Abstract
Fixation of tendon transfers about the foot in children typically involves creating a bone tunnel through which a suture is passed and tied over an external button. An internal suspension system, such as the Endobutton (Smith & Nephew) is an alternative fixation method which has demonstrated excellent fixation strength and minimal intraosseous tunnel displacement in various adult procedures. Application of the Endobutton technique has no risk of skin ulceration, does not require suture removal and may provide more secure fixation. The purpose of this study is to compare the biomechanical properties of the external button and Endobutton fixation techniques. Our primary outcome measure was intra-osseous displacement of the suture, during both static and dynamic loading, in cadaver feet.
Nine adult cadaver feet were utilised. A bone tunnel was drilled in the lateral cuneiform and #1 braided non-absorbable suture was passed through the tunnel. One end was secured to a carabiner to be attached to the materials testing system and the other to the fixation device. The external button and Endobutton fixation techniques were tested once in each cadaver, randomising the order of testing to minimise bias. Each fixation technique underwent static and dynamic cyclic loading. A custom Matlab script was used to process video and materials testing system data. The relative displacement of the suture within the bone tunnel, as a function of time and load magnitude, was recorded during static and dynamic cyclic loading. Both fixation groups were analysed and compared for statistical significance using a paired T-test and an alpha value of 0.05.
The Endobutton group had significantly less displacement within the bone tunnel, during both static and dynamic loading, than the external button. The average displacement during static loading was 0.42 mm for the Endobutton and 2.17 mm for the external button (p=0.0019). Similarly, during dynamic cyclic loading, the mean displacement was 0.32 mm for the Endobutton and 0.66 mm for the external button (p=0.0115).
The Endobutton internal suspension technique demonstrates significantly less displacement during static and dynamic loading than the external button, during biomechanical testing in cadaver feet. The Endobutton may provide superior fixation than the traditional external button technique for tendon transfers in children. In addition, this technique avoids the risk of skin ulceration from the button and the need for suture removal.
