breeds such as Rottweilers, Labradors and Newfoundlanders present considerably more often than, for example, German shepherds or Dachshunds. Nevertheless, the diagnosis is seen in all breeds and sizes of dog.
If a dog presents with one cruciate ligament tear, there is a 60-70% chance that the other knee will also be affected.
The knee is a hinge joint. It is formed by the tibia (shin bone), fibula (calf bone), femur (thigh bone) and patella (knee cap). The joint is controlled on the sides by two collateral ligaments. These ligaments stabilise the rotation point of the thigh and lower leg by hindering the lower leg from sliding forward. The meniscus functions as a damper between the upper and lower leg.
Diagnosis of torn cruciate ligament
When the cruciate ligament is torn, the upper leg is no longer kept from sliding backwards, and displays the so-called "drawer phenomenon". Here, the lower leg can be moved forward while the upper leg remains fixed. A positive drawer phenomenon is evidence of a torn cruciate ligament.
Untreated torn cruciate ligaments lead to osteoarthritis of the affected knee in a very short time. Running normally and pain free is no longer possible for the patient.
In terms of surgical treatments, diverse methods have been established. In all methods, the knee, including the meniscus, is inspected and any loose parts of ligament or meniscus are removed and the joint is thoroughly washed.
Dogs that weigh up to 8kg can be treated with capsular fascial imbrication (Meutstege method) with no problems.
For dogs up to 25kg, treatment can also take the form of an extracapsular band replacement (Flo or De Angelis' method). Non-absorbable sutures are anchored outside the joint to stabilise the knee. The thread is looped around the fabella and then put through the tibia. Therefore, the thread is orientated parallel to the orientation of the torn ligament.
Near the end of the 1990s new operative techniques were introduced into veterinary medicine by veterinary surgeons and biomechanics. They are able to be used to treat torn cruciate ligaments in all breeds and sizes of dog, but are primarily used with medium to large dogs.
One operative technique that is used largely with medium to large dogs is TTA (Tiberal Tuberosity Advancement).
In this method, the forward edge of the tibia is brought forwards again to inhibit the sliding of the lower leg.
This method is innovative as the function of the anterior cruciate ligament is compensated for by a change in the biomechanics, so that the forces acting on the ligament are reduced to 0. This is achieved by creating a 90°angle between the patellar ligament and the tibial plateau.
As shown in diagram 1, body weight exerts force FJ upon the tibial plateau. The tensile force of the quadriceps muscles on the patellar ligament (FP) counteracts this force. If FP and the tibial plateau form a 90°angle, the forces FP and FJ are cancelled out. There is then no more shear force that can induce backward sliding of the upper leg. The loss of the stabilising function of the anterior cruciate ligament is therefore compensated for.
By sawing off the tibial tuberosity and introducing a placeholder (cage, see TTA Materials) the clearance angle of the patellar ligament to the tibial plateau is changed. At the same time the pressure of the patella (kneecap) on the cartilage surfaces of the femur is reduced. This facilitates the mobility of the knee joint. The sawn-off piece of the tibial tuberosity is locked onto a titanium plate (plate, see TTA Materials), chosen depending on the size of the dog, by a locking hook strip (prong, TTA Materials ) and the plate is then bolted on the tibial shaft.
The rotation point of the knee joint and its congruence are not changed by TTA. The pressure relations of the knee joint remain. Both the reduced pressure of the patella and the retention of the original pressure conditions reduce the formation of osteoarthritis.
The osteotomy in the non-load bearing part of the tibia allows rapid mobilisation of the patient.
Early postoperative functional rehabilitation, explained in detail to the owner after the operation, is of utmost importance for the success of the procedure.
Until the threads are removed twelve to fourteen days after surgery a pain medication should be administered.
Supporting physiotherapy is highly recommended.
X-ray check-ups four and eight weeks after operation are performed to check the fit of the implants and the bone regeneration at the operation site.
Cages are available in four different widths from 6 to 15 mm, and in various lengths up to 22 mm. The cage is anchored through the two eyelets with 2.4 mm wide screws in both the tibia and the tibial tuberosity. The width of the cage ultimately determines the extent of forward displacement of the patellar ligament.
The plates are available in sizes from two to eight holes. It is affixed to the tibia with screws through the two round holes. The square punched fields are used to lock the so-called prong with the sawn-off portion of the tibial tuberosity.