TENSION BAND WIRING CONCEPT: A BIOMECHANICAL STUDY

Abstract

Introduction: Traditionally the fixation of choice as recommended by the AO ASIF group for transverse fractures of the Olecranon and the Patella is the tension band wiring technique.

The concept of tension band wiring is based on the fact that the distractive force applied to one surface of the bone will result in compression on the opposite articular surface.

Clinical outcomes of TBW are not equivocal. It is associated with significant morbidity such as non union, failure of fixation, especially in osteoporotic bone and infection which sometimes leads to amputation. Often a second procedure for removal of prominent metal work is required.

In our biomechanical study we investigated this concept as we believe that the forces generated by TBW construct do not generate significant compressive forces required for healing of fracture.

Materials and Methods: We used 4th generation composite bones (Sawbones^®, Malmoe, Sweden.). These bone analogues have been validated to closely simulate human bone characteristics for fracture toughness, tensile strength, compressive strength, fatigue crack resistance and implant subsidence.

The advantage of using 4th generation composite bone model is that it provides uniformity which is not achievable in cadaveric studies. Two different bone models representative of Olecranon and patella were used. Transverse fractures were created in the bones and fixed with TBW technique as described in A.O. manual.

Two 0.062-inch Kirschner wires and figure of eight configuration of 18G Stainless steel wire with single knot technique was used. Micro motion transducers (DVRT: MicroStrain, Williston, Vermont) with an accuracy of ± 1μm were placed across the fracture site both anteriorly and posteriorly. Continuous information regarding fracture distraction and compression, as determined by the transducers was recorded from both sites simultaneously during the experiment.

The tension band wire construct was loaded up to a maximum force of 4000 Newtons for patella and 500 for the olecranon. The fractures were subjected to cyclic loading at 1Hz using a servo hydraulic materials-testing system (model 8500; Instron, Canton, Massachusetts). The results were analysed on a computer and statistical analysis performed.

Results: During the application of cyclical loading, we noted a gap at the articular surface ranging from 1.1± 0.4mm and 2.1± 0.6mm for Olecranon and patella constructs respectively. During most of the duration of the experiment no transducer displacements were recorded at the articular surface.

Conclusion: The concept that distractive forces at one end could be converted to compression at the other end through the TBW does not hold true in our biomechanical study. A simpler construct may suffice for fixation of patellar and Olecranon fractures which can reduce the complications associated with TBW fixation.