MRI investigations

MRI of the cervical spine was performed on 20 of the TE group at the Department of Radiology of Sahlgrenska University Hospital and it was performed on the remaining seven individuals with TE at their regional hospital, for practical reasons. The protocol used was identical for all examinations.

The MRI examinations in the TE group were carried out in 2008 on three different 1.5T (Tesla) scanners: 23 (85%) using a Philips Medical Systems scanner (Intera), 3 (11%) using a Siemens scanner (Symphony), and in one (4%) using a GE Medical Systems scanner (SignaExcite). A standard protocol for the cervical spine was used, including sagittal T1-weighted turbo spin echo (T1W-TSE) sequence with repetition and echo time (TR/TE) of 400–597/8–10 milliseconds (ms) and T2W-TSE sequence with TR/TE of 3500–4920/104–120 ms. Axial images included were T2W gradient-recalled echo (GRE) sequence with TR/TE of 537–960/14–17ms and T2W-TSE images with TR/TE of 1100–2500/100–120 ms. For all sequences, field of view (FOV) was 10cm, slice thickness 3–6 mm and matrix size 576 x 576 to 512 x 512.

Since the MRI examinations for the CTR were performed based on various clinical indications, few patients had an axial image included—which is why only sagittal images were evaluated. Sagittal T1W and either sagittal T2W or short tau inversion recovery (STIR) sequences were included for all individuals with 25 of the 27 (93%) examinations performed on 1.5T Philips Medical Systems scanners (Achieva/Intera). The sagittal T1W-TSE and T2W-TSE sequences were performed almost identically as for the TE group. STIR imaging was performed with TR/TE of 1776–4000/60–90 ms and inversion time (TI) of120–170 ms.

In each subject, C2 to C7 were evaluated. Each disc level was assessed for the degree of degeneration according to Pfirrmann [26], narrowing of disc space, presence of anterior or posterior osteophytes, anterior or posterior disc bulge, disk herniation, foraminal stenosis, anterior compression of the dural sac and presence of malformations such as block vertebrae. [27–29]. At least 25% loss of height of a single disc relative to adjacent normal levels was defined as disc space narrowing. Disc bulge was assessed on sagittal T1W and T2W images, and referred to a diffuse protrusion of the disc by more than 2 mm away from the vertebral margins anteriorly or posteriorly [27]. Disc herniation was defined as a localized/focal protrusion of the disc more than 2 mm from the vertebral margins when, in at least one plane, any distance between the edges of the disc material beyond the disc space was greater than the distance between the edges of the base. The direction of disc herniation (central, right or left paracentral, or right or left foraminal) was noted. Foraminal stenosis was assessed on sagittal T1W images and defined as obliteration of the intraforaminal fat. The degree of spinal cord impingement/compression adjacent to a site of disc bulging and presence of anterior or posterior osteophytes was also evaluated.

In the TE group both sagittal and axial sequences were used for assessment of disc bulge/ herniation and foraminal stenosis whereas only sagittal sequences were used in the CTR due to the lack of axial sequences. All other parameters evaluated were assessed in an identical manner.

All evaluations were analyzed first for occurrence of a specific variable in each subject, and thereafter analyzed for the total number of levels for all 27 individuals of each group, i.e. 27 subjects with five levels each makes a total of 135 levels.

The parameters were evaluated independently by one resident and one senior radiologist at the Sahlgrenska University Hospital. Blinded regarding the first evaluation, the resident repeated the evaluation process after four weeks.