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The use of composite materials in orthopaedic surgery permits the design of implants with varying degrees of stiffness. A system of carbon fibre reinforced epoxy hip stems was investigated and compared to the mechanical safety of metal ones. Special attention has been paid to the fact that torsional moments are the common failure mechanism of composite materials. In total 74 hip stems (three different sizes) have been tested under static and dynamic loading conditions according to ISO 7206. A group of 27 implants was pre-conditioned for 75 days in 80 degrees C Ringer's solution to discover potential degradation effects of absorbed fluids. The carbon fibre hip stems proved to reach run-out loads higher than conventional metal ones. Moisture absorption didn't influence the mechanical properties within the range of the experimental accuracy. The calculated fatigue stress of 750 MPa permits further optimization of stiffness parameters without the risk of implant fracture.

The reconstruction of the anterior cruciate ligament deficient knee with the patellar tendon is the "gold standard". Dislocation of the patella, rupture of the patellar tendon and fracture of the patella were reported to occur. In this biomechanical investigation on the changes of the patellar tendon following harvesting of a graft, 51 sheep knee underwent destructive testing at t0 (n = 11), 4 weeks p.op. (n = 5), 3 months p.op. (n = 14), 6 months p.op. (n = 15), and 12 months p.op. (n = 6). Harvesting of a graft produces a stiffness and strength of the patellar tendon of 50-70% of normal. There was no significant change of free patellar tendon length up to 12 months p.op. The cross-sectional area is definitely increased (p < 0.05). The tensile stress is always above normal, nevertheless the strength shows a massive decline until 6 months p.op. and does not regain normal strength by one year p.op. Stiffness shows comparable biomechanical pattern like tensile stress. There are time-dependent changes, the structural weakness is compensated by an increase of cross-sectional area. There is no restitution of the patellar tendon ad integrum, the remainder is a defect with scar tissue and alterated biomechanical properties. Revision surgery using the same host patellar tendon cannot be recommended.

Allogeneic and xenogeneic biological tendon and ligament materials for ligament replacement were tested in the knee of rabbits and sheep. In-vitro and ex-vivo biomechanical tests as well as micromorphological investigations following implantation were performed. The preparation procedure mainly consists in cross linking of collagen by dicarboxylic acids (DC). Modifications in the method induce changes in the biomechanical stability also after implantation. Sheep with autologous patellar tendons substitutions and glutaraldehyde (GA) fixed bovine tendons served as controls. Because of biocompatibility reasons the later seem to be not yet suitable for clinical applications. The DC-tendons need for improved midterm stability prior to clinical implantations; the biocompatibility appears to be excellent.

The influence of changes in physicochemical parameters on the biomechanics of articular cartilage is investigated using relaxation tests in healthy rabbit cartilage. A mathematical model is established. An increase in ionic strength and osmolarity, as well as a rise in temperature lead to an increase in the compliance of cartilage. The majority of these phenomena are nonlinear and in most cases so characteristic that they can be associated with particular molecular processes in the cartilage matrix. The experimental results allow an insight into the functioning of articular cartilage and put another pathogenetical factor of arthrosis up for discussion by demonstrating the lability of the ideal mechanical condition.

The development of preventive provisions is an important topic of sport accident research. We demonstrate the stepwise procedure of judging a provision taking the analysis of a gymnastic exercise. This includes determination of the inner and outer reasons of accidents, the biomechanical conditions of the exercise and leads to mathematical and experimental simulation of the dangerous movement. The specific exercise we studied was the efficiency of a coach in protecting position for the handstand somersault with 1 1/2 breakneck leap. The reaction ability of the coach during the exercise and his force capacity to prevent an accident is explored by a newly developed reaction time analyzer and by a catapult apparatus throwing a dummy. Our results show the inadequacy of the prevention provision of a coach in protecting position for the special gymnastic exercise.