![]() ![]() Unstable C1 ring fractures can generally be reduced by the application of cranial traction. Stable, minimally displaced (< 7 mm LMD) atlas fractures are treated by immobilization in a semi-rigid cervical collar or halo vest for 8–12 weeks. The most common associated fractures involve the odontoid process. Approximately 53% of atlas fractures are associated with other spinal fractures. If the sum of these two distances (lateral mass displacement, or LMD) is greater than 7 mm, complete rupture of the transverse ligament is presumed to be present. This can be evaluated on plain radiographs by measuring the distance from the lateral edge of C1 to the lateral edge of C2 on both sides on the AP open-mouth radiograph or coronal CT scan. A magnetic resonance imaging (MRI) scan is useful for those with associated neurological injuries or suspected ligamentous instability.įractures of the atlas are considered unstable when the transverse ligament is ruptured. CT scans are useful to evaluate the fracture pattern further. Initial radiological evaluation includes odontoid (open-mouth), anteroposterior (AP), and lateral views of the cervical spine, which will pick up 80–95% of atlas fractures. Patients with neck pain following trauma should be treated with a high index of suspicion regarding a possible cervical fracture. 2.1C) or comminuted fractures of the lateral masses ( Fig. Less common fracture patterns involve anterior arch fractures ( Fig. Severe variants of this injury are associated with a rupture of the transverse ligament, which allows the lateral masses to spread widely. Classically, there are four breaks in the ring in front of and behind each of the lateral masses however, other variations are seen. The force is transmitted through the lateral condyles, which fracture and are then forced laterally outward. 2.1B) make up about a third of atlas fractures and result from an axial load applied to the skull. 2.1 (A) A posterior arch fracture (B) burst (Jefferson) fracture (C) anterior arch fracture (D) lateral mass fracture.īurst fractures (Jefferson fractures) ( Fig. ![]() The injury is best seen on a lateral radiograph or sagittal and axial computed tomography (CT) images.įig. The relatively weak posterior arch is compressed between the occiput and the neural arch of the axis. This injury occurs after forced hyperextension of the skull and cervical spine. 2.1A), which accounts for almost two-thirds of all atlas fractures. The most common type is an isolated fracture of the posterior arch ( Fig. There are four basic types of C1 fractures. Neurologic injuries are rare with isolated C1 ring fractures, because of the ample size of the spinal canal in relation to the spinal cord. The vertebral arteries pass laterally through the foramen transversarium, then curve medially across the posterior/inferior portion of the ring before entering the cranium. This complex enables the unique mobility of the head in relation to the spine. The odontoid process is held firmly to the posterior aspect of the anterior arch of the atlas by the transverse ligament. The atlas ring surrounds both the odontoid process and the spinal cord. Superiorly, the lateral masses support the occipital condyles, and inferiorly they articulate with the upper surface of the axis. ![]() Two arches of bone, one anterior and one posterior, are joined together by two lateral masses to form a ring. The anatomy of the C1 ring is unique and contributes to the typical fracture patterns that are seen. In current practice, over half of C1 ring fractures are associated with other musculoskeletal injuries. Historically, these fractures were thought to be universally fatal, although in reality most fractures were missed until the advent of modern imaging modalities, with many isolated C1 ring fractures recovering without complications. C1 ring fractures were first described by Cooper in 1822 but are better known from the descriptions of Jefferson in 1920, whose name is often associated with the four-part C1 ring fracture. Greg Andersonįractures of the C1 vertebra, or atlas, make up 2–13% of all spine fractures and 1–2% of skeletal fractures. ![]()
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