Abstract
Since 1989 more than 5000 Zweymuller stems have been implanted in the Orthopaedic Institute G. Pini, Milan, Italy. This uncemented stem which has been produced since 1979 nowadays is though to be one of the best prothesical solutions and this can be affirmed both on the easy operative techniques and on the bases of our clinical studies of follow up. This is also the most used uncemented coxofemural system in Europe. The advantages in the Zweymuller design are due to the rotatory stability and the slight volume of the implant, which in the international literature are referred as the key points of this success. The bone anchorage and the distribution of the weights is achieved both proximally and distally thanks to the conical stem, which in the proximal region is anchored on one side by the great wing of the trocanteris on the other side by the wedge effect.
In the distant cortical instead the borders of the stem get wedged in the bone. This very wide anchorage allows a great stability reflected also by the lack of weigh pain at diafisys level.
The same stem is used both for first implant as well as revisions (after evaluation of the bone stock, achieved in our studies by dexa) but also for intertrocanteric osteotomies.
The chance of a rapid mobilization of the patient makes this stem convenient also in geriatric orthopaedic cases. The material is a alloy of Ti, Al and Nb: this material has been studied directly for medical appliances and not only it doesn’t contain toxic or allergenic components but provide an high resistence to breaks. Osteointegration is favoured by the rough surfaces.
In our last clinical study on the follow up of patients treated with this kind of implant in the last 18 months we have seen a difference in those cases in which a pneumatic driver for nailing had been used in the operative room. Not only the operative time for the positioning has been reduced of one third but the implant resulted to be more precise.
The use of this driver allows a better fitting of the stem to the femural shaft as the cut is more precise. In fact the surgeon has a controlled magnitude and direction of the driving force and this force is anyway limited.
There is a remarkable reduction of cases of intra operative fractures. So we have collected datas on 70 randomized patients in whom this device had been used compared to the same number of patients operated without this apparel: the operative time is reduced of 15 minutes in average and as a consequence the risk of fat emboly has diminished; revisions for malpositioning and intraoperative fractures are almost worthless. Moreover the blood loss has reduced of 100 cc. This are only partial datas but seem to suggest that this device can provide a great help to the orthopaedic surgeon in the operative room as well as reducing complicances in patients: we plan that this driver together with the Zweymuller stem will represent in the future one of the most safe solution in the total hip replacement when the surgeon puts the indication for an uncemented implant.
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.
