Preclinical Analysis to Assess Aseptic Loosening of Orthopaedic Implants

Although it is long accepted that aseptic loosening is the main reason for revision of total joint replacements, preclinical assessment methods of primary fixation are not well developed. Reasons for aseptic loosening are multifactorial including the patient, surgical approach, biological reactions, wear, micro-motion at the implant–bone interface, load transfer from the joint to the host bone, and bone adaptation. The objective of this study was to highlight a few preclinical methods to investigate orthopaedic implant primary fixation relative to the transfer of loads and displacements at the implant–bone interface. The last generation of metal-on-metal hip prostheses used a high-precision low clearance bearing to provide a low friction ball and socket joint. During implantation the acetabular component deforms under a press-fit; however, excessive deformation of the acetabular component can lead to premature failure of the joint replacement. It is therefore important to establish an accurate method of quantifying cup deformation and develop finite element models to better understand the effects of the press-fit. Methods to measure press-fit deformation of monoblock acetabular cups for metal-on-metal total hip arthroplasty and resurfacing were investigated. The purpose of the present study was to compare cup deformation with two experiments simulating press-fit of an acetabular cup into the pelvis. Rim deformation and cup strain were measured for two common tests: (1) a two-point pinching of the cup rim and (2) a press-fit implantation into a cavitated polyurethane foam block. In the pinch test, the rim displaced linearly and symmetrically with force. The press-fit test, ostensibly a closer representation of surgical procedure, produced more complex displacement and strain responses due to the foam block shape, and the cup surface-foam block interaction. The current study demonstrated two methods to measure real-time hip cup deformation and strain during press-fitting that may be used for preclinical assessment of primary fixation.