Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation

Introduction

The Endobutton (EB) is the most widely used femoral fixation device worldwide that is designed specifically for soft tissue grafts. Pioneered by Dr. Thomas Rosenberg and introduced around 1990, it was the first device specifically designed to hold soft tissue grafts. As originally designed, the surgeon would tie a Dacron tape connecting the button to the tendon. This technique was subsequently supplanted by use of the EB-CL (continuous loop), which obviated the need to tie knots. Due to the longevity of the device, there is a much wider body of literature concerning it than any of the other newer, soft tissue–specific devices.

Biomechanics

Numerous studies have analyzed the pullout strength and stiffness of this device. There was much discussion at one point about a so-called bungee effect, in which the device’s fixation on the cortex and not in the tunnel supposedly resulted in lower stiffness. However, it has subsequently been shown that the greater stiffness resulting from cortical anchorage dwarfs the slightly reduced stiffness from the greater length of the construct. Also, as described elsewhere in the text, stiffness has no bearing on ultimate stability. This is because the stiffness of all grafts is independent of their mode of fixation once tunnel healing has occurred at about 2 months postoperatively. After this time, load is borne by the healed fibers that connect the graft to the tunnel, not by the device. Because the fixation device is not load bearing after this time, its stiffness is irrelevant. However, even before that time, stiffness is less important because the stiffness represents only elastic deformation of the graft. It is only plastic deformation, not elastic deformation, that will result in greater ultimate clinical laxity. In fact, reduced stiffness, or greater elasticity, in the graft-fixation construct will diminish the forces that tend to displace the fixation device in cyclical loading. This reduction in stiffness diminishes these forces by partially dissipating them in temporary elastic deformation of the graft. Therefore, ultimately, stability may actually be enhanced by protecting the construct from plastic deformation or fixation device slippage while tunnel healing is occurring.

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