Traumatic Atlantoaxial Rotatory Fixation

h1 class=”calibre8″>9 Traumatic Atlantoaxial Rotatory Fixation

Darnell T. Josiah and Daniel K. Resnick

Abstract

Traumatic atlantoaxial rotatory fixation is a rare entity that is seen in children after minor trauma with inherent ligamentous laxity, whereas the principal cause in adults is high-energy trauma. In this chapter, we review the etiologies along with the injury patterns and treatment options available in caring for these patients.

Keywords: atlantoaxial rotatory subluxation, classification, torticollis, atlantoaxial subluxation

9.1 Introduction

Rotatory deformities of the atlantoaxial joint are relatively rare in adults. Persistent subluxation causing torticollis was termed rotatory fixation of the atlantoaxial joint by Wortzman and Dewar in 1968. The condition was later referred to as atlantoaxial rotatory fixation (AARF) by Fielding and Hawkins in 1977, as fixation of the atlas on the axis may occur with subluxation. ¹ This condition has been also previously termed rotatory dislocation, rotatory subluxation, rotatory displacement, and rotatory fixation. Pediatric patients with AARF typically present with torticollis in a “cock-robin” posture. Infections followed by trauma are the leading cause of AARF. ²^,³^,⁴ The differential diagnosis of nontraumatic AARF includes congenital anomalies, metastatic tumors, ankylosing spondylitis, general ligamentous laxity (which can result from Down syndrome, Morquio syndrome, Marfan syndrome, and rheumatoid arthritis), and eosinophilic granulomas. ² Grisel syndrome typically occurs in children after a serious head and neck infection, and causes subluxation of the atlantoaxial joint due to inflammatory ligamentous laxity. ³^,⁵ Traumatic AARF, while predominantly a pediatric disorder, does occur in the adult population and should be included in the differential for patients presenting with torticollis even after minor trauma. Two classification systems have been described: The White and Panjabi system, and the more frequently used Fielding and Hawkins classification system. ¹^,³ This chapter discusses traumatic AARF.

9.2 The Atlantoaxial Joint

The atlantoaxial joint is specialized, highly complex, and moves approximately 600 times per hour. ⁶ The joint contributes to nearly 50% of axial neck rotation. The normal physiological range of motion of the atlas on the axis is 25 to 53 degrees to either side. ⁴^,⁷

9.2.1 Functional Anatomy

The transverse ligament (located behind the odontoid process) and the facet joint capsule prevent excessive anterior translation of C1 on C2. The paired alar ligaments, which connect the posterolateral apex of the odontoid to the lateral aspect of the foramen magnum, bilaterally limit anterior shifting and excessive rotation of C1 on C2 to approximately 50 degrees. The alar ligaments also act as secondary stabilizers; cadaveric studies have shown that if the transverse ligament is cut, anterior subluxation past 4 to 5 mm is prevented by these structures. ¹^,⁴^,⁷ Rotation > 56 degrees or a right to left difference of > 8 degree is suggestive of hypermobility. Rotational hypomobility is indicated if motion is < 28°. ⁴^,⁸ The spinal canal, which is widest at C1–C2, narrows during physiological rotation of the atlas on the axis due to the ipsilateral lateral mass moving posteriorly. During physiological rotation to the right, the right vertebral artery traveling in the transverse foramina is stretched while the left vertebral artery is kinked. The corollary occurs when turning the head to the left. ⁹

9.3 Classification of Atlantoaxial Rotatory Fixation

Two classification systems, largely based on imaging findings, have been described to determine the direction of atlas displacement on the axis. Fielding, in 1977, divided AARF into four categories of instability. These include the following:

Type 1: Rotatory fixation with less than 3 mm anterior displacement of the atlas. There is translation of the facets without any increase in the atlantodental interval. Rotation occurs within the normal physiological range.
Type 2: Rotatory fixation with 3 to 5 mm anterior displacement of the atlas. One of the articular masses acts as a pivot and there is deficiency of the transverse ligament. This is the second most common type.
Type 3: Rotatory fixation with greater than 5 mm anterior displacement of the atlas. There is deficiency of the transverse and alar ligaments.
Type 4: Rotatory fixation with posterior displacement of the atlas. This is the rarest form and occurs with a deficiency of the odontoid process. ¹ Fielding reported on a series of 17 patients and assessments were based on plain radiographs before computed tomography (CT) was available. Five of these patients ultimately required cervical fusion despite cervical traction. ¹

9.4 Diagnosis

Clinically, these patients have painful torticollis with lateral neck flexion and contralateral rotation. Physical exam and a high index of suspicion are the key along with appropriate imaging for early diagnosis. CT imaging is essential for initial evaluation; axial CT scans along with sagittal and coronal cuts of the upper cervical spine aid in identifying the rotated position of the atlas on the axis (▶ Fig. 9.1a, b). ⁴ Injury in adults is most commonly related to high-energy trauma such as car crashes, falls, or sports accidents. ¹⁰ These patients often present with articular cartilage damage and facet joint fractures; extent of neurological injury depends on the integrity of the transverse ligament, the anterior or posterior displacement of C1 on C2, and the degree of encroachment of the spinal canal. ³^,¹¹

Fig. 9.1 (a) Axial computed tomography (CT) scan of the cervical spine showing the rotation of C1 to the right relative to C2. (b) Sagittal CT scan of the cervical spine showing the translation of C1 right lateral mass relative to C2.

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