RESUMO
BACKGROUND: The rotation stress test is a pre-manipulative screening test used to examine upper cervical instability. This in vitro study simulates the clinical application of the rotation stress test before and after alar ligament transection. METHODS: After the dissection of the superficial structures to the alar ligament and the fixation of C2, ten cryopreserved upper cervical columns were manually mobilized in right and left rotation without and with right alar ligament transection. Upper cervical rotation range of motion (RoM) and mobilization torque were recorded using the Vicon motion capture system and a load cell. FINDINGS: Ligament transection resulted in a larger rotation range of motion in all specimens (contralateral rotation (3.6°, 12.9%) and ipsilateral rotation (4.6°, 13.7%)). The mobilization torque recorded during rotation varied among the different specimens, with a trend towards reduced torque throughout the test in contralateral rotation. INTERPRETATION: This study simulated the rotation stress test before and after alar ligament transection. Unilateral transection of the alar ligament revealed a bilateral increase of the upper cervical rotation. Additional in vivo studies are necessary to validate the results of this study in patients with suspicion of upper cervical instability.