In Vivo Three-Dimensional Image Analysis for the Craniovertebral Junction in Rheumatoid Arthritis +1, 2Takatori, R; 1Tokunaga, D; 1Hase, H; 1Imai, K; 2Makinodan, A; 2Aomori, K; 3An, H, S; 3Inoue, N; 1Kubo, T

1Kyoto Prefectural University of Medicine, Kyoto, Japan. Ryota Takatori r-taka@koto.kpu-m.ac.jp

INTRODUCTION:

The involvement of the craniovertebral junction (CVJ) occurs with a high frequency in rheumatoid arthritis (RA) patients. The CVJ has very unique structures, and consists of the occipital condyle, atlas and axis [1]. Radiograph, CT and MRI are often used in order to evaluate the CVJ, however, these two-dimensional evaluation have the limitation because the CVJ has complicated three-dimensional (3-D) structures. Recently, 3-D visualization of the CVJ is available using the 3-D CT or MRI images, however, quantitative 3-D analysis for the CVJ are not well-established. The purpose of the current study was to establish the measurement for the 3-D morphology and kinematics of the CVJ using a custom subject-based 3-D CT model and to reveal the abnormal pattern and relationship among them in the rheumatoid deformities.

METHODS:

Six healthy volunteers (all males; aged 26-36 yrs; mean age, 29 yrs; the control group) and 24 RA patients (21 females, 3 males; aged 43-84 yrs; mean age, 66 yrs; the RA group) with the cervical involvement diagnosed by radiographs, underwent CT of the cervical spine from the basilar of occipital bone to the axis in the neutral and flexion positions (1.0 mm contiguous slices, 140 kV, AEC 10-15 sec duration, 50 cm field of view, 512 × 512 matrix, IRB approved). The model consisted of 3-D geometrical data reconstructed from CT images for each subject (Mimics, Materialise Inc). The 3-D morphology of the occipital condyle, atlas and axis were classified by deformed occipital condyle, lateral mass collapse and periodontoid lesion defined as continuous bony lesion between atlas and odontoid process (Figs. 1,2). The 3-D kinematics in occipito-atlanto and atlanto-axial joints were evaluated using the volume merge method, in which a custom-made software program was used as previously described [2-4]. Total rotational and translational motions in three major planes were used for following analyses. Differences between the control and RA groups or among the groups in segmental motions were compared by Mann-Whitney U-test and Kruskal-Wallis test (α = 0.05). Minimum effective number for statistical analysis was defined as 5 in a group.

RESULTS: 3-D morphology (Table 1): All healthy volunteers had no deformities in the CVJ. Five RA patients had unilateral deformed occipital condyle (Group II), and 3 patients had bilateral deformed occipital condyle (Group III). Unilateral mass collapse was shown in 9 patients (Group 2) and bilateral mass collapse was shown in 6 patients (Group 3). Periodontoid lesion was found in 12 patients (Group B). 3-D kinematics (Table 1): Occipito-atlanto joint: Translational motion was marginally higher in the Group II and Group 3. Translational segmental motion in the Group B was higher than that in the Group A (p<0.05). Atlanto-axial joint: Rotational motion was marginally higher in the Group III and Group 2, and lower in the Group 3. In the Group B, translational motion was lower (p<0.05), and rotational motion was marginally lower as compared with that in the Group A. DISCUSSION:

The current study showed that the new in vivo subject-based 3D CT model was effective for measurement of the 3-D morphology and kinematics of the occipito-atlanto and atlanto-axial joints in the healthy subjects and RA patients with cervical involvement. In the CVJ of RA patients with cervical involvement, deformities between the atlas and axis occurred more frequency compared with the deformities between the occipital condyle and atlas. Halla JT et al reported non-reducible rotational head tilt deformity in RA was related with unilateral mass collapse in atlas or axis [5]. It has been reported that bilateral mass collapse led to vertical subluxation [6], erosion and collapse in the lateral atlanto-axial joint caused spontaneous stabilization, and occasional ankylosis led to atlanto-axial impaction [7]. The findings of the current study are consistent with these reports. The current study suggests that unilateral mass collapse and bilateral deformed occipital condyle may lead to severe rotational instability in the atlanto-axial joint, and bilateral mass collapse and periodontoid lesion may stabilize the abnormal motion. Also, unilateral deformed occipital condyle and

stabilized atlanto-axial joint may affect translational instability in the occipito-atlanto joints as an adjacent effect. These kinematic parameters were able to be measured three-dimensionally in the RA patients in the current study, and this non-invasive technique would be useful to predict the prognosis of deformities of the CVJ in the RA patients.

Fig. 1 3-D CT model at the craniovertebral junction.

Fig. 2 Classification by 3-D morphology. Group I: no deformed occipital condyle, Group II: unilateral deformed occipital condyle, Group III: bilateral deformed occipital condyle; Group 1: no lateral mass collapse, 2: unilateral mass collapse, 3: bilateral mass collapse; Group A: no periodontoid lesion, Group B: periodontoid lesion. Table 1 Segmental motion in each group. (mean ± SEM; unit: rotation; degree, translation; mm)

Atlanto-occipital joint Atlanto-axial joint Rotation Translation Rotation Translation

Control (n=6) 4.3 ± 1.5 1.5± 0.2 3.9 ± 0.5 2.6 ± 0.4 RA (n=24) 3.9 ± 0.8 4.3 ± 1.6 4.1 ± 1.6 3.0 ± 0.3 Group I (n=16) 3.5 ± 0.7 2.7 ± 0.4 2.4 ± 0.4 2.8 ± 0.3 Group II (n=5) 5.7 ± 2.6 9.0 ± 7.7 3.1 ± 1.2 3.3 ± 0.4 Group III (n=3) 2.4 ± 0.6 4.6 ± 2.5 14.4 ± 12.5 3.9 ± 1.8 Group 1 (n=9) 4.8 ± 1.7 1.9 ± 0.3 3.0 ± 0.5 3.1 ± 0.5 Group 2 (n=9) 3.5 ± 1.2 3.2 ± 0.9 6.8 ± 4.1 3.1 ± 0.7 Group 3 (n=6) 2.8 ± 0.7 9.5 ± 6.1 1.5 ± 0.4 2.8 ± 0.5 Group A (n=12) 4.0 ± 1.4 2.4 ± 0.7 5.9 ± 3.1 3.7 ± 0.5 Group B (n=12) 3.7 ± 0.9 6.2 ± 3.1 2.2 ± 0.5 2.3 ± 0.3

REFFERENCES: [1] Smoker WR. Radiology 1994;14:255-77. [2] Ochia RS, et al. Spine 2006;31:2073-8. [3] Ochia RS, et al. Spine 2007;32:1394-9. [4] Takatori R, et al. Clin Exp Rheumatol 2008;26:442-8. [5] Halla JT, et al. Arthritis Rheum 1982;25:1316-24. [6] Santavirta S, et al. J Rheumatol 1988;15:217-23. [7] Kauppi M,, et al. J Rheumatol 1996;23:831-4. AFFILIATED INSTITUIONS FOR CO-AUTHORS: 2Nishijin Hospital, Kyoto, Japan 3Rush University Medical Center, Chicago, IL

Poster No. 1739 • 55th Annual Meeting of the Orthopaedic Research Society