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In endoprosthetics alumina ceramic femoral heads have been established for many years and their outstanding wear characteristics are scientifically proven. The taper connection between the hard but brittle ceramic head and the metallic stem must be performed by the operating surgeon intraoperatively. Thereby it is left to the surgeon to interpret imprecise and strongly deviating instructions given from manufacturer to manufacturer. This study clarifies the enormously large variations of interpretation in the clinical everyday life based on interviews and force measurements during handling when assembling. In comparable situations the axial cone setting forces, applied by a total of 39 operating surgeons from German hospitals, varied between 273 N and 7848 N. An additional coupling strength examination in the laboratory shows that torque loadings necessary for loosening several cone connection designs are in the range of those occurring under usual in vivo situations. This leads to the conclusion that for low-force-connected cone tapers joint friction of the artificial hip joint can cause a rotation and thus a loosening of the ceramic head of the implant neck during everyday activities. The authors proclaim the urgent necessity for clear handling references and the supply of a reproducibly safe taper lock method.

Bionic systems are aiming to integrate natural observing into mechanical solutions. This has been realized in the design of metal on metal bearing in total hip resurface arthroplasty. The articular side of the femoral cup is covered with a dimple like surface. Under laboratory condition this so called "surf-metal-cup" achieved a reduction of the mechanical wear to almost a third part in comparison to a metal-cup with plane surface. This advantage, caused by the reduced friction-coefficient due to improved hydrodynamic lubrication could also be proved under laboratory conditions. The clinical introduction is expected to offer a significant extension of durability in this prosthetic system and needs to be proved in a long-term study.

An uncemented implanted acetabular cup must ensure primary stability and postoperative osteointegration. For both conditions the immediate postoperative contact between bone and the structured surface of the cup is of decisive importance. Two different types of acetabular cups manufactured by ESKA (standard model and Kapuziner model) were implanted in the innominate bones of elderly deceased persons. After plastination, thin serial sections were obtained. On the basis of X-rays of these sections, contact between bone and the reticulate surface of the cups was quantified. The quality of the contact was analysed densitometrically.

Modern navigation technology appears to be acquiring an established place in the fields of orthopedics and orthopedic surgery. This technology helps the surgeon to apply his manual skills with greater precision and thus more effectively, and its positive impact on the quality of surgical treatment has already been demonstrated. The SURGETICS navigation system described in this paper shows that the technology can be adapted to the requirements of daily surgical practice, without compromising its utility for the surgeon and, in the last resort, the patient. Provided that due consideration is given to clinical needs, this technology will surely become a standard tool, not only in European hospitals.

A percutaneous osseointegrated anchoring device for above-knee implantation designed to enable permanent attachment of an artificial limb is described. In addition to a technical description, the two-stage operative procedure, together with the rehabilitation process in an 18-year-old man, is also detailed. Following amputation and complete healing of the soft tissues, a surface-structured metal pin capable of supporting large loads, is driven into the medullary canal of the thigh bone. A metal sleeve having an identical surface structure serves to close off the medullary canal and provide an interface with the soft tissues. Screwed to the end of the pin is a conical metal adapter to which is attached a silicone cylinder whose right-angled distal end is located subcutaneously and ends in a titanium mesh. The first part of the implantation procedure is concluded by closing the silicone cylinder with a plastic plug for 6 weeks to permit osseous integration and the ingrowth of tissue into the mesh. In a second step, the plastic plug is removed via a skin incision, and the permanent load-bearing metal adapter fitted. In the above-mentioned patient wound healing at the metal/tissue interface was complication-free, since the implanted silicone cylinder prevented the "wedge effect" caused by the build-up of "luxuriant" tissue. After a further healing phase of 6 weeks, rehabilitation with an exoprosthesis took only 2 weeks, after which time, the patient was able to walk without a walking aid, and returned to work.

ESKA-Ceram is a new material for use in hip endoprostheses, and comprises two-thirds polyurethane and one-third Al2O3 ceramic powder. Its wear rates are of a similar low order of magnitude as those reported for metal-metal and ceramic-ceramic combinations. A great advantage of the material is that it permits the production of asymmetrical inserts for acetabular cups.

Normal post-operative function, permanent stable fixation and long life for the implant material are determined mainly by the correct biomechanical positioning of the knee joint prosthesis. We have identified six measures within the surgical procedure that are of vital importance for achieving biomechanically correct positioning. Because of their great importance, we call these measures "The Golden Six", and describe their application using the ESKA Resurfacing Knee System (RKS). This system, which is so designed that it enables a maximal bone saving resection technique, makes use of a diagonal screw-fixation of the endoprosthetic elements, resulting in increased primary stability. For the safe and reliable implementation of our measures, we have developed a special set of instruments. Anatomical, kinematic and surgical studies have shown that with the aid of the above-mentioned six measures biomechanically correct positioning of all the implanted elements can be achieved, thus ensuring trouble-free post-operative function of the knee joint and the least possible mechanical stressing of the implanted materials.

The present study was conducted with the aim of establishing whether minimally invasive percutaneous techniques used to stabilize osteoporotic vertebrae are technically feasible. Two different methods were investigated in human thoracolumbar cadaveric vertebrae. In the first technique, special titanium implants were placed via a postero-lateral approach. With the second method, the vertebrae were filled with different types of cement of different viscosities. After each procedure, the vertebrae were examined with conventional X-ray and CT scans. The first technique proved quite unsuccessful--the insertion of the titanium implants proving difficult despite the use of special instruments. The results achieved with the second method were much better. The use of low-viscosity bone cement produced the best results. Despite a single lateral point of entry, the vertebrae were almost completely filled right into the contralateral side. Lumbar vertebrae required an average volume of cement of 7 ml (range: 6.5-10 ml) and thoracic vertebrae 5.5 ml (range: 4-7 ml). Specially developed cement application devices made possible problem-free, controlled introduction of the cement.

The ESKA femoral neck prosthesis introduces a new metaphyseal anchorage principle for total hip replacements. Primary stability of the conical-oval shaped implant is achieved through the use of a lateral traction screw, and permanent stability through bony growth into the macroporous TRIPO metal structure. The system is used in combination with the standard ESKA acetabulum, and metal-polyethylene, ceramic-polyethylene, ceramic-ceramic and metal-metal articulations are all possible.

Since 1987, cementless THR acetabular components with coarsely reticulate surfaces (S&G, ESKA) have been implanted in the Department of Orthopaedic Surgery of the Alfried Krupp Hospital in Essen. By 31st December 1995, 590 of these components had been implanted. Follow-up of the first 51 of these completely cement free THRs revealed loosening in an only single case (2%). Despite these good medium-term results, however, it must be expected that over a ten-year period, the life of the THR will decrease, the probable reason being increasing debris caused by polyethylene (PE) wear leading to aseptic loosening. An alternative to the PE/ceramic system of opposing materials would be ceramic/ceramic. Experience to date has shown that the biological inertness of ceramic does not allow ingrowth and bony integration to take place. Against this background an acetabular component employing a metal backing with the 3-dimensional reticulate surface mentioned above and a Biolox ceramic cup insert articulating with a Biolox ceramic femoral head was designed. The result is a cement free modular THR with optimal bony integration properties and articulating surfaces. To investigate the superiority of this new concept, a comparative study involving two groups of 50 patients each, one group receiving the PE/ceramic system, the other the new ceramic/ceramic system, has been initiated.