Introduction

Anterior cruciate ligament (ACL) reconstruction is one of the most frequently performed knee surgical procedures today. Through the years, the various technical modifications together with the introduction of better instrumentations have led to the improved outcome currently reported in the various orthopaedic literature.

Conventional techniques of reconstructing the torn ACL employ the use of either a bone–patellar tendon or hamstring graft. The majority of these reconstruction techniques, however, basically reconstructs the anteromedial (AM) bundle of the cruciates as the femoral tunnel is placed between the 10- and 11-o’clock position for the right knee (or 1- and 2-o’clock position for the left knee). Although good results have been generally demonstrated concurrent with its ability to restore the knee’s anteroposterior (AP) stability, questions remain regarding its efficiency in restoring rotational stability.¹ Recently, the performance of an anatomical double-bundle reconstruction technique has generated renewed interests as several in vitro analyses demonstrated better results in terms of restoring knee rotational stability.^2–8

Performing an anatomical double-bundle reconstruction usually entails the use of both the semitendinosus (ST) and gracilis (Gr) autografts, requiring the use of independent femoral and tibial fixations.^5,9,10 With this technique, therefore, the surgery becomes more costly with the additional fixation required. Moreover, with the use of both the ST/Gr, hamstring strength deficits can become apparent, as has been demonstrated by previous studies.^3,4,11

This section illustrates a modification of the anatomical double-bundle technique using a single ST autograft with independent femoral but single tibial fixation system. This double-bundle, single-tendon (DBST) technique enables the surgeon to achieve an anatomical reconstruction without compromising the hamstring function while at the same time avoiding the use of additional fixations limiting the cost of the surgery.

Anatomy of the Anterior Cruciate Ligament

Anatomical studies have shown that the ACL consists of two functional bundles, the AM and the posterolateral (PL) bundle, whose nomenclature is related to their insertion in the tibial plateau.^1,12 These two bundles are already identifiable between the 16th to 22nd weeks of fetal development. Analyzing the insertions of these two bundles reveals that they do not lie on the same coronal plane; the AM bundle originates more proximally than the PL bundle. Biomechanically, the AM bundle tightens in flexion while the PL bundle slackens. On the other hand, the PL bundle tightens in extension while the AM bundle loosens.^1,13 The ACL attaches to the femur and tibia as a collection of fascicles that fan out as they approach their insertions sites.

Scientific Rationale

Early cadaveric investigations performed by Radford and Amis¹ demonstrated the superior AP knee stability achieved through various ranges of flexion with a double-bundle reconstruction compared with single-bundle ACL reconstruction. Their investigation, however, did not include tests for rotational stability. Yamamoto et al,¹⁴ on the other hand, reported no significant differences between double-bundle and single-bundle ACL reconstruction of the PL bundle in terms of response to rotatory loads. However, single PL bundle reconstruction was found to be associated with increased anterior tibial translation with application of anterior loads. A more recent cadaveric study emphasized that single-bundle ACL reconstruction is mostly successful in restoring AP knee stability but is inadequate in controlling the combined rotatory loads of internal tibial torque and valgus torque.

In a biomechanical study by Yagi et al⁶ restoration of the knee kinematics, particularly in terms of rotational control, was also demonstrated to be better with a double-bundle versus single-bundle reconstruction technique. Further in vivo studies by Tashman et al⁵ also revealed that single-bundle reconstruction sufficiently restores AP tibial translation but failed to provide rotational stability during dynamic loading.

In general, the available studies thus far have demonstrated that single-bundle ACL reconstruction can only partially restore the normal knee kinematics because it limits anterior translation but is unable to control pivot shift. In addition, biomechanical analysis of an anatomically reconstructed knee also demonstrated that anterior tibial translation for double-bundle reconstruction is significantly closer to that of an intact knee and produces better rotatory stability.^7,8

Surgical Technique

Following the administration of either a spinal or general anesthesia, the patient is positioned supine on the operating table. A tourniquet is placed at the proximal aspect of the thigh with sufficient distance from the expected exit point of the Beath needle in the thigh’s lateral aspect. A lateral post for thigh support and a foot bar are then placed to enable the knee to be positioned at 90 degrees of flexion on the table during surgery. This set-up also allows sufficient provision for full range of motion (Fig. 24-1).

Fig. 24-1 A, The femoral posterolateral (PL) tunnel guide with a customized arm capable of reaching either the 9-o’clock or 3-o’clock position for anatomical placement of the PL tunnel. B, Outside-in technique for preparing the PL tunnel. C, Arthroscopic view of the guide pin as it emerges on the medial wall of the lateral condyle where the PL tunnel would be positioned.

Once standard prepping and draping are completed, the tourniquet is inflated to 300 mmHg. A 3-cm vertical incision is then made, centered approximately 5 cm below the medial joint line, midway between the tibial tubercle (Gerdy’s tubercle) and the posteromedial (PM) aspect of the tibia. The sartorial fascia is incised, and the ST tendon is dissected. The tendon is completely detached from its proximal attachment with an open tendon stripper. On its tibial end, the tendon’s length is maximized, preserving as much length as possible by detaching the ST close to the bone. Ideally, a length of more than 28 cm is desired.

Arthroscopic Anterior Cruciate Ligament Reconstruction

Using standard anterolateral (AL) and AM portals, the knee joint is visualized and prepared for tunnel placements (Fig. 24-2). The anatomical footprints of the native ACL on both the femoral and tibial sides are identified. The PL femoral tunnel is initially prepared using an “outside-in” technique. To properly achieve this step, a customized PL tunnel guide is used. This customized guide has a component arm designed to reach either the 9- or 3-o’clock position. The arm of the PL guide is inserted in the AL portal and positioned at either 9 o’clock or 3 o’clock on the medial wall of the lateral condyle while the handle is maneuvered at the area of the junction of the distal femur and lateral condyle to fix the entry point for the tunnel. A guidewire is inserted from the outside, which is followed by a 4.5-mm cannulated drill to prepare the pilot hole. Once the length of this hole is measured, a 6-mm PL tunnel with its appropriate depth is drilled.

Fig. 24-2 A, Once the tibial tunnels are done, the femoral anteromedial (AM) tunnel is prepared using the AM portal. B, A 6-mm reamer is used to complete the AM tunnel.

Once the PL tunnel is completed, preparation of the AM tunnel follows. The standard technique is used to prepare the 7-mm tunnel positioned at either the 11- or 1-o’clock position. At the end of these steps, two anatomically positioned divergent tunnels are achieved.

Attention is then placed at the tibial tunnels. We prepare our tibial tunnels at an angle of 60 degrees with the entry points separated by a distance of 1 to 1.5 cm. These tunnels converge on the ligament’s footprint intraarticularly. Once the guide pins are properly positioned, the 6-mm tibial PL tunnel and the 7-mm AM tunnel are drilled accordingly.

Once the femoral and tibial tunnels are completed, the 6-mm graft is placed inside the PL tunnel and locked in position with an Endobutton. This is then followed by the placement of the 7-mm graft in the AM tunnel (Fig. 24-3). The fixation of both grafts are double-checked to determine whether they are securely anchored against the femoral cortex. At this time, it is also possible to arthroscopically check the grafts for impingement.

Fig. 24-3 A, The posterolateral (PL) bundle demonstrated here with the attached Endobutton-CL is initially inserted. B, The anteromedial (AM) bundle is then inserted. Both bundles are checked to ensure that they are properly anchored against the cortical surface of the femur.

With the femoral end of the grafts securely positioned, fixation on the tibial end is achieved using a single screw-post construct. This simple construct allows fixation of the two bundles at the prescribed angles. The AM bundle is fixed at 40 to 60 degrees of flexion while the PL bundle is fixed at full extension (Fig. 24-4).

Fig. 24-4 A, B, Tibial fixation is achieved using a post-screw construct. The anteromedial (AM) bundle is fixed at 60 degrees of flexion while the posterolateral (PL) bundle is fixed at full extension.

Prior to wound closure, the knee is examined for range of motion and stability (Fig. 24-5). Postoperatively, radiographs are taken to check the position of the grafts, and the patient is started on a standard ACL rehabilitation regimen¹⁷ (Fig. 24-6).

Fig. 24-5 A, The grafts are then checked for impingement and stability. B, The knee is also checked for full range of motion.

Fig. 24-6 Anteroposterior (AP) and lateral postoperative radiographs are taken to check the position of the grafts. Femoral fixation (yellow circle) is achieved with end buttons while tibial fixation (green circle) is secured with a screw.

Preliminary Results

Preliminary investigations comparing the results between the first 25 cases we treated with an anatomical double-bundle ACL reconstruction demonstrated that the results are comparable with those obtained with a single-bundle quadrupled ST graft, as no significant differences were noted in terms of the standard knee scales (subjective, Lysholm, Noyes, and IKDC) used at a short-term follow-up of 2 years. Computerized analysis of anterior knee translation, however, demonstrated slightly better results with the double-bundle reconstruction. In some instances in which second-look arthroscopy was performed within the first 3 months following reconstruction, sufficient stability with Lachman’s and rotational (internal and external) tests were documented. The graft was also observed to have complete vascularization at this stage.

Other Applications

Other possible applications for this technique would be the reconstruction of isolated tears of either the AM or PL bundle of the ACL. In these instances, the possibility of restoring the ligament to its original form is achieved. Furthermore, even cases previously reconstructed but with persistent instability can be revised by augmenting the in sufficient ligament with isolated reconstruction of either the AM or PL bundle. Functional recovery from such a procedure is usually fast and uneventful.

Special Considerations

The primary concern with this DBST technique is the length of the available ST autograft. Ideally, it is preferable to have a minimum of 70 mm of graft length to have at least 20 mm of graft in the femoral and tibial tunnels and 30 mm intraarticularly. Some surgeons, however, would prefer to have a graft length of 25 mm within the femoral tunnel, whereas others have reported successful outcomes with 15 mm of the graft in contact with the tunnels.¹⁷ In our experience using DBST reconstruction, a 20-mm length of graft within the AM and PL femoral tunnels is usually sufficient. With this length, the surgeon then has the option of using a 20- or 25-mm Endobutton-CL for the AM bundle and a 15- or 20-mm Endobutton-CL for the PL bundle, considering that the average AM tunnel length ranges between 40 and 45 mm, whereas PL tunnel length usually ranges from 35 to 40 mm.

Of the two femoral tunnels needed, proper placement of the PL tunnel is the more technically demanding because it can be quite a challenge to reach the 3-o’clock (or the 9-o’clock) position with an “inside-out” technique. To avoid this problem, careful attention to anatomical landmarks must be observed in both the flexed and extended position of the knee. To facilitate drilling, an “outside-in” technique is used with the aid of a PL tunnel guide. The tip of the guide’s arm is pointed at either the 9- or 3-o’clock position on the medial wall of the lateral condyle, depending on which knee is being reconstructed. The other end of the guide is directed midway through the AP plane of the junction of the distal femur and the lateral condyle to create the entry point for the pilot hole of the PL tunnel, which is angulated 20 to 30 degrees from the horizontal plane. In this position, an average PL tunnel length of 35 to 40 mm can be expected. By strictly observing these measures, problems associated with tunnel positioning can be avoided.

In instances where the semitendinosus tendon graft obtained is less than 28 cm, it is advisable to abandon the double-bundle reconstruction in favor of a triple ST reconstruction technique.

Recently, the possibility of predicting the length of the hamstring graft prior to ACL reconstruction has been achieved by using simple anthropometric measurements. Inclusion of this computation to the preoperative evaluation of the patients would facilitate the identification of the appropriate reconstruction technique to be used.

TroubleShooting

Concerns related to the performance of an anatomical double-bundle reconstruction involve the proper placement of the AM and PL tunnels. Ideally, the PL tunnel is positioned at the 3- or 9-o’clock position. To accurately do this, an “outside-in” technique should be used with a PL tunnel guide. However, other surgeons performing a double-bundle reconstruction prefer to drill the PL tunnel through an accessory AM portal. Currently, no prospective comparative studies have been made to determine which of these two techniques is better in terms of accuracy and reproducibility in preparing the PL tunnel.

Another concern associated with this technique is the risk of encountering tunnel blow-out between the adjacent walls of the closely positioned tibial or femoral tunnels. Conventional ACL techniques also carry this risk when femoral tunnels are placed too posteriorly. Therefore, with the double-bundle procedure, this risk becomes more apparent as adequate distance between the two femoral and two tibial tunnels must be maintained. In our experience, a distance of at least 1 cm between the guidewires would be sufficient to maintain the integrity of the tunnels’ adjacent wall. In addition, correct orientation of the tunnels (diverging for femoral tunnels, converging for tibial tunnels) should always be observed to minimize the chances of encountering this problem. Furthermore, even if the tibial tunnels appear to be intact immediately after drilling, there is greater risk of breaking the common wall separating the AM and PL tunnels during fixation, especially when using interference screws. Therefore, to avoid this complication we prefer to use indirect fixation for the tibial end with a screw-post construct where we can anchor the two bundles at the recommended angle of fixation.

Other useful measures to observe when preparing the PL tunnel include maintaining the guidewire after drilling the pilot hole and tunnel. Doing otherwise would make it difficult to relocate the entry point for this tunnel from the outside when passing the nitinol loop to pull the PL bundle into the tunnel.

Finally, in terms of patient positioning we prefer to have the knee positioned at 90 degrees of flexion on top of the table with the use of a lateral thigh post and a foot bar, instead of having the leg hang from the side of the table. This position offers the surgeons more room to make tunnel preparations more comfortable. At the same time, the combined position of the knee flexed at 90 degrees makes orientation easier when drilling the femoral and tibial tunnels.

At present, it is obvious that several issues remain regarding the use of an anatomical double-bundle reconstruction. Some of these include the determination of the ideal means by which to measure rotational stability (computer navigation, motion analysis, or high-speed radiography) and the identification of the specific group of patients who would benefit most from a double-bundle reconstruction procedure.

In the future, with the numerous clinical trials under way, we expect to see the long-term functional outcome of the double-bundle ACL reconstruction and to compare these results with the long-term outcome of conventional techniques currently used.