Abstract
Introduction
From a tribological point of view and clinical experience, a ceramic-on-ceramic bearing represents the best treatment option after rare cases of ceramic component fracture in total hip arthroplasty (THA). Fractured ceramic components potentially leave small ceramic fragments in the joint capsule which might become embedded in PE acetabular liners.
Purpose
This in vitro study compared for the first time the wear behaviour of femoral ball heads made of ceramic and metal tested with PE liners in the presence of ceramic third-body debris.
The contamination of the test environment with third-body ceramic debris, insertion of ceramic fragments into the PE liners and implementation of continuous subluxation simulated a worst-case scenario after revision of a fractured ceramic component.
Materials and Methods
Ceramic femoral ball heads (ϕ 32 mm) made of alumina matrix composite (AMC; BIOLOX® delta, CeramTec, Germany) were tested in combination with PE and cross-linked liners and compared to metal femoral ball heads (CoCrMo) of the same diameter. All PE liners were fixed into Ti-6Al-4V metal shells by conical fixation as intended for clinical use. The tests were performed based on ISO 14242-1 utilizing a hip simulator (EndoLab, Germany). Alumina ceramic debris (BIOLOX® forte, CeramTec, Germany) of about 2 mm diameter (maximum 5 mm) were inserted into the PE liners in predefined specific points corresponding to the main load transfer area before the test. The acetabular liners were tested at an inclination of 45° in the medial-lateral plane with the specimens placed in an anatomically correct position. During the test, additional alumina ceramic debris was introduced into the articulation area as a part of the test fluid (calf serum) used in the simulator test chambers. All specimens were tested up to 5 million cycles. Damages to the surfaces of the materials were assessed visually. The wear of the femoral ball heads was measured gravimetrically.
Results
High wear rates were found for metal femoral ball heads, being 1,010 times higher when compared to ceramic femoral ball heads tested with XPE liners and 560 times higher when compared to ceramic femoral ball heads tested with conventional PE liners. The conventional and crosslinked PE liners used in combination with metal femoral ball heads clearly exhibited a scratched surface, whereas the surface of the liners tested with ceramic femoral ball heads exhibited significantly less scratching.
Discussion and Conclusion
This study demonstrates that apart from the recommended ceramic-on-ceramic option also ceramic-on-PE and ceramic-on-crosslinked PE bearing couples may be a viable treatment option after fracture of a ceramic component. The use of a ceramic femoral ball head after fracture of a ceramic articulation component minimizes wear and wear-related complications caused by third-body wear. Based on the results of this in vitro study and clinical findings, the use of a metal femoral ball head in articulation with any PE liner after a ceramic fracture is contraindicated.
