Evaluation of a high density polyethylene fixing system for hydroxyapatite ceramic implants

A fixing system made of high density polyethylene (mini ROC fastener system, Innovasive Devices Inc., Marlborough, MA, USA) was applied to artificially porous hydroxyapatite (HAP) implants. Their fixing ability was assessed with pull-out tests and a preliminary study was done to determine the most suitable drill hole diameter and depth. Effectiveness of the combined use of drill-free titanium screws (Martin GmbH & Co. Ltd., Tuttlingen, Germany) and the mini ROC fastener system was also evaluated. The pull-out strength of the system differed according to the hole diameter and depth of insertion. The strongest physical strength was obtained with holes 2.10 mm in diameter and 6 mm in depth. If inserted under optimum conditions, the mini ROC fastener system was deemed to have adequate fixing ability for clinical applications pull-out strength more than 7 kgf. In addition, the combined use of a drill-free screw for microplate with the mini ROC fastener system had a pull-out strength of around 10 kgf which was superior to the mini ROC fastener system alone. The mini ROC fastener system is best suited to fix HAP implants to the soft tissues such as muscle, tendon or periosteal tissue as well as for plate fixation when used with drill-free screws. The fact that effective fixing was achieved should result in a further increase in the clinical use of artificial HAP implants.