Restriction of Cervical Intervertebral Movement with Different Types of External Immobilizers: A Cadaveric 3D Analysis Study

Study Design. Cadaveric radiostereometric analysis study. Objective. To quantify the ability of five commonly used immobilizers to restrict cervical spine movement, including intervertebral movement, in three directions. Summary of Background Data. Evidence about the ability of many clinically used cervical immobilizers to restrict cervical movement is limited. Furthermore, their effect on intervertebral movement is unknown. Methods. Radiographic inert beads were implanted in the cervical vertebral bodies of five fresh-frozen human cadavers. After application of different immobilizers (Stifneck, Sternal Occipital Mandibular Immobilizer (SOMI), halo-traction, spineboard, halo-vest) and controlled flexion-extension, lateral bending, and rotation torques, radiostereometric analysis was used to determine the overall and intervertebral three-dimensional movement of each vertebral level. Restriction of cervical movement was described as a mean restriction percentage (MRP) and classified on an arbitrary basis (poor: <20%, fair: 20%-40%, moderate: 40%-60%, substantial: 60%-80%, nearly complete: >80%). Results. Most of the restriction of flexion/extension was observed at C0-C1, while most rotational restriction was seen at C1-C2. Lateral bending was restricted at C1 to C7. The Stifneck provided the least immobilization with a moderate restriction of flexion-extension (MRP: 41%, SD: 14%), fair restriction of lateral bending (MRP: 29%, SD: 13%), and substantial restriction of rotation (MRP: 64%, SD: 15%). The halo-vest was the most restrictive immobilizer and reduced movement of the cervical spine substantially for flexion-extension (MRP: 70%, SD: 11%), substantially for lateral bending (MRP: 77%, SD: 14%), and nearly complete for rotation (MRP: 92%, SD: 3%). Conclusion. The restriction of movement from lowest to highest was: Stifneck, SOMI, halo-traction, head blocks on a spine board, and halo-vest. Notably, the standard deviations of the restrictions were smaller for the cranio-thoracic devices than for the cervico thoracic devices. With this new knowledge of external immobilizers and their ability to restrict intervertebral cervical movement, their indication and application in clinical practice can be improved for all patients with (suspected) cervical injury.