Abstract
The durable years of artificial hip joints have progressively improved. Due to certain factors, such as aliment, burdens during the daily activity, and deterioration of the material with aging, however, the implant tends to need replacement because of partial but fatal wear. Understanding the relation of the wear and executing a proper mounting angle have therefore become important. In this study, we estimated the load charged on the socket head from an extirpated artificial hip joint. The surface properties of two samples were measured and inverse analysis was performed using the finite-element method (FEM) to determine the factor. The joint heads were measured with a heliumneon laser and shearing interferometer. The results showed that the deformations of the samples were between 1.5μm and 1.7μm. The abrasions found were similar in both implants. This is explained by the similarity of two subjects' physical situation; the implants were both placed in the right hip, and both subjects were trained to walk on a crutch. Results of the FEM inverse analysis show that the burden is loaded mainly from two directions. The load toward the longitudinal direction is extrapolated as body weight, since it fits the data previously covered in a medical report. The load toward the lateral direction matches the direction of the force from the muscles that stabilize the joint and the force that is applied from the gluteus maximus in gait. The calculated results, the computed force in the gravity direction divided by the subject's body weight and implant's period of usage, using an analysis on contact problem of Hertz, were in the range of 2.69 to 4.43 in subject A and 2.33 to 4.00 for subject B. As seen, the values for subject A were larger. The conjectured cause for this difference is that the joint in subject A had a duration of usage seven years longer than that of subject B. The analysis method in this study proved its effectiveness by presenting a match between our results and the medical report data. We intend to add more samples to the database using our measuring and analysis method. Our goal is to improve the ideal form and surface properties for designing an artificial hip joint socket head that is suitable for Japanese subjects.
