The alar ligaments are small paired spinal ligaments that attach from the occiput to the proximal portion of the odontoid process of the second cervical vertebra (C2). Injury to the upper cervical spine in children is infrequent, and isolated injury of the alar ligaments is even more uncommon, with only a report of two cases, in German, appearing in the literature1. Here we describe isolated alar ligament disruptions in three children. This injury caused persistent torticollis and neck pain in which neither fracture nor anterior or posterior listhesis was detected on radiographic studies. The injury did not lead to instability in the upper cervical spine in any of the patients.
Medical records and radiographs of three patients with isolated alar ligament disruption were reviewed. Data collected included age of the patient at the time of injury, mechanism of injury, presentation of the patient, method of treatment, time to healing, complications, post-treatment physical therapy, and final range of motion of the neck. This report includes case descriptions and radiographic studies of these three patients. We attempted to contact our patients and, when possible, our patients were informed that data concerning their cases would be submitted for publication. The protocol for this case series was reviewed by our institutional review board and was given exempt status.
Case 1. A seventeen-year-old female pedestrian was struck by a motor vehicle and sustained a painful neck injury and a fractured femur. Radiographs revealed that the thoracic and lumbar spine were normal. Computed tomography scans demonstrated widening of the space between the dens and the C1 left lateral mass (Fig. 1-A). Magnetic resonance imaging showed hyperintensity to the left of the dens, indicating edema and ligamentous injury (Fig. 1-B). The injury to the cervical spine was treated with halo immobilization for twelve weeks, with no complications, and the patient returned to full activities. Seven months after the injury, lateral radiographs revealed that the cervical spine was stable in flexion and extension (Figs. 1-C and 1-D). Nineteen months after the injury, anteroposterior and flexion, extension, and neutral lateral radiographs showed that the cervical spine was normal.
Case 2. A fifteen-year-old girl was involved as a passenger in a motor-vehicle collision and sustained a painful neck injury and a fractured femur. Plain anteroposterior and lateral radiographs showed that the cervical spine was normal. A computed tomography scan showed widening of the space between the dens and the C1 lateral mass on the left, and a magnetic resonance imaging scan showed hyperintensity to the left of the dens. The patient was treated with halo immobilization for twelve weeks. Six months after the injury, she had full, painless neck motion and normal findings on flexion and extension lateral radiographs of the cervical spine. She returned to full activities.
Case 3. A five-year-old girl was a restrained front-seat passenger in a motor-vehicle collision. Following the collision, she had torticollis and injury to cranial nerve IV. Radiographs of the cervical spine, including lateral radiographs of the cervical spine in flexion and extension, showed no fractures, malalignment, or instability. A computed tomography scan showed no fractures or atlantoaxial rotatory subluxation but did suggest slight asymmetry of the space between the dens and the C1 lateral mass on the right. The patient was managed with a hard cervical collar and physical therapy, but the torticollis persisted and she was referred to our institution. She had full active and passive motion of the neck, but she held her head slightly tilted and rotated. A magnetic resonance imaging scan obtained four months after injury showed increased space between the dens and the C1 lateral mass on the right as well as increased fat signal (Figs. 2-A and 2-B), and a chronic disruption of the alar ligament was diagnosed. She was managed with diazepam and a soft collar for two additional months, and the resting position of the neck gradually improved with a physical therapy strengthening program over the course of one year. During this time, the torticollis resolved and the final neck motion was full and painless. At 1.5 years after the injury, anteroposterior radiographs and lateral radiographs of the cervical spine in flexion, extension, and neutral position showed normal findings.
The upper cervical spine is defined as the region between the occiput and the C2-C3 disc space. Trauma to the upper cervical spine is relatively rare in the pediatric population2, and the mechanism of injury may include birth trauma, nonaccidental injury, sport-related injuries, falls, and motor-vehicle accidents. Injury to this area most commonly results in dislocation or fracture through the osseous or cartilaginous elements, with or without neurologic compromise.
Several characteristics of the developing spinal column contribute to the unique injury patterns seen in children. The horizontal orientation of the facet joints allows a large amount of motion3. The elasticity in the spinal column may exceed the elasticity of the spinal cord, allowing for neurologic injury as a result of cartilaginous or ligamentous injury that may not be apparent on radiographs4.
Complex connections exist between the upper cervical spine and occiput, allowing motion and providing stability (Fig. 3). The stability at the occiput-C1 level is provided by the osseous cup-shaped joints between the occipital condyles and the superior articular facets of C1. Ligamentous stability at that level is provided by the capsular ligaments and the tectorial membrane, which is a continuation of the posterior longitudinal ligament, and injury here is rare5,6. The atlantoaxial joint derives osseous stability from the odontoid process of C2 and the anterior arch of C1. At this level, the ligaments that stabilize this joint during rotation of C1 on C2 include (1) the apical ligament, which runs from the odontoid to the foramen magnum; (2) the transverse ligament of the atlas, which holds the dens against the ring of C1; and (3) the paired alar ligaments, which run from the odontoid to the occipital condyles7. The alar ligaments contain the blood supply for the tip of the odontoid.
The biomechanics of the ligaments in the upper cervical spine have been extensively studied. Fielding et al. termed the alar ligaments and the transverse ligament of the atlas "auxiliary ligaments" and found that the force required to rupture the alar ligaments was equal to that required to rupture the transverse ligament8. In their study, the transverse ligament of the atlas ruptured after the generation of 75 kp (735.50 N) of force within the ligament, and then the alar ligaments failed in stretch after the generation of similar peak force as the displacement continued. In other biomechanical studies, the alar ligaments were found to be stretched most when the head was rotated and flexed, and therefore the ligaments were thought to be most vulnerable to injury in this position9,10.
Injury to the alar ligaments is rarely reported in the absence of fracture. Two cases of isolated injury to the alar ligaments in children were described by Briem et al. in the German literature1. These children were injured in gym class, presented with persistent neck pain and muscle spasm, and were diagnosed on the basis of magnetic resonance imaging of the upper cervical spine after radiographs revealed normal findings. Four weeks of immobilization in a hard collar was recommended for treatment, and both patients healed without consequences.
Magnetic resonance imaging is extremely useful for the evaluation of the upper cervical spine. The magnetic resonance imaging appearance of intact alar ligaments in adults has been described, and the ligaments are best visualized on coronal and sagittal images11,12. Willauschus et al., who acquired magnetic resonance images of cadaver specimens before and after sectioning of the alar ligaments, were able to demonstrate lesions13. Injury to the alar ligaments is represented by hyperintense areas on magnetic resonance imaging; these hyperintense areas are thought to be due to edema and hematoma formation in patients with acute injury or to fatty replacement in patients with chronic injury14,15. Magnetic resonance imaging has been found to be helpful in the assessment of the cervical spine in children when ligamentous injury is suspected after trauma but no fracture can be identified on computed tomography scans16.
In the cases of our three patients, all were either children or adolescents at the time of injury, and all three sustained high-energy injuries. Femoral fractures occurred in the two adolescent patients, and an associated injury to cranial nerve IV occurred in the youngest patient. All had asymmetry of the space between the dens and the C1 lateral mass, with high signal in the space on magnetic resonance imaging. In the most recent patient (Case 1), a computed tomography scan of the cervical spine was acquired rather than initial lateral radiographs. Over the past five years, our pediatric Level-I trauma center has moved away from making radiographs of the cervical spine at the time of evaluation of the injury. All pediatric trauma patients under the age of eighteen years who complain of neck tenderness, have neurologic deficits, have an abnormal result on the Glasgow Coma Scale, or have distracting pain from another injury undergo a computed tomography scan of the cervical spine as part of the trauma workup according to our hospital's protocol. A recent study found that computed tomography scanning of the cervical spine in pediatric trauma patients at our institution was associated with a sensitivity of 1.0 and a specificity of 0.97617.
We recommend that the type of immobilization to treat this injury be individualized on the basis of the mechanism of injury. A halo vest is commonly used to stabilize C1-C2 after injury to the transverse ligament of the atlas; however, because an isolated alar ligament injury does not destabilize the upper cervical spine, a halo vest may not be needed. Briem et al. reported that a hard cervical collar was effective in their two patients with low-energy injuries1. In our adolescent patients with high-energy injury, halo immobilization was used without complication. The younger child in our report sustained a high-energy injury and was treated with a hard cervical collar for an extended period of time and then with a soft collar when symptoms persisted. If this high-energy injury had initially been treated with a halo vest, it might have decreased the treatment time for this patient.
A weakness of this extended case report is the short follow-up time (nineteen months, six months, and eighteen months); however, the patients were all doing well and had no instability of the cervical spine at the time of their most recent follow-up visit as of the time of this writing. None of the patients underwent further axial imaging, and thus the final status of the space between the dens and the C1 lateral mass is unknown. As the quality of axial imaging improves and as pediatric trauma protocols evolve, this injury may be recognized more frequently and its natural history could be studied more effectively on a larger scale.
From the cases of our three patients, we can conclude that alar ligament disruption can be a cause of persistent neck pain and torticollis after neck injury in children and adolescents. In addition, isolated alar ligament injury should be considered in the differential diagnosis in children who have persistent neck pain and torticollis after injury. 
Note: The authors gratefully acknowledge the editorial assistance of Kristi Overgaard during the preparation of this manuscript.