[Principles of fixation of the cementless modular revision stem Revitan]. / Fixationsprinzipien des zementlosen modularen Hüftrevisionsschaftes Revitan. Eine anatomische Studie.

AIM AND METHOD: To analyse the femoral fixation of a modular cementless revision endoprosthesis, eight prosthetic combinations of the Revitan-System (Centerpulse, Winterthur, Switzerland) were implanted in four cadavers. On three cadavers a curved revision Revitan stem was implanted by an endofemoral approach on one side and by a transfemoral approach on the contralateral side. On the fourth cadaver a straight Revitan stem was implanted on one side and a curved Revitan stem on the contralateral side using a transfemoral approach. Transversal slides of 7-8 mm thickness were performed at the fixation areas of each implant and the implant-bone contact was analysed macroscopically and using contact radiography. RESULTS: The straight stem implanted by a transfemoral approach showed a double-conical press-fit fixation with cutting of the eight longitudinal fins into the cortical bone. The curved revision stems implanted by the same approach had a circular surface fixation similar to the press-fit fixation of the straight stem. In contrast, the curved stems implanted by the endofemoral approach (without a window) showed a three-surface fixation. Hereby the two distal fixation areas led to the primary implant stability by three of the four double edges of the octagonal cross-sectional area cutting into the cortical bone. At the proximal fixation zone the implant only had contact of two implant double edges to the cortical bone. CONCLUSION: Different approaches for implantation lead to different fixation techniques of a curved revision stem. This should be considered by analysing postoperative sintering rates of cementless revision stems.

The ion sensitive field effect transistor (ISFET) pH electrode: a new sensor for long term ambulatory pH monitoring.

Intraluminal pH monitoring in man should be performed with disposable multichannel assemblies that allow recordings at multiple sites and prevent transmission of infection. Currently available glass electrodes are unsuitable for this purpose because of their size and price. We have thus constructed and tested a small, combined ion sensitive field effect transistor (ISFET) pH electrode incorporating an integral reference electrode. In vitro studies showed that both ISFET and glass electrodes (440-M4, Ingold, Switzerland) have a linear response over the pH range 1.3-8.0 and that they are comparable with regard to response time and 24 hour drift. Twenty one hour intragastric pH recordings were performed simultaneously in eight healthy volunteers using a glass electrode and an ISFET electrode, placed no more than 2 mm apart in a combined assembly. This was located in the gastric corpus under fluoroscopic control. The 21 hour pH curves recorded by each electrode type showed identical patterns: an early morning rise in pH with three meal-associated pH peaks lasting for about two to three hours. The means of the 21 hour pH medians were 2.09 and 2.07 as measured by the glass and the ISFET electrodes respectively. Thus, ISFETs are suitable for the construction of inexpensive and hence disposable multichannel pH monitoring assemblies of small diameter. Provided that they can be produced in large numbers with appropriate technical support, ISFETs have the potential to replace glass electrodes for long term monitoring of gastrointestinal luminal acidity.