Effect of alar ligament transection in side-bending stress test: A cadaveric study

Abstract Background The side-bending stress test is a pre-manipulative screening test for assessing upper cervical instability. To our knowledge, there is no study that simulates the clinical application of side bending stress test before and after alar ligament transection with fixation of C2. Objective To simulate the effect of alar ligament transection in the side bending stress test for an in vitro validation. Design In vitro study. Methods After the dissection of the superficial structures to the alar ligament and the fixation of C2, ten cryopreserved upper cervical spines were manually mobilized in right and left lateral flexion with and without right alar ligament transection. Upper cervical lateral flexion range of motion and mobilization force were measured with the Vicon motion capture system and a load cell respectively. Results The right alar ligament transection increased the upper cervical spine (UCS) range of motion (ROM) in both side bendings (1.30°±1.54° and 1.88°±1.51° increase for right and left side bending respectively). As an average, with standardized forces of 2N, 4N and 6N, right alar ligament transection increased both right and left lateral flexion UCS ROM. Conclusion This in vitro study simulates the clinical application of the side bending stress test with intact and right transected alar ligament. Unilateral transection of the alar ligament revealed a predominantly bilateral increase in upper cervical side bending and variability in the mobilization force applied during the test.