The halo skeletal fixator. Principles of application and maintenance.

The halo skeletal fixator, originally developed for use in patients with poliomyelitis, is now widely used with many types of cervical spine instabilities. Despite its demonstrated effectiveness, certain problem areas, including pin loosening and infection, have been identified. These problems have subsequently inspired detailed studies of skull osteology, biomechanics of pin fixation, and comparisons of techniques of application. Based on these studies, specific recommendations concerning the application and maintenance of the halo have developed. Anterior pin sites should be located in the safe zone approximately 1 cm superior to the orbital rim, cephalad to the lateral two-thirds of the orbit, and below the greatest circumference of the skull. The optimal posterior pin sites are located posterolaterally, diagonal to the corresponding contralateral anterior pins. Pins should be inserted perpendicular to the skull, tightened to eight inch/pounds (0.90 Newton-meter), and retightened once at 48 hours. A subsequent loose pin may be retightened once to eight inch/pounds if resistance is met; otherwise, it should be removed and a new one placed in a different location. Infected pins require antibiotic therapy, wound care, and possibly pin-site change and wound debridement.