432 - Exploration of a CT-based Alternative to the Rule of Spence for Assess...

#432 Exploration of a CT-based Alternative to the Rule of Spence for Assessing Transverse Ligament Integrity

Oral Posters: Cervical

Presented by: N. Rodriguez-Martinez

Author(s):

N. Rodríguez-Martínez (1)
L. Perez-Orribo (1)
S. Kalb (1)
D. Malhotra (1),N. Theodore (1)
N.R. Crawford (1)

(1) Barrow Neurological Institute, Spinal Biomechanics, Phoenix, AZ, USA

Abstract

Introduction: The Rule of Spence for assessing integrity of the transverse atlantal ligament (TAL) suffers from poor specificity and sensitivity, frequently incorrectly reflecting the condition of the TAL. Since CT scans are quickly and easily obtained in trauma centers, we propose using a special sequence of two CT scans for more accurate diagnosis of injury to the TAL. We sought to assess the sensitivity of the CT method for TAL injury diagnosis in a laboratory setting.

Methods: Ten human cadaveric specimens were mounted horizontally in a supine posture with wooden inserts attached to the back of the skull to maintain neutral or slightly flexed (10°) postures. Specimens were scanned in neutral and flexed postures in four conditions: (1) intact (N=10), (2) after simulated Jefferson fracture with TAL intact (N=5), (3) after TAL disruption without fracture (N=5), and (4) after TAL disruption with simulated fracture (N=10). Atlanto-dens interval (ADI) from sagittal slices of the CT image was measured to assess anteroposterior instability of C1-C2; cross-sectional canal area was measured to assess canal encroachment caused by the flexed posture.

Results: In going from neutral to slight flexion, ADI increased by 0.02 mm (2.5%) in intact spines, 0.08 mm (6.25%) after Jefferson fracture without TAL disruption, 0.4 mm (34%) after TAL disruption without fracture, and 0.42mm (25%) after TAL disruption with fracture (Fig.1). ADI increases from neutral to flexed were not significant (p>0.33, paired Student's t-test) in normal condition or with fracture without TAL disruption. However, ADI increases were significant with TAL disruption or TAL disruption+fracture (p< 0.035). Increases in canal area were < 0.8% and were not significant (p>0.74).

Discussion: This study explores the possibility of utilizing two CT scans to evaluate TAL integrity. The neutral scan would represent the scan as it is currently obtained, and the slightly flexed scan would represent a scan taken with some support behind the patient's head to induce slight but not full flexion. The change in ADI between these two postures was very sensitive in distinguishing TAL injury from atlas fracture. The results of this study indicate that this method should be more sensitive than the Rule of Spence for evaluating TAL integrity. Additionally, the degree of flexion is small enough to not cause canal encroachment in case of instability. Further clinical research is needed to establish clinical sensitivity and specificity of this method.

Fig 1. Mean ADI in neutral and flexed postures.