Introduction: Jefferson's fracture, first described in 1927, represents a bursting fracture of the C1 ring with lateral displacement of the lateral masses. In 1970, Spence, et al. determined that if the total lateral mass overhang (LMO) exceeds 6.9mm, there is high likelihood of transverse atlantal ligament (TAL) rupture. Several recent radiographic studies have questioned the accuracy and validity of the "rule of Spence" and there is a paucity of biomechanical evidence to support the previously purported measurements.
Methods: Using a universal materials testing machine, cadaveric TALs were stretched laterally until failure. A high-resolution, high-speed camera was utilized to measure the displacement of the lateral masses upon TAL failure.
Results: 5 cadaveric specimens were tested (N=5). 4 of the 5 TALs ruptured and 1 TAL avulsed from its attachment to the lateral mass. The average displacement upon TAL failure was 2.65mm (± 0.84mm). The average force required to cause failure of the TAL was 235N (± 121N).
Conclusions: Our findings suggests that the rule of Spence is conceptually valid; however, TAL failure occurs at an average lateral mass displacement of 2.7mm, which is significantly less than previously stated. Based on this study, we strongly encourage clinicians to have a high index of suspicion for TAL injury if the lateral mass displacement exceeds 2.7mm.
Patient Care: It provides a reliable measurement for the clinician to identify transverse atlantal ligament insufficiency based on biomechanical data.
Learning Objectives: By the conclusion of this session, participants should be able to:
1. Describe the clinical importance of the "rule of Spence"
2. Discuss the accuracy of previously published threshold values for lateral mass overhang that indicate transverse atlantal ligament injury.
3. Identify an accurate threshold for lateral mass displacment that will indicate transverse atlantal ligament compromise.
References: 1 Jefferson G. Remarks on fractures of the first cervical vertebra. Br Med J, 1927; 2: 153-157.
2 Spence KF, Decker S, Sell KW. Bursting altantal fracture associated with rupture of the transverse ligament. J Bone Joint Surg [Am] 1970; 52: 543-9.
3 Heller JG, Viroslav S, Hudson T. Jefferson fractures: the role of magnification artifact in assessing transverse ligament integrity. J Spinal Disord, 1993, 6: 392-396.
4 Radcliff KE, Vaccaro, AR. Does C1 Fracture Displacement Correlate with Transverse Ligament Integrity? Orthopedic Surgery, 2013; 5: 94-99
5 Perez-Orribo L, et al. Comparison of CT versus MRI measurements of transverse atlantal ligament integrity in craniovertebral junction injuries. Part 1: A clinical study. J Neurosurg Spine. 2016