Evaluating the Feasibility and Reproducibility of a Novel Insertion Method for Modular Acetabular Ceramic Liners.

Modern hip implants have a modular design. In case of wear or other damage it allows surgeons to change the tribological partners, i.e., the acetabular liner and femoral ball. In both revision and primary surgery, the secure joining of the implant components is important for the success of the operation. The two components, namely the ceramic liner and hip cup, are connected via a conical press connection and should be concentrically aligned to avoid chipping. Malseated liners can reduce the life span in situ. The amount of the joining force, which is usually applied via a hammer, depends on the surgeon. In this study, an alternative joining method for acetabular ceramic liners in hip cups was investigated, which intends to make the process more reproducible and thus safer. For this purpose, a handpiece was used to apply a defined force impulse of 4 kN. For the concentric alignment of a ceramic liner in the hip cup, an adapter was developed based on findings via a qualitative finite element (FE) analysis. Insertion and pushout tests of the acetabular cup-liner connection were performed in the laboratory with the new instrument (handpiece with the connected adapter) to evaluate the functionality of the instrument and the reproducibility of the new insertion method. For comparison, liners and acetabular cups were joined using a testing machine according to the standard. The presented results demonstrate the technical proof-of-concept of the new joining method under laboratory conditions. They meet the acceptance criteria of established manufacturers, which proves the equivalency to proven methods for joining modular implant components. To verify the improvement of the new joining method compared to the conventionally used joining method, an application-oriented study with different surgeons and the new joining instrument under clinical conditions is necessary.