DUAL-ENERGY X-RAY-ABSORPTIOMETRIC (DEXA) MEASUREMENT OF BONE-MINERAL DENSITY AROUND EXPERIMENTAL CEMENTLESS FEMORAL PRESS FIT-GLIDING STEMS

Problem: Periprosthetic bone atrophy caused by stress shielding is one of the problems of non-cemented femoral stems of hip arthroplasty. St ress shielding and thus the loss of bone mass and their dissemination in the proximal part of the femur of conventional non-cemented femoral stems depends on stiffness (E-modules of the material and the geometr y) of the implant and on the bonding between implant and bone. All cur rently implanted noncemented femoral stems lead to proximal bone loss which goes up to 40-50% of the original bone mineral content. The seni or author (E. M,) developed a femoral stem (Press Fit-Gliding Stem PFG S) which shifts relativ movements of force-transmission from the bone- implant interface into the interior of the prosthetic system (Inner Be aring System) and which only transfer forces proximal into the femur. Method: The examinations were made in 21 patients between 1 and 6 year s after implantation of a Press Fit-Gliding Stem compared with a norma l contralateral femur (12), with bilateral PFGS (3) and other bilatera l arthroplasty (6). Results: In all 21 patients supplied with a PFGS a n increase of bone mineral content (BMC) and bone mineral density (BMC ) in zone 7 as well as a marked smaller deviation around the mean valu e in all zones respectively could be noticed. Conclusions: With the Du al Energy X-ray Absorptiometry (DEXA.) - measurement of bone mineral c ontent (BMC) and bone mineral density (BMD) in all zones according to Gruen could be shown that it is not only possible with regard to a fav orable force transmission to avoid the inevitable bone atrophy but on the contrary to induce an increase of bone at the point of local force transmission that is in the region of the calcar femorale (zone 7).