Radiographic analysis of the upper cervical spine was performed in patients with rheumatoid arthritis who had C1-C2 instability.
To assess whether neck retraction or neck protrusion movements can cause C1-C2 subluxation in patients with C1-C2 instability.
Cervical protrusion is the position where the head is maximally translated anteriorly with zero sagittal rotation, and this position has been shown to produce maximal C1-C2 extension. In contrast, cervical retraction is the position where the head is maximally translated posteriorly, and this position produces maximal C1-C2 flexion. To date, there have been no studies evaluating the effects of these two positions on C1-C2 status in patients with C1-C2 instability.
Twenty-four patients with rheumatoid arthritis who showed an atlantodental interval of at least 5 mm during neck flexion were evaluated in this study. These patients were instructed to actively hold the neck in protrusion and retraction positions, as well as in flexion and extension positions. Lateral cervical radiographs were taken to measure the C1-C2 angle and the atlantodental interval in the sagittal plane in each position.
Retraction produced both maximal C1-C2 flexion and anterior C1-C2 subluxation, of a degree just the same as that produced by cervical flexion. Protrusion reversely produced maximal C1-C2 extension. However, 9 of 24 patients exhibited C1-C2 subluxation even in this protrusion position, in marked contrast to the cervical extension position in which only 2 of 24 patients showed C1-C2 subluxation. The patients who showed C1-C2 subluxation in the protrusion position tended to have more severe C1-C2 instability and less capacity for C1-C2 extension than the other patients who achieved a reduction of C1-C2 in the protrusion position.
In patients with C1-C2 instability, not only cervical flexion but also cervical retraction constantly led to both maximal C1-C2 flexion and subluxation. In some patients with severe C1-C2 instability, protrusion also resulted in C1-C2 subluxation, even though the C1-C2 was maximally extended.