SPINE - CHANCE FRACTURE
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What is a Spine Chance Fracture?
A Chance Fracture, also known as a “seatbelt injury", is a bad spine injury that occurs after a high energy accident, like a high speed car crash.
It gets the name “seatbelt injury" because of the mechanism of injury, which is described as “flexion-distraction” to the spine. While the seatbelt will likely save a passengers life during a high speed crash, the belt can also cause this type of spinal injury by holding a persons lower body in the car seat while the upper body is bent forward (flexed) and pulled away from the seat (distracted) due to the force of momentum. The momentum of your upper body places significant strain on a very focused area along the spine. This can cause spinal ligament tears and spinal cord injury (or even a spinal cord tear).
Lets quickly review some anatomy of the spine so we have a clearer picture of how the spine is injured. The spine gives structural support that holds the body upright, and it protects the spinal cord. The spine is made up of vertebral bones stacked on each other like blocks. Each of our vertebrae has a hole in the center and when the vertebrae are stacked up, each hole lines up perfectly, and together they form the spinal canal (this is where the spinal cord runs, from our brain to our lower back).
The spine has mobility, and this is great because it allows us to bend and twist our torso. During normal bending or twisting, there are many strong ligaments that hold the vertebral bodies in position to prevent any displacement which could damage the spinal cord. However, if there is a big enough force acting on the spinal column, these ligaments can tear, and then vertebrae can shift out of position (now the holes don't line up and the spinal cord doesn't have a clear path).
In the case of a Chance Fracture, the ligaments along the back of the spine (the middle and posterior spine column) are under significant tension (they are being pulled apart), while the bone in the front of the spine (the anterior column) is compressed (its being squished).
Injury to both the front and the back of the spine requires a lot of force and so doctors are mainly concerned for a Chance Fracture during a high speed accident (its much less common to occur after a fall from standing, or from lifting a heavy box, for example).
How is a Spine Chance Fracture diagnosed?
A Chance Fracture is suspected when a person complains of severe back pain after a high-energy injury.
X-rays are often the first step in evaluating a spine injury, however, these days may Emergency Rooms that treat high energy trauma will take patients directly to the CAT scanner before getting x-rays. CAT scans are best thought of as a collection of many x-ray slices, which are taken from multiple angles, that provide a 3D picture of the spine. They are very helpful in showing spine fractures (broken vertebrae) or vertebrae displacement, however, a MRI is often ordered as well to look for injury to the spinal ligaments and the spinal cord itself (a CT scan is great at showing bones, but not very helpful in showing soft tissue injury, like tendons, ligaments, and nerves).
In addition to getting all of these images of the spine, a very detailed neurologic examination is necessary to determine the degree of spinal cord damage, and also to localize the site of injury. By assessing where a patient is feeling muscle weakness or numbness, doctors are able to pin point which vertebrae in the spine are likely to be damaged. All of this information is critical when doctors decide on a plan of treatment.
How is a Spine Chance Fracture treated?
The treatment of a Chance Fracture first depends on degree of neurologic symptoms.
If a patient presents with signs of spinal cord injury, and the CT scan or MRI shows a high likelihood of injury to the spinal cord, then surgery is recommended. The surgery is performed to take pressure off the spinal cord, and to stabilize an otherwise unstable spine using metal rods and screws (this prevents the vertebrae from moving further out of position, thus further pressing against the spinal cord).
Treatment of a Chance Fracture in someone that doesn't have signs of neurologic injury is more controversial. The primary goal is to protect the spinal cord from further injury (this occurs if the spine is unstable and the vertebral bones slip even further out of position). If spine is not significantly deformed, and there isnt significant damage to the posterior spinal ligaments, then patients can be treated safely with a brace that goes around the chest and back to provide stability while the injury heals. If however, there are signs on MRI of posterior ligament injury, or progressive change in the vertebral alignment on x-ray, then surgery is typically indicated to prevent the progression of spinal deformity and potential risk for future neurologic issues.
A scoring system called the TLICS (pronounced t-licks) attempts to give more definitive recommendations for surgery vs. nonsurgical treatment by scoring an injury based on 1) the fracture pattern of the affected bone (vertebrae), 2) if the posterior ligamentous complex is injured; and 3) if there is a neurologic deficit. Although it has been adapted by many respected medical institutions, the use of this scoring system for deciding treatment remains controversial.
What is the long term outcome?
The fractures will typically heal well when given time. The key is to ensure they heal with good alignment, so theres no pressure on the spinal cord. Oftentimes ligaments are very slow to heal, if at all, and that is why rods and screws are used to stabilize the spine. Our natural ligaments are replaced by metal support. Sometimes there is an injury to the posterior ligaments that is not full appreciated and the injury is treated without surgery, and then a follow up x-ray taken months or years later can show a progressive spinal deformity called kyphosis (or better known as a hunched back).
Unfortunately, recovery from neurologic injury is less understood. Some people are able to recover, while others see only a partial or sometimes very little recovery. It depends on the force of the initial injury as well as the age of the patient and other variables that doctors don't fully understand.
Reference
1) Mikles MR et al. Posterior instrumentation for thoracolumbar fractures. JAAOS 2004; 12: 424-35. full article. review.
2) Vaccaro AR et al. The thoracolumbar injury severity score: a proposed treatment algorithm. J Spinal Disord Tech 2005; 18: 209-15. full article. first description of TLICS (called TLISS).
3) Vaccaro AR et al. Surgical decision making for unstable thoracolumbar spine injuries: results of a consensus panel review by the Spine Trauma Study Group. J Spinal Disord Tech 2006; 19: 1-10. full article. updated TLICS.