A Novel Halo Orthosis to Reduce Pin Loosening

Pin loosening is a frequent complication associated with the use of halo orthoses. Efforts to reduce pin loosening incidence include increasing the number of halo pins, increasing the torque specification, and proactively retightening the halo pins. Although these approaches lower pin loosening incidence rates, none addresses the cause of pin loosening, which is the inability of current halo ring designs to accommodate changes in geometry of the skull. A novel four-pin adaptive halo ring is introduced that can accommodate changes in geometry of the skull and provide a nearly constant pin force. To quantify pin loosening in a halo ring, tests were performed using a fixture that was capable of simulating the changes in skull geometry that are responsible for pin loosening. Both the four-pin adaptive halo and a conventional halo were tested. After $1.1mm$ of radial recession of the skull at the pin site, the average halo pin force in the conventional halo decreased by 78% while the average halo pin force in the four-pin adaptive halo decreased by 12%. In addition, the four-pin adaptive halo had significantly less variation in initial halo pin force (⁠$p$-value $<0.0001$⁠) than that of the four-pin adaptive halo.