Effects on Initial Fixation of Cementless Tibial Trays in Total Knee Arthroplasty

Bone mineral density (BMD), among other factors, largely effect the initial stability of the cementless tibial tray component in a total knee replacement (TKR), where increased motion at the tray-bone interface hinders bony ingrowth. With a lack of bony ingrowth, the cementless implant will not experience long-term success. Understanding which factors influence initial stability yields insight into surgical technique considerations and help inform a surgeon’s implant choice. The objective of this study was to evaluate factors influencing the initial stability of cementless tibial trays using a 6-degree of freedom (6-DOF) robotic joint simulator, the AMTI VIVO, and combined loading scenarios replicating physiological loads experienced in vivo such as gait, stair descent and deep knee bending cycles. Prior to testing, cadaveric tibia were implanted with either cementless DePuy Attune RP, cementless DePuy Attune FB or cementless Stryker Triathlon FB and were impacted with either a traditional mallet or the Kincise, an automated surgical impaction device by a board certified orthopaedic surgeon. Medial, central and lateral markers were then placed on the anterior portion of the tibia and tibial tray to accurately measure displacements using a Digital Image Correlation (DIC) camera and software. Preoperative CT scans of the tibia were used to perform a virtual surgery on the specimen, and the segment of the tibial bone from the proximal cut to the distal tip of the tray’s central cone were isolated. This tibial segment was meshed with 0.8-mm tetrahedral elements (Hypermesh, Altair, Troy, MI) and Hounsfield units for each element were extracted from the DICOM using custom Matlab scripting and converted to bone mineral density using the known densities of the phantom. The ratio of tray coverage, the tibial plateau area of the tray within the peripheral border, was approximated and evaluated as a potential factor influencing initial stability. BMD was found to be a strong contributing factor to initial stability, especially for RP tibial trays. Conversely, tray coverage was not a strong contributing factor. The Kincise yielded positive results as compared to the mallet for tibia with high BMD values and tibia implanted with RP tibial trays. These findings assist in reforming surgical technique and help discern variables a surgeon should consider when selecting the optimal implant for a patient