What is Odontoid Fractures?
The odontoid process, also known as the dens, is a bone stickup from the second neck bone (also known as C2 or the axis). The odontoid process plays a key role in sideways rotation of your neck because the first neck bone (C1 or the atlas) spins around it. This rotation is the most significant part of turning your neck side to side.
Fractures or breaks in the odontoid process can be classified into three types: type I, type II, and type III. These types are determined based on where the fracture is and what it looks like.
What Causes Odontoid Fractures?
Odontoid fractures happen due to injuries to the neck area, usually from high-power incidents like car accidents, skiing, or diving. These incidents are more common in young people. In older adults, these fractures can result from lower-powered impacts like falls while standing up. The main way these injuries occur is through excessive bending of the neck, forcing the head and the first bone in the spinal column backward. If the force is strong enough, the odontoid, a small bony protrusion at the top of the spine, can break. The risk is even higher if the person’s bones are already weak due to conditions like osteopenia or osteoporosis.
There is a ligament (a band of tissue that connects bones) behind the odontoid that links to the sides of the first spinal bone. If the neck bends too much, this ligament can push too hard on the odontoid, causing it to break.
Risk Factors and Frequency for Odontoid Fractures
Odontoid fractures, also known as neck fractures, account for 10% to 20% of all neck-related injuries in adults. These fractures are particularly common in individuals who are 65 years or older. The most commonly injured vertebra in the neck, the axis, is where these fractures primarily occur. In fact, about half of all injuries to this vertebra are due to odontoid fractures.
Interestingly, these fractures seem to occur more often in two specific age groups – young adults and old-aged individuals. The cause of the fracture varies between these age groups. Young people often sustain these fractures due to high-impact forces like sports injuries, while in older people, even minor injuries can result in a fracture due to poor bone quality.
The way an odontoid fracture occurs is through a process called hyperflexion injury. The skull and the first vertebra in the neck (C1) cause strain on the odontoid process, a projection on the second vertebra (C2), resulting in a fracture.
These fractures are categorized into three types – type I, II, and III. The most common type is the type II, which includes over half of all odontoid fractures. The next common is the type III, while type I fractures are pretty rare. Road traffic accidents are often the cause of most odontoid fractures. In a study of over 30,000 patients, it was found that the average age was 77, with 54% of the patients being female.
Signs and Symptoms of Odontoid Fractures
An odontoid fracture, or a break in one of the bones in your neck, often happens because of some kind of trauma. Younger patients usually experience this type of fracture as a result of significant incidents like car accidents, sports injuries, diving mishaps, or falls from high places or down stairs. On the other hand, older individuals, whose bones might not be as sturdy, could suffer an odontoid fracture from minor accidents. These could be as simple as falling on flat ground or bumping into a door or piece of furniture. These are in addition to the types of incidents seen in younger patients.
When doctors examine people with odontoid fractures, they often find certain symptoms. Patients may complain of severe neck pain in the back, especially when they move. The neck might also be tender when touched. Some patients may find it difficult to swallow. This could be due to a blood clot at the back of the throat or swelling around the throat. Other patients may show signs of myelopathic spinal cord injuries. These symptoms can include tingling in the limbs, weakness, and other problems with nerve function. That being said, it’s interesting to note that odontoid fractures usually lead to fewer spinal cord injuries. This is because the space within the spinal column where the odontoid bone is located is relatively larger compared to the size of the spinal cord.
Testing for Odontoid Fractures
If your doctor suspects you have an odontoid fracture, which is a type of neck injury, they’ll probably start with x-rays of your neck from different angles. While a CT scan provides a more precise picture, experienced doctors can still spot suspected injuries using x-rays. They might also do a flexion-extension x-ray to check if the topmost part of your neck is unstable, especially for certain odontoid fractures.
CT scans of the neck are very useful in this situation. They provide clear pictures of the bones, letting doctors identify and study the odontoid fractures more closely. Certain anomalies, like defects in the back arch of the first cervical vertebra, can also be recognized through a CT scan, which can help determine the treatment. If there’s a chance the fracture has affected blood vessels, your doctor might also order a CT angiogram.
An MRI might be used if the doctor needs to check the health of the transverse ligament, a major neck ligament, or the spinal cord. This is particularly necessary if the patient shows signs of neurological deficits, like impaired movement or sensation.
The Anderson and D’Alonzo classification and the Grauer classification are commonly used to categorize odontoid fractures into different types, depending on the precise location and nature of the fracture. Some fractures are stable and don’t generally pose major risks, while others might be unstable, necessitating different treatment approaches or further imaging tests.
Treatment Options for Odontoid Fractures
The main objective of managing a fracture is to ensure stability. This can oftentimes be achieved through a fibrous union. In scenarios where the injury isn’t unstable or the ligaments aren’t damaged, an external brace or halo vest can help the fracture heal, usually within 12 weeks.
A conservative treatment approach might be suitable for patients with good alignment, no instability, and no neurological deficits. This type of approach can be particularly effective in treating Type I, II, or III fractures. For these cases, using a halo vest or cervical traction and a stiff neck collar has shown high rates of successful fusion, with Type I fractures usually seeing a 100% success rate, Type II at 90%, and for Type III fractures the success rate drops to 60%.
A stiff neck collar is seen as superior to a halo brace since it comes with minimal risks of complications from the device itself. Some studies have found that for older patients, soft collars can be just as effective as stiff ones. Additionally, using a halo vest doesn’t increase the risk of death, and conservative treatments and surgery have similar risks of in-hospital death.
In the case of Type II fractures, surgery may become necessary if the fracture is unstable, can’t be reduced, nonunion, or the patients present with deficits.
Whether it’s an anterior or posterior fixation technique, both methods yield equivalent outcomes. The anterior approach of using an odontoid screw preserves neck movement while giving an 80-100% fusion rate. Meanwhile, the posterior inferior fracture type with concurrent transverse ligament tear is suited for posterior fixation.
The advent of the Goel posterior joint manipulation technique allowed for most previously irreducible atlantoaxial dislocations to be reduced, almost eliminating the need for transoral odontoidectomy. This technique limits neck movements and increases the risk of impingement on the spinal canal.
The anterior odontoid screw fixation technique is recommended for fractures that are younger than 6 months old, have an anterior-inferior sloping fracture line, or are transverse fractures without any comminuted segments at the base. This technique comes with a low risk of damaging the vertebral artery and causing minor functional limitations after surgery.
However, not all cases are suitable for anterior odontoid screw fixation. A few of these scenarios include: Type IIA fractures, ruptured transverse ligament, a concurrent atlantoaxial dislocation, bone loss, injuries older than 6 months, anterior oblique fracture slope, a short neck, a barrel-shaped chest , or severe kyphosis.
In geriatric patients, there’s a high risk of nonunion, which indicates a level II recommendation for surgical stabilization. In these cases, a meta-analysis found the fusion to be superior with posterior fixations.
Significant variations exist in the treatment strategies, follow-up and imaging algorithms. Major health conditions and older age are significant factors in avoiding surgical fixation.
What else can Odontoid Fractures be?
Before concluding that there is an odontoid fracture (break in a specific part of your neck), it’s essential to be aware of certain conditions that can look like an odontoid fracture but aren’t.
One of these is called ‘Os odontoideum.’ This is an anatomical variant, a different but normal formation of our skeleton. As the spine grows, it has multiple areas of bone formation. If the areas of bone formation in the odontoid process (the tooth-like structure at the top of the second vertebra) and the body of the vertebra do not merge as they should, it can appear as though the odontoid process is detached from the vertebra (which looks like a type II odontoid fracture). This is particularly common in children, whose spine is still growing and forming.
Another condition is ‘Persistent Ossiculum Terminale.’ Again, this arises from the unique growth patterns of the spine. The very tip of the odontoid process develops from a separate source of bone formation compared to the rest of the odontoid. If these two sources are unable to combine, a gap can exist, which can look like a type I odontoid fracture.
What to expect with Odontoid Fractures
Kids usually achieve successful bone healing with the help of a device called a halo immobilizer. However, adults who are 50 years or older have a 21 times greater chance of bones not fusing correctly when using a halo immobilizer.
Successful bone fusion after an injury occurs in 88% of cases if surgery happens within 6 months of the injury. But, if surgery is postponed more than 18 months after the injury, the success rate falls to 25%. When the use of external immobilizers fails and if it’s been less than 6 months since the injury, inserting a screw into the front of the tooth-like bone at the top of the spine can be a good option.
For instances where a portion of the fractured bone is displaced or the spinal joint is misaligned causing pressure on the spinal cord, and it can’t be fixed with traction, surgery via the mouth might be necessary before fusing the bones in the back of the neck. Alternatively, a recent solution for this issue involves manually aligning the bones through the throat, followed by internal fastening.
Possible Complications When Diagnosed with Odontoid Fractures
It’s been observed that 25% to 40% of patients pass away at the time of an injury. Surprisingly, most who survive tend not to suffer from any permanent damage to the nervous system. However, there’s still a risk of instability in the upper neck region and injuries to the spinal cord. This risk can lead to a range of complications like Brown-Sequard syndrome, spinal cord transection, soft paralysis, myelopathy, and persistent neck pain, which, interestingly, happens to approximately 25% of patients.
Dealing with odontoid fractures can be quite complicated. This is partly because other injuries often occur at the same time, and these can make the situation worse. These concurrent injuries can take many forms such as:
- Anterior cervical wedge fracture
- Atlantooccipital dissociation
- Cervical burst fracture
- Cervical facet dislocation
- Cervical spinous process fracture
- Extension cervical teardrop fracture
- Flexion cervical teardrop fracture
- Hangman’s fracture
- Isolated transverse process fractures
- Jefferson fracture
Preventing Odontoid Fractures
After surgery, it’s important for patients to be checked for certain complications. These can include a buildup of blood in the area behind the throat, difficulty swallowing, inhaling food or liquid into the lungs, paralysis of the vocal cords, and infections at the surgery site. Patients should be aware of these potential issues and contact their surgeon’s office right away if they notice anything unusual.
