Radiologic criteria to predict injury of the transverse atlantal ligament in unilateral sagittal split fractures of the C1 lateral mass

Abstract

Unilateral sagittal split fracture (USSF) of the C1 lateral mass (LM) has been recently recognized as a rare variant of C1 atlas fracture. To date, there has been no study to investigate whether radiologic criteria can be applied to determine the presence or absence of transverse atlantal ligament (TAL) injury in USSF of the C1 LM.Twenty six consecutive cases of USSF of the C1 LM were included in this study. According to Dickman classification, 16 cases were TAL injury, and 10 cases were TAL intact. Radiologic parameters were measured and compared between the 2 groups.Total LM displacement (LMD) of the 2 sides (5.9 ± 2.0 mm vs 1.2 ± 2.0 mm), unilateral LMD of the fracture side (4.3 ± 1.2 mm vs 1.0 ± 1.1 mm), atlanto-dental interval (ADI) (2.0 ± 0.9 mm vs 1.5 ± 0.4 mm), and fracture gap (6.9 ± 2.7 mm vs 2.1 ± 1.1 mm) were statistically higher in the TAL injury group than the TAL intact group. However, basion-dental interval, clivus canal angle, and atlanto-occipital joint axis angle were not different between the 2 groups. Total LMD and unilateral LMD positively correlated with ADI and fracture gap. The incidence of fracture gap larger than 7 mm was statistically higher in the TAL injury group than the TAL intact group (81% vs 30%).In conclusion, total LMD > 5.9 mm or unilateral LMD > 4.3 mm suggests the presence of TAL injury in USSF of the C1 LM. The possibility of diagnostic error for TAL injury can be further reduced in USSF of the C1 LM by considering the fracture gap larger than 7 mm.

Diagnosis and management of isolated C1 fractures: A systematic review

“…A total of 305 articles were returned in the database searches, of which 13 articles were included in this systematic review. [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] [ Figure 1 ] demonstrates the PRISMA flow diagram for this study. Study design included 10 (73.3%) case series and 2 (20.0%) retrospective cohort studies and 1 (6.7%) prospective cohort study.…”

“…Three articles reviewed various diagnostic factors relevant to the management of isolated atlas fractures [ Table 1 ]. [ 19 , 20 , 23 ] All three studies examined TAL injury in patients with atlas fractures. Lin et al .…”

“…determined that total LMD >5.9 mm and unilateral LMD >4.3 mm were associated with TAL injury in patients with unilateral sagittal split fracture of the lateral mass of C1. [ 23 ] Liu et al . reported that LMD <6.9 mm was inaccurate in either excluding TAL injury or predicting clinical outcomes in nonoperatively treated atlas fractures, while LMD >6.9 mm accurately determined TAL injury but not atlantoaxial stability.…”

“…[ 20 ] Other heuristics have arisen, including a C1:C2 maximal width >1.10 as predictive of TAL injury[ 19 ] and a novel diagnostic rule for predicting TAL instability in unilateral sagittal split fractures. [ 23 ] Clearly, while Dickman's classification seems to be increasingly favored for identifying TAL disruption, the optimal classification system for isolated atlas fractures remains to be determined.…”

The relationship between radiologic parameters and transverse atlantal ligament injury obtained from MRI scans in patients with an isolated atlas burst fracture

“…However, if a TAL injury is present, the fracture is regarded as unstable and surgery is performed. [8][9][10] According to the "Rule of Spence," instability is assumed if the C1 overhang exceeds 6.9 mm on an open mouth anterior-posterior view X-ray, although it has been proposed by Heller et al that this number be adjusted to 8.1 mm to account for radiographic magnification factors. [11] However, recent studies have shown that there is little correlation between bony displacement visible through computed tomography (CT) scans and TAL integrity, casting doubt on the utility of the "Rule of Spence" for assessing TAL integrity.…”