Chapter 25 Anatomical Double-Bundle Reconstruction of the Anterior Cruciate Ligament

Anthony Buoncristiani, Paul Fotios Tjoumakaris, James S. Starman, Freddie H. Fu

Introduction

Anterior cruciate ligament (ACL) reconstruction remains one of the most common procedures performed by orthopaedic surgeons in the United States, with approximately 100,000 performed per year.¹ ACL surgery has evolved tremendously from the original open techniques to modern procedures focusing on endoscopic reconstruction of the anteromedial (AM) bundle using a variety of graft choices and fixation techniques. However, the success of single-bundle ACL reconstruction ranges from 69% to 90%.^2,³ In addition, according to Fithian et al,⁴ 95% of patients who underwent single-bundle ACL reconstruction developed medial compartment degenerative radiographic changes after 7 years, and only 47% were able to return to their previous activity level. Because arthrosis was observed medially, it could not be attributed to the initial subluxation event, which usually results in a bone contusion or a concomitant meniscal tear involving the lateral compartment.⁴

Single-bundle ACL reconstruction is the “gold standard,” but some authors have noted persistent instability with functional testing of single-bundle ACL reconstruction.^5,⁶ Thus, there is a growing trend toward a more anatomical ACL reconstruction that recreates both the AM and the posterolateral (PL) bundles. The double-bundle anatomy of the ACL was first described in 1938 by Palmer et al.⁷ The terminology of the AM and PL bundles are chosen according to their tibial insertions. The tibial and femoral insertion sites of both the AM and PL bundles have been well described.^8,⁹ The femoral origin has an oval shape, with the center of the AM bundle close to the over-the-top position and the center of the PL bundle close to the anterior and inferior cartilage margin. The femoral origin site changes as the knee is taken through an arc of motion. The two bundles are parallel with a vertical orientation when the knee in extension (i.e., the AM footprint is situated directly superior to the PL footprint). This changes to a more horizontal orientation, with the PL footprint becoming actually anterior to the AM footprint when the knee is flexed beyond 90 degrees. The changing orientation of the two bundles’ footprints as the knee is taken through an arc of motion leads to the observed crossing pattern of the independent components of the ACL. Although the two bundles are intertwined, their functional tensioning pattern is independent throughout the knee’s range of motion.¹⁰ Close to extension, the AM is moderately loose and the PL is tight. As the knee is flexed, the femoral attachment of the ACL takes a more horizontal orientation, causing the AM bundle to tighten and the PM bundle to loosen. The ACL has been described as a restraint to anterior tibial displacement and internal tibial rotation. The rotational stabilizing component might be better attributed to the PL bundle.

The idea of reconstructing both bundles of the ACL was described by Mott and Zaricznyj in the 1980s.^11,¹² They independently described a double-bundle technique. Mott drilled two separate tunnels, whereas Zaricznyj used a single femoral and two tibial tunnels. Despite publishing their results, the technique did not become mainstream. Recent biomechanical evidence supports the anatomical double-bundle ACL reconstruction as more accurately recreating the natural anatomy.^13,¹⁴ Both translational and coupled rotational translation were significantly less in the specimens with double-bundle ACL reconstruction. We present the senior author’s (F.H.F) technique of anatomical double-bundle ACL reconstruction with two femoral and tibial tunnels using two tibialis anterior allografts.

Preoperative Considerations

History: Signs and Symptoms

ACL injuries occur frequently in sports that involve running, jumping, and cutting movements. They can occur without contact when the foot is anchored to the playing surface—usually by way of cleats or a rubber sole—and the body rotates beyond the tolerance of the ligament as the knee buckles. Thus, it is important to ask the patient how the injury occurred and the position of the knee during the injury, which may also allude to the ACL bundle injury pattern.¹⁵ This may be associated with an audible “pop.” Asking whether the athlete was able to continue to play will give you an idea of the severity of the injury. Knee pain and a hemarthrosis are usually present acutely. A complaint of instability is also common, especially with walking downhill or down stairs.

Physical Examination

Inspect and palpate for an effusion. If a large effusion is present, consider aspiration for pain relief, and inspect the aspirate for any fat globules, which would be suggestive of a fracture. Check the range of motion; if it is limited, magnetic resonance imaging (MRI) should be ordered to ensure that no displaced meniscal tear is present. The physical examination of an isolated ACL tear is usually significant for a side-to-side difference with regard to Lachman and pivot-shift maneuvers. If a discrepancy between the Lachman and pivot-shift maneuvers exists, this may signify a partial tear involving either the AM or PL bundles. The PL bundle is mainly responsible for rotational stability, and a large pivot shift will be evident if it is torn. Similarly, the AM bundle is mainly responsible for translational stability when the knee is flexed, and a large Lachman maneuver will be present if the AM bundle is torn. A KT-1000 test can also be used to confirm a side-to-side difference in anterior translation. A more prominent anterior drawer compared with a Lachman test should alert the examiner to consider a concomitant posteromedial or posterior horn medial meniscal injury. Varus/valgus instability testing should be performed to ensure no collateral injury is present. Dial testing and posterolateral drawer testing at 30 degrees should be performed to assess for a posterolateral knee injury. Gait analysis should be performed to inspect for any underlying varus laxity. Tests for possible meniscal pathology should also be performed (i.e., joint line tenderness, McMurray maneuver), but it may be difficult to distinguish between a lateral meniscal tear and a bone contusion acutely. Thus, appropriate imaging is important.

Imaging

A complete knee series consisting of weight-bearing anteroposterior and notch, lateral, and patellofemoral sunrise views should be obtained. The soft tissues can be inspected for an effusion. The bony anatomy should be inspected for any fractures or subtle signs of a rotational injury, such as segond or reverse segond capsular lesion. In addition, the status of the physes and any arthritic changes should be noted. Long cassette films should be obtained for any patient with varus alignment on examination or if any arthritic changes are noted on the knee series obtained. This will help determine whether an osteotomy should be performed. An MRI is essential not only to confirm an ACL injury but, more importantly, to assess for any concomitant ligamentous or cartilage injuries that will affect the operative plan. The PL bundle is more easily visualized on coronal sectioning. Specifically, it may be seen at the level of the first cut, which includes the PCL.

Indications

The absolute indications for double-bundle ACL reconstruction are evolving. Even though single-bundle ACL reconstruction is considered the “gold standard,” the technique can be improved. Gait analysis after single-bundle reconstruction has demonstrated that rotatory instability persists.⁵ Furthermore, biomechanical cadaveric studies have shown that even lowering the femoral insertion site to the 3- or 9-o’clock position does not fully prevent rotatory instability.¹⁶ Clinically, as many as one-fifth of the patients do not resume preinjury activities and usually complain of vague instability symptoms that objectively correspond to a mild persistent pivot shift.¹⁷ In comparison, double-bundle ACL reconstruction does restore the rotational component in a cadaveric model.¹⁴ It has been suggested that a positive pivot shift after ACL reconstruction is correlated with the development of later osteoarthrosis.¹⁸ Perhaps with reconstruction of both the AM and PL bundles, the decreased rotational instability will provide improved overall knee kinematics and may prevent or slow the degenerative changes seen after single-bundle ACL reconstruction.⁴ A contraindication to performing the double-bundle technique is in the young athlete with open physes. Two tunnels would risk physeal arrest with subsequent malalignment and possible leg length discrepancy.