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Calcification of the alar ligament mimics fracture of the craniovertebral junction (CVJ): An incidental finding from computerised tomography of the cervical spine following trauma.
Ligaments stabilizing the atlantoaxial junction (C1-C2 joint), which are shown in Figure 1, include the tectorial membrane, the cranial extension of the posterior longitudinal ligament that limits axial distraction; the alar ligaments, which transfix the dens to the occipital condyles to restrain rotational motion; and the transverse atlantal ligament (TAL), which restricts the dens from impacting the cord in flexion.
Based on the observation of incomplete rupture of other ligaments--such as those in the shoulder, knee, and ankle joint [22]--we can anticipate that if scarring forms in the disrupted, over-stretched alar ligament, it would manifest as an inhomogeneous, asymmetrical band mass.
Anderson and Montesano12 Classification of Occipital Condyle Fractures Type Description Biomechanics Type I Impaction Results from axial loading; ipsilateral alar ligament may be compromised, but stability is maintained by contralateral alar ligament and tectorial membrane Type II Skull base extension Extends from occipital bone via condyle to enter foramen magnum; stability is maintained by intact alar ligaments and tectorial membrane Type III Avulsion Mediated via alar ligament tension; associated disruption of tectorial membrane and contralateral alar ligament may cause instability Table 2.
Analysis of MRI and MRI video findings in craniocervical instability pathology of 420 patients with clinical symptoms consistent with possible spinal instability Findings Patients n (%) Complete alar ligament rupture [*] 20 (4.8) Incomplete alar ligament rupture, [*] 52 (12.4) Alar signal-pattern variation; instability 81 (19.3) Alar signal-pattern variation; no instability 102 (24.3) Normal alar signal pattern; no instability 158 (37.6) Dens variation 4 (1.0) Elasticity syndromes 3 (0.7) Total 420 (100) (*.)These 72 patients (17.1%) were referred to a neurosurgeon.
The magnetic resonance imaging (MRI) findings suggest that the alar ligament injury is the most important cause for atlantoaxial subluxation (11,14).
MRI is especially critical in determining the integrity of the major ligamentous structures of craniocervical junction including the tectorial membrane, occipitocervical joint capsules, alar ligaments, and transverse ligament [7, 18].
Afterwards, the transverse ligament was cut firstly and the alar ligaments were destroyed secondly using a transspinal approach (Figure 3).