Abstract
The Pyramid stem is a tecnical evolution of the previous Zweimuller, in order to have the best press fit. It has no more longitudinal grooves and neck, but has a distal arcuate fissura to improve the elasticity and to avoid distal stress by a uniform contact with the bone. We show the breaking test and resistence test. It has a rectangular section, a uniform thickness along all its lenght to have a good diaphyseal anchorage on four zones of the internal cortex to avoid torsional stress and to maintain endomi-dollar vascularization. This stem has the maximum contact surface not only with the dyaphysis, but also with the metaphysis and the trochanter. It has been studied with the femur morfology, to fill the bigger ones with a cylindric canal and the smallest ones with a conic canal. Transverse section has increased by the pyramids that increase contact surface bone-prosthesis, primary stability and press-fit. It is straight both in the frontal and in the sagittal plane to realise a good primary stabilization according with the concept of the three support point. We present our surgical experience to obtain a correct position of the stem, and the best use of the instrumentation. From June 1997 to May 2001 we have used this stem in 257 hips; we have obtained excellent and good results in 87% of patients. We show some cases and the only one stem removed. This stem allows a rapid postoperative rehabilitation following our protocol as explained.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
