Alar Ligament Test

Alar Ligament Test is used to assess the alar ligament integrity and quality of side-bending and rotation between the occiput Atlas and axis. Rotation and side bending tighten the contralateral alar (e.g., rotation or side bending to the right tightens the left alar), whereas flexion tightens both alar ligaments.

How do you perform the Alar Ligament Test?

The patient lies supine with the head in the physiological neutral position, the examiner stabilizes the axis with a wide pinch grip around the spinous process and lamina. The examiner then attempts to side flex the head and axis.

See Also: Facet Joint Dysfunction

What does a positive Alar Ligament Test mean?

Under normal conditions, rotation & side bending tightens alar ligament. Thus, the spinous process should move immediately in the contralateral direction to side bending.

If the C2 transverse process does not move as soon as the head begins to rotate, laxity of the alar ligament should be suspected (most common in patient with RA).

To confirm the findings in Alar Ligament Test, the point of rotation is maintained, as the patient’s head is cradled by the clinician, and while monitoring the motion at the C2 segment, the clinician introduces side bending through the craniovertebral joints to slacken the alar ligament. Further rotation should now be possible.

Test Accuracy

The diagnostic value of Alar Ligament Test is as yet unknown.

Alar Ligament Anatomy

The alar ligaments connect the superior part of the dens to fossae on the medial aspect of the occipital condyles, although they can also attach to the lateral masses of the atlas.

A study of 44 cadavers found the orientation of the ligament to be superior, posterior, and lateral. In another study, upper cervical spine specimens were dissected to examine the macroscopic and functional anatomy of alar ligaments. The study found that the most common orientation was cauda-cranial, followed by transverse. In two of the specimens, a previously undescribed ligamentous connection was found between the dens and the anterior arch of the atlas, the anterior atlantodental ligament.

In 12 specimens, the ligament also attached via caudal fibers to the lateral mass of the atlas. The posteroanterior orientation of the ligaments in 17 of the 19 subjects was directly lateral from the dens to the occipital attachment or slightly posterior.

The function of the ligament is to resist flexion, contralateral side bending, and contralateral O-A rotation. In addition, the alar ligaments restrict anteroposterior translation of the occiput on C1 to some degree. Because of the connections of the ligament, side bending of the head produces a contralateral or ipsilateral rotation of C2, depending on the source.

Insufficiency of the alar ligaments increases the potential for occipitoaxial instability. The degree of instability can be determined in conjunction with other clinical findings, such as neurologic or vascular compromise, pain, and deformity.

References

1. Dvorak J, Panjabi MM, Gerber M, et al.: CT functional diagnostics of the rotary instability of the upper cervical spine and experimental study in cadavers. Spine 12:197–205, 1987.
2. Dvorak J, Panjabi MM: Functional anatomy of the alar ligaments. Spine 12:183, 1987.
3. Okazaki K. [Anatomical study of the ligaments in the occipito-atlantoaxial complex]. Nihon Seikeigeka Gakkai Zasshi. 1995 Dec;69(12):1259-67. Japanese. PMID: 8586911.
4. Panjabi M, Dvorak J, Crisco J, et al.: Flexion, extension, and lateral bending of the upper cervical spine in response to alar ligament transections. J Spinal Disord 4:157–167, 1991.
5. O , Brien MF, Lenke LG: Fractures and dislocations of the spine. In: Dee R, Hurst L, Gruber M, et al., eds. Principles of Orthopaedic Practice, 2nd ed. New York, NY: McGraw-Hill, 1997:1237–1293.
6. Vangilder JC, Menezes AH, Dolan KD: The Craniovertebral Junction and its Abnormalities. Mount Kisco, NY: Futura Publishing Co, 1987.
7. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.