We all know not all vertebra look the same, however did you know this means they don't behave the same way during trauma, too?
Let's look more closely at the cervical vertebra, for a moment.
C1-C2 are a common site of subluxation, especially in young small breed dogs. Congenital C1-C2 subluxation is not considered a traumatic subluxation in most situations. Traumatic C1-C2 subluxation does occur in developmentally normal dogs especially in circumstances when a collar may have resulted in a rapid deceleration of motion (hanging). Cervical vertebra are also "roomier" meaning that the ratio of cord to canal is smaller resulting in more fat in the epidural space compared to the thoracolumbar vertebra. This allows for a traumatic event to cause less clinical neurologic disease and may be a reason why dogs with cervical fractures and subluxations often recover well with medical management. Finally, cervical vertebra have more rotation and flexion or extension capacity compared to thoracolumbar vertebra therefore making them more resistant to fracture and subluxation.
Did you know that 5-10% of dogs have a site of a second spinal fracture/subluxation that is masked by a more cranial trauma? Please consider taking radiographs of the entire vertebral column in a post traumatic patient NOT just in the area of neuroanatomic lesion localization.
Three Column System of Stability
There is some debate about the validity of this system but I will mention it because many surgeons and neurologist ascribe to the principles. This system is used to determine the need to treat a fracture and does not base the need to treat solely on neurologic signs. (Although these are still important!) Instability is considered likely if 2 or more of the columns are affected.
Dorsal column: Dorsal process, dorsal laminal and dorsal ligaments
Middle column: Dorsal longitudinal ligament, dorsal anulus, middle, dorsal part of the vertebral body
Ventral column: Ventral longitudinal ligament, ventral anulus, and ventral body with lateral processes or rib heads.
How to use this information: Evaluate the fracture in two views, whenever possible. If two or more segments are affect, surgical correction should be entertained with the owner (and local surgeon/neurologist if you aren't correcting it yourself). If not (ex: fractured dorsal process), you may be able to avoid surgical correction. There are exceptions to every rule, so if you're unsure please reach out! (As a side note: I don't perform fracture reduction surgery but I am happy to help with the neurologic assessment, and to help facilitate referral.)
A few other notes about the difference between cervical and thoracolumbar vertebra:
Fractures/subluxation in the C6-T2 region may carry a worse prognosis due to disruption of the LMN to the thoracic limbs.
The paraspinal musculature of the thoracolumbar region is protective! Don't disrupt it if you don't need to.
The lumbar vertebra have large articular processes, which protect them from subluxation.
Thanks for reading and I hope you have a great rest of the week! As a reminder - I'm off to Texas for the week so please email if you have any questions but calling/texting may be time delayed due to my lecture schedule.