202. Radiologic criteria to predict injury of transverse atlantal ligament in unilateral sagittally split fracture of C1 lateral mass

Abstract

BACKGROUND CONTEXT If lateral mass displacement (LMD) exceeds 6.9 mm, burst fracture of the C1 atlas is considered an unstable fracture due to transverse atlantal ligament (TAL) injury. Recently, unilateral sagittal split fracture (USSF) of C1 lateral mass (LM) was recognized as a rare variant of C1 atlas fracture. Conservatively-treated USSF of C1 LM is reported to cause late deformity of occipitocervical junction requiring major reconstructive surgery. Therefore, it is necessary to verify whether such LMD criteria can be applied to determine TAL injury in USSF of C1 LM. PURPOSE We performed the current study to investigate radiologic criteria to predict the presence of injury of TAL in USSF of C1 LM. STUDY DESIGN/SETTING Retrospective case analyses. PATIENT SAMPLE Twenty-six consecutive cases of USSF of C1 LM were included in this study. The fractures associated with other cervical spines, such as C2 and occiput, were excluded from the study. The mean age was 52 years-old; 16 were male and 10 were female. OUTCOME MEASURES Two radiologists determined presence of TAL injury in MRI using Dickman's classification and divided the cases into two groups: TAL injury and TAL intact. If the results of two judgements were not identical, the third radiologist re-evaluated. The radiologic results were measured and compared between TAL intact and TAL injury. METHODS Three spine surgeons measured radiologic parameters and the averages were used as final results: total LMD of both sides, unilateral LMD of the fracture side, atlanto-dental interval (ADI), and fracture gap. Radiologic parameters were measured and compared between TAL injury and TAL intact. RESULTS Sixteen were TAL injury group (9 type I and 7 type II) and 10 were TAL intact group. Total LMD (5.9 mm vs 1.2 mm, p CONCLUSIONS Compared to the rule of Spence (LMD > 6.9 mm) in C1 burst fracture, total LMD > 5.9 mm (or unilateral LMD > 4.3 mm) are the radiological criteria to predict the presence of TAL injury in USSF of C1 LM, which is considered as an unstable fracture. In addition, if fracture gap more than 7 mm is considered together, the possibility of diagnostic error for TAL injury can be further reduced in USSF of C1 LM. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.