Single-bundle ACL Reconstruction

Don Johnson, M.D., FRCSC
Sports Medicine Clinic Carleton University
Ottawa ON

My preference is to do an anatomic single-bundle ACL reconstruction for various reasons.

Even though there is support for the double-bundle concepts both from anatomy and biomechanics, there is insufficient clinical published evidence to support the double-bundle reconstruction. Most of the RCT's comparing single- vs double-bundle show no subjective improvement and only a slight reduction in the incidence of a positive pivot shift with the double-bundle reconstruction.


The single tunnel ACL reconstruction has been a successful procedure. In the AJSM in 2008 Bach reviewed 11 clinical trials comparing single-bundle patellar tendon and hamstring grafts consisting of 1,024 reconstructions. The outcome measurements were: complication rate 6%, graft failure 4%, negative pivot shift 81%, negative Lachman test 59%, KT SSD less than 5 mm in 86%. Bach's conclusion was that, after review of a considerable body of unbiased outcome data on single-bundle ACL reconstruction, it is a safe consistent surgical procedure affording reliable results. It's true that these are not optimum results, but I think that the outcome can be improved more by anatomic tunnel single placement rather than switching to a double-bundle procedure.

If everyone were to switch to the double-bundle procedure, we would have more complications, increased cost of the procedure (twice as many implants), surgeons frustrated with the very steep learning curve; with only a very marginal improvement in outcomes. If the outcomes were significantly better than single-bundle, then perhaps we could justify these issues.

This is not really an argument for or against double-bundle reconstruction, but is  rather all about anatomic ACL reconstruction. Dr. Fu has brought to our attention the importance of anatomic placement of the tunnels. For the past 15 years the most common technique in North America was to create the femoral tunnel through the tibial tunnel. This often resulted in a high anterior femoral tunnel. When this was recognized, the tendency was to place the tibia tunnel more posterior on the tibia to reach the lower position on the femur. We were then creating a tibial PL to femoral AM position with the single tunnel. The position of the femoral tunnel was improved by drilling through the AM portal. This is not without its problems: damage to the femoral condyle with the drill bit, cutting the anterior horn of the medial meniscus, and incorrect placement of the femoral tunnel due to loss of orientation with hyperflexion. All of these are overcome as the surgeon becomes more experienced with the technique. Identifying the anatomic site of the ACL, marking this, and confirming the position by viewing from the medial portal all help to find this position with hyperflexion.

A new technique of drilling from the outside-in with the flipcutter is another method to place the femoral tunnel in the correct position without putting the knee into hyperflexion. In this situation, the guide is placed through the anterolateral portal and viewing is done via the medial portal. The exact anatomic position may be determined precisely when viewing from the medial portal. Avoiding the hyperflexion position makes it easier to convert from the tibial tunnel technique.

The position of the anatomic single tunnel should overlap both the AM and PL anatomic sites. The previous concept of going at the 11 o'clock position, and as far posterior as possible, is no longer considered ideal.

Figure 1. The femoral tunnel is low, and overlaps both the AM and PL anatomic sites.

In my opinion, not everyone should be attempting a double-bundle reconstruction. For the occasional surgeon performing ACL reconstruction, the technique should be kept as easy as possible. There probably is an indication for double-bundle but right now I am not sure what it is. Should the patient with the gross pivot shift, or one that has a touch of posterior lateral laxity be considered?

The current method of evaluating rotational laxity is with the pivot shift test. This is a very subjective evaluation, yet it is the only outcome measurement that is used in these comparison studies. In my mind, that may introduce a significant bias. In one study comparing the single- versus double-bundle, the author quoted a 27% positive pivot shift in the single-bundle group. Either he is not placing the single-bundle in the correct position or there is an element of bias in the data.

In summary, the anatomic single tunnel ACL reconstruction is an easy, reproducible technique that has few complications, a minimal learning curve, and the cost of converting to a new variant such as outside-in drilling is minimal.