Primärstabilität proximal fixierter Hüftendoprothesen - eine biomechanische Studie

In hip arthroplasty, the femoral component is usually fixed in the diaphysis. As consequence of the distal load transfer, a proximal bone atrophy occurs which can be the cause of prosthesis loosening. Femoral neck prostheses are required to prevent this processing by preservation of a physiological strain pattern. Moreover their implantation demand less resection of bone tissue which improves conditions in case of revision. Nevertheless, the small size of these prostheses is critical for their primary stability and relative motion between implant and bone is increased. Therefore, measurement of primary stability of these prostheses is subject of the presented study. According to in-vivo investigations osteointegration of prostheses are observed in relative motions < 20μm respectively < 40μm, whereas motions > 150μm result in formation of fibrous tissue membrane. Indeed, in several in-vitro studies of shaft prostheses with similar test conditions the measured values reach 190μm respectively 300μm. Although the increasing clinical use of femoral neck prostheses, measurements have not been realized so far. In the presented study a special measuring method has been developed and subsidence as well as relative motion of different femoral neck prostheses, including two prototypes and one shaft prosthesis have been determined. In study I, six femoral neck prostheses and one shaft prosthesis have been implanted in artificial bones and a dynamic load bearing from 50 to 2100N during 1000 cycles has been proceeded by means of a material testing machine. Relative motions were slightly increased with maximum values of 200μm to 600μm what can partly be explained by the bad material properties of the bones. In a second study human bones have been used and motions of a clinical successful (thrust plate prosthesis) and a new-developed femoral neck prosthesis have been measured. In some cases under “worst case conditions” bone fractures occurred whereas in successful tests relative motions of 210μm (TPP) resp. 207μm (Silent) have been shown. Primary stability of the tested prostheses was higher or equal in comparision to the literature. Above all implant design, surface property of the prosthesis, quality of bone stock as well as the amount of load are important. Precise surgical technique is essential with regard to form fit between implant and bone, CCD-angle and the level of resection. Further studies are necessary to prove clinical success of each prosthesis.