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Validation of Computer-assisted Double-bundle Anterior Cruciate Ligament Reconstruction

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Abstract

The goal of this study was to establish the reliability of a navigation system for femoral tunnel placement in arthroscopic double-bundle anterior cruciate ligament (ACL) reconstruction. Guidewires were inserted to the center of the anteromedial and posterolateral femoral tunnels of eight porcine knees using an image-free navigation system. The relative position of the guidewires in reference to the height and depth of the lateral condyle was determined by the navigation system and a digital camera and compared. The average differences in high-low and deep-shallow position between the two measurement systems were 2.6%±1.3% (range, 0.6%-4.9%) and 1.6%±1.4% (range, 0.1%-4.0%) for the anteromedial tunnels and 2.7%±1.4% (range, 0%-3.9%) and 2.6%±1.3% (range, 1.1%-4.3%) for the posterolateral tunnels. The data suggest that the navigation system provided surgeons with reliable information to determine the femoral tunnel location in arthroscopic double-bundle ACL reconstruction.

Because it has been shown that a more anatomically oriented anterior cruciate ligament (ACL) graft is required to obtain biomechanical function closer to the natural ACL,¹ multibundle reconstruction has begun to replace conventional single-bundle reconstruction as the technique of choice. Recent biomechanical studies demonstrate that anteromedial and posterolateral grafts transplanted in an ideal location in double-bundle ACL reconstruction share the resultant force in several loading conditions similar to that of the original bundles in a healthy knee.^2,3 Although the ideal tunnel position has not been determined, it is a key factor in double-bundle ACL reconstruction. During arthroscopic reconstruction, surgeons determine the tunnel placement in reference to intraarticular anatomic landmarks, such as footprints of the native ACL, bony geometry of the tibial plateau and femoral condyle, and insertions of menisci and anterior edge of the posterior cruciate ligament (PCL), under arthroscopy view. Placing the tibial tunnel too anteriorly must be avoided to prevent intercondylar roof impingement that may cause loss of knee extension as well as laceration of the transplanted graft. However, misplacement of the tibial tunnel does not occur frequently, because the tibial ACL remnant remains in normal appearance in most ACL-deficient knees and it helps surgeons to place the tibial tunnel correctly. In contrast, femoral attachment of the ACL is frequently injured by peeling off from the lateral condyle and obscured by coverage and adhesion with scar tissue formation. This limited anatomic information makes it difficult to identify proper femoral tunnel position. Furthermore, small alternations of the femoral tunnel position affect tensioning pattern and force distribution of the grafts.^4,5 Several surgical techniques for double-bundle ACL reconstruction have been reported^6-8; however, a gold standard that ensures precise and uniform placement of the femoral tunnels to anatomic insertions of anteromedial and posterolateral bundles has not been established.

Image-free navigation is a new technology in ACL reconstruction, providing surgeons with real-time information to determine tunnel position. Potential errors related to registration of the extraarticular and intraarticular anatomic landmarks, however, often lead to incorrect description of the tunnel position. The purpose of this study was to validate the tunnel position obtained from the navigation system in arthroscopic double-bundle ACL reconstruction by comparing to the position evaluated with a digital camera.

Materials and Methods

Specimen Preparation

Eight porcine knees were used in this study. The hip and ankle joints were transected, and all soft tissues except ligaments, menisci, and joint capsule were removed. The lateral capsule was longitudinally incised, and the intrapatellar fat pad was resected to obtain the intraarticular working space and clear visualization. The ACL was transected at the femoral and tibial attachment. To obtain 0° of knee flexion, the meniscofemoral ligament was released at the femoral attachment. The knee joint was masked with a tubular drape so that the inside of the joint was completely obscured from direct visualization.

Navigation Procedures

The kinematic-based image-free navigation system (OrthoPilot, B. Braun Aesculap, Tuttlingen, Germany) with ACL software version 2.0 was used. The reference fixator was fixed to the femur and the tibia with 2.5-mm K wires. The standard extraarticular landmarks, such as the tibial tuberosity, the anterior crest of the tibia, and the medial and lateral edge of the tibial plateau, were registered. Registration of the intraarticular landmarks, such as the anterior face of the PCL; the anterior horn of the lateral meniscus; the medial tibial eminence; the osteocartilage transition line of the medial and lateral femoral condyle (3 o’clock and 9 o’clock positions); the anterior outlet of the intercondylar notch; the ACL footprint on the femur; the 12 o’clock over-the-top position; and the lateral over-the-top position; were performed under lateral infrapatellar arthroscopic view (Figure 1). The center of the femoral tunnels for the anteromedial and posterolateral bundles were registered using the femoral punch with a tracking reference. Two 1.2-mm K wires were inserted from the center of the tunnel for the anteromedial and posterolateral bundles via the medial infrapatellar portal. The K wires were advanced so that the bottom of the wires was flush with the intercondylar cortex of the lateral condyle. Then the femoral condyle was cut in the sagittal plane through the intercondylar midline, and the medial aspect of the lateral condyle was photographed using a digital camera (EOS20D; Canon, Tokyo, Japan).

Evaluation of Tunnel Position Using the Navigation System

For the description of the tunnel position in the sagittal plane, the direction parallel to the femoral shaft axis was defined as deep and shallow, and the direction perpendicular to the femoral shaft axis was defined as high and low for convenience in arthroscopic view. The position of the center of the femoral tunnel was represented as the combination of the high-low and deep-shallow descriptions. The following reference points and parameters were defined according to the methods described by Watanabe (Figure 2)⁹ as follows:

1. Reference point O: 12 o’clock over-the-top position.
2. Reference point A: highest point of the anterior outlet edge of the intercondylar notch.
3. Reference point I: lowest point of the osteocartilage transition line of the lateral femoral condyle (3 o’clock in right knee and 9 o’clock in left knee).
4. Distance A was measured parallel to the femoral shaft axis between the center of the femoral tunnel and point O.
5. Distance B was measured parallel to the femoral shaft axis between point A and point O.
6. Distance C was measured perpendicular to the anteroposterior axis between the center of the femoral tunnel and point O.
7. Distance D was measured perpendicular to the anteroposterior axis between point I and point O.

Ratios A/B and C/D defined deep-shallow and high-low positions of the center of the femoral tunnel.

Evaluation of Tunnel Position Using the Digital Camera System

The photographic data from the digital camera was loaded into a personal computer. The reference points and the parameters noted previously were determined on the photographs using graphic software (CanvasX, ACD Systems of America, Miami, Fla). The ratios A/B and C/D were determined and compared with those obtained from the navigation system, and the relationship was statistically analyzed.

Results

Measurement data obtained from the navigation system and the digital camera system are presented in Table 1 for the anteromedial tunnel and in Table 2 for the posterolateral tunnel. For the anteromedial tunnel, the absolute value of the difference between the navigation system and the digital camera system was 2.6%±1.3% (range, 0.6%-4.9%) for the high-low position and 1.6%±1.4% (range, 0.1%-4.0%) for the deep-shallow position. For the posterolateral tunnel, the value was 2.7±1.4% (range, 0%-3.9%) for the high-low position and 2.6%±1.3% (range, 1.1%-4.3%) for the deep-shallow position. Statistical analysis showed a strong correlation coefficient between the measurement data from two systems (Figure 3).

Discussion

Navigation systems provide additional information for correct placement of the bone tunnel in arthroscopic ACL reconstruction.^10-13 Unbiased data from navigation systems help reduce variability in the tunnel position for surgeons as well as help produce successful patient outcomes. Furthermore, the navigation system is a valuable tool in obtaining kinematics data related to the knee laxity in response to anteroposterior and rotatory loads during surgery.^14-16 Klos et al¹⁷ reported that use of the computer-assisted system associated with fluoroscopy statistically reduced the standard deviation (SD) of the tibial tunnel placement from 6% to 3% and the SD of the femoral tunnel placement from 9% to 3%. Eichhorn¹⁸ demonstrated that navigated ACL reconstruction improved the tibial tunnel placement from a position considered overly posterior and the femoral tunnel placement from a position considered overly vertical compared with nonnavigated ACL reconstruction. Picard et al¹⁹ showed that computer-assisted ACL reconstruction produced a smaller distance from the ideal tunnel placement to the femoral and tibial tunnels compared with that obtained in conventional ACL reconstruction. Plaweski et al²⁰ reported that the variability of the postoperative laxity in the ACL-reconstructed knee was significantly smaller in navigated surgery compared with that in nonnavigated surgery. However, the question of how accurately the navigation system measures tunnel position remains.

The navigation system, using infrared cameras to track the reflective markers fixed on the surgical instruments, the femur, and the tibia, is accurate within 1 mm and 1° of variance.²¹ During surgery, however, potential microdisplacement of the reflective markers caused by bending or loosening of the fixation wires contributes to the misreading of the 3-dimensional (3D) position of the instruments and the knee joint and possible error in the resulting data about the tunnel position. Furthermore, inadequate registration of the extraarticular and intraarticular landmarks leads to misconstruction of the 3D coordinate of the knee joint. The goal of this study was to establish the reliability of navigated placement of the femoral tunnel in arthroscopic double-bundle ACL reconstruction. We determined the relative position of the femoral tunnel in reference to the height and depth of the lateral condyle and compared those in the navigation system and in the digital camera system. The difference in both high-low and deep-shallow positions of the anteromedial and posterolateral tunnels between the two systems was less than 5%. The data suggested that the description of the femoral tunnel position provided by the navigation system is reliable for choosing tunnel location. Panisset²² demonstrated an excellent correlation between the computer data and radiographic measurement of the femoral tunnel position, supporting the results obtained in this report.

The first limitation of this study was that the porcine specimens were used instead of human cadavers. The size and shape of porcine knees are different from those of human knees and this may be a factor in the 3D coordinate of the knee joint. The second limitation was that the soft tissues surrounding the knee joint were removed, a procedure not performed in standard surgery. Registration of the extraarticular landmarks without interposition of the soft tissues was easier to perform, and there was less mislocation. Furthermore, rejection of the traction of the fixation wire by deformed surrounding soft tissues could prevent the microdisplacement of the reflective markers and reduce misreading.

This study did not address the issue of optimal location of the tunnel in double-bundle ACL reconstruction. In combination with the knee kinematics data during surgery, however, a navigation system that measures the tunnel position with high accuracy helps the surgeon determine the desirable tunnel location so that the anteromedial and posterolateral grafts function properly. Additional information to establish more sophisticated double-bundle ACL reconstruction could be obtained from the navigation system.

References

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Authors

Drs Tsuda, Ishibashi, Fukuda, Tsukada, and Toh are from the Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Hirosaki, Japan.

Correspondence should be addressed to: Eiichi Tsuda, MD, Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Zaifu-cho 5, Hirosaki, Aomori 036-8562, Japan.

Drs Tsuda, Ishibashi, Fukuda, Tsukada, and Toh have no financial relationships to disclose.