An evaluation of halo pin insertion torque on outer table penetration in elderly patients

An experimental anatomic study performed on elderly cadaveric skulls.

(1) To determine the pin penetration depths in outer table of skull at different torques in the elderly population during halo pin insertion and (2) to validate a safe range of torque for use in this population.

The elderly are at an increased risk of falls, which can lead to cervical fractures. The halo pins used to stabilize these injuries present unique problems in this population owing to osteoporosis, and intracranial pin penetration should always be avoided.

A halo ring was used to insert pins in 4 standard positions on 10 elderly cadaveric skulls. Incremental torques were used to drive the pin into the outer table, and the penetration of each pin was measured using computed tomography imaging at each stage.

Eight to Twelve in-lb of torque was not sufficient to fully penetrate the outer table of the skull. Only at 16 in-lb of torque was the outer table penetrated, and only anterolaterally, hence the posterolateral outer table is more resistant to penetration than the anterolateral outer table.

Despite age-related bone changes in the elderly, it is still safe to use 8 in-lb of torque when inserting pins for a halo vest. However, as the anterolateral outer table is weaker than the posterolateral outer table, a new pin design with broader shoulders should be used anterolaterally to ensure maximal patient safety.