The occipitoatlantal capsular ligaments are the primary stabilizers of the occipitoatlantal joint in the craniocervical junction: a finite element analysis

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OBJECTIVE

There is contradictory evidence regarding the relative contribution of the key stabilizing ligaments of the occipitoatlantal (OA) joint. Cadaveric studies are limited by the nature and the number of injury scenarios that can be tested to identify OA stabilizing ligaments. Finite element (FE) analysis can overcome these limitations and provide valuable data in this area. The authors completed an FE analysis of 5 subject-specific craniocervical junction (CCJ) models to investigate the biomechanics of the OA joint and identify the ligamentous structures essential for stability.

METHODS

Isolated and combined injury scenarios were simulated under physiological loads for 5 validated CCJ FE models to assess the relative role of key ligamentous structures on OA joint stability. Each model was tested in flexion-extension, axial rotation, and lateral bending in various injury scenarios. Isolated ligamentous injury scenarios consisted of either decreasing the stiffness of the OA capsular ligaments (OACLs) or completely removing the transverse ligament (TL), tectorial membrane (TM), or alar ligaments (ALs). Combination scenarios were also evaluated.

RESULTS

An isolated OACL injury resulted in the largest percentage increase in all ranges of motion (ROMs) at the OA joint compared with the other isolated injuries. Flexion, extension, lateral bending, and axial rotation significantly increased by 12.4% ± 7.4%, 11.1% ± 10.3%, 83.6% ± 14.4%, and 81.9% ± 9.4%, respectively (p ≤ 0.05 for all). Among combination injuries, OACL+TM+TL injury resulted in the most consistent significant increases in ROM for both the OA joint and the CCJ during all loading scenarios. OACL+AL injury caused the most significant percentage increase for OA joint axial rotation.

CONCLUSIONS

These results demonstrate that the OACLs are the key stabilizing ligamentous structures of the OA joint. Injury of these primary stabilizing ligaments is necessary to cause OA instability. Isolated injuries of TL, TM, or AL are unlikely to result in appreciable instability at the OA joint.

ABBREVIATIONS AA = atlantoaxial; AACL = AA capsular ligament; AL = alar ligament; AOD = atlantooccipital dislocation; CCI = condylar–C1 interval; CCJ = craniocervical junction; FE = finite element; FEM = FE method; OA = occipitoatlantal; OACL = OA capsular ligament; Oc = occiput; ROM = range of motion; TL = transverse ligament; TM = tectorial membrane.

Article Information

Correspondence Douglas L. Brockmeyer: University of Utah, Primary Children’s Hospital, Salt Lake City, UT. douglas.brockmeyer@hsc.utah.edu.

INCLUDE WHEN CITING Published online February 15, 2019; DOI: 10.3171/2018.10.SPINE181102.

Disclosures Dr. Dailey reports being a consultant for K2M and Zimmer. He received clinical or research support for the current study from K2M.

© AANS, except where prohibited by US copyright law.

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Figures

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    CCJ FE model of a 14-year-old girl (Model 4). Anterior view of discretized CCJ FE model (upper left). Images showing various structures: OACL (A), AACL (B), anterior atlantooccipital membrane (C), anterior atlantoaxial membrane (D), posterior atlantooccipital membrane (E), posterior atlantoaxial membrane (F), TM (G), TL (H), apical ligament (I), and alar ligament (J).

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    Model 4 normal CCJ ROM at 1.5 Nm. Each row of images represents an ROM in different views (lateral, anterior, posterior, and top down). A: Flexion. B: Extension. C: Axial rotation. D: Lateral bending. The colors represent relative change in ROM from fixed C2 (0°).

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    Comparison of linear and nonlinear range of motion for Model 5. C0 = occiput (Oc).

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    Model 4 normal (left) and OACL injury (right) ROM comparison in degrees. A: Flexion. B: Extension. C: Axial rotation. D: Lateral bending. The colors represent relative change in ROM from fixed C2 (0°).

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    Percentage increase from normal in flexion (A), extension (B), axial rotation (C), and lateral bending (D). *Significant difference from the normal, noninjured model. #Indicates n = 4 used for the extension comparison for the OACL+TL+TM injury because Model 2 did not converge. Figure is available in color online only.

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    A 5-year-old boy involved in a motor vehicle collision. Parasagittal CT reconstructions showing abnormal CCI distances on the right (A) and left (B). Parasagittal MRI STIR sequences showing abnormal signal through the right (C) and left (D) OA joint. The joint is marked by arrows. Postoperative radiograph (E) showing an occipitocervical instrumentation and fusion construct.

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