Biomechanical study in vitro on the use of self-designed external fixator in diaphyseal III metacarpal fractures in horses.

Diaphyseal fractures of the III metacarpal bone represent 22% of all fractures of the long bones in horses. Treatment of such cases is difficult. The most popular solution used in these types of fractures is two plates applied directly to the bone surface, but they are not applicable on contaminated and infected fractures. External fixators are quite commonly used in human medicine, although in veterinary practice there is no typical stabilizer designed for the treatment of diaphyseal fractures of the III metacarpal bone so far. In this study, an external semicircular fixator of our own design was used and in vitro strength tests were conducted to determine the maximum force which would lead to the destruction of non-fractured bone and fractured bone treated with the stabilizer. On the basis of the strength tests, we can conclude that the stabilizer can be strong enough to allow the horse to stand up after surgery. It also has many favorable features which make it easy to assemble and to take care of a wound, while being safe enough for the animal at the same time.

Experimental study of mechanical properties of composite carbon screws.

Carbon-carbon composite was used to manufacture carbon screws as possible material for osteosynthesis. The mechanical properties were optimized including the fibre orientation in the composite volume, the effect of the size of the thread and the thread shape. The mechanical properties of the carbon screws were compared with conventional OSTEO steel cortical screws. Two types of carbon specimens were used, varying in fibre orientation along the screw axis. The mechanical properties of the carbon screws including the failure force for one thread and the critical shear stress were determined. The force destroying the connection of the carbon screw with bone was determined. The holding capacity of the carbon screw was compared to the steel screw. The extraction tests demonstrated 50% less holding force than the OSTEO steel screw.

Static and dynamic fatigue properties of carbon ligament prosthesis.

The aim of the present paper was to characterize the static and dynamic mechanical properties of carbon braids used in medicine as prostheses of ligaments and tendons. A computing system (PC software) was used to register and analyze the data of mechanical tests. Tensile static tests (creep testing) were utilized to determine the failure-free value of static force. Fatigue dynamic properties of carbon braids in tensile-tensile cyclic tests including the effect of simulated body conditions were analyzed. The braids were immersed in isotonic solution at 37 degrees C. Fatigue life was markedly lowered in air in comparison with simulated body conditions. For a given value of maximum cyclic force, decreasing the minimum/maximum force ratio decreased the number of cycles to failure. The mechanical approach of fatigue behavior based on approximately maximum fatigue force and number of cycles to failure by analytical expression was given. Energy dissipation due to the hysteresis loop was considered.