The clinical usefulness of preoperative dynamic MRI to select decompression levels for cervical spondylotic myelopathy

Abstract

The study subjects included 54 patients with cervical spondylotic myelopathy who underwent a selective laminoplasty. The patients were divided into three groups according to the number of decompressed levels: two levels, three levels and four or five levels. The number of cord compressions at every intervertebral level was determined in the flexion, neutral, and extension position using a dynamic magnetic resonance imaging (MRI) scan in consideration of both static and dynamic compressions. For each group, the clinical outcomes were evaluated. Moreover, the patients were divided into two groups according to their age. Then, the appearance ratios of cord compression between the neutral and extension position were compared at each intervertebral level. The clinical outcomes were satisfactory. There were no statistical differences among the three groups, except for the age and operation time. The position of the neck influenced the number of cord compressions. The appearance ratios of cord compression, which were especially prominent at C2/3, C3/4 and C4/5, showed high scores in the aged. The preoperative dynamic MRI scan was clinically useful. In the aged, attention should be given to C2/3, C3/4 and C4/5.

Introduction

Cervical spondylotic myelopathy (CSM) is the most common disease of the spinal cord that occurs during and after middle age. It has been thought that static and dynamic compressions to the spinal cord were responsible for CSM. It has been reported that static compressions were caused by hypertrophy of the ligamentum flavum, disk protrusion, osteophyte formation, and congenital canal stenosis [1], [2], and that dynamic compressions were attributed to infolding of the ligamentum flavum and canal stenosis by vertebrolisthesis [3], [4], [5], [6], [7].

Conventional laminoplasty for CSM has been the widely accepted method to release a compressed spinal cord. This approach was originally developed about 30 years ago, and follow-up studies have shown excellent long-term results [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. This technique has made it possible to shift the decompressed spinal cord posteriorly and to release the static and dynamic compressions [19], [20], [21]. After this operative treatment, however, some postoperative problems remained such as persistent axial pain, malalignment, restricted neck motion and C5 palsy [22], [23], [24], [25], [26]. Several laminoplasty techniques have been developed to prevent these problems [9], [11], [14], [16], [17], [18]. In 2002, the method of selective laminoplasty (Shiraishi method) was described [27], [28]. This procedure did not decompress from C3 to C7, but selectively decompressed the intervertebral levels. However, there have so far been no reports demonstrating how to determine the exact levels to be decompressed.

Regarding dynamic stenosis, various authors have reported on the use of plain radiographic or myelographic studies [3], [4], [5], [6], [7]. Recently, dynamic magnetic resonance imaging (MRI) studies have been performed to define the physiological changes that occur in the subarachnoid space and cervical cord during flexion and extension of the neck [29], [30], [31]. However, the application of the dynamic MRI for clinical decision-making has not yet been reported. We have selected the levels requiring decompression with a preoperative dynamic MRI, in consideration of both the static and dynamic compressions, and herein reported on the utility of preoperative dynamic MRI. The purpose of this study was to clarify the clinical merit of the preoperative dynamic MRI for CSM, and to evaluate the intervertebral levels which caused dynamic stenosis by age bracket (Un64: 64 years and under, and Ov65: 65 years and over).