Abstract
Introduction
Ceramic ball heads are well known in hip arthroplasty for their superior tribology performance and high burst strength. To assess the ball head performance and the in-vivo fracture risk Pandorf et al 2008 examined the burst strength of BIOLOX®forte (pure aluminium oxide ceramic, CeramTec GmbH, Plochingen, Germany) ball heads on clean standard test tapers and contaminated test tapers. They found that fat tissue and scratches are reducing the burst strength to 40% and to 20% of the reference burst strength, respectively. The aim of this work is to investigate if BIOLOX®delta (alumina matrix ceramic, CeramTec GmbH, Plochingen, Germany) ball heads show a similar behaviour as BIOLOX®forte ball heads with respect to taper contamination.
Materials and Methods
Each test series consisted of n=5 BIOLOX®delta 28–12/14 L ball heads and n=5 metal test tapers (Ti-6Al-4V, ISO 5832-3). For the reference series the metal tapers remained untouched representing the CeramTec standard test procedure. For the fluid series the ball heads were filled up with tap water or calf blood serum. For the solid series the metal test tapers were contaminated with small particles of bovine bone, commercially available bone cement and porcine fat tissue in the engagement zone. A chisel and a slight hammer tap were used to scratch the proximal region of the metal test taper. The ball heads were then manually attached to the contaminated metal test tapers without further force appliances. An apparatus according to ISO 7206-10 was used for burst testing. The tests were performed at CeramTec in-house test laboratory.
Results
The contamination of the taper region showed an influence on the resulting burst strength which was qualitatively similar to the previously performed investigations with pure alumina ball heads.
Discussion
Sterilized water is used for cleaning the surgical wound before attaching the ball head on the metal taper. A contamination of the metal taper with water is reducing the burst strength of BIOLOX®delta ball heads to 80% reference burst strength. Remains of blood and bone particles on the metal taper can lead to 63% of the reference burst strength. Remains of fat tissue on the metal taper can lead to 38% of the reference burst strength. The fat tissue is reducing the coefficient of friction, which leads in further consequence to a change of the stress distribution and a raise of the stress magnitude in the ceramic ball head. Scratches and grooves have the ability to reduce the burst strength to only 29% reference burst strength. The results confirm that the taper connection of the components have to be clean and dry in order to provide a sufficient and strong connection.
