Design and initial testing of a novel halo orthosis

A halo orthosis is a medical device used to limit the motion of the skull and cervical spine in order to properly heal an injury sustained in the cervical spine. A difficulty with current halo designs is that the pins which engage the skull can become loose over time. This pin loosening is caused by the inability of halo systems to adapt to small changes in skull geometry due to abrasion, remodeling, and stress relaxation at the pin sites. The inability to adapt is caused by the over-constrained mobility of current halo systems. To address this issue, a nearly exactly-constrained halo prototype that can adapt to most changes in the skull geometry was designed and fabricated. The prototype was tested using a device that simulates the natural geometry changes in the skull. The prototype retains an average of 93% of the initial pin force over a radial recession in the skull of 0.95 mm at each pin site. Comparatively, the current clinical four pin halo only retains an average of 11% of the initial pin force with 1 mm radial recession at each pin site.