INFLUENCE OF SELECTED CLINICAL AND IMPLANT FACTORS ON THE RATE AND DISTRIBUTION OF WEAR OF POLYETHYLENE INSERT OF THE ARTIFICIAL KNEE JOINT

INTRODUCTION / BACKGROUND The most common indications for revision (or causes for dissatisfaction) in total knee arthroplasty (TKA) include prosthetic joint infection (PJI), malposition of the implant, wear of the tibial polyethylene insert (PEI) and consequent induced osteolysis and aseptic loosening, mechanical failure, instability and stiffness of the prosthetic joint. Increased wear of PEI is the result of a multifactorial problem that involves factors from the implant, the surgeon, and the patient. There is also a large number of patients with failed knee arthroplasty where the exact cause for failure is not known. In these cases, probably, a single cause alone would not lead to a problem, but a combination of causes could generate severe dissatisfaction finally leading to revision without clearly defined diagnosis. The appropriate diagnosis in these knees might be extremely difficult to clarify.

Analyses on retrieved PEI allows for a better understanding of TKA failure mechanisms and the detection of factors that cause increased wear rates. There is a lack of research on homogeneous PEI samples, which are analyzed using modern methods and information on the 3D wear distribution of the articular surface in different clinical causes for TKA failure. To our knowledge, it has not been investigated, whether PEI size and the femur to PEI size ratio (within the manufacturer's guaranteed compatibility) affect the wear rate.

PURPOSE AND HYPOTHESIS The purpose of the study is to measure and compare the wear rates of retrieved PEI after failed TKA with respect to various causes for revision surgery, implant size, surgical and patient factors as well as to identify a characteristic linear wear distribution pattern of the articular surface in most common causes of TKA failure. Consequently, we want to contribute to a better understanding of wear mechanisms and identify a possible additional factor for increased PEI wear in TKA.

We expect increased polyethylene wear rates of prosthesis failed due to aseptic causes compared to those failed due to PJI and different linear wear distribution patterns in different failure causes. We expect higher wear rates in smaller PEI and in PEI with a lower femoral to PEI component size ratio (within the framework of the compatibility guaranteed by the manufacturer).

MATERIALS AND METHODS The study will include approximately 60 retrieved Sigma® Cruciate-Retaining Curved GVF i2 from DePuy Synthes (Johnson & Johnson, Warsaw, IN 46582, USA) PEIs, that were removed during the revision operation between 1.1.2013 (start of Institutional storage of removed knee endoprosthesis components) and 31.12.2021. The listed Sigma® PEI represents the largest share of inserted PEV in primary total knee arthroplasty in Valdoltra Orthopedic Hospital (VOH) in the last decade (from 1.1.2012 to 31.12.2021) and the highest number of single types retrieved PEIs in this period and represents the only reason why we selected this particular implant.