Evaluation of current extrication orthoses in immobilization of the unstable cervical spine. An experiment was designed to evaluate the comparative stabilizing efficacy of several widely used semi-rigid orthoses applied to unstable fresh cadaver cervical spines subject to load. Cadaver specimens were surgically destabilized at the C4-5 segment. Lateral radiographs of the destabilized spine were obtained before and after collar placement and after the application of a 5-pound flexion force. Data analysis employing a one-way analysis of variance showed no statistically significant difference in the Necloc's, Philadelphia Collar's, or the Stifneck's ability to stabilize the cervical spine against a deforming flexion force (P greater than 0.05). They all provide translational stability while allowing angular changes to occur with application of the flexion force. The Philadelphia Collar Halo System is statistically superior to all three of the aforementioned collars in prevention of both translation and sagittal rotation (P less than 0.05). 