Swan Neck Deformity of the Cervical Spine
If you look at the average person from the side, the neck appears straight up and down. But, in fact, there is a backward curve called lordosis that helps keep the head and neck in perfect alignment. Injury, deformity, or arthritis can change this head-neck relationship causing a condition referred to as swan neck deformity.
In this study, surgeons report on the results of fusion surgery to correct the malalignments that occur when there is chronic atlantoaxial (A-A) dislocation. Atlantoaxial dislocation refers to the abnormal movement of the head (skull) over the first cervical vertebra. Ligamentous damage causing laxity (looseness), vertebral fracture, or deformity from rheumatoid arthritis can lead to this type of instability.
As a result of the cervical spine changes associated with a swan neck deformity, the upper portion of the neck becomes kyphotic (develops a forward curve of the neck opposite of lordosis). The lower portion of the cervical spine then compensates by becoming hyperlordotic. These changes occur as the head, neck, body complex attempts to keep the head balanced over the neck and the eyes on a straight plane to protect vision.
Surgery to fuse the head and neck (C0-C2) is done to stop the abnormal movement of the atlantoaxial junction. This is the first report published for a series of patients (total of 68 people ages four to 68) who had this procedure under the care of one single surgeon. The goal was to see (and report on) changes in overall neck alignment with this procedure. X-rays viewing the cranium (skull) and neck and change in function and neurologic status were used to measure before and after results.
The surgery was successful for all but two patients who continued to have painful and neurologic symptoms that continued to get worse over time. In all the other patients, posterior fusion of the upper cervical spine actually resulted in the body auto-correcting the lower (subaxial) cervical spine (below the level of the fusion). This was a hoped for but uncertain favorable outcome.
The authors concluded that reversal of subaxial cervical alignment does occur in patients with atlantoaxial dislocation that is stabilized with posterior fusion of C0 to C2. The amount of change in the lower cervical spine (C2-C7) was significantly and directly linked with the amount of change at the C0-C2 levels.
This is the first study to report on the effect of such a correction in patients with this complex swan neck deformity. The type of fusion hardware used (screw and plate system) has been approved in China but not by the United States Food and Drug Administration (FDA).
Auto correction and reversal of the swan neck deformity in these severe and complex cervical spine deformities may occur as a result of the body attempting to achieve global (overall) alignment or to maintain visual orientation required for upright posture. Future studies are needed to determine the exact mechanism by which the subaxial alignment of the lower cervical spine improves when the upper cervical area is surgically fused.
Peter G. Passias, MD, et al. The Reversibility of Swan Neck Deformity in Chronic Atlantoaxial Dislocations. In Spine. April 1, 2013. Vol. 38. No. 7. Pp. E379-385.