Biomechanical Principles
It was Fredric Pauwels who first developed and explained the concept of load transfer within the bone. He found a tension side in addition to the compression side in a curved tubular structure under axial load. He showed the compression and tension forces within the bone under the axial stress with the help of the model of an inconsistently loaded femur. He demonstrated the principle of tension band through his classical load strain diagram.
Thus, this tension band is the principle of converting tension forces that are acting on the fracture line into compressive forces by using the device inconsistently or to the curved side of the bone or tube. As the fractured bone that is to be joined needs mechanical stability. When this stability is achieved by compression it reacts negatively under repeated distraction and tension then neutralization of such forces becomes necessary for the healing process. This is essential particularly for articular fractures because these fractures require early movement for a good functional result. The Latest implants are made available by titanium implants manufacturing companies that have made the reconstruction of the radial head with open reduction and internal fixation possible in maximum cases.
However, severely comminated radial head fracture with associated instability needs replacement of radial head with a radial head prosthesis that allows the early motion and thus optimizes the functional result. Thus, the purpose of the tension band is to achieve absolute stability, healing of fracture and reduction, and compression.
In fractures of olecranon and patella, muscle pull during movement is likely to distract the fragments, in such condition the use of a tension band neutralizes these forces and these forces are converted into compression when the joint is curved. In the same way, a bone fragment can be changed at the insertion of a ligament or tendon. And the changed fragment can be reattached by the tension band firmly and allow immediate movement of the concerned joint.
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Concept of application
Originally, a circumferential wire loop also known as Cerclage was first explained by Berger in 1892. Numerous changes have been seen in the technique since then. The combination of wiring with screws and the k-wire fixation. K-wires or lag screws make the fragments stable in opposition to rotational forces, it can act as a port for the material of the tension band.
The principle of tension band is also applicable in diaphyseal fractures for instance, in a delayed union or non- union and the femur shaft fracture in which the tension side of the bone is shown by the existence of angular deformity. And to neutralize these forces, the use of any internal or external implant is essential. Usually, the bony union takes place systematically. Thus, the function of a tension band can be carried out not only by loops of wires, cables, resorbable and non-resorbable stitching material but also by an external fixator or a plate.
A band that generates compression while an application is a static tension band such as at the medial malleolus. Because the forces present at the fracture zone stay unchanged when the ankle moves. But band in which the force of compression rises with movement is known as the dynamic tension band as in the patella with bended knee.
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