Mechanical evaluation of four- versus eight-pin halo fixation

Fixation of the halo device in the skulls of young children is sometimes compromised because of a thinner cortex and the increased jarring and trauma that small children experience during their everyday activities of life at that age. To assess the increased fixation that an eight-pin halo fixation would provide over the more standard four-pin fixation, the stiffness of fixation of a halo orthosis was evaluated in four dried human cadaver skulls. Two different fixation systems were used: the first one with four pins in the standard locations and the second with four additional pins. A compressive force was applied to the halo ring at a constant rate of 1.27 mm/min. Load and deflection data were recorded simultaneously until a force of 400 N was reached. Results for the two-pin systems were analyzed and compared statistically by using paired t tests. Statistically significant differences were established between the two sets of results with the 8-pin system providing an increase of 24.2% in the stiffness of fixation.