Aim: In cemented total hip arthroplasty cup loosening occurs earlier than stem loosening in most of the cases. This is mainly caused by the lack of stabile adhesion between the hydrophobic bone cement and the hydrophilic bone surface of the acetabulum. The aim of this study was to develop a multilayer amphiphilic bonding system which prevents the hydrolytic debonding at the bone cement-bone interface, thus optimizing the compound stability.
Method: In a first series of tests a standardized three-point-bending test was performed to determine the compound stability of the bone cement-bone interface. The bony test specimens were immersed into physiologic NaCl solution to simulate the hydrolytic in situ conditions and contaminated with blood to simulate the intraoperative bleeding of prepared acetabular bone surfaces. In a second series of tests polyethylene cups were implanted into the acetabular cavity of sheep using the current cementing technique. Acetabular bone stock was prepared differently (subchondral sclerotic zone preserved vs. removed, additional drilling into the acetabular roof, with vs. without the multilayer bonding system) in intra-individual comparison of both acetabular sides. To ascertain the bone cement-bone stability a torsional-turn out test was performed on an universal testing machine.
Results: In the three-point-bending tests the compound stability between bone cement and bone was 50- to 100-times higher with the use of the multilayer system. In the torsional-turn out tests the compound stability showed in mean a 1.8-fold increase of the interface strength in case of preconditioned acetabular cavities with the multilayer bonding system.
Conclusion: The developed multilayer bonding system optimizes the interface strength between acetabular bone stock and bone cement significantly for cemented cups in total hip arthroplasty. In contrast to cementing techniques with complete removal of the subchondral sclerotic zone (in order to optimize micro-interlocking) the biologically effective and load bearing acetabular bone stock can be preserved using the newly developed multilayer bonding system. This aspect might be highly important especially with regard to possible acetabular bone defects caused by the process of aseptic cup loosening.