Introduction:
The cervical spine (neck bones) comprises seven stacks of bones called cervical vertebrae. They are named in order from above as C1 to C7. These bones are assembled in a ring-like fashion with a hole in the center that accommodates the spinal cord and important vessels and nerves. The first bone, C1, is called the atlas.
The atlas is ring-shaped, with the front curve (anterior arch) and a back curve (posterior arch connected on the sides (lateral mass). The upper portion of the atlas joins with the back of the skull (occiput), and the lower portion articulates with the second cervical vertebra (C2 - called the axis). These joints are named occipito-atlantal and atlantoaxial articulations, forming the craniocervical junctions.
What Is a C1 (Atlas) Fracture?
The craniocervical junction accounts for more flexible movements of the neck through the ligaments between occiput-atlas (O-C1) and (atlas-axis) C1-C2. Thus, they are also more prone to injuries. The incidence of C1 injuries has bimodal distribution occurring in people in the age group of around 30 and 80.
C1 fractures mostly occur at the front and back arches of the atlas. A neurologist named Sir Geoffrey Jefferson presented a review of four C1 fracture cases in 1920. Hence these fractures are named after him and known as Jefferson fractures.
What Are the Causes of C1 (Atlas) Fractures?
The most common cause of C1 fracture is trauma. The trauma can be caused by,
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A fall from diving and hitting on the head at the bottom.
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A blow or load to the back of the head.
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A vehicle accident where the head hit against the roof.
Basically, C1 fractures occur as a result of axial loading (force directed along the axis of the bone position).
What Are the Types of C1 Fractures?
Generally, C1 fractures can be of three types,
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Type 1: In this type, either the anterior or the posterior arch of the atlas bone gets fractured.
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Type 2: Simultaneous anterior and posterior arch breaks.
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Type 3: Fracture is present in the lateral mass.
Another common classification was devised by Levine in 1991 that describes the C1 fracture into five variants.
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Type I: The transverse process of the C1 bone gets fractured. The fragments are stable but may involve the vertebral artery (the main artery that supplies blood to the brain and spine) and foramen.
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Type II: Isolated posterior fracture.
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Type III: Isolated anterior fracture.
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Type IV: Lateral mass fracture.
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Type V: Burst fracture involving multiple breaks involving three to four pieces.
What Are the Symptoms of C1 Fracture?
Patients with a C1 fracture will have:
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Upper neck pain.
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Poor balance.
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Loss of muscle control.
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Swelling at the injured site.
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Radiating pain in the legs.
Clinical presentations of the C1 fracture include,
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Bruising.
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Stiffness in the neck.
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Altered gait (walking style), indistinct speech, and brain dysfunction if nerves are involved in the injury.
Who Is at Risk of Acquiring a C1 Fracture?
Persons who are more prone to accidents and trauma are at the risk of C1 fracture.
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Drivers and sports persons (especially contact sports) are at risk of acquiring a C1 fracture.
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Patients with osteoporosis have a higher risk of fractures in the vertebra.
How Is a C1 Fracture Diagnosed?
At first, the medical history and the specific symptoms are reviewed by the physicians. Later the patients are physically examined for injury site bruising and swelling.
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A plain X-ray will help to locate the break and also reveal the size and extent of the fracture.
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A computed tomography (CT) scan will exhibit a cross-sectional view of the fracture to identify the changes in alignment.
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Magnetic resonance imaging (MRI) is helpful for assessing ligament and tendon injuries in the neighborhood.
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An angiogram can be performed if there is a suspicion of injury to the vertebral artery.
Radiologically some significant criteria to be considered are,
Atlanto-Dens Interval (ADI):
This measurement is evaluated on the radiographic film of the lateral cervical spine. The atlanto-dens interval is the distance between the front arch of the atlas and the front outer portion of the dens. The inferences are
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Less than 3 mm and 5 mm is normal in adults and children, respectively.
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3 mm to 5 mm refers to an injury to the transverse ligament without any damage to the alar and apical ligaments.
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Greater than 5 mm means injury to the transverse, alar ligament, and tectorial membrane.
Lateral Mass Displacement or Rule of Spence:
The lateral displacement is viewed in the open mouth odontoid view (X-rays passed through the front of the face with an open mouth position). This parameter is used as a prognostic factor of transverse ligament injury.
The total lateral displacement of greater than 7 mm indicates transverse ligament tear.
How Is C1 Fracture Treated?
The treatment plan for C1 fracture depends on two factors:
1. Isolated Fracture of the Atlas:
If the fracture is limited to the bone without any displacement, a bracing device, namely a halo vest, is used to immobilize the bone until the healing takes place. This device surrounds the head and stabilizes them using side rods. These rods extend on the neck and shoulders and get attached to the vest worn by the patient. Halo vest immobilization is not recommended for old people as its usage is associated with complications.
2. A Fracture Involving the Transverse Ligament:
The transverse ligament is the one that stabilizes the atlas in the neck. If the transverse ligament is involved in the injury, then surgical fixation is the only option.
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The surgery entails the fixation of C1 to C2. In some cases, the back of the skull is directly fixed to the C2 vertebra to reduce extreme instability.
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Surgical decompression may be needed to remove any bony fragments that are pressing or crushing over the nerve.
Physical therapy after immobilization surgery is required to reduce the stiffness and regain the range of motion in the cervical spine.
Conclusion:
C1 fractures are relatively more common and can be serious and life-threatening. With relevant treatment planning, the overall outcome is good, even with conservative management. Rarely do C1 fractures present with neurological issues. Immobilization may be needed for up to four months for complete healing. Later neck collars and extensive rehabilitation will serve the purpose. Sometimes C1 fractures are associated with nerve injuries. Since their clinical presentation and its impact are difficult to predict, it is advisable to follow the doctor's advice on encountering a C1 fracture.
