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[Comparative periprosthetic bone density measurements of the proximal femur shaft using dual energy x-ray absorptiometry (DEXA) with experimental "Press Fit-gliding Stem Prosthesis"].

PROBLEM
Periprosthetic bone atrophy caused by stress shielding is one of the problems of non-cemented femoral stems of hip arthroplasty. Stress 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 geometry) of the implant and on the bonding between implant and bone. All currently implanted non-cemented femoral stems lead to proximal bone loss which goes up to 40-50% of the original bone mineral content. The senior author (E. M.) developed a femoral stem (Press Fit-Gliding Stem PFGS) which shifts relative movements of force-transmission from the bone-implant interface into the interior of the prosthetic system (Inner Bearing-System) and which only transfers forces proximal into the femur.


METHOD
The examinations were made in 21 patients between 1 and 6 years after implantation of a Press Fit-Gliding Stem compared with a normal contralateral femur (12), with bilateral PFGS (3) and other bilateral arthroplasty (6).


RESULTS
In all 21 patients supplied with a PFGS an increase of bone mineral content (BMC) and bone mineral density (BMC) in zone 7 as well as a marked smaller deviation around the mean value in all zones respectively could be noticed.


CONCLUSIONS
With the Dual Energy X-ray Absorptiometry (DEXA)-measurement of bone mineral content (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 favorable 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).


CLINICAL RELEVANCE
The Press Fit-Gliding Stem is still in the clinical test-program.