1058 THE JOURNAL OF BONE AND JOINT SURGERY The effect of rheumatoid arthritis on the anatomy of the female cervical spine A RADIOLOGICAL STUDY K. Higashino, K. Sairyo, S. Katoh, S. Nakano, T. Enishi, N. Yasui From The University of Tokushima, Tokushima, Japan  K. Higashino, MD, PhD, Assistant Professor  K. Sairyo, MD, PhD, Associate Professor  S. Katoh, MD, PhD, Associate Professor  S. Nakano, MD, PhD, Associate Professor  T. Enishi, MD, Orthopaedic Surgeon  N. Yasui, MD, PhD, Professor and Chairman Department of Orthopedics, School of Medicine The University of Tokushima, 3-18-15 Kuramoto, Tokushima 770-8503, Japan. Correspondence should be sent to Professor N. Yasui; e-mail: nyasui@clin.med.tokushima- u.ac.jp ©2009 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.91B8. 22300 $2.00 J Bone Joint Surg [Br] 2009;91-B:1058-63. Received 13 January 2009; Accepted after revision 20 March 2009 The effect of rheumatoid arthritis on the anatomy of the cervical spine has not been clearly documented. We studied 129 female patients, 90 with rheumatoid arthritis and 39 with other pathologies (the control group). There were 21 patients in the control group with a diagnosis of cervical spondylotic myelopathy, and 18 with ossification of the posterior longitudinal ligament. All had plain lateral radiographs taken of the cervical spine as well as a reconstructed CT scan. The axial diameter of the width of the pedicle, the thickness of the lateral mass, the height of the isthmus and internal height were measured. The transverse diameter of the transverse foramen (d1) and that of the spinal canal (d2) were measured, and the ratio d1/d2 calculated. The width of the pedicles and the thickness of the lateral masses were significantly less in patients with rheumatoid arthritis than in those with other pathologies. The area of the transverse foramina in patients with rheumatoid arthritis was significantly greater than that in the other patients. The ratio of d1 to d2 was not significantly different. A high-riding vertebral artery was noted in 33.9% of the patients with rheumatoid arthritis and in 7.7% of those with other pathologies. This difference was statistically significant. In the rheumatoid group there was a significant correlation between isthmus height and vertical subluxation and between internal height and vertical subluxation. Between 36% and 86% of patients with rheu- matoid arthritis (RA) have some involvement of the cervical spine, 1-3 and atlantoaxial sub- luxation is relatively common. 4-9 Most of these patients can be managed conservatively, although operative treatment may be needed to treat progressive neurological impairment or radiographic instability. 4-10 Chung et al 11 have reported that the axis in patients with RA has a thinner isthmus and lateral mass than is found in other patients. Otherwise, the effects of RA on the anatomy of the cervical spine have not yet been fully explained. Atlantoaxial transarticular screw fixation is a standard procedure for patients with atlanto- axial instability and provides rigid fixation and a high fusion rate. 12,13 For patients whose cer- vical anatomy renders them unsuitable for this procedure, lateral mass fusion with a plate or screws may be used. 14-16 Pedicle screw fusion has been used successfully in those with disease of the mid to lower cervical spine. 17-19 It may be combined with atlantoaxial fusion to pre- vent progressive adjacent level instability, which is seen in some patients with RA. 6-8,10 However, injury to the vertebral artery, spinal cord or nerve roots may occur because of the complex anatomy of the occipitocervical region. 13,19-28 Consequently, pre-operative CT imaging is essential to avoid critical damage with its resultant complications. 24,29-32 The purpose of this study was to identify the anatomical variation that occurs in female patients with RA. We felt that this information would help to prevent the complications and poor outcomes that can occur with this type of surgery. We concentrated on females, as RA is eight times more prevalent in women than men. 33 Materials and Methods Between April 2004 and September 2007, 129 women had plain lateral radiographs and reconstructed CT scans of the whole cervical spine taken at our university hospital. The patients fell into two groups: 90 with RA and 39 with other pathologies. The mean age of those with RA were 62.7 years (23 to 86). The diagnosis of RA was confirmed by a rheumatologist (SN). Each patient had a history of RA for more than two years (2 to 43) and no clinical history of major cervical trauma. Four of the patients with RA had previously undergone a posterior atlanto- axial fusion.