Biomechanical assessment of bilateral C1 laminar hook and C1-2 transarticular screws and bone graft for atlantoaxial instability.

UNLABELLED: STUDYDESIGN: In vitro biomechanical test was conducted to compare the stability of 5 different atlantoaxial posterior fusion techniques. OBJECTIVE: To evaluate the biomechanical stability of an atlas laminar hook combined with transarticular (TA) screws relative to 4 different conventional fusion techniques. SUMMARY OF BACKGROUND DATA: The atlantoaxial instability caused by fractures, rheumatoid arthritis, congenital deformity, or traumatic lesions of the transverse ligament often result in acute or chronic spinal cord compression, a possible threat to a patient's life. Posterior atlantoaxial fixations are used to reconstruct the stability of atlantoaxial articulation. Conventional posterior atlantoaxial fixations are associated with high rates of pseudoarthrosis and carry the potential risk of neurologic complication. TA screw fixation can provide an excellent biomechanical stability. As a modified 3-point fixation technique, the bilateral C1-2 TA screws have been combined with C1 laminar hook and bone grafts. This modified technique had carried good clinical outcomes. METHODS: Eight human specimens (C0-C4) were loaded nondestructively with pure moments and the range of motion at the level of C1-C2 was measured. Eight specimens were implanted with each of the following techniques, respectively: Gallie fixation, C1-2 TA screw fixation combined with Gallie fixation, C1-2 TA screw fixation, C1 laminar hook combined with C1-2 TA screw fixation plus bone grafts, and the C1 lateral mass screws in the atlas combined with C2 isthmic screws in axis. RESULTS: Although the C1-2 TA screws best restricted lateral bending and axial rotation, the modified 3-point fixation technique additionally restricted flexion-extension and provided the excellent stability. Differences in axial rotation and lateral bending (with + or - 1.5 Nm load) were observed when the 3-point fixation techniques (TA + Gallie and TA + hook) were compared with atlas lateral mass screws in the atlas combined with isthmic screws in axis. CONCLUSIONS: The modified C1 laminar hook combined with C1-2 TA screws and bone graft fixation provided the best biomechanical stability. The C1 lateral mass screws in the atlas combined with isthmic screws in axis fixation is a sound alternative when the C1-2 TA screw fixation is not feasible.

Sleep apnea in rheumatoid arthritis patients with occipitocervical lesions: the prevalence and associated radiographic features.

Since sleep apnea is a risk factor for high mortality of rheumatoid arthritis (RA) patients, this study examined the prevalence in RA patients with occipitocervical lesions, and the associated radiographic features. Twenty-nine RA patients requiring surgery for progressive myelopathy due to occipitocervical lesions (3 males, 26 females, average age 65 years) were preoperatively evaluated. Twenty-three (79%) had sleep apnea defined as apnea-hypopnea index >5 events per hour measured by a portable monitoring device, and all of them were classified as the obstructive type. Among gender, age, bone mass index (BMI), and radiographic parameters related to occipitocervical lesions: atlantodental interval (ADI), cervical angles (O/C1, C1/2, and C2/6), and cervical lengths (O-C2 and O-C6), the ADI and cervical lengths were shown to be significantly associated with the presence of sleep apnea by parametric statistical analysis. Since there were positive correlations between the ADI and cervical lengths by Pearson's test, we performed a multivariate logistic regression analysis after adjustment for confounding factors and found that small ADI was the principle parameter associated with sleep apnea. We therefore conclude that the prevalence of sleep apnea is higher than that in a general RA population that was reported previously, and believe that occipitocervical lesions are an independent risk factor for this condition. Small ADI and short neck, secondary to the vertical translocation by RA, may cause obstructive sleep apnea, probably through mechanical or neurological collapse of the upper airway.

C1 arch regeneration, tight cisterna magna, and cervical syringomyelia following foramen magnum surgery.

BACKGROUND: Although bone regrowth following craniocervical decompression has been rarely reported to cause late recurrence of Chiari symptoms, syringomyelia has not been observed in such cases. We report a unique case of cervical syringomyelia resulting from spontaneous regeneration of the posterior C1 arch after foramen magnum decompression. CASE DESCRIPTION: A 38-year-old male patient underwent resection of a symptomatic foramen magnum meningioma. Three years later, he developed neuropathic pain in his left upper extremity with worsening dysphagia and dysphonia. MRI revealed regeneration of the posterior arch of C1 with tight tonsillar impaction of the foramen magnum and extensive cervical syringomyelia. Surgical exploration was undertaken. Neo-ossification of the posterior arch of C1 and thick arachnoid adhesions were found to obstruct cerebrospinal fluid flow through the foramen of Magendie. Foramen magnum decompression, arachnoid dissection, and duraplasty were thus performed and cerebrospinal fluid flow was reestablished through the foramen of Magendie. Postoperatively, patient's symptoms improved dramatically and repeat MRI showed complete resolution of the syrinx cavity. CONCLUSION: Spontaneous bone regrowth and arachnoid scarring may lead to the development of cervical syringomyelia several years after foramen magnum surgery. Neurosurgeons should be aware of this rare complication whose management is similar to that of Chiari malformations, namely craniocervical decompression and establishment of a patent foramen of Magendie.

Case report: nonoperative treatment of an unstable Jefferson fracture using a cervical collar.

The treatment of unstable burst fractures of the atlas (Jefferson fractures) is controversial. Unstable Jefferson fractures have been managed successfully with either immobilization, typically halo traction or halo vest, or surgery. We report a patient with an unstable Jefferson fracture treated nonoperatively with a cervical collar, frequent clinical examinations, and flexion-extension radiographs. Twelve months after treatment, the patient achieved painless union of his fracture. The successful treatment confirms prior studies reporting unstable Jefferson fractures have been treated nonoperatively. The outcome challenges the clinical relevance of treatment algorithms that rely on the "rules of Spence" to guide treatment of unstable Jefferson fractures and illustrates instability may not necessarily be present in patients with considerable lateral mass widening. Additionally, it emphasizes a more reliable way of assessing C1-C2 stability in unstable Jefferson fractures is by measuring the presence and extent of anterior subluxation on lateral flexion and extension views.

Indications for surgery in upper cervical spine injury.

20% of all spine injuries are cervical spine injuries. Surgical treatment of these injuries must take into account the great mobility of this part of the spinal column. Therefore, biomechanical aspects must be considered, especially in the upper cervical spine-C1 and C2. Describing our own therapeutical regimen in 35 patients with unstable upper cervical spine injuries we explain the biomechanical back-ground and review the literature. It becomes evident that ventral approaches are superior to dorsal techniques for decompression, reposition, and stabilization with minimal loss of mobility.

Assimilation of the atlas with associated syringomyelia and Chiari 1 malformation (Klippel-Feil type 2).

This case report describes an unusual congenital anomaly of the craniovertebral junction in a 14 year old male. Cervical radiographs showed the bony anomaly, while thin slice CT (with 2-D and 3-D reformations), MR imaging, and angiography were particularly useful in accurately assessing the bony, soft tissue and vascular anatomy, prior to and following surgery.

Radio-functional analysis of the cervical spine using the Arlen method. A study of 699 subjects. Part Two: Paradoxical tilting of the atlas.

The authors describe a peculiar movement of the first cervical vertebra: the so-called paradoxical tilting of the atlas, which consists of extension in relation to McGregor's line during flexion of the cervical spine. This physiological phenomenon has already been reported by several authors. The purpose of this study was to determine the mean amplitude and frequency of paradoxical tilting of the atlas in subjects with no known cervical pathology and to evaluate some of the factors that may influence it. The younger the subject the more frequent and more ample this paradoxical tilting: it occurs very often before the age of 40 years and is present in more than 93% of subjects under 20. Its amplitude diminishes with age, until it is replaced by mobility in flexion.

Torticollis in children caused by congenital anomalies of the atlas.

Hemi-atlas is a rare congenital anomaly in the formation of the first cervical vertebra. It may cause a rather severe and progressive torticollis. When a child is young, the neck, despite the deformity, is flexible and the torticollis can be passively corrected. However, in some patients it becomes increasingly severe and fixed. I describe the findings in seventeen patients, seven of whom were operated on between 1975 and 1983. Treatment with a brace was shown to be ineffective. In patients with severe deformities, fusion of the upper part of the cervical spine is recommended. Fusion was obtained in all seven patients in whom it was attempted, and there was good postural correction in all. Early operation is recommended if the deformity is increasing. Gradual correction in a halo cast followed by posterior fusion is recommended as the treatment of choice in patients with severe torticollis.

Chronic atlanto-axial instability in Down syndrome.

We studied the radiographs of thirty-two patients with Down syndrome for evidence of atlanto-axial instability. One of the patients had instability in 1970 and seven had it in 1983. The interval between the atlas and the odontoid process in the patients who demonstrated motion at that interval radiographically averaged 2.78 millimeters in 1970 and 6.93 millimeters in 1983 (p less than 0.005). Four patients whose radiographs showed atlanto-axial motion in 1970 lost that motion by 1983, and in seven patients who did not show atlanto-axial instability in 1970 it developed by 1983. Atlanto-axial instability was more likely to develop in boys who were more than ten years old. Accessory upper-cervical ossicles became evident in three patients, none of whom had atlanto-axial motion. However, one of these three patients had an abnormally wide atlanto-axial interval.