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Comparing graft options for ACL: Which offers the most benefits today?

Double-bundle grafts may offer long-term advantages, but surgeons await clinical proof.

Issue: Issue 2 2006

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Looking back on the history of ACL surgery, one could conclude that the first decade was devoted to proving it was needed, the second to showing that it should be intra-articular, and the third to demonstrating that good results can be obtained with several different graft sources.

As a result of all these efforts, most athletes sustaining an ACL tear today undergo successful surgical reconstruction and return to the sport of their choice at or very near their pre-injury level of performance. Why, then, do surgeons continue to look for new ways to address ACL injuries?

Perhaps one reason is that ACL tears affect our best and brightest — ie, the young and athletically gifted. These individuals place extremely high demands on their knees, and even a small increment of improvement in function would be valuable.

Patients with ACL reconstructions generally do well, but some never seem to exhibit their “athleticism.” Is this weakness, loss of proprioception, subtle instability, or the sequelae of the associated articular cartilage and meniscal trauma? Furthermore, some patients have their stability restored only to develop premature degenerative arthritis. Could improved surgical techniques change these outcomes?

Recently, several major orthopaedic meetings have devoted an entire session to single-vs. double-bundle ACL reconstruction. Double-bundle techniques have been promoted as being more “anatomic” and more effective in restoring rotational stability to the knee. Orthopaedics Today’s panelists have participated in these presentations and are some of the “thought leaders” in this area. The international makeup of the panel reflects the fact that efforts to “perfect” ACL surgery are being made worldwide.

This round table addresses some fundamental questions regarding the pertinent anatomy, the need for double-bundle reconstruction, the potential benefits and risks, and the evidence so far regarding effectiveness. While it may be too soon to determine whether or not this new technique is an advance or a step in the wrong direction, it is a good time to begin asking questions.

Ben Graf, MD
Moderator

Ben Graf, MD: How long have you been performing double-bundle ACL reconstruction?

Konsei Shino, MD, PhD: I started with Rosenberg’s bi-socket from 1995 to 1999 and shifted to anatomic bi-socket (two femoral sockets–single tibial tunnel) from January to December 2000. I used an anatomic double-bundle via twin femoral and tibial tunnels from December 2000 to March 2004 and an anatomic triple-bundle via two femoral and three tibial tunnels from April 2004 to the present.

Graf: What factors made you decide to change to this technique?

Shino: I changed to pursue the more natural graft resembling the normal ACL, and to enlarge contact area between the graft and bone tunnel wall in the hopes of earlier graft remodeling and its better biomechanical performance as the restraint.

Graf: What have been your results, and how do they compare to your single-bundle experience?

Shino: As we are always trying to do better procedures for our patients, we have not performed randomized controlled trials to compare the results between single- and double-bundle techniques. I would rather be a good physician than an excellent scientist. However, I could say the results of the double- or triple-bundle technique are better and more consistent than those of the single-bundle technique performed in the past.

Graf:Do you still perform any single-bundle reconstructions?

Shino: Yes, I am still doing single-bundle reconstructions using bone- patellar tendon-bone graft. However, the grafting is performed using the double-bundle grafting concept. Thus, the rectangular tunnels are created in the footprints for the anterior portion of the graft to function as the antero-medial bundle of ACL, and for the posterior portion to work as the post-lateral bundle of ACL. This technique was recently published in the Journal of Arthroscopy.

Graf: What concerns do you have about the double-bundle technique?

Shino: As all drillings are currently performed in an outside-in fashion with the anterolateral entry femoral aimer (anterolateral entry femoral aimer without 6-mm offset tip, Ref. #7210984, Smith & Nephew Endoscopy) under good visualization (ie, viewing femoral footprint through the antero-medial portal), there is no concern anymore. However, there were concerns such as slightly inconsistent femoral tunnel location due to poor visual field through the anterolateral portal, blowout of the femoral tunnels during inside-out drilling and/or insecure femoral fixation with Endo-button by interposing soft tissue overlying the femur.

Anastasios D. Georgoulis, MD: ACL rupture can lead to increased anterior translation and excessive internal-external rotation of the tibia. Single-bundle ACL reconstruction is successful in limiting anterior tibial translation but, according to cadaveric studies, fails to restore the excessive internal tibial rotation. In vivo biomechanic studies have shown that the excessive tibial rotation is partially restored during walking. However, during high-demand activities that include high-rotational loads, such as pivoting, single-bundle ACL reconstruction does not seem to restore the abnormal tibial rotation.

However, there is biomechanical evidence that a more oblique placement of the ACL graft in both dimensions (anterior-posterior and medial-lateral) can diminish but not restore the increased internal-external rotation found in the ACL-deficient knee.

The double-bundle reconstruction restores the excessive internal-external rotation. However, this has been shown only in in-vitro and not in in-vivo biomechanic studies. The patients do not feel whether the pathological rotation is diminished.

Although the double-bundle reconstruction may be promising, we must keep in mind that it is a new method and it is more technically demanding than the single-bundle reconstruction. In addition, it has not been thoroughly investigated in biomechanical, histological or clinical studies.

We are in the beginning of a new era, and a large number of experienced orthopaedic surgeons are working on this method. Soon, some problems will be solved and new instruments will be developed so that many orthopaedic surgeons — not just the specialists — can perform the method.

Graf: You have worked extensively in the laboratory on the biomechanics of ACL reconstruction. What do we know about the biomechanics of single- vs. double-bundle reconstructions?

Freddie H. Fu, MD: In order to understand the biomechanics of single- and double-bundle ACL reconstruction, it is essential to first consider the anatomy of the amteromedial (AM) and posterolateral (PL) bundles. Studies of the anatomy of both normal and ACL-injured knees, as well as the biomechanics of normal, ACL-injured, and ACL-reconstructed knees have been valuable in shaping our approach to reconstruction.

Anatomical study of the ACL in greater than 30 fetuses demonstrates distinct AM and PL bundles of the ACL as early as 16 weeks. Analysis of more than 60 cadaver knees also demonstrates the two bundles and their insertions. Finally, arthroscopic assessment of the ACL in patients undergoing surgery for unrelated pathology shows that all patients (more than 300 to date) have both an AM and PL bundle, although the relative sizes of the AM and PL bundles are variable from patient to patient.

A key point, evident from these studies, is that the alignment of the femoral insertion sites of the AM and PL bundles changes during flexion, moving from a vertical alignment (in extension) to a horizontal alignment (in 90º flexion). As a result, the AM and PL bundles change from being parallel in extension to crossed in flexion. This consideration is critical, since we understand the femoral insertion sites of the ACL at 0º but we perform surgery at 90º. It also highlights the unique biomechanical role of each bundle.

In the area of biomechanics, studies have determined that the PL bundle is at its highest level of tension when the knee is in extension, and it becomes relaxed in flexion. The PL bundle also becomes tight when the knee is internally or externally rotated. The AM bundle is at its highest tension at 60º, and is more relaxed during extension. The AM bundle is most closely associated with anterior-posterior (A-P) translation control, whereas the PL bundle functions more in rotational stability and to prevent the pivot shift.

This principle has been supported by the study of AM and PL-deficient cadaver knees by Gabriel et al, and by an investigation comparing single-bundle and double-bundle reconstructions in cadaver knees by Yagi et al, which demonstrated that anatomic ACL double-bundle reconstruction better restores the rotation of the knee joint compared to single-bundle techniques. Other laboratories have studied rotation stability and found similar results, as seen in publications by Amis and Georgoulis. Finally, in an in vivo study by Tashman et al, single-bundle reconstruction was shown to restore A-P stability but did not restore rotation. Data on double-bundle reconstruction is currently pending from this study.

To summarize, the ACL consists of two functional bundles, the AM and PL bundles, and each bundle contributes in a unique way to the kinematics of the knee based on their different insertion sites and tensioning patterns. The PL bundle is tightest in extension, whereas the AM bundle is tightest at 60º of flexion. Biomechanical studies demonstrate a major role in rotational stability for the PL bundle and A-P stability for the AM bundle. Therefore, from an anatomical and biomechanical standpoint, reconstruction of both the AM and PL bundles is a logical approach to restoring normal kinematics.

Graf: If double-bundle appears to work better in the lab, should we be using this technique for all patients, or just for select patients?

Fu: Clearly, experience with single-bundle ACL reconstruction has shown that it sucessfully allows most patients to return to activities and sports following surgery, although there is a subset of patients who continue to have a sense of instability or givinig way of the knee despite correct graft position. If the main goal of surgery is to allow return to sports and activities, double-bundle is not likely to produce a dramatic improvement in results over current techniques. The biggest potential advantage of double-bundle reconstruction is with respect to improving long-term outcomes, by reducing problems such as degenerative joint disease (DJD). This is a benefit that may be extended to all ACL patients.

Although the absolute difference in rotational stability between normal knees and single-bundle reconstruction is small, it may still alter knee kinematics enough to lead to degenerative changes over time.

Double-bundle ACL reconstruction offers a chance to more accurately restore rotational stability, and this may produce real improvements in long-term outcomes. However, we still need the results of an in vivo model to demonstrate the restoration of rotational stability, and clearly we need to complete careful outcomes studies to evaluate the effects of double-bundle reconstruction on long-term rates of DJD.

Graf: What concerns do you have about the double-bundle technique?

Fu: There have been many issues raised about the double-bundle technique, including the learning curve for inexperienced surgeons, possible increased risk of fracture, tunnel enlargement, impingement, range of motion, and difficulties in revision. I will address each of these.

First, as with any technique, there is a learning curve associated with doing the double-bundle surgery, and the margin of error for proper tunnel placement is smaller when compared to single-bundle surgery.

Therefore, at this point it is probably not advisable for surgeons who do not do a large volume of ACL surgeries to try double-bundle reconstructions. However, the fact that double-bundle ACL reconstruction is more technically challenging is not a justification for avoiding its use altogether.

If we can restore the normal anatomy more accurately, and we can demonstrate that there are potential long-term benefits of this technique, we should look for ways to allow the surgery to be performed on all patients who may benefit from it, whether through improved instrumentation or other means. However, it is important to acknowledge that we have not yet clinically proven the long-term benefits of a double-bundle approach over single-bundle.

I must also note that since the double-bundle approach references the normal ACL anatomy as a guide for tunnel placement, it is in some ways easier than single-bundle, since tunnel location is more clearly defined. Prior to removing the remnants of each bundle, the insertion site of each bundle can be located and marked, facilitating tunnel positioning later in the procedure.

In single-bundle reconstruction, there is so much space from which to choose to place the tunnel. Thus, it is very easy to end up with a poor tunnel position and a resultant failure.

To address the concern of fracture risk, we have performed a computer modeling study at our institution using finite element modeling to study forces on the femur in the native state and following one- vs. two-tunnel drilling. Our results have demonstrated that there is an increased risk of fracture for one tunnel vs. the native state, but that the additional fracture risk of a second tunnel is minimal. It is important to achieve divergent tunnels, and the anatomy allows this without much difficulty since the two bundles naturally follow different trajectories.

Tunnel enlargement has also been raised as an issue, but in our experience this has not been problematic. One reason is that the anatomic position of tunnels for double-bundle is able to reduce the windshield-wiper effect often seen with single-bundle. In addition, the tunnel diameter used for single-bundle is larger than with double-bundle, so there is less healing surface available for graft incorporation. Collection of radiologic data as part of clinical outcomes studies will help investigate this area more rigorously.

Impingement has also been questioned, but again, the anatomic position of the grafts in double-bundle reconstruction seems to avoid this problem. The AM graft is positioned in a relatively flat trajectory, and although its tibial position is located slightly anterior to traditional single-bundle tunnel, results with postoperative range of motion have been excellent.

A study on range of motion comparing a previous cohort of single-bundle patients with our current group of double-bundle patients was recently completed. Both extension and flexion in the early postoperative period were significantly better in the double-bundle group. Since the position of the grafts is more anatomical, it is possible to use more total graft material and still achieve full motion of the knee.

Finally, difficulty in revision has been cited as a concern. This is a valid point, and it underscores why surgeons who do not do a large volume of ACL surgery should probably not yet perform double-bundle ACL reconstruction. At our institution, we had one patient with a double-bundle reconstruction retear the ACL, but we were able to complete a revision double-bundle reconstruction without much difficulty by using the same tunnels as the initial procedure.

Graf: The double-bundle technique adds complexity to the procedure that most orthopaedists have been doing for years. Is this technique too difficult for the general orthopaedist? How about for the average sports medicine specialist?

Fu: As I have previously stated, at this point it is probably advisable to reserve double-bundle reconstruction for surgeons with a high volume of ACL surgery, since it is indeed more technically challenging and there is less margin for error.

However, all surgeons performing ACL reconstruction can use the principles of the double-bundle approach to complete a more anatomical reconstruction. Guided by improved knowledge of the insertion sites of the AM and PL bundles, as well as their changing alignment throughout flexion and extension, it is possible to achieve a more accurate placement of a single-bundle tunnel at the midpoint of the two bundles. This may not allow for complete restoration of normal kinematics, but it could lead to improved outcomes over traditional single-bundle surgery and a decrease in the number of revision surgeries required.

Therefore, while I do not recommend that all surgeons use double-bundle at this time, I do recommend that all surgeons pay close attention to the anatomy of the normal and injured ACL to help guide their approach to ACL surgery and tunnel position.

The understanding of the anatomical double-bundle ACL reconstruction concept will also help surgeons with single-bundle reconstruction.

Graf: Dr. Bach, you have worked for years perfecting the single-bundle technique for ACL reconstruction. Is there a need for a double-bundle reconstruction? What concerns do you have regarding this technique?

Bernard R. Bach Jr., MD: In October 1991, I transitioned to the single-incision endoscopic technique performed almost exclusively with patellar tendon autograft or allograft tissues. We have reported our initial results in the American Journal of Sports Medicine. Our experience over time has only improved and I feel very comfortable with this technique. I have made a considerable effort focusing on the technical aspects of this procedure and feel that the success of this procedure is highly technique dependent.

Although Dr. Fu has some fascinating data generated in his lab, I do not currently believe that a double-bundle reconstruction is necessary. In experienced hands we can eliminate the pivot shift phenomenon in 90% of our patients with a single tunnel technique.

In fact, most surgeons feel that the likelihood of tearing the contralateral ACL is higher than disrupting the ACL graft. We have experienced very few macrotraumatic retears, our patient subjective satisfaction level indicates that 95% of our patients are completely or mostly satisfied. Our reoperation rate for symptomatic knee flexion contractures has been 1% annually since 1993. I personally do not believe that my results will improve with a two-tunnel procedure.

Graf: The double-bundle technique adds complexity to the procedure that most orthopaedists have been doing for years. Is this new technique too difficult for the general orthopaedist? For the average sports medicine specialist?

Bach: The two-tunnel technique is a challenging procedure. At the AAOS meeting last year, Stephen Howell, MD, presented radiographs from several leaders who espoused the double-bundle procedure. Considerable variation was demonstrated among tunnel locations selected by these experts. One must keep in mind that the experience of ACL surgery is similar to that of total knee arthroplasty; the majority of ACL reconstructions performed nationally are performed by individuals who do fewer than 10 reconstructions annually.

My concerns include a steep learning curve for the average general or sports medicine orthopaedist. An important consideration is that even with this technique there will be failures.

Revision procedures with two tunnels in the femur and two tunnels in the tibia most likely will necessitate staged revisions to bone graft the tunnels. If soft tissue grafts are being used with two-tunnel procedures, we may see overlapping tunnel expansion, which may be difficult to manage. Perhaps we are trading one perceived problem for another.

In most failed ACL procedures that are referred to our office, I can identify a technical component that may have contributed to graft failure. Most commonly this involves abnormal tunnel placement.

In my opinion, we have seen a transition with the endoscopic technique to creating a vertically oriented tunnel on the femur that may approach the 12 o’clock position. This is technically related to creating a tibial tunnel in a too sagitally oriented plane if one is using a transtibial drilling technique.

One must recognize that the transtibial technique mandates a drill entry position that is approximately midway between the tibial tubercle and the posteromedial border of the tibia.

If the drill entrance position is placed close to the tibial tubercle, that tibial tunnel will be too sagitally oriented and the resultant femoral tunnel will be vertically oriented. A vertically oriented femoral tunnel will result in a Lachman test that may be normal but does not control rotation; a positive pivot shift phenomenon can frequently be elicited in these patients who may have acceptable KT-1000 parameters.

Tunnel placement is one of many factors that can impact our results. Graft harvesting, graft tunnel mismatch management and graft fixation are technical factors that also can impact our results. These factors have been addressed in many of our technical manuscripts. Additionally, the articular or meniscal injuries that accompany the ACL injury may be the long-term rate-limiting factors that impact our results.

I am currently not convinced that transitioning to a double-bundle technique will improve my results. Having performed over 1500 ACL reconstructions since 1986, I believe that we currently have a technique that allows predictable results when performed properly.

Whether an ACL reconstruction is performed with the two-incision or one-incision technique, and regardless of graft, the technical a\spects for the procedure are the factors that we can most control as surgeons.

I would advise surgeons to sit back and critically appraise their own techniques, follow their patients carefully, and determine what techniques work best in their hands. It is unfair to assume that we all have the same experience or technical skills to perform a procedure, which is a series of careful, refined steps.

Primum non nocere. Do not jump on the latest technical bandwagon.

For more information:

• Andriacchi TP, Dyrby CO. Interactions between kinematics and loading during walking for the normal and the ACL deficient knee. J Biomech 2005; 38: 293-298
• Bach BR Jr, Levy ME , Bojchuk J, Tradonsky S, Bush-Joseph CA, Khan NH: Single-Incision Endoscopic Anterior Cruciate Ligament Reconstruction Using Patellar Tendon Autograft-Minimum Two Year Follow-Up Evaluation. Am J Sports Med. 1998;26(1):30-40.
• Ferrari JD, Bush-Joseph CA, Bach BR Jr. Anterior cruciate ligament reconstruction using bone patellar tendon bone grafts: autograft and allograft endoscopic techniques and two-incision autograft technique. In (Drez D Jr., DeLee JC-eds., Bach BR Jr-Guest editor) ACL Surgical Techniques. Operative Techniques in Sports Medicine Philadelphia: W.B. Saunders. 1999;7(4):155-171.
• Ferrari JD, Bush-Joseph CA, Bach BR Jr. Arthroscopically assisted ACL reconstruction using patellar tendon substitution via endoscopic technique. In Bach BR Jr (ed) ACL Surgical Techniques, Techniques in Orthopaedics, New York: Lippincott-Raven. 1998;13(3):262-27.
• Flik K, Bach BR Jr: Endoscopic ACL Reconstruction using patellar tendon autograft-technique, in Bach BR Jr (Guest ed.) Techniques in Orthopaedics: Patellar Tendon for ACL Surgery. 2005;20(4):361-371.
• Georgoulis A, Papadonikolakis A, Papageorgiou C, Mitsou A, Stergiou N. Three-dimensional tibiofemoral kinematics of the anterior cruciate deficient and reconstructed knee during walking. Am J Sports Med 2003;31(1):75-79.
• Hardin GT, Bach BR Jr, Bush-Joseph, Farr J: Endoscopic Single Incision ACL Reconstruction Using Patellar Tendon Autograft-Surgical Technique. Am J Knee Surg 1992;5(3):144-155.
• Ristanis S, Giakas G, Papageorgiou CD, Moraiti T, Stergiou N, Georgoulis AD. The effects of anterior cruciate ligament reconstruction on tibial rotation during pivoting after descending stairs. Knee Surg Sports Traumatol Arthrosc. 2003 Nov;11(6):360-5.
• Ristanis S, Stergiou N, Patras K, Vasiliadis HS, Giakas G, Georgoulis AD. Excessive tibial rotation during high-demand activities is not restored by anterior cruciate ligament reconstruction. Arthroscopy. 2005;21(11):1323-9.
• Shino K, Nakata K, Nakamura N, et al. Anatomic anterior cruciate ligament reconstruction using two double-looped hamstring tendon grafts via twin femoral and triple tibial tunnels. Operative Tech in Orthoped. 2005;15:130-134.
• Yoo JD, Papannagari R, Park SE, DeFrate LE, Gill TJ, Li G. The effect of anterior cruciate ligament reconstruction on knee joint kinematics under simulated muscle loads. Am J Sports Med. 2005 Feb;33(2):240-6.
• Woo SL, Kanamori A, Zeminski J, Yagi M, Papageorgiou CD, Fu FH. The effectiveness of anterior cruciate ligament reconstruction by hamstrings and patellar tendon: a cadaveric study comparing anterior tibial load vs rotational loads. J Bone Joint Surg Am. 2002;84-A(6):907-914.