Not all dog breeds have the same risk of ACL (Anterior Cruciate Ligament) tears, ruptures or cruciate disease. Some breeds that we see significantly MORE cruciate issues in at our Adelaide Vet clinics are Labradors, Golden Retrievers, Staffies (Both British Staffordshire Bull Terriers AND American Staffordshsire Bul Terriers) and Rottweilers.
However studies have also shown that the American Cocker Spaniel, Chow Chow, German Shorthaired Pointer, Saint Bernard, Bullmastiff, Boxers, Neopolitan Mastiff and Akita have an increased risk of crucaite tears.
Interestingly these American studies don't show an increased risk or prevelance for our common Staffy (ie British Staffy) - BUT we definately see more of these breeds affected than most others! It may be that they don't have this lovely breed there, only their American counterparts.
Notably the German Shepherd was shown to have a lower prevelance/risk of ACL tears in one major study.
There was also an increased risk detected for DESEXED dogs but no difference between males and females. AND an increased risk for overweight dogs.
There are also lists of dog breeds that have been shown to have a 'Heritable' incidence of cruciate disease, meaning that it is shown to be genetically passed on BUT many of these actually don't show up in lists of increased risk or incidence when compared to the over all dog breed populations! Strange ... these dog breeds include: Australian Shepherd, Bearded Collie, Border Collie, Bloodhound, Bernese Mountain Dog, Bouvier des Flandres, Flat Coated Retriever, Giant Schnauzer and the Irish Setter.
The cause of the increased risk of cruciate tears remains under discussion and investigation however the main concensus is that ongoing microtrauma to the crucaite ligament is the main cause. This means that there has been an initial minor injury that then is subject to ongoing, recurrent further minor strain injuries, leading to the gradual weakening and the final rupturing of the ACL.
The angle of the tibial plateau (the slope of the flat top of the tibia or shin bone) is implicated in many cases, such that just standing places increased forces on the ACL, constantly stressing it.
Most would be a result of injury, often involving some degree of twisting or turning just as the dog's weight is placed on the leg. Once even a tiny degree of strain has occured to the cruciate ligament, this ever-so-slight lengthening of the ACL due to the stretching injury means that at every twist or turn, the strained ACL allows even more rotation about it and the posterior or caudla cruciate ligament that it crosses over. This leads to repeated strain injury to the crucaite, causing further slight stretching/lengthening and weakening ... which will eventually snap fully. All of these affected dogs have significant arthritis in their stifle (knee joint) when it comes time to x-ray and/or perform surgery.
Some breeds are thought to have a form of autoimmune disease that causes chronic inflammation and damage to the ACL and the rest of the joint, gradually reducing its strength and effectiveness. Studies have struggled to identify this but it is still seriouly considered a highly likely cause in some dogs.