A Methodology for Prediction of Periprosthetic Injuries in Occupants with TKR Implants in Vehicle Crashes

Periprosthetic fractures refer to the fractures that occur in the vicinity of the implants of joint replacement arthroplasty. Most of the fractures during an automotive frontal collision involve the long bones of the lower limbs (femur and tibia). Since the prevalence of persons living with lower limb joint prostheses is increasing, periprosthetic fractures that occur during vehicular accidents are likely to become a considerable burden on health care systems. It is estimated that approximately 4.0 million adults in the U.S. currently live with Total Knee Replacement (TKR) implants. Therefore, it is essential to study the injury patterns that occur in the long bone of a lower limb containing a total knee prosthesis. The aim of the present study is to develop an advanced finite element model that simulates the possible fracture patterns that are likely during vehicular accidents involving occupants who have knee joint prostheses in situ. Initially, an NCAP test simulation is carried out for a compact passenger car (Dodge Neon) with a belted Hybrid 3 dummy in the driver's seat. The femoral load history of the left leg is correlated with the NCAP test result. An equivalent sub-system model for the NCAP test simulation is then created by isolating the left legform of the Hybrid 3 dummy and impacting the same against a relevant portion of the instrument panel of the Dodge Neon model. A similar model is then formulated by replacing the legform of the Hybrid 3 dummy with a validated finite element model of a human-like legform with actual human tissue properties assigned to it. Later, the same setup is used for assessing the effect of incorporating a TKR into the human-like knee model. The femoral loads obtained from the sub-system level analyses are compared and it is noticed that there is a successive drop in peak femoral load in the intact human-like and TKR-implanted legforms relative to the peak load in the legform of the Hybrid 3 dummy. The said reductions in loads in the more representative models of a human leg have been found to be due to damages in the inter- and supra-condylar regions of the femoral bone. It is also noted that the magnitude of peak load obtained with the TKR implanted legform is lower than that obtained with the intact knee legform. This reduction in peak load is due to the relatively early initiation of damage that is caused due to reduced amount of high density cortical bone following the TKR. The higher susceptibility of a TKR-implanted knee to bone fracture in a frontal crash scenario as compared to a normal human knee has been brought into focus perhaps for the first time in the current study.