The Study Of Changes In Femoral Stresses After Total Hip Arthroplasty And The Effect Of Tersion

OBJECTIVE: The Total hip Arthroplasty (THA) is a reliable and general measure for hip diseases treatment. THA can reform the hip malformation, release the pain, increase the activity of the hip, recover the function, and elevate the patience's quality of life. But the prosthetic loosening is a main complication after THA and main cause to revision of the hip arthroplasty. It is known that the factors of Biomechanics have been considered the main causes to prosthetic loosening and the torsion is a very important factor. The purpose of this study was by in vitro biomechanical test and three dimension limit element analysis to find biomechanical differences between before and after implantation of hip prosthesis and the effect of the torsion, and to reforming prosthetic materials , ameliorating prosthetic design and improving operation techniques to decrease the rate of revision of the hip arthroplasty. METHODS: A right femur of a healthy volunteer who is 170mm and 60Kg was scanned to acquire the CT data. Then DICOM3.0 and Pro/ENGIEER were used to process the data and establish the three-diamensional finite element models. The data of the three- diamensional finite element models was transmitted to ANSYS6.1. Applied with hip joint loading and related muscles strength, this study is quantitatively to measure stresses changes of an intact femur with correspongding femur insertion of the hip prosthesis, especially the changes of stresses in proximal femur.RESULTS: The global axial direction stress of the femur is not changed after THA compared with before THA. The medial side of femur is distributed by compression stress and the lateral side by tensile stress. The value of stress is the highest at the beginning of femur component body and descends abruptly and then gradually increases to distal femur. The stress of the proximal of femur is declined, at the same time, the stress of the middle and distal femur is decreased after insertion implant in to the femoral canal. This result illustrates that the stress-shielding occurs in the proximal femur, especially in the area of calcar femorale. The torsion takes an important and negative factor in the causes of the prosthetic loosening. CONCLUTIONS: According to the analyses of the stress changes of the femur after THA, it is clear that there is notable stress-shielding in the proximal femur. The stress-shielding effect induces the serious bone substance to lose, according to Wolff' law regarding bone remodeling in response to stress, bone resorption occurs with decreased stress and bone hypertrophy occurs with increased stress. The bone resorption causes a femur side unsteady, at last the hip prosthesis loosening. So it is important to increase the stress and avoid the stress-shielding to decrease the rate of hip prosthesis loosening.