Understanding normal craniocervical rotation occurring during the rotation stress test

The rotation stress test is suggested for assessing alar ligament integrity. Although some authors, in the literature dealing with 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. The objectives of the researchers who undertook this study were: (1) to study 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. A within-subject experimental study was conducted consisting of 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). Measurement of rotation of the occiput relative to a stabilized axis ranged between 1.7 and 21.5 degrees.

While sustaining the test position for imaging increased the potential for loss of end-range position and image quality. and testing could be performed only in the neutral position rather than in 3 planes as often described, the study was able to conclude that 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.

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