Chapter 50 Bone–Patellar Tendon–Bone Anterior Cruciate Ligament Reconstruction Using the Endobutton Continuous Loop Bone–Tendon–Bone Fixation System

The Endobutton Continuous Loop (CL) (Smith & Nephew, Andover, MA) for bone–tendon–bone (BTB) grafts is a femoral fixation system for grafts that have a bone block for the femoral attachment, such as BTB autografts, BTB allografts, and Achilles tendon allografts. The Endobutton-CL BTB offers several advantages compared with other forms of fixation, including interference fixation. The technique is easy, reproducible, and dependable while at the same time offering possibly the strongest fixation for BTB grafts available. Several advantages include a short learning curve; fewer steps than interference fixation; no needed calculations, minimizing error; and complete apposition of the bone block in the femoral tunnel. Complete apposition of the bone block allows for circumferential healing of the bone block within the tunnel. It also means that revision cases do not run the risk of voids in the bone left from interference screws. More advantages include the fact that perforation of the posterior femoral cortex will not compromise fixation. Another advantage that I enjoy the greatest is that the BTB graft can be “automatically” countersunk in the femoral tunnel, allowing the tibial bone block to easily end flush with the tibial cortex. This eliminates the problem of the graft being “too long” and thus eliminates the tibial bone block protruding out the tibial tunnel. In other words, there is no longer a risk of the graft being too long whether using autografts or allografts and therefore no need for tricks to accommodate this, such as steeper angles on the tibial tunnel. Having the tibial bone block end flush with the tibial cortex also makes tibial fixation much easier. Continued advantages are that this technique avoids complications seen from interference fixation such as screw divergence, posterior blowout, laceration of the graft, screw breakage, and retained hardware or voids encountered during revision surgery. Finally, as already alluded to, revision anterior cruciate ligament (ACL) surgery becomes much easier for all these reasons. Revision ACL surgeries are usually as simple as primary ACL reconstructions.

The Endobutton-CL is a small metal button that is attached to a continuous loop of nylon. The continuous loop means that there is no knot, thus eliminating the risk of knots loosening or tightening under a load; both situations lead to a lengthening of a construct and thus failure. The continuous loop (CL) comes threaded through the metal Endobutton. The loop is then threaded through the graft and back on itself. Thus it is a closed loop system that eliminates a weak link. This minimizes creep or failure of the construct. It is well accepted that the weak link in ACL reconstruction surgery is fixation of the graft during the immediate postoperative period. The Endobutton-CL offers one of the strongest forms of fixation available, with pullout strengths averaging 1345N compared with interference screws that average approximately 700N.*

Technique Overview

To emphasize the simplicity of the technique, an overview is presented first, followed by a more detailed description with pearls.

1 Standard knee arthroscopy is performed.

2 Prepare the BTB graft in the usual manner.

3 Ream the tibial tunnel in the usual manner.

4 Ream the femoral tunnel to a depth of the length of the BTB graft as measured directly off the reamer at the opening of the tibial tunnel. Then ream an extra 10 mm to allow room for the Endobutton to flip when passed.

5 Leave the guide pin in place, and drill over it with the 4.5-mm Endobutton drill bit through the lateral femoral cortex.

6 Measure the length from the lateral femoral cortex to the opening of the tibial tunnel, and set the “stop” on the depth gauge.

7 The length of the needed CL is measured directly off the depth gauge when the graft is set beside it.

8 Attach the CL to the graft.

9 Pass the graft, flip the Endobutton, and tension the graft.

10 Fix the tibial bone plug.

Technique in Detail

The technique has a small learning curve with no needed calculations, which minimizes error. Standard setup and knee arthroscopy are performed. The bone–patellar tendon–bone graft is prepared in the usual manner, regardless of whether an autograft or allograft is used. Personally I leave the bone plugs no longer than 20 mm. Grafts are usually 9 or 10 mm in diameter.

Tibial and femoral tunnels are likewise drilled in the usual manner. In fact, the femoral tunnel can be drilled right off the posterior femoral cortex without fear of breaking through of the posterior wall, as it will not compromise fixation. I use a 6-mm offset guide for a 10-mm tunnel, which places the femoral tunnel immediately against the posterior femoral cortex. Before reaming the femoral tunnel, check the length of the graft. Grafts usually measure approximately 80 to 90 mm in total length (Fig. 50-1). Ream the femoral tunnel to a depth of the length of the graft as measured directly off the reamer at the tibial cortex. For example, if the graft length is 90 mm, ream to a depth of 90 mm as measured on the reamer at the opening of the tibial tunnel (Fig. 50-2). By doing this, the reamer is mimicking the graft itself and therefore mimicking where the graft will be placed, thus allowing the tibial bone plug to end flush with the tibial cortex. It is no longer necessary to measure the femoral tunnel; however, as a check, the femoral tunnel is usually reamed to a depth of approximately 30 mm. Then ream an extra 10 mm deeper to allow room for the Endobutton to flip outside of the lateral femoral cortex. Try to not perforate the lateral femoral cortex with the reamer. On longer grafts, you can run the risk of running out of room for the femoral tunnel. One way to effectively add length to the femoral tunnel is to flex the knee less than 90 degrees. This lessens the angle of the femoral tunnel, placing it more in line with the femur, and therefore adds length to the femoral tunnel if needed for longer grafts (Fig. 50-3). However, if there is inadvertent perforation of the femoral tunnel, it can be dealt with using the Xtendobutton, which is discussed later in this chapter.