A comparative evaluation of halo pin designs in an immature skull model

To design an improved halo pin for use in pediatric patients, three commonl y used halo pins were evaluated with a mechanical testing apparatus and seg ments of prepared fetal calf skull. The pins mere driven through the bone s egments while the load at the bone-pin interface was measured, New pins wer e designed with respect to pin tip and flange width and similarly compared. Mean maximum loads to penetration, normalized for bone segment thickness, were 55.6 N/mm for the PMT Corporation pin, 61.5 N/mm for the Bremer pin, a nd 73.6 N/mm for the Ace pin. Four new, short tipped pins were designed and compared with the Ace pin, and there was no significant difference. Finall y, four new pins were designed with varying flange widths. Mean maximum loa ds, normalized for bone segment thickness, were 68.9 N/mm for the 4.2 mm fl ange, 72.2 N/mm for the 4.7 mm flange, 92.9 N/mm for the 5.2 mm flange, and 96.4 N/mm for the 5.7 mm flange, The findings of this investigation are cl inically important because they may help to explain the variability in the complication rates seen with the use of different halo systems in children. The three halo pins currently on the market hare different pin designs, in cluding tip lengths and flange distances, which contribute to the differenc e in load to penetration for each pin. The new, wide flanged, short tipped halo pin design might decrease the complication rate of halo use in childre n by providing an improved capacity to resist penetration despite increased loads of application.