Volumetric Wear Assessment and Characterization of Striated Pattern of Retrieved UHMWPE Tibial Inserts
thesisposted on 21.10.2015, 00:00 by Elmira Moslemi Rad
Failure of total knee replacements due to the generation of polyethylene wear debris remains a crucial issue in orthopedics. Unlike the hip, it is difficult to accurately determine knee implant wear rates from retrievals. Several studies have relied on thickness measurements to estimate penetration, but the complicated geometry of contemporary tibial inserts poses a challenge for accurate wear assessment. Quantifying the surface damage of tibial retrievals is critical to improve future implant designs. Aside from implant designs, materials and surgical techniques, patient factors can affect the wear rate of the insert and longevity of the implant as well. Also, some early wear patterns such as striations may lead to more severe damage of the tibial insert; therefore, understanding the surface changes relate to changes in molecular structure of ultra high molecular weight polyethylene (UHMWPE) of the tibial articulation surface is crucial. For the first aim of this study, the volume loss and maximum linear penetration on retrieved tibial inserts of a collection of 81 total knee replacements (TKR) (Nexgen CR, Zimmer, Warsaw, IN) were calculated with the help of an autonomous mathematical reconstruction algorithm. Also, the impact of patient factors on wear has been investigated. In the second aim, the impact of striated patterns on wear was determined, and surface characterization techniques (Raman spectroscopy and attenuated total reflectance-Fourier transform infrared (ATR-FTIR)) were utilized to analyze structural alterations within these patterns. The results suggest that penetration is not a good surrogate measure for estimating wear volume of individual TKR polyethylene components, but may be useful for large cohort studies. Also, patient age and weight might have an impact on volumetric wear rate. The quantification of crystallinity on very fine features as the striated patterns is challenging. In this study, the ATR-FTIR method could not detect any structural change, whereas Raman spectroscopy showed a higher crystallinity on the hills compared to the troughs of striated patterns as hypothesized. The findings of this study provide valuable input to improve the implant designs and materials to increase the longevity of total knee replacements.