Traumatic vertical atlantoaxial instability in a case of atlanto-occipital coalition

STUDY DESIGN: This is a report of a woman with an atlanto-occipital coalition who experienced a traumatic vertical atlantoaxial facet dislocation and severe associated neurologic injury. OBJECTIVE: To describe the radiographic and pathoanatomic characteristics of the injury process. SUMMARY OF BACKGROUND DATA: Severe injuries of the occipito-atlantoaxial complex are uncommon and only rarely are associated with patient survival. This is the first report of this particular injury. METHODS: Plain radiography and tomography demonstrated the facet dislocation and instability of the injury. Surgical exploration for repair of the torn dura mater and bony arthrodesis demonstrated the gross pathoanatomy. RESULTS: The patient's vertical atlantoaxial instability was stabilized, her dura mater reconstructed, and her necrologic status has improved to allow mobilization with a cane. CONCLUSION: Vertical atlantoaxial instability has not been described previously. From the somewhat subtle radiographic findings, one might underestimate the severity of the neurologic damage. Aggressive work-up and management of this injury is suggested to avoid potential further necrologic sequelae.     

Anatomic considerations of anterior transarticular screw fixation for atlantoaxial instability

STUDY DESIGN: Anatomic parameters of C1 and C2 were measured in 30 dried human cervical spines. Anterior transarticular C1-C2 screws were placed in 15 cadaveric spines. OBJECTIVE: To provide anatomic data for anterior transarticular atlantoaxial screw or C1-C2 screw and plate fixation. SUMMARY OF BACKGROUND DATA: A posterior approach to fixation in the atlantoaxial joint has been well described. Damage to the vertebral artery is documented as a rare complication of posterior atlantoaxial transarticular screw fixation. An anterior surgical approach to exposing the upper cervical spine for internal fixation and bone graft recently has been developed. No anatomic information regarding the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 is available in the literature. METHODS: Direct measurements using digital calipers and a goniometer were taken from 30 pairs of dried human C1 and C2 vertebrae. The anterior transarticular C1-C2 screw insertion point is at the junction of the lateral edge of the C2 vertebral body to 4 mm above the inferior edge of the C2 anterior arch. The parameters related to anterior transarticular atlantoaxial screw fixation or screw and plate fixation between the C1 lateral mass and the C2 vertebral body were measured. Fifteen embalmed cadavers were used for anterior C1-C2 transarticular screw placement. Longer screws (30-40 mm) were used to detect whether the screw tips violated the upper cervical canal or vertebral arteries. RESULTS: In the anterior transarticular atlantoaxial screw placement, lateral angulation of the screw placement relative to sagittal plane ranged from 4.8 +/- 1.8 degrees to 25.3 +/- 2.6 degrees. The posterior angulation of the screw placement relative to the coronal plane ranged from 12.8 +/- 3.1 degrees to 22.6 +/- 3.2 degrees. The length of the medial screw path ranged from 14.7 +/- 1.5 mm to 25.4 +/- 2.8 mm. In the anterior screw and plate fixation, the anteroposterior diameter of the inferior facet articular surface ranged from 16.2 +/- 1.6 mm to 17.1 +/- 1.8 mm. The anteroposterior diameter of the C2 vertebral body ranged from 9.3 +/- 1 mm to 16.2 +/- 1.8 mm. The anterior prevascular retropharyngeal approach appropriately exposed the atlantoaxial joint for anterior transarticular C1-C2 screw placement. No screws violated the vertebral artery and cervical canal. CONCLUSIONS: An anterior transarticular atlantoaxial screw 15-25 mm long can be inserted with a lateral angulation of 5-25 degrees relative to the sagittal plane and a posterior angulation of 10-25 degrees relative to the coronal plane. Additionally, in C1-C2 anterior plate fixation screws 15 mm long could be anchored in the inferior facet of the C1, and screws 9-15 mm long could be anchored in the C2 vertebral body.     

Posterior C1-C2 transarticular screw fixation for atlantoaxial arthrodesis

OBJECTIVE: To assess the outcomes associated with C1-C2 transarticular screw fixation. METHODS: The clinical outcomes of 121 patients treated with posterior C1-C2 transarticular screws and wired posterior C1-C2 autologous bone struts were evaluated prospectively. Atlantoaxial instability was caused by rheumatoid arthritis in 48 patients, C1 or C2 fractures in 45, transverse ligament disruption in 11, os odontoideum in 9, tumors in 6, and infection in 2. RESULTS: Altogether, 226 screws were placed under lateral fluoroscopic guidance. Bilateral C1-C2 screws were placed in 105 patients; each of 16 patients had only one screw placed because of an anomalous vertebral artery (n = 13) or other pathological abnormality. Postoperatively, each patient underwent radiography and computed tomography to assess the position of the screw and healing. Most screws (221 screws, 98%) were positioned satisfactorily. Five screws were malpositioned (2%), but none were associated with clinical sequelae. Four malpositioned screws were reoperated on (one was repositioned, and three were removed). No patients had neurological complications, strokes, or transient ischemic attacks. Long-term follow-up (mean, 22 mo) of 114 patients demonstrated a 98% fusion rate. Two nonunions (2%) required occipitocervical fixation. In comparison, our C1-C2 fixations with wires and autograft (n = 74) had an 86% union rate. CONCLUSION: Rigidly fixating C1-C2 instability with transarticular screws was associated with a significantly higher fusion rate than that achieved using wired grafts alone. The risk of screw malpositioning and catastrophic vascular or neural injury is small and can be minimized by assessing the position of the foramen transversaria on preoperative computed tomographic scans and by using intraoperative fluoroscopy and frameless stereotaxy to guide the screw trajectory.     

Risk factors of myelopathy at the atlantoaxial level in spondyloepiphyseal dysplasia congenita

Spondyloepiphyseal dysplasia congenita (SEDC) can be accompanied by hypoplasia of the odontoid and/or lax ligaments which may lead to spinal cord compression. Since an early diagnosis of myelopathy is essential for rational treatment, identification of the high-risk factors is imperative. Sixteen patients were retrospectively reviewed, 10 male and 6 female, and their average age at the time of examination was 18 (range 3-37) years. Myelopathy was seen in 6 individuals. Five were associated with atlantoaxial subluxation, and the critical value of space available for the spinal cord at the level of the atlas was 10 mm or less. Their height was less than -7SD of average Japanese of the same age, and all were associated with severe coxa vara. Although SEDC itself is a risk factor, marked short stature of less than -7SD and severe coxa vara are particularly high-risk factors for cord compression at the level of the atlas.     

Two year followup of anterior and vertical atlantoaxial subluxation in ankylosing spondylitis

OBJECTIVE: To describe the clinical and radiological 2-yr followup of 22 patients with anterior atlantoaxial subluxation (AAS) from a prospective cohort of patients with ankylosing spondylitis. METHODS: The 2-yr assessment included a structured questionnaire for rheumatologic and neurologic complaints and lateral cervical radiographs in maximal flexion view. Initial and 2-yr radiographs were assessed blind to patient data. The course of anterior AAS was classified as unchanged (< 1 mm), progression (> or = 1 mm) or regression (> or = 1 mm) at 2 yrs compared with baseline. Vertical AAS was classified using the Sakaguchi-Kauppi method. Magnification factor was corrected using the ratio of C3 width. RESULTS: Anterior AAS was detected in 22 patients at baseline examination. Two patients also had vertical AAS; 86% were male. Mean age was 33 +/- 9 yrs and mean disease duration was 12 +/- 7 yrs. At followup, one patient had died of acquired immunodeficiency syndrome, 3 could not be reached, and 2 had undergone surgical fusion due to severe myelopathy and now showed complete neurological recovery. Of the remaining 16 patients, 7 (32%) showed progression and 9 (41%) showed no change in the C1-odontoid distance. Vertical AAS developed in one patient. After the 2-yr assessment, 3 additional patients had surgical fusion because of notable progression of AAS, despite absence of neurological signs. CONCLUSION: Anterior AAS progressed in a number of these patients in the 2 yrs following its detection, and with or without neurological signs, surgical management was thought appropriate in a considerable number of them.     

Delayed closed reduction of rotatory atlantoaxial dislocation: case report and literature review

The effect of inhaled nitric oxide (iNO) on bleeding time and platelet aggregation was studied in nine newborn infants with resolving pulmonary hypertension. Infants treated with iNO at 40 ppm for 30 minutes had bleeding times that were nearly twofold longer than those obtained 24 hours after iNO was discontinued. iNO had no effect on in vitro platelet aggregation studies.     

Isolated atlantoaxial rotatory fixation in a child with seronegative spondyloarthropathy presenting with torticollis

In situ hybridization histochemistry was used to investigate acute estrogen effects on serotonin 5HT1A receptor mRNA levels in limbic-related brain areas in the female ovariectomized rat. Acute administration of 17 beta-estradiol (10 micrograms) decreased 5HT1A receptor mRNA expression levels within the medial amygdala (after 2 and 24 h), piriform cortex (after 2 and 24 h), and perirhinal cortex (after 24 h). No changes in 5HT1A mRNA levels were observed in hippocampus or retrosplenial cortex. The findings suggest specific regional effects of estrogen on 5HT functions mediated through regulation of the 5HT1A gene.