Collapse of the lateral mass of the atlas could induce the progression of vertical subluxation in patients with rheumatoid arthritis.

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1 Collapse of the lateral mass of the atlas could induce the progression of vertical subluxation in patients with rheumatoid arthritis. Toshiyuki DOKAI MD Hiroshi HAGINO MD Hideki NAGASHIMA MD Yoshiro NANJO MD Atsushi TANIDA MD Ryota TESHIMA MD Department of Orthopedic Surgery Faculty of Medicine, Tottori University Yonago, JAPAN

2 Introduction Vertical subluxation (VS) - is the most severe and a fatal condition of the cervical spine in rheumatoid arthritis (RA). - results from the synovial destruction of lateral atlantoaxial and occipitoatlantal joints. To prevent development of VS, it is important to understand its etiology; however, there have been few reports on this issue. Purpose The purpose of this study was to reveal the etiology and the characteristics of VS in RA. Especially, the evaluation was performed using computed tomogram (CT). Study Design Observational Study

3 Materials & Methods Patient samples: 80 females with definite RA - were fulfilled with the criteria of American College of Rheumatology in gave the fully informed written consent about this study. - necks were assessed by plain films and CT. - were divided into two groups: Group 1; VS+ Group 2; VS -(VS; Redlund-Johnnell value(r-j)< 29mm) Setting for CT - placed in a supine position on the CT table. - necks were set in an extended position using a special pillow. - phantoms were set in front of their necks - CT gantry was tilted toward caudally to avoid halation.

4 CT analysis Evaluation of anatomical parameters 1:odontoid height 2:lateral mass height of the atlas (C1-LMH) 3:lateral mass height of the axis (C2-LMH) 4:facet angle of the atlas (C1-FA) 5:facet angle of the axis (C2-FA) Evaluation of the volume of upper cervical spine (Software for analysis) 3D-TBSAS: 3 dimensional Teijin Bone Structural Analysis System 1: volume of the atlas(v1) 2: volume of the axis (V2) 3: volume of C1-2 (V1-2) (TEIJIN Pharma, Tokyo,JAPAN) the coronal reconstructed computed tomograms; which was paralleled with the axis of odontoid process.

5 Demographic data Group 1 (VS+) Group 2 (VS-) p value N Age (yrs) 69.9 (60-82) 63.3 (34-87) Symptom duration (mos) 91.7 (11-384) 72.4 (12-456) Body height (cm) ( ) ( ) Body weight (kg) 43.4 ( ) 51.4 ( ) Disease activity score 3.68 ( ) 4.02 ( ) Rheumatoid factors (IU/ml) ( ) ( ) C-reactive proteins (mg/μl) 1.10 ( ) 0.66 ( ) BMD spine (g/cm 2 ) BMD hip (g/cm 2 ) Results ( ) ( ) ( ) ( ) (Mann-Whitney U test)

6 Results Anatomical parameters Group 1 (VS+) Group 2 (VS-) p value C1-LMH (rt) (mm) 7.1 ( ) 9.7 ( ) C1-LMH (lt) (mm) 7.5 ( ) 9.4 ( ) C2-LMH (rt) (mm) 9.8 ( ) 12.9 ( ) C2-LMH (lt) (mm) 9.4 ( ) 12.6 ( ) C1-FA (rt) ( ) 41.7 ( ) 54.8 ( ) C1-FA (lt) ( ) 49.7 ( ) 55.6 ( ) C2-FA (rt) ( ) 20.8 ( ) 21.3 ( ) C2-FA (lt) ( ) 21.3 ( ) 21.1 ( ) Odontoid height (mm) 29.7 ( ) 32.2 ( ) (LMH; lateral mass height, FA; facet angle ) (Mann-Whitney U test) Group 1 had a significantly lower C2-LMH and smaller C1-FA than Group 2.

7 Results The relationships between the anatomical parameters Correlation coefficient p value Redlund-Johnnell vs. C1-LMH (rt) C1-LMH (lt) C2-LMH (rt) C2-LMH (lt) C1-FA (rt) < C1-FA (lt) C1-FA (rt) vs. C1-LMH (rt) C1-FA (lt) vs. C1-LMH (lt) (LMH; lateral mass height, FA; facet angle) (Spearman s rank correlation coefficient) These results indicated that the progression of VS had the association with the collapse of lateral mass of C1 and C2, and the leveling of atlantal facets.

8 Results Volumetric analysis by using 3D-TBSAS For 25 patients without VS, we measured the volume of upper cervical spine (V1,V2 and V1-2). Separation V ml ( ) V ml ( ) V ml ( )

9 Results The relationships between the anatomical and the volumetric parameters Correlation coefficient p value Redlund-Johnnell vs. V V V V1 vs. V < V < C1-LMH (rt) C1-LMH (lt) (LMH; lateral mass height, V; volume) (Spearman s rank correlation coefficient) Without the destructive changes due to RA, the volume of upper cervical spine decreased according to the collapse of lateral mass of the atlas.

10 Discussions Features of upper cervical spine Mechanical axial loading In craniovertebral junction - On the lateral masses and facets (1) At subaxial region - On the lateral masses and facets (1) - On vertebral bodies and discs (2) (1) Synovial destruction of RA occipitoatlant joint atlantoaxial joint - synovial joints. - are destructed in RA. (2) These are the reasons why the destruction of lateral mass are frequently observed in RA.

11 Discussions The development of VS in RA C1-LMH and C1-FA became smaller according to the development of VS. Female Menopause Use of glucocorticoids Severity of RA Type of RA (Mutilant) The risk factors for VS in RA (Smith PH 1972, Rasker JJ 1978, Rudge SR 1981, Boden SD 1993) These are also the risk factors for osteoporosis. In this study, the patients of VS had the smaller BMD in lumbar spine; therefore, osteoporosis could induce the development of VS.

12 Conclusion The progression of VS could be induced by destruction of the lateral mass of the atlas and axis and could be induced by the leveling of the C1 facet joint. Bone strength in upper cervical spine should be analyzed. Limitations This study was the observational study; therefore, the prospective study should be performed to reveal the details of the progression of VS. Disclosure declaration We received technical supports from TEIJIN Pharma to analyze the volume of upper cervical spine.