How much can a vibrational diagnostic tool reveal in total hip arthroplasty loosening?

Objective. To investigate how much information a vibrational technique can reveal regarding the loosening of the femoral component of a total hip arthroplasty. Design. Numerical modal analysis using finite element method and computer simulation. Background. Existing work suggested that this technique is capable of revealing total hip arthroplasty loosening. However, the potentials of this technique are not fully studied yet. There is a need to establish the limitation of this technique. Methods. Numerical modal analysis was conducted to obtain the natural frequencies and mode shapes of femoral models under free vibration. An absent interface portion was hypothesized at specified locations the data from modal analysis were then used in a computer simulation to visualize the vibration diagnosis. Results. The effects of interface failure on the femoral component stiffness vary with the locations and sizes of failure. Nominal critical, reliable, and nondetectable levels of interface failure are found. Conclusion. When the size of failure is more than one-third of the stem length, this tool is able to provide a reliable diagnosis. The critical detectable interface failure size is one-fifth of the stem length. It was found that the motion at higher harmonics is the most sensitive to the interface failure. This tool is unlikely to differentiate the slight differences in natural frequencies that occur when the interface failure length is less than one-sixth of the stem length. It is likely to fail in detecting failures located at the stem central portion regardless of their length. Relevance: A numerical study of the vibration tool is important prior to pursuing clinical trials of the tool and may guide the characterizations involved in the trials. © 2003 Elsevier Science Ltd. All rights reserved

Defect-induced fatigue microcrack formation in cement mantle

Acoustic emission (AE) was used to monitor the progress of the fatigue damage process in the cement mantles of two cemented femur stem constructs that contained naturally occurring defects. After the fatigue tests, morphological features of the defects were investigated using an environmental scanning electron microscope. It showed that the regions with no visible defects were mainly microcrack free, whereas the defect regions were the main sources generating microcracks. Two types of microcracks were identified: type I and type II. Signal energies associated with type I microcracks were about an order of magnitude higher than that of type II. The microstructural investigations of the defects and the areas in the vicinity of the defects suggested their categorization into stable and unstable. The accumulative energy-time relationships revealed that stable and unstable microcrack curves had convex (d2ΣU1/dt2 \u3c 0), and concave (d 2ΣU1/dt2 \u3e 0) shapes, respectively. The progress of fatigue microcrack formation occurred over three distinct phases: initiation, transition, and stableness. © 2005 Wiley Periodicals, Inc