Toward Understanding Normal Craniocervical Rotation Occurring During the Rotation Stress Test for the Alar Ligaments

Background The rotation stress test is recommended for assessing alar ligament integrity. Although some authors, in the literature regarding the rotation stress test, accept that rotation will occur during testing, estimates of range occurring with a normal test response vary between 20 and 40 degrees. None of these estimates are based on formal examination of the test.

Objective The purposes of this study were: (1) to examine the range of craniocervical rotation occurring during rotation stress testing for the alar ligaments in individuals who are healthy and (2) to investigate a measurement protocol for quantifying rotation.

Design A within-subject experimental study was conducted.

Methods Sixteen participants underwent magnetic resonance imaging in neutral and end-range rotation stress test positions. Measurements followed a standardized protocol relative to the position of the axis. A line connecting the transverse foramena of the axis created a reference plane. The position of the occiput in the head-neutral position was calculated as the angle formed between a line joining the foramena lacerum and the reference plane. Measurements were repeated at the end-range test position. Total rotation of the occiput was calculated as the difference in angles measured in neutral and test positions. Measurement was performed on 4 occasions, and reliability of measurements was assessed using the standard error of measurement (SEM) and the intraclass correlation coefficient (ICC).

Results Measurement of rotation of the occiput relative to a stabilized axis ranged between 1.7 and 21.5 degrees (X̅=10.6, SD=5.1, SEM=1.14, ICC=.96, 95% confidence interval=.90–.98).

Limitations Sustaining the test position for imaging increased the potential for loss of end-range position and image quality. Testing could be performed only in the neutral position, not in 3 planes as commonly described.

Conclusions The range of craniocervical rotation during rotation stress testing of intact alar ligaments should typically be 21 degrees or less. Rotation may be quantified using the method protocol outlined.