Healio
Healio
October 01, 2006
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Future of Double-bundle Anterior Cruciate Ligament (ACL) Reconstruction: Incorporation of ACL Anatomic Data into the Navigation System

Abstract

This study compares anatomy and tunnel placement during double-bundle procedures. Double-bundle anterior cruciate ligament (ACL) reconstruction reproduces both the anteromedial and posterolateral bundles. Thirty-six knees from cadavers were used for anatomic study, and 38 navigated double-bundle ACL reconstructions were evaluated for tunnel placements. With the exception of femoral tunnels of anteromedial bundles, all tunnel placements were in accordance with the anatomic measurements of the native ACL. The investigators concluded that incorporating ACL anatomic information into navigation systems would enhance double-bundle procedures.

As an orthopedic procedure, endoscopic anterior cruciate ligament (ACL) reconstruction has recently advanced; however, short-term and long-term clinical studies reveal unsatisfactory postoperative results among patients.1,2 Traditional, single-bundle ACL reconstruction procedures may produce unsatisfactory postoperative results because of the complexity of ACL functions.3,4 Anatomically, an ACL can be divided into two functional bundles, the anteromedial bundle and the posterolateral bundle.5 Both bundles provide anterior and rotational knee stability and are important in restoring normal knee kinematics.6-8

Anatomic double-bundle ACL reconstruction reconstructs anteromedial and posterolateral bundles, and improves clinical results.9-11 In previously conducted cadaveric studies,7,8 the double-bundle procedure displayed several biomechanical advantages over single-bundle procedures in terms of achieving knee kinematics and ACL graft function closer to those knee kinematics and graft functions for the normal ACL. Recently, several clinical and biomedical studies also reported the advantages of the double-bundle procedure.12-15

Despite reported advantages of double-bundle reconstruction, achieving proper tunnel placement is difficult.16 Few studies have been conducted to show femoral and tibial footprints of anteromedial and posterolateral bundles for double-bundle reconstruction.11,17,18 The traditional clockwise method that describes femoral tunnel placement is proven to be inaccurate in representing the femoral tunnel footprint of a posterolateral bundle, which is distal to each point on the clock and located vertically at the posterior outlet of the intercondylar notch.11

In the authors’ previous anatomic study,19 footprints of anteromedial and posterolateral bundles were evaluated as the basis for the reference points and were obtained under arthroscopic view.20-22 This study evaluates tunnel placements during double-bundle ACL reconstruction and compares these evaluations with anatomic data obtained in a previous study. If anatomically accurate double-bundle reconstruction was achieved, then tunnel positions were approximated to anatomic data. In the future, the incorporation of ACL anatomic information into navigation systems will enhance double-bundle reconstruction procedures.

Materials and Methods

The OrthoPilot ACL system (B. Braun Aesculap, Tuttlingen, Germany) has been used in Hirosaki University’s School of Medicine in Japan for >250 navigated ACL reconstructions since December 2003. The OrthoPilot ACL version 2.0 system evaluates tunnel placement in detail for femoral tunnel position of anteromedial and posterolateral. From July 2005 to April 2006, 55 consecutive patients received ACL reconstruction with hamstring or bone-patellar tendon-bone grafts using the navigation system. Of the patients (12 men and 26 women) included in the study, 38 received anatomic double-bundle ACL reconstruction with hamstring tendons. The average age at the time of surgery was 20.8 years (range: 14 to 56 years). One surgeon performed all ACL reconstructions and navigation procedures using an endoscopic technique. Navigation recorded information on the femoral and tibial tunnel positions of anteromedial and posterolateral bundles, and the information was subsequently compared with anatomic data, as described below.

Surgical Procedure

According to Yasuda et al,11 double-bundle ACL reconstruction anatomically reproduces anteromedial and posterolateral bundles using hamstring tendon grafts and is performed with patients under general anesthesia. Using a tendon stripper, semitendinous tendons were cut in half, and gracilis tendons were resected so that portions could be used for grafts. The proximal halves of semitendinous tendons and gracilis tendons were doubled and used for anteromedial bundle reconstruction. The distal halves of semitendinous tendons were doubled and used for posterolateral bundle reconstruction. A suture plate (B. Braun Aesculap) was attached to the proximal end of each graft using No. 5 Ethibond (Ethicon Inc, Somerville, NJ), and the length of the suture loop was matched to femoral tunnels measured during reconstruction. The distal end of each graft was connected with No. 2 Ethibond (Ethicon Inc), using grove suture methods for screw-post fixation.

After arthroscopic treatment of meniscal injury, the ACL remnant was removed, and footprints of anteromedial and posterolateral bundles were identified. Notchplasty was not performed. The tibial and femoral tunnels were then constructed under control of arthroscopic visualization and navigation. First, a tibial tunnel and a femoral tunnel for the anteromedial bundle were created. The tibial drill guide of the OrthoPilot navigation system was introduced within the joint, and the tip of the guide located in the tibial footprint of the anteromedial bundle was directed to the femoral footprint of the anteromedial bundle. The guide pin was drilled into the sleeve in the tibia, and the tibial tunnel was made with a cannulated drill corresponding to the measured diameter of the prepared graft. For the femoral socket of the anteromedial bundle, a 5-mm or 6-mm step-off guide (Arthrex, Naples, Fla) was used to confirm the center of the femoral attachment of the anteromedial bundle, defined as the anteromedial point, and the guide pin was drilled at 1:30 o’clock orientation for the left knee and at 10:30 o’clock orientation for the right knee. After the navigation system registered the anteromedial point, the femoral socket was made with a cannulated drill. Next, a tibial tunnel and femoral socket for the posterolateral bundle were created using the navigation tool. The center of the tibial attachment and femoral attachment of the posterolateral bundle, defined as the posterolateral point, was confirmed using Yasuda et al11 methods.

figure

Figure: Arthroscopic nomenclature map for femoral tunnel position. Shallow/deep and superior/inferior are used along the wall of the notch keeping the knee in flexion.20,21

After creating two tibial tunnels and two femoral sockets, the graft for the posterolateral bundle was introduced through the tibial tunnel to the femoral tunnel using a passing pin. The suture plate was flipped on the femoral cortical surface, and the graft for the anteromedial bundle was placed in the same manner. The knee was flexed and extended several times to precondition the grafts. Finally, the posterolateral and anteromedial bundles were fixed simultaneously at 10° to 15° of knee flexion using a screw and washer.

Navigation Process

Before the navigation process, preoperative radiograph measurements, including the width and anteroposterior diameter of the tibia plateau, length of Blumensaat’s line, and actual tibial and femoral graft diameters, were registered by the system. The femoral and tibial transmitters were firmly secured to the femur or tibia fixation instruments with two K-wires (2.5 mm) each. To enable the computation of the tibial exit point and the femoral insertion point of the tunnels, several extra-articular and intra-articular landmarks were registered by the system using the straight or hook pointer. The extra-articular landmarks were the tibial tuberosity, anterior edge of the tibia, and medial and lateral points of the tibial plateau. The intra-articular landmarks were the anterior edge of the posterior cruciate ligament on the tibia plateau, anterior horn of the lateral meniscus, spine of the medial intercondylar tubercle, anterior notch outlet, ACL insertion area on the femur, 12 o’clock over-the-top position, and the lateral over-the-top position. Knee kinematics between 0° to 90° of knee flexion were also registered to enable the system to correctly compute impingement and isometry of the selected tibial tunnel exit point and insertion point of the femoral tunnels.

In the revised program, different intra-articular landmarks were also needed to confirm the detail positions of the femoral tunnel, which are the medial and lateral points of the interface between bone and cartilage rather than the medial and lateral notch wall (3 and 9 o’clock positions) in the original program (ACL version 2.0). Based on the intra-articular landmarks, femoral tunnel positions were located using arthroscopic nomenclature mapping, in which shallow/deep and superior/inferior plane are used along the wall of the notch, keeping the knee in flexion (Figure 1).20,21 Femoral tunnel position data of anteromedial and posterolateral bundles were expressed in percentage in the wall of the notch, in a manner similar to that in the anatomic study described below.

Anatomic Study of the Femoral and Tibial ACL Footprint

Thirty-six knees from embalmed cadavers (average age: 78 years) were used for anatomic evaluation of footprints of anteromedial and posterolateral bundles. To expose the femoral attachment of the ACL, the femur was split in the sagittal plane using an oscillating saw through the highest point of the anterior outlet of the intercondylar notch. The anteromedial and posterolateral bundles were identified, the contour of the femoral and tibial footprints of the ACL was marked carefully, and the ACL was detached from the femur and tibia. The central footprint points of the anteromedial and posterolateral bundles on the femoral and tibial side were then identified.

The distance between the central points of the anteromedial and posterolateral footprints and the anterior edge or the medial edge of the tibial plateau was measured on the tibial side and expressed in percentages in the longitudinal distance (sagittal plane) and transverse distance (coronal plane) of the tibial plateau. The longitudinal and transverse widths of the tibial plateau were designated distance B and distance D. Distance A was defined as the distance between the central points of each bundle and anterior edge of tibial plateau along the sagittal plane of tibial plateau. Distance C was defined as the distance between the central points of each bundle and the medial edge along the coronal plane. The central points of anteromedial and posterolateral bundles were expressed as percentages (A/B% and C/D%).

Femoral reference points can be identified under arthroscopic view and also during navigation.17,22 The first point, point O, was defined as the over-the-top-position. Point A was the anterior notch outlet point, and point I, the third point, was the most inferior point of the interface between the bone and cartilage. In the sagittal plane (shallow/deep), point O and point A were used as reference points.

Distance a was defined as the distance between the central points of each bundle and point O, and distance b was defined as the distance between point A and point O along the femoral axis. The central points of anteromedial and posterolateral bundles were measured for distance from point O (from the deep plane) and were expressed as percentages (a/b%) along the femoral axis. In superior and inferior axial planes, point O and point I, respectively, were used for reference points. Distance c was defined as the distance between the central points of each bundle and point O, and distance d was defined as the distance between point I and point O. The central points of anteromedial and posterolateral bundles were measured for distance from point O (from superior) and were expressed as percentages (c/d%).

Results

Navigated double-bundle ACL reconstructions were performed successfully in all knees. Malpositioning of the tibial tunnel or femoral sockets was identified in postoperative radiographs, and complications resulting from the navigation process did not occur.

table 1

Navigation information and anatomic data of anteromedial and posterolateral bundles are summarized in Tables 1 and 2. The exit points of the anteromedial tunnel on the tibial plateau were slightly medial compared with the posterolateral bundle exit points, and more anterior than the posterolateral tunnel on the tibial plateau. Compared with anatomic data of a native ACL, tibial tunnels of both bundles were created relatively similarly to the original footprint of the anteromedial and posterolateral bundles (Table 1).

The femoral anteromedial tunnel was superior to the femoral posterolateral tunnel, and although the femoral posterolateral tunnel was created approximately at the original footprint of the posterolateral bundle, the femoral anteromedial tunnel was located deeper (near the over-the-top position) than the original footprint of the anteromedial bundle (Table 2).

table 2

Discussion

Studies show that surgeons experienced in ACL reconstruction still may achieve varying results in tunnel placement procedures. Reducing abnormal tunnel placements, which result in graft failure and a diminished range of knee motion, ensures successful ACL reconstruction.23,24 Computer-assisted surgical navigation devices recently adopted in ACL reconstruction improved the accuracy of tunnel placement.25-33 Navigation systems assist surgeons with deciding on the proper tunnel placement during surgery and with assessing the surgical procedure and knee kinematics before and after ACL reconstruction.12 Presently, however, a navigation system for double-bundle ACL reconstruction does not exist.

Several anatomic studies conducted recently assessed the anteromedial and posterolateral footprints for double-bundle reconstruction.8,11,17-19,22 Although the traditional clockwise method for description of femoral tunnel placement is relatively straightforward for surgeons, the method is inaccurate in describing the posterolateral bundle.11 The quadrant method is an optimal and reproducible method for describing the posterolateral bundle, but it is not directly applicable to arthroscopic surgery and image-free navigations because it is a radiographic assessment.34 Therefore, Watanabe et al22 developed a three-dimensional femoral tunnel evaluation, which is applicable to computer-assisted surgery. Using the three-dimensional evaluation method, the authors measured the footprint of the anteromedial and posterolateral bundles and obtained data that correlates with previous anatomic studies.19

Although double-bundle ACL reconstruction may be technically challenging for experienced surgeons, the procedure has several biomechanical and biological advantages.7-9,11 Proper tunnel placements for anatomic reproduction of the anteromedial and posterolateral bundles ensure successful results. The femoral posterolateral tunnel is considered more difficult to assess than the femoral anteromedial tunnel, because the posterolateral tunnel has no distinct landmark such as the over-the-top position. Interestingly, the femoral posterolateral tunnel was created in a manner similar to that of the original footprint of the posterolateral bundle in this study, and the femoral anteromedial tunnel was created deeper than the original footprint of the anteromedial bundle. The study used a step-off guide to identify the anteromedial point and for traditional single-bundle reconstruction, in which the femoral tunnel was created in a manner similar to that for the over-the-top position. A shallower femoral tunnel may be beneficial for the anteromedial bundle, but further study is necessary to clarify the optimal tunnel placement for double-bundle procedures.

Conclusion

Navigation has only recently been used for ACL reconstruction and will be enhanced with a program that helps surgeons identify the exact tunnel position during double-bundle procedures. Double-bundle ACL reconstruction may become an easier and reproducible procedure with the incorporation of detailed anatomic information about the ACL into the navigation system.

References

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Authors

Drs Ishibashi, Tsuda, Fukuda, Tsukada, and Toh are from Hirosaki University School of Medicine, Hirosaki, Japan.