Quantitative study of the effect of atlas posterior arch resection on cervical posterior decompression

Abstract

Objective To quantitatively compare the effect of preservation or removal of atlas posterior arch on cervical posterior decompression, so as to provide a basis for reasonable selection of upper cervical spine decompression range and determination of surgical indications for atlas posterior arch resection. Methods The data of 45 patients with posterior decompression of upper cervical spine were retrospectively analyzed. According to the decompression range, the patients were divided into C2-C7 group and C1-C7 group. There were 25 cases in the C2-C7 group, 19 males and 6 females, with an average age of 56.3 years (40-71 years), 4 cases of cervical spondylotic myelopathy and 21 cases of ossification of the posterior longitudinal ligament of cervical spine. All of the 25 patients underwent open-door laminoplasty: 20 cases with hinge side anchoring procedure and 5 cases with preservation of the unilateral posterior muscular-ligament complex procedure (titanium cable procedure). There were 20 cases in C1-C7 group, 12 males and 8 females, with an average age of 58.4 years (44-75 years). All of the 20 cases underwent atlas posterior arch resection as well as C2-C7 open-door laminoplasty, including anchoring procedure in 1 case, titanium miniplate procedure in 4 cases, and titanium cable procedure in 15 cases. Standardized vertebral-cord distance (SVCD) at each level from atlas to level C6,7 was measured on T2-weighted images of MR on the mid-sagittal plane in the neutral position performed 3-12 months postoperatively at each individual level. As the main outcomes, the SVCD values obtained at the same level of the two groups were compared between the two groups. Shapiro-Wilk normality test was performed on the SVCD values at C1,2 and C2 levels of two groups. The area under the normal distribution curve of SVCDs was used to calculate the corresponding residual compression rate with different magnitude of compression mass to further discover the difference of the decompression effect between the two groups. Results The SVCD obtained at the level of the anterior arch of atlas (C1), the junction of odontoid process and axis (C1,2) and the middle part of axis body (C2) in the C2-C7 group was 9.91±1.34 mm, 8.35±1.27 mm, and 8.22 ±1.43 mm, respectively. The SVCD at the same levels was 11.02±1.60 mm, 9.72±1.24 mm, and 9.12±1.11 mm, respectively. SVCDs differed significantly in the above range between the two groups. However, from level C2,3 to C6,7, there was no significant difference in SVCDs between the two groups. The JOA score of group C2-C7 was 11.8±2.7 preoperatively and increased significantly to 14.7±1.8 at 12 months postoperatively(t=-7.006, P<0.001) with a recovery rate of 57.0%±32.2%. The JOA score of group C1-C7 was 11.7±2.8 preoperatively and increased significantly to 14.2±2.3 at 12 months postoperatively(t=-6.177, P<0.001) with a recovery rate of 51.9%±32.1%. Conclusion Atlas posterior arch resection can significantly increase the decompression effect of posterior cervical surgery from the anterior arch of atlas to the middle part of axis body, but it would not increase the decompression effect at level C2,3 or below. When the magnitude of the ventral compression factor exceeds the decompression limit (8.5 mm) available with C2-C7 decompression in the range from atlas to the middle of the axis body, extending the decompression range by atlas posterior arch resection is an effective means to achieve adequate decompression. Key words: Cervical atlas; Axis; Ossification of posterior longitudinal ligament; Spinal cord compression; Decompression, surgical