Identification of thoracic intervertebral spaces by means of surface anatomy: a magnetic resonance imaging study.

BACKGROUND: Successful thoracic epidural analgesia depends on the sensory blockage of specific dermatomes following appropriate placement of the epidural catheter. This study aimed to ascertain how accurately anaesthesiologists identify thoracic intervertebral spaces, and whether counting from the prominent vertebra is easier than using the iliac crest as an anatomical landmark. METHODS: Five anaesthesiologists attempted to locate one out of five consecutive intervertebral spaces (Th7-Th8 to Th11-Th12) on patients referred for magnetic resonance imaging of the vertebral column. The intended thoracic interspace and the counting reference point (C7-Th1 or L3-L4) were marked with oil capsules. The body mass index, gender and position of the patient were recorded. The exact capsule positions were determined by a radiologist after the study. RESULTS: In 92 patients, 26.7% of the thoracic interspaces were correctly identified. The counting reference point was the only variable studied with a significant influence on error. The accuracy increased when the iliac crest was used as an anatomical landmark rather than the prominent vertebra (odds ratio, 0.29). The majority (76.4%) of all the incorrectly placed capsules were found cephalad to the intended level. CONCLUSION: We recommend that the caudal of two to three possible interspaces should be used when placing an epidural catheter in the thoracic spine. Because of the inaccurate localization of the thoracic intervertebral spaces, documentation should state the site of puncture as being in the upper or lower thoracic spine instead of claiming to be in an exact interspace.

MR analysis of the transverse ligament in the late stage of whiplash injury.

PURPOSE: To analyse and classify structural changes in the transverse ligament in the late stage of whiplash injury by use of high-resolution MRI, and to evaluate the reliability of our classification. MATERIAL AND METHODS: Ninety-two whiplash-injured (2-9 years previously, mean 6 years) and 30 non-injured individuals underwent proton-weighted MR imaging of the craniovertebral junction in three orthogonal planes. Structural changes in the transverse ligaments were graded twice (grades 1-3) based on increased signal, independently by 3 radiologists with a 4-month interval. Inter- and intraobserver statistics were calculated by ordinary and weighted kappa (K). RESULTS: Image quality was excellent in 109 cases and slightly reduced in 13. Twenty-two out of 30 ligaments in the control group were classified as normal (73%) compared with only 32 out of 92 in the injured group (36%). Two or all 3 observers agreed in their grading in 101 out of 122 ligaments (83%). Intraobserver agreement (weighted K) was fair to good (0.33-0.73). Pair-wise interobserver agreement was fair (0.24-0.39). Reasons for divergent grading were insufficient knowledge of normal variations, low signal intensity in the peridental soft tissue obscuring the ligament and interpretation flaw. CONCLUSION: Whiplash trauma can damage the transverse ligament. By use of high-resolution proton-weighted MR images such lesions can be detected and classified. The reliability of this classification still needs improvement.

MRI of the tectorial and posterior atlanto-occipital membranes in the late stage of whiplash injury.

Our aim was to characterise and classify permanent structural changes in the tectorial and posterior atlanto-occipital membranes several years after a whiplash injury, and to evaluate the reliability of our classification. We obtained sagittal proton density-weighted images of the craniovertebral junction of 92 whiplash-injured and 30 uninjured individuals. Structural abnormalities in the two membranes were classified as grades 1-3 independently by three radiologists blinded for clinical information. Grading criteria were based on reduced tectorial membrane thickness, and elongation or rupture of the posterior atlanto-occipital membrane/dura mater complex. The same images were reassessed 4 months later. Image quality was graded good in 104 cases, slightly reduced in 13 and unsatisfactory in five. Of 117 tectorial membranes 31 (26.5%) showed grade 2 or 3 lesions, in the uninjured group none were grade 3 and only three were grade 2. Pair-wise interobserver agreement (weighted kappa) was moderate (0.47-0.50), while the intraobserver agreement was moderate to good (0.51-0.70). Of 117 posterior atlanto-occipital membranes 20 (17.1%) had grade 2 or 3 lesions; there was no grade 3 and only one grade 2 lesion in the uninjured group. Inter- and intraobserver agreement was good (0.61-0.74 and 0.65-0.86, respectively). Reduced image quality was the main reason for disagreement, but partial thinning and lateral tapering, as normal tectorial membrane variations, created difficulties in some cases. This study strongly indicates that whiplash trauma can damage the tectorial and posterior atlanto-occipital membranes; this can be shown on high-resolution MRI. Better knowledge of normal anatomical variations and improved image quality should increase the reliability of lesion classification.

MRI assessment of the alar ligaments in the late stage of whiplash injury--a study of structural abnormalities and observer agreement.

Our aim was to characterise and classify structural changes in the alar ligaments in the late stage of whiplash injuries by use of a new MRI protocol, and to evaluate the reliability and the validity of this classification. We studied 92 whiplash-injured and 30 uninjured individuals who underwent proton density-weighted MRI of the craniovertebral junction in three orthogonal planes. Changes in the alar ligaments (grades 0-3) based on the ratio between the high signal area and the total cross-sectional area were rated twice at a 4-month interval, independently by three radiologists. Inter- and intraobserver statistics were calculated by ordinary and weighted kappa. Cases classified differently were reviewed to identify potential causes for disagreement. The alar ligaments were satisfactorily demonstrated in all cases (244 ligaments in 122 individuals). The lesions, 2-9 years after the injury, varied from small high-signal spots to high signal throughout the cross-sectional area. Signal was highest near the condylar insertion in 82 of 94 ligaments, indicating a lesion near that insertion, and near the dental insertion in eight, indicating a medial lesion. No grade 2 or 3 lesion was found in the control group. At least two observers assigned the same grade to 214 ligaments (87.7%) on the second occasion. In 30 ligaments (12.3%) this agreement was not obtained. Pair-wise interobserver agreement (weighted kappa) was fair to moderate (0.31-0.54) in the first grading, improving to moderate (0.49-0.57) in the second. Intraobserver agreement (weighted kappa) was moderate to good (0.43-0.70). Whiplash trauma can cause permanent damage to the alar ligaments, which can be shown by high-resolution proton density-weighted MRI. Reliability of classification of alar ligament lesions needs to be improved.