Elsevier

The Spine Journal

Volume 11, Issue 4, April 2011, Pages e6-e9
The Spine Journal

Case Report
A fourth atlantoaxial joint: an initial description

https://doi.org/10.1016/j.spinee.2011.02.016Get rights and content

Abstract

Background context

The presence of a supernumerary posterior atlantoaxial facet joint has not been reported in the literature.

Purpose

To describe a patient who presented with a unilateral anomalous posterior facet joint and discuss its possible embryological origin.

Study design/setting

Case report.

Methods

A 35-year-old woman presented with severe neck pain, headaches, and tingling radiating down her left arm. Radiological studies showed an anomalous right C1–C2 facet joint causing dorsal compression of the spinal cord and cord compression secondary to a C5–C6 herniated disc. The patient underwent resection of the abnormal facet via a posterior approach followed by anterior cervical discectomy and fusion at C5–C6.

Results

The patient reported marked improvement in her neck pain and partial improvement in her left upper extremity numbness and tingling. Postoperative radiographs showed no abnormal motion at C1–C2.

Conclusions

The authors hypothesize that, in this patient, the C1 and C2 sclerotomes may have fused abnormally posteriorly, followed by the initiation of events at this site that eventually led to the formation of a morphologically normal synovial joint in an abnormal location.

Introduction

The C1–C2 (atlantoaxial) articulation is the most complex articulation in the spine. The first two vertebrae are structurally different from the other vertebrae and together form an articular system whose primary function is to allow rotation and flexion/extension of the head. The concave inferior facet surfaces of the paired lateral masses of C1 are angled internally and articulate with the convex laterally angled superior C2 facets. A semicircular depression on the posterior surface of the anterior arch marks the third atlantoaxial synovial articulation between the anterior arch and the odontoid process.

The development of the atlantoaxial joint is complex. It begins in utero and is not typically complete until the eleventh year of life [1], [2]. This complexity allows for the possibility of congenital anomalies, and, although many have been documented, to our knowledge there have been no reports of the formation of a supernumerary (fourth) atlantoaxial synovial facet joint. In this report, we present the case of a 35-year-old woman who presented with a unilateral anomalous posterior facet joint, and we discuss its possible embryological origin.

Section snippets

Case report

A 35-year-old woman presented with an 18-month history of posterior neck pain and headaches. Her neck pain was significantly worse with flexion or extension and better at rest. Additionally, she was experiencing tingling and numbness of the left arm and hand.

On neurological examination, the patient had full strength in all muscle groups. Sensation was intact to light touch and pinprick, and joint position sense was intact. Her reflexes were two plus in both her upper and lower extremities.

Plain

Discussion

Several congenital anomalies occur in the occipitocervical region (occiput–C1–C2), including occipitalization of the atlas, defects of the anterior or posterior rings of the atlas, basilar invagination, posterior arch defects of the axis, and anomalies of the odontoid [3]. A rare anomaly described by Rao [4], termed the median occipital condyle or condylus tertius, is analogous to the anomaly found in our case in that there is an extra joint at the atlanto-occipital articulation. In that case,

Acknowledgments

We thank Kristin Kraus, MSc, for editorial assistance in preparing this article.

References (10)

There are more references available in the full text version of this article.

FDA device/drug status: not applicable.

Author disclosures: RIR (grants, Stryker Spine).

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