The results of cementless hip arthroplasty with use of the first-generation Spongiosa implant were excellent at a minimum of twenty years of follow-up. The probability of survival of the acetabular component exceeded that of the femoral stem.

The objective of the study was to evaluate the precision, concordance, practicability and the early clinical outcome of the use of a computerised navigation system in a comparative study with a group of 100 patients. Two groups of 50 patients each underwent implantation of a bicondylar knee prosthesis either by means of the freehand navigation system or by means of technical instrumentation. We found that the computerised navigation system provided a higher precision than the technically instrumented implantation: 94% of the prostheses implanted with the navigation system have an alignment within a range of -3°to 3°on of the Mikulicz line. Only 46% of the patients operated by means of the technical instrumentation reached this aspired result. Furthermore, the navigation system showed smaller ranges in the deviation of the aspired alignment. The radiological and computer-modeled alignment values differed both pre-and postoperatively, but to a larger extent before surgery. The varus or valgus deviations of the axis were more distinct radiologically under the weight of the patient's body than in the computer model. The clinical outcome examined by the use of the HSS score after a mean followup of 7 months is good in both groups, and without significant differences. On average, the duration of surgery was 13 minutes longer in the computerised navigation group. We conclude that the benefit of the computerised navigation system is represented by the high improvement of precision. Achieving early clinical results identical to those in the technical instrumentation group, we expect a reduction of aseptic loosening in the computerised navigation group.

No abstract

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.