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Mathematical Precision Key to Implant Success in Miniature Dogs

07 October 2015

CANADA - Miniature dog breeds often encounter specific health challenges and their small size can make surgeries particularly difficult.

One of the most challenging procedures performed by veterinary neurosurgeons is surgical repair of atlantoaxial (AA) instability, a frequent cause of spinal cord injury in toy breed dogs, such as Yorkshires and Chihuahuas.

In AA instability, the first and second vertebrae of the spine are destabilized. Any spinal injury can be devastating to an animal, but injuries occurring at the level of the first and second vertebrae carry a higher risk of mortality.

Surgery to stabilize the two vertebrae, using a combination of pins, screws and surgical cement, is considered the best route for this condition. However, the small size of affected dogs means the margin of error is small when placing these implants.

“It is very challenging to place these implants and stressful for surgeons,” says Dr. Guillaume Leblond, who is completing a DVSc in Neurology with advisor Dr. Luis Gaitero in the University of Guelph’s Ontario Veterinary College’s Clinical Studies department.

Even a slight miscalculation when placing the screws and pins used in surgery can have disastrous consequences if the implant damages the spinal cord or caudal brainstem, where the respiratory centre lies, add Leblond.

He recognized a clear need to define how to place these implants during surgery on miniature dogs.

Dr. Guillaume Leblond, with Dr. Luis Gaitero, used CT imaging to determine safe corridors for implants during spinal cord surgery in miniature dog breeds.

Leblond investigated three different surgical techniques–two implants, five implants with surgical cement, and six implants with surgical cement–to assess the strongest biomechanical option while examining the safety of each technique and determining the best location for implants in the two vertebrae without inadvertently damaging the spinal cord.

While the biomechanics are important, safety of the technique is the most important, stresses Leblond.

Through CT imaging and 3D reconstruction, Leblond was able to identify and characterize ideal, safe implant corridors in 18 toy breed dogs studied. It turned out to be a mathematical and engineering challenge. Leblond also acknowledges the work of Professor John Runciman, UofG’s School of Engineering, who provided expertise on the engineering details.

While CT imaging has been used to determine safe corridors to insert implants in other sites along the spine, similar research had not been conducted for AA instability.

Using the data from the CT imaging study, Leblond calculated the entry point and angle for each implant. He worked with UofG’s Physics department to create a drill guide to assist in placing the implants.

Using the calculations he generated, the drill guide was set to the precise entry and angle for each implant. While the drill guide needs some refinement, the results are very encouraging, says Leblond. The research showed the calculations and guide successfully placed implants for the three different techniques.

His research also determined the method using only two implants was markedly weaker than the techniques using surgical cement.

There is a lot of reluctance to do this type of surgery, says Leblond. “Now I am much more confident when offering this surgery to clients. This research provides better understanding of where to place the implants, however this remains very challenging surgery”.

Leblond recently presented his findings at the 2015 American College of Veterinary Internal Medicine Forum in Indiana.

Leblond’s DVSc position is funded by OVC Pet Trust (@OVCPetTrust). The funding was invaluable to his research. “Pet Trust is definitely a huge help,” says Leblond.

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