EFFECTS OF ALAR LIGAMENT TRANSECTION ON UPPER CERVICAL-SPINE ROTATION

Fresh human cadaveric specimens of occiput (C0) to C3 were subjected to axial torque. The resulting physiological motions were studied in an unconstrained three-dimensional manner. Effects of sequential transections of the left and right alar ligaments on the relative motions of C0-C1 and C1-C2 were studied. After transection of the left alar ligament, ranges of motion-due to 1.5 Nm torque-increased at both the C0-C1 and C1-C2 joints. Increases were small, on average 1.9-degrees to each side and at each level. Increases due to subsequent cutting of the right alar ligament were, on average, only 0.5-degrees and statistically not significant. In general, neutral zones showed greater increases, e.g., 3.9-degrees to each side at the C1-C2 joint. Comparing right and left axial rotations, after transection of the left alar ligament, showed greater percentage increases for the right, as compared to the left, axial rotation, at both C0-C1 and C1-C2 joints. Functional loss of the alar ligaments indicates a potential for rotatory instability, which, however, must be determined in conjunction with other clinical findings, such as neurological dysfunction, pain, and deformity.