Ankle--Effect of implants on

The purpose of this study is to evaluate two plastic materials, PMMA and UHMWPE, by using a material testing device "Robotic arch cycle motor" to imitate a normal body weight of 150 lbs. on Vo's artificial ankle implant. In this experiment, there are 82 sets of a three hours for UHMWPE, and 34 sets for PMMA have been applied to these materials with maintaining of 165 lbs. or 110% of a normal body weight person. In addition, timer, saline solution 0.5%, and thermometer are employed to set up a vivo human environment to maxim the accuracy dada collection. Number of cycles is recorded by computer and to be converted to the lifetime of Vo's ankle implant. The result shows that UHMWPE has a greater performance of 0.0176in in Vo's artificial ankle implant than PMMA.

Current ankle implant designs have shown significant improvements in last ten years. However, failure rates are still high and about 30% of patients ended up with fusion joint or lower leg amputation after ten years of first operations because of long term associated pain. A new ankle joint implant presenting in this study (Vo-ankle implant) was designed to base on the Design for Assembly (DFA) principles to optimize the device biomechanically. It overcomes most of problems shown in current ankle implants. The new ankle implant has four major advantages over the current models. First, the new ankle constructed to distribute loads evenly on the joint implant with variable axes of motion. Second, the implantation requires much less bone resection. Third, the new ankle design has a simpler and easier technique to implant. Lastly, the new ankle design employs one joint intact operation same as that of a true ankle joint.

The artificial ankle joint implant has been developed since 1970 after the relatively successful total hip and knee arthroplasty. The main goal of ankle replacement is to eliminate pain and preserve joint motion. Unfortunately, total ankle replacement (TAR) has not been effective as implant of other joints. Recently, published studies of early series showed that the newer second-generation ankle prosthesis have been improved with time. However, only one of the three current ankle designs is allowed by FDA to be used widely in the U.S. This study provides a new ankle design with an advanced approach in designs, biomechanical rationale, and implantation using finite element method (FEM). The new ankle prosthesis in designed to be optimal in terms of ultimate stress, implant parameter that correlating with minimal bone removal using finite element model created from CT scan. In addition, its implantation is less invasive and traumatic compared to the current TAR with longer expecting service life time. Case study showed that the thickness meniscus of the new ankle design obtained from FEM is well within the recommendation ranges by the expert in the ankle joint implantation field.