Investigation of the effect of cement viscosity in total knee arthroplasty using digital image correlation

Abstract

Approximately 581,000 knee replacements are performed in the United States each year. Micromotion at the bone-cement and cement-implant interfaces causes bone resorption and loosening of the prosthesis. Aseptic loosening of the tibial implant is a prevalent reason for failure in Total Knee Arthroplasty (TKA). The cement viscosity at the time of application to the bone is vital for cement penetration and mechanical stability of the construct. High viscosity cements greatly reduce operating time, yet, may result in decreased penetration into the bone and reduced stability. It is hypothesized that this positive feature comes at the expense of decreased penetration into the bone and reduced stability of the construct. Micromechanics of implant-cement-bone composite interdigitization is investigated using a controlled biomechanical testing and digital image correlation. Twelve Sawbone models were instrumented with Zimmer NexGen-LPS tibial plates and fixed with one of four cements of differing viscosities: Simplex-P, Endurance, DePuy II, and Palacos (n= 3). The constructs were subjected to cyclic compressive loading (600 N) in the sagittal plane of the tibial implants for 6000 cycles. After cyclic loading, the constructs were loaded to 3000 N at the rate of 20 N/s using MTS 810 Testing Machine. Digital Imaging Correlation (DIC) was used to determine displacements between image frames taken from a fixed CCD camera. These techniques allowed the transverse and sagittal-plane micromotions to be quantified. Simplex had the smallest micromotion of all cements in sagittal plane (n=3, P = .002 vs. Palacos and Endurance, and P=.2794 vs. Depuy-2). In transverse plane, Simplex had the lowest micromotion (0.0234mm±0.0175mm, n= 3, P= .01 vs. Endurance; P > .2 vs. Depuy-2 and Palacos). There was no statistically significant difference among cements when comparing maximum force at failure and composite stiffness. These results have direct clinical relevance for TKA patients suffering from aseptic loosening.