Laurie's Blogs.

Because cruciate ligament disease (CLD) is such a common problem, its not surprising that researchers are trying to figure out way to screen for predisposition to this condition. Headway has been made with Labrador retrievers, with a genetic test now being available commercially (https://www.vetmed.wisc.edu/lab/corl/canine-genetic-testing/). However, this test is Labrador specific, and cannot be applied to other breeds because it appears that the genes responsible for developing CLD are different for each breed. It is my understanding that the same researchers that developed the screening test for Labs are now working on developing one for Newfoundlands.

Another way researchers were looking to determine which dogs are predisposed to CLD is by analyzing the radiographic conformation of the tibia in mature dogs. Using the tibial plateau angle (TPA) as a predictor of future CLD has been looked at by several researchers but the results were mixed, showing no clear correlation between an increasing TPA and a predisposition of toward CLD. Those same researchers did wonder if a greater caudal inclination of the proximal tibial shaft in relation to its distal axis might be considered a risk factor for steep TPA, and by extension CLD.

This led to a paper released several years ago (2017), which has not received much attention, but has some interesting findings. It investigated the anatomical-mechanical axis angle (AMA-angle) between 2 breeds that are not predisposed to CLD (German Shepherd dogs and Basset hounds), compared to 185 large breed dogs and 17 West Highland white terriers diagnosed with unilateral, surgically confirmed CLD. They found that the AMA angle was significantly smaller for the breeds not predisposed to CLD, and that an AMA-angle higher than 1.87 had a sensitivity of 0.941 and a specificity of 0.965 for predicting CLD.

The AMA-angle is a way to measure the amount of caudal tibial angulation. The mechanical axis is represented by the same line that is used to calculate the TPA, from the midpoint between the intercondylar tubercles of the tibial plateau to the midpoint between the cranial and caudal aspects of the trochlea of the talus. The anatomic axis connects the midpoint between the cranial and caudal cortex of the tibia at 50% and 75% of the tibial shaft length. The angle between these 2 lines forms the AMA-angle.

Of course, one paper does not a screening test make. However, there seems to be real potential here. It would be nice if breed organizations started asking that lateral tibial radiographs be taken and submitted at the same time as elbow and hip radiographs. Collecting AMA-angle data by breed would allow us to learn the normal range, and average values, for each breed. Once we know the average values, breeders can selectively breed dogs with lower AMA-angle values. This is similar to PennHIP, where a poor score for one breed might represent an above average score for another. Knowing where a given dog places on the bell curve, relative to others of the same breed, can enable better decision making.

Just some food for thought.

Figure 1: 1 degree AMA-angle measurement of another breed (whippet) that infrequently gets CLD

Figure 2: 3.9 degree AMA-angle measurement in a patient that had CLD of the opposite hindlimb

Figure 3: 7.5 degree AMA-angle measurement in a patient that had and extreme (60 degree) TPA

REFERENCE

Guénégo L, Payot M, Charru P, Verwaerde P. Comparison of tibial anatomical-mechanical axis angle between predisposed dogs and dogs at low risk for cranial cruciate ligament rupture. Vet J. 2017 Jul;225:35-41. doi: 10.1016/j.tvjl.2017.04.011. Epub 2017 May 3. PMID: 28720297.

About the Author:

Dr. David Lane owns and operates Points East West Veterinary Services based out of Squamish, BC (Canada).  https://www.pointseastwest.com/    He is a specialist in canine sports medicine and rehabilitation therapy.  His research on the clinical effectiveness of combining chiropractic techniques with acupuncture therapy in dogs is the first of its kind. He was the first researcher to demonstrate the link between lower back pain and canine urinary incontinence; that treating back pain can reduce or eliminate symptoms in the majority of dogs. He also developed and published a minimally invasive surgical technique for resolving biceps tendon injury in dogs. 

Current areas of interest include documenting success rates when using stem cells to repair partially torn tendons, and developing a treatment algorithm for addressing injury to the biceps tendon.

His work with sporting dogs has brought him to numerous regional and national events, as well as travelling with the national team to the World Agility Championships in Spain and the Netherlands.

PS  He's looking for another rehab vet to come work with him.  Check out his practice!!