- Email: [email protected]
Computer-Navigated Double-Bundle Anterior Cruciate Ligament Reconstruction
Computer-Navigated Double-Bundle Anterior Cruciate Ligament Reconstruction Eiichi Tsuda, MD, and Yasuyuki Ishibashi, MD Unsatisfactory results in restoring the rotatory stability in single-bundle anterior cruciate ligament (ACL) reconstruction prompted knee surgeons to develop double-bundle ACL reconstruction, in which both anteromedial and posterolateral bundles were replaced. It has been demonstrated in cadaveric studies that the combination of the anatomically replaced anteromedial and posterolateral grafts functions closer to the normal ACL. In arthroscopic surgery, however, the question how to precisely and consistently place the double-bundle grafts with anatomical orientation still remains unsolved. Although several surgical techniques specifically for the tunnel placement have been proposed for doublebundle reconstruction, the widespread standard has not been established. The aim of computer-navigated surgery is to improve accuracy and decrease the range of surgical variability. The navigation system has already been used successfully for knee endoprosthesis and is applicable to ACL surgery for determining the tunnel position. In addition, the navigation system is capable to provide the real-time data of the knee kinematics during surgery. This sophisticated technology enables surgeons to evaluate the function of the transplanted graft in vivo. This article will provide the technical details of computernavigated double-bundle ACL reconstruction. Oper Tech Sports Med 16:165-170 © 2008 Elsevier Inc. All rights reserved. KEYWORDS anterior cruciate ligament reconstruction, navigation, anteromedial bundle, posterolateral bundle
C
urrent trends in anterior cruciate ligament (ACL) reconstruction surgery focus on more anatomical oriented graft placement rather than isometric placement. Since it has been revealed that the anteromedial-bundle (AMB) and posterolateral-bundle (PLB) of the normal ACL share the biomechanical function,1,2 multibundle ACL reconstruction has been recommended to restore the normal knee kinematics.3,4 Recently, some prospective comparison studies of clinical outcomes reported better postoperative knee laxity in double-bundle reconstruction compared with single-bundle reconstruction.5-8 Placing the tunnels in the original attachment of the ACL precisely is essential to replicate the ACL anatomy, and it is one of the most important keys to take full biomechanical advantage of double-bundle ACL reconstruction. Especially, misplacement of the femoral tunnel drastically alters the graft function and behavior in double-bundle
Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Hirosaki, Japan. Address reprint requests to Eiichi Tsuda, MD, Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Zaifu-cho 5, Hirosaki, Aomori 036-8562, Japan. E-mail: [email protected]
1060-1872/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.otsm.2008.10.007
reconstruction,9,10 thus, inaccurate positioning of the femoral tunnel could result in inferior postoperative knee laxity. Computer navigation is a new technology that has been introduced in ACL reconstruction and provides surgeons real-time information to determine the position of the tunnel. It has been reported that the navigation system reduced variability in the tunnel position and postoperative knee laxity in single-bundle ACL reconstruction. Klos and colleagues11 reported that use of a 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%. Hart and colleagues12 reported that computer-navigated technique resulted in more accurate femoral tunnel placement than traditional arthroscopic technique. Eichhorn13 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 al14 showed that computer-navigated ACL reconstruction produced a smaller distance from the ideal tunnel placement to the femoral and tibial tunnels compared 165
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166 with that obtained in conventional ACL reconstruction. Plaweski et al15 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. The combination of double-bundle ACL reconstruction and computer navigation technique might more accurately replicate the anatomy and the function of the normal ACL. In this article, we will introduce the general and specific technical details of navigated double-bundle ACL reconstruction.
Surgical Procedures
Arthroscopic Preparation The standard anterolateral and anteromedial portals are established and the status of the ACL, menisci and cartilage is arthroscopically determined. The meniscus and cartilage treatment is performed before the ligament procedures when required. The ACL remnant is débrided with a radiofrequency device preserving anatomical bony contour to identify the tibial and femoral footprints of the AMB and the PLB. The remnant adhering to the posterior cruciate ligament is completely removed for registration of its anterior surface. The posterior edge of the intercondylar notch is thoroughly cleaned up for correct registration of the over-the-top position.
Setup of the Navigation System The navigation system that we use for ACL reconstruction surgery is the OrthoPilot ACL, version 2.0 (B. Braun AESCULAP, Tuttlingen, Germany), which is a kinematicbased image-free navigation system requiring no preoperative computed tomography scan images or intraoperative fluoroscopy. Two infrared cameras on the navigation system can track the position of the passive transmitter with an accuracy of less than 1 mm and 1°.16 The computer system provides surgeons not only the information for the tibial and femoral tunnel placement but also real-time knee kinematics such as the anteroposterior tibial translation, the knee extension/flexion, and the internal/external tibial rotation.17 The OrthoPilot equipment cart is positioned on the opposite side of the knee to be operated on with a distance of approximately 2 meters (Fig. 1). The infrared camera position is adjusted to the knee with help of a laser pointer contained in the camera handle. The surgical data, ie, the surgeon’s name, the patient’s name, the side to be operated, and the type and diameter of the graft structures, is entered according to the program steps. The following x-ray planning data measured on the preoperative anteroposterior and lateral x-ray images and the scale ratio is entered: (1) the anteroposterior depth of the tibial plateau, (2) the distance between the anterior edge of the tibia plateau and the spine of the medial intercondylar tubercule, (3) the width of the tibial plateau, (4) the distance between the medial edge of the tibia plateau and the spine of the medial intercondylar tubercule, and (5) the length of the Blumensaat’s line. Although this step can be skipped, we recommend performing it to ensure reliable navigation, if the x-ray images are available.
Graft Preparation The semitendinosus tendon is harvested with a tendon harvester through an anteromedial oblique skin incision. This same incision serves as the tibial tunnel entry sites for both AMB and PLB. The proximal and distal halves of the semitendinosus tendon are looped and used as the AMB and the PLB, respectively. In cases with thinner semitendinosus tendon, the gracilis tendon is harvested and added to the graft for the AMB. The looped end of the tendon is linked to a suture plate (B/Braun AESCULAP, Tuttlingen, Germany) with No. 5 Ethibond (Ethicon, Inc., Somerville, NJ) and the free ends are sutured with No. 2 Ethibond.
Registration of Anatomical Landmarks and Knee Kinematics The transmitters are fixated to the tibia and the femur after the arthroscopic treatment of the meniscus and cartilage and the preparation for the tunnel placement (Fig. 2A). Two Kwires with 2.5-mm diameter are inserted just distal of the adductor tubercle on the medial femoral condyle. The femoral transmitter is fastened to the K-wires using a fixation element. Another 2 K-wires with drilling tip are inserted to the center of the tibial penetrating the anteromedial and lateral cortices. The tibial transmitter is fastened in same manner as the femoral side. Excessively proximal placement of the tibial transmitter should be avoided so that the arthroscope-guiding hand of the operating surgeon or the tibial drill instruments do not hide the tibial transmitter from the navigation camera view. The standard extra-articular landmarks; such as the tibial tuberosity (Fig. 2), the anterior crest of the tibial shaft, and the medial and lateral edges of the tibial plateau, are registered with a straight pointer with the instrument transmitter. The extension/flexion kinematics is acquired by moving the knee from full extension to 90° of flexion. At this time point, the preoperative knee laxity can be obtained by measuring the anterior tibial translation and the tibial rotation under the clinically available knee laxity test in several flexion angles (Fig. 3). Registration of the intraarticular landmarks, such as the anterior face of the posterior cruciate ligament, the anterior horn of the lateral meniscus, the spine of the medial intercondylar tubercule, the medial and lateral walls and the anterior outlet of the intercondylar notch (Fig. 4), and the ACL footprint on the femur, are registered using the straight pointer. The 12- o’clock and lateral over-the-top positions are registered with a hook pointer (Fig. 5).
Registration of the Tunnel Position The guidewire for the tibial tunnel is inserted using the tibial drill guide with the instrument transmitter. The tip of the drill guide is set on the anteromedial and the posterolateral ACL footprint for the AMB and PLB tunnels, respectively. The tibial tunnel placement is navigated on the computer monitor (Fig. 6). A curved line and 2 straight lines, which respectively represent the registered curve of the anterior outlet and medial and lateral wall of the intercondylar notch,
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Figure 1 The set-up of the navigation system. The OrthoPilot equipment cart is positioned on the opposite side of the knee to be operated on and the infrared camera is adjusted so that the range of camera vision covers the surgical field.
are projected onto the tibia plateau with the leg in extension. A target circle indicates the tibial tunnel exit on the tibial plateau. Any overlap of the curved line and the straight lines with the target circle indicates potential notch roof or notch wall impingement and, thus, it should be avoided. The position of the tibial tunnel exit is also displayed on the anteroposterior and mediolateral percentage scales of the tibial plateau. Furthermore, the direction of the tibial tunnel reference to the proximal/distal tibial axis in the coronal and sagittal planes is shown on the displayed. The tibial tunnel direction is important to place the femoral tunnel into desired position using a transtibial endoscopic technique. From our clinical data of 38 patients who received navigated double-bundle ACL reconstruction, the tibial tunnel position was 31.1 ⫾ 9.5% on the anteroposterior scale and 44.5 ⫾ 3.9% on the mediolateral scale for the AMB tunnel, and those are 43.7 ⫾ 10.7% and 45.7 ⫾ 4.8% for the PLB tunnel.18 The diversion angles of the tibial tunnel recommended from our anatomical study are 25 to 30° in the coronal plane and 40 to 45° in the sagittal plane for the AMB tunnel and 35 to 40° and 30 to 35° for the PLB tunnel.19 After the surgeon double-checks the position and direction of the guidewire under arthroscopic view, the tibial tunnel is completed by overdrilling to the diameter of the graft. The femoral footprint of the ACL is arthroscopically identified through the anteromedial portal. The position of the
Figure 2 The transmitters are fixated to the tibia, the femur and the straight pointer (A). The tip of the pointer is stabilized by the opposite surgeon’s hand and pressed to the skin on the tibial tuberosity according to the registration program steps displayed on the monitor screen (B).
Figure 3 The navigation monitor screen during recording of the knee kinematics under the manual knee laxity test. The amount of anterior tibial translation, the tibial rotation angle and the knee flexion angle are recorded.
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E. Tsuda and Y. Ishibashi for the AMB tunnel and 39.7 ⫾ 19.9% and 45.2 ⫾ 14.5% for the PLB tunnel in our previous clinical study. Once the position of the femoral tunnel is registered, the guidewire is inserted by the surgeon using the transtibial technique, and the femoral tunnel is completed by overdrilling to the diameter of the graft and the depth of 25 to 30 mm.
Graft Fixation and Recording of the Postoperative Knee Kinematics Both AMB and PLB grafts are introduced through the tibial tunnel to the femoral tunnel with the use of a passing pin. The grafts are secured on the femur by flipping the suture plates and on the tibia by tying the Ethibond sutures to the suture mini discs (B/Braun AESCULAP, Tuttlingen, Germany) applying 40 N of the initial tension at 15° of knee
Figure 4 The arthroscopic view (A) and the navigation monitor screen (B) during the registration of the anterior outlet of the intercondylar notch.
femoral tunnels is also navigated using the transtibial femoral pointer with the instrument transmitter. The transtibial femoral pointer is aimed at the 10:30-o’clock position for the AMB tunnel (Fig. 7A), and the point, which is on the virtual vertical line drawn from the contact point between the lateral femoral condyle and the tibial plateau at 90° of knee flexion and 5 to 8 mm from the edge of the joint cartilage for the PLB.20 The “clock” position, the distance from the over-thetop position, and the deviation of the isometry are shown on the navigation monitor screen (Fig. 7B). The area with potential intercondylar roof or wall impingement is displayed as a red segment of the curve line in the right-bottom field of the screen. In addition, the femoral tunnel position in the sagittal plane is represented as the combination of the superior-inferior and deep-shallow descriptions in nomenclature mapping.18 Those values were 18.3 ⫾ 14.7% and 17.4 ⫾ 8.7%
Figure 5 The arthroscopic view (A) and the navigation monitor screen (B) during the registration of the 12 o’clock over-the-top position.
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Future of Navigated ACL Reconstruction The concept of double-bundle ACL reconstruction is to restore the function of the normal ACL by replicating the anatomy of the anteromedial and posterolateral bundles. Although several surgical techniques to determine the tunnel potion have been recommended, it is still controversial. Since the femoral footprint of the posterolateral bundle is far from the over-the-top position, it is not suitable to define the tunnel position of the posterolateral bundle using the o’clock position. Recently, the resident’s ridge, which is observed to be located anterior to the femoral footprint under arthroscopic view, is recommended as a bony landmark for the femoral tunnel placement of the posterolateral bundle.22 FurFigure 6 The navigation monitor screen for the tibial tunnel placement. The curved line turned to red indicates that the registered position of the tibial tunnel has potential intercondylar roof impingement of the graft.
flexion. The postoperative knee kinematics is recorded in the same manner it was recorded before reconstruction.
Potential Risk of Inaccurate Navigation It is indispensable for the correct and precise navigation that the transmitters keep their position and orientation throughout the entire navigation process. The displacement of the passive transmitter caused by bending or loosening of the fixation wires contributes to the misreading of the 3-dimensional position of the instruments and the knee joint and possible error in the resulting tunnel position data. The fixation elements should be fastened immediately above the skin to obtain maximum stability. The insertion position of the fixation wires should be changed when excessive skin traction occurs in any flexion angles between full extension to 90°. To minimize incautious rough hitting of the transmitters with the surgeon’s hands or surgical instruments, the transmitters are fixated to the tibia and the femur just before the procedures for the tunnel placement. If there are any discrepancies in the tunnel position between the arthroscopic view and the navigation descriptions, the surgeons should check whether the transmitters are fixed securely on the patient and the surgical instrument. The description of the tunnel position provided by the navigation system is reliable when the extra- and intraarticular anatomical landmarks are correctly registered.21 Inadequate registration of the landmarks, however, leads to misconstruction of the 3-dimensional coordinates of the knee joint. For correct registration of the extra-articular landmarks, the bony landmarks are carefully palpated, and the tip of the pointer is stabilized by the opposite surgeon’s hand and pressed to the skin on the appropriate position to compensate for the thickness of the overlying soft tissue (Fig. 1). Severely obese patients in whom it is difficult to palpate the extra-articular landmarks, especially the medial and lateral edges of the tibial plateau, should be excluded.
Figure 7 The arthroscopic view (A) and the navigation monitor screen (B) during the femoral tunnel placement. The area with potential intercondylar roof or wall impingement is displayed as a red segment of the curved line in the right-bottom field of the screen.
E. Tsuda and Y. Ishibashi
170 ther anatomical studies of the ACL footprint may provide new anatomical landmarks to be registered for more accurate and consistent placement of the tunnels in navigated doublebundle ACL reconstruction. Another advantage of computer navigation in ACL reconstruction is ability to accurately assess the real-time knee kinematics intraoperatively. Limited quantitative techniques to measure the in vivo kinematics of the ACL-reconstructed knees are available. The measurement of knee laxity under not only the simple uniplanar load but also more complex multi-planar load in the navigation system help understanding of the biomechanical characteristics of single- and multibundle grafts transplanted in different reconstruction techniques.
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References 1. Sakane M, Fox RJ, Woo SL, et al: In situ forces in the anterior cruciate ligament and its bundles in response to anterior tibial loads. J Orthop Res 15:285-293, 1997 2. Gabriel MT, Wong EK, Woo SL, et al: Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads. J Orthop Res 22:85-89, 2004 3. Yagi M, Wong EK, Kanamori A, et al: Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction. Am J Sports Med 30:660-666, 2002 4. Mae T, Shino K, Matsumoto N, et al: Force sharing between two grafts in the anatomical two-bundle anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 14:505-509, 2006 5. Järvelä T: Double-bundle versus single-bundle anterior cruciate ligament reconstruction: A prospective, randomized clinical study. Knee Surg Sports Traumatol Arthrosc 15:500-507, 2007 6. Muneta T, Koga H, Mochizuki T, et al: A prospective randomized study of 4-strand semitendinosus tendon anterior cruciate ligament reconstruction comparing single-bundle and double-bundle techniques. Arthroscopy 23:618-628, 2007 7. Yagi M, Kuroda R, Nagamune K, et al: Double-bundle ACL reconstruction can improve rotational stability. Clin Orthop Relat Res 454:100107, 2007 8. Yasuda K, Kondo E, Ichiyama H, et al: Clinical evaluation of anatomic double-bundle anterior cruciate ligament reconstruction procedure using hamstring tendon grafts: Comparisons among 3 different procedures. Arthroscopy 22:240-251, 2006 9. Zantop T, Diermann N, Schumacher T, et al: Anatomical and nonana-
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tomical double-bundle anterior cruciate ligament reconstruction: Importance of femoral tunnel location on knee kinematics. Am J Sports Med 36:678-685, 2008 Mae T, Shino K, Matsumoto N, et al: Anatomical two-bundle versus Rosenberg’s isometric bi-socket ACL reconstruction: A biomechanical comparison in laxity match pretension. Knee Surg Sports Traumatol Arthrosc 15:328-334, 2007 Klos TV, Habets RJ, Banks AZ, et al: Computer assistance in arthroscopic anterior cruciate ligament reconstruction. Clin Orthop Relat Res 354:65-69, 1998 Hart R, Krejzla J, Sváb P, et al: Outcomes after conventional versus computer-navigated anterior cruciate ligament reconstruction. Arthroscopy 24:569-578, 2008 Eichhorn J: Three years of experience with computer navigation assisted positioning of drilling tunnel in anterior cruciate ligament replacement. Arthroscopy 20:e31-e32, 2004 (suppl 1) Picard F, DiGioia AM, Moody J, et al: Accuracy in tunnel placement for ACL reconstruction. Comparison of traditional arthroscopic and computer-assisted navigation techniques. Comput Aided Surg 6:279-289, 2001 Plaweski S, Cazal J, Rosell P, et al: Anterior cruciate ligament reconstruction using navigation: A comparative study on 60 patients. Am J Sports Med 34:542-552, 2006 Koh J, Koo SS, Leonard J, et al: Anterior cruciate ligament (ACL) tunnel placement: A radiographic comparison between navigated versus manual ACL reconstruction. Orthopedics 29:S122-S124, 2006 (10 suppl) Ishibashi Y, Tsuda E, Fukuda A, et al: Intra-operative biomechanical evaluation of anatomical anterior cruciate ligament reconstruction using a navigation system: Comparison between hamstring tendon and bone-patellar tendon-bone graft. Am J Sports Med 36:1903-1912, 2008 Ishibashi Y, Tsuda E, Fukuda A, et al: Future of double-bundle anterior cruciate ligament (ACL) reconstruction: Incorporation of ACL anatomic data into the navigation system. Orthopedics 29:S108-112, 2006 (10 suppl) Ishibashi Y, Tsuda E, Sato H, et al: Anatomical study of appropriate tibial tunnel direction for anatomic femoral tunnel placement and lateral femoral tunnel placement. J Japan Arthrosc Assoc 29:39-43, 2004 Yasuda K, Kondo E, Ichiyama H, et al: Anatomic reconstruction of the anteromedial and posterolateral bundles of the anterior cruciate ligament using hamstring tendon grafts. Arthroscopy 20:1015-1025, 2004 Tsuda E, Ishibashi Y, Fukuda A, et al: Validation of computer-assisted double-bundle anterior cruciate ligament reconstruction. Orthopedics 30:S136-S140, 2007 (10 suppl) Ferretti M, Ekdahl M, Shen W, et al: Osseous landmarks of the femoral attachment of the anterior cruciate ligament: An anatomic study. Arthroscopy 23:1218-1225, 2007
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urrent trends in anterior cruciate ligament (ACL) reconstruction surgery focus on more anatomical oriented graft placement rather than isometric placement. Since it has been revealed that the anteromedial-bundle (AMB) and posterolateral-bundle (PLB) of the normal ACL share the biomechanical function,1,2 multibundle ACL reconstruction has been recommended to restore the normal knee kinematics.3,4 Recently, some prospective comparison studies of clinical outcomes reported better postoperative knee laxity in double-bundle reconstruction compared with single-bundle reconstruction.5-8 Placing the tunnels in the original attachment of the ACL precisely is essential to replicate the ACL anatomy, and it is one of the most important keys to take full biomechanical advantage of double-bundle ACL reconstruction. Especially, misplacement of the femoral tunnel drastically alters the graft function and behavior in double-bundle
Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Hirosaki, Japan. Address reprint requests to Eiichi Tsuda, MD, Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Zaifu-cho 5, Hirosaki, Aomori 036-8562, Japan. E-mail: [email protected]
1060-1872/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.otsm.2008.10.007
reconstruction,9,10 thus, inaccurate positioning of the femoral tunnel could result in inferior postoperative knee laxity. Computer navigation is a new technology that has been introduced in ACL reconstruction and provides surgeons real-time information to determine the position of the tunnel. It has been reported that the navigation system reduced variability in the tunnel position and postoperative knee laxity in single-bundle ACL reconstruction. Klos and colleagues11 reported that use of a 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%. Hart and colleagues12 reported that computer-navigated technique resulted in more accurate femoral tunnel placement than traditional arthroscopic technique. Eichhorn13 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 al14 showed that computer-navigated ACL reconstruction produced a smaller distance from the ideal tunnel placement to the femoral and tibial tunnels compared 165
E. Tsuda and Y. Ishibashi
166 with that obtained in conventional ACL reconstruction. Plaweski et al15 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. The combination of double-bundle ACL reconstruction and computer navigation technique might more accurately replicate the anatomy and the function of the normal ACL. In this article, we will introduce the general and specific technical details of navigated double-bundle ACL reconstruction.
Surgical Procedures
Arthroscopic Preparation The standard anterolateral and anteromedial portals are established and the status of the ACL, menisci and cartilage is arthroscopically determined. The meniscus and cartilage treatment is performed before the ligament procedures when required. The ACL remnant is débrided with a radiofrequency device preserving anatomical bony contour to identify the tibial and femoral footprints of the AMB and the PLB. The remnant adhering to the posterior cruciate ligament is completely removed for registration of its anterior surface. The posterior edge of the intercondylar notch is thoroughly cleaned up for correct registration of the over-the-top position.
Setup of the Navigation System The navigation system that we use for ACL reconstruction surgery is the OrthoPilot ACL, version 2.0 (B. Braun AESCULAP, Tuttlingen, Germany), which is a kinematicbased image-free navigation system requiring no preoperative computed tomography scan images or intraoperative fluoroscopy. Two infrared cameras on the navigation system can track the position of the passive transmitter with an accuracy of less than 1 mm and 1°.16 The computer system provides surgeons not only the information for the tibial and femoral tunnel placement but also real-time knee kinematics such as the anteroposterior tibial translation, the knee extension/flexion, and the internal/external tibial rotation.17 The OrthoPilot equipment cart is positioned on the opposite side of the knee to be operated on with a distance of approximately 2 meters (Fig. 1). The infrared camera position is adjusted to the knee with help of a laser pointer contained in the camera handle. The surgical data, ie, the surgeon’s name, the patient’s name, the side to be operated, and the type and diameter of the graft structures, is entered according to the program steps. The following x-ray planning data measured on the preoperative anteroposterior and lateral x-ray images and the scale ratio is entered: (1) the anteroposterior depth of the tibial plateau, (2) the distance between the anterior edge of the tibia plateau and the spine of the medial intercondylar tubercule, (3) the width of the tibial plateau, (4) the distance between the medial edge of the tibia plateau and the spine of the medial intercondylar tubercule, and (5) the length of the Blumensaat’s line. Although this step can be skipped, we recommend performing it to ensure reliable navigation, if the x-ray images are available.
Graft Preparation The semitendinosus tendon is harvested with a tendon harvester through an anteromedial oblique skin incision. This same incision serves as the tibial tunnel entry sites for both AMB and PLB. The proximal and distal halves of the semitendinosus tendon are looped and used as the AMB and the PLB, respectively. In cases with thinner semitendinosus tendon, the gracilis tendon is harvested and added to the graft for the AMB. The looped end of the tendon is linked to a suture plate (B/Braun AESCULAP, Tuttlingen, Germany) with No. 5 Ethibond (Ethicon, Inc., Somerville, NJ) and the free ends are sutured with No. 2 Ethibond.
Registration of Anatomical Landmarks and Knee Kinematics The transmitters are fixated to the tibia and the femur after the arthroscopic treatment of the meniscus and cartilage and the preparation for the tunnel placement (Fig. 2A). Two Kwires with 2.5-mm diameter are inserted just distal of the adductor tubercle on the medial femoral condyle. The femoral transmitter is fastened to the K-wires using a fixation element. Another 2 K-wires with drilling tip are inserted to the center of the tibial penetrating the anteromedial and lateral cortices. The tibial transmitter is fastened in same manner as the femoral side. Excessively proximal placement of the tibial transmitter should be avoided so that the arthroscope-guiding hand of the operating surgeon or the tibial drill instruments do not hide the tibial transmitter from the navigation camera view. The standard extra-articular landmarks; such as the tibial tuberosity (Fig. 2), the anterior crest of the tibial shaft, and the medial and lateral edges of the tibial plateau, are registered with a straight pointer with the instrument transmitter. The extension/flexion kinematics is acquired by moving the knee from full extension to 90° of flexion. At this time point, the preoperative knee laxity can be obtained by measuring the anterior tibial translation and the tibial rotation under the clinically available knee laxity test in several flexion angles (Fig. 3). Registration of the intraarticular landmarks, such as the anterior face of the posterior cruciate ligament, the anterior horn of the lateral meniscus, the spine of the medial intercondylar tubercule, the medial and lateral walls and the anterior outlet of the intercondylar notch (Fig. 4), and the ACL footprint on the femur, are registered using the straight pointer. The 12- o’clock and lateral over-the-top positions are registered with a hook pointer (Fig. 5).
Registration of the Tunnel Position The guidewire for the tibial tunnel is inserted using the tibial drill guide with the instrument transmitter. The tip of the drill guide is set on the anteromedial and the posterolateral ACL footprint for the AMB and PLB tunnels, respectively. The tibial tunnel placement is navigated on the computer monitor (Fig. 6). A curved line and 2 straight lines, which respectively represent the registered curve of the anterior outlet and medial and lateral wall of the intercondylar notch,
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Figure 1 The set-up of the navigation system. The OrthoPilot equipment cart is positioned on the opposite side of the knee to be operated on and the infrared camera is adjusted so that the range of camera vision covers the surgical field.
are projected onto the tibia plateau with the leg in extension. A target circle indicates the tibial tunnel exit on the tibial plateau. Any overlap of the curved line and the straight lines with the target circle indicates potential notch roof or notch wall impingement and, thus, it should be avoided. The position of the tibial tunnel exit is also displayed on the anteroposterior and mediolateral percentage scales of the tibial plateau. Furthermore, the direction of the tibial tunnel reference to the proximal/distal tibial axis in the coronal and sagittal planes is shown on the displayed. The tibial tunnel direction is important to place the femoral tunnel into desired position using a transtibial endoscopic technique. From our clinical data of 38 patients who received navigated double-bundle ACL reconstruction, the tibial tunnel position was 31.1 ⫾ 9.5% on the anteroposterior scale and 44.5 ⫾ 3.9% on the mediolateral scale for the AMB tunnel, and those are 43.7 ⫾ 10.7% and 45.7 ⫾ 4.8% for the PLB tunnel.18 The diversion angles of the tibial tunnel recommended from our anatomical study are 25 to 30° in the coronal plane and 40 to 45° in the sagittal plane for the AMB tunnel and 35 to 40° and 30 to 35° for the PLB tunnel.19 After the surgeon double-checks the position and direction of the guidewire under arthroscopic view, the tibial tunnel is completed by overdrilling to the diameter of the graft. The femoral footprint of the ACL is arthroscopically identified through the anteromedial portal. The position of the
Figure 2 The transmitters are fixated to the tibia, the femur and the straight pointer (A). The tip of the pointer is stabilized by the opposite surgeon’s hand and pressed to the skin on the tibial tuberosity according to the registration program steps displayed on the monitor screen (B).
Figure 3 The navigation monitor screen during recording of the knee kinematics under the manual knee laxity test. The amount of anterior tibial translation, the tibial rotation angle and the knee flexion angle are recorded.
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E. Tsuda and Y. Ishibashi for the AMB tunnel and 39.7 ⫾ 19.9% and 45.2 ⫾ 14.5% for the PLB tunnel in our previous clinical study. Once the position of the femoral tunnel is registered, the guidewire is inserted by the surgeon using the transtibial technique, and the femoral tunnel is completed by overdrilling to the diameter of the graft and the depth of 25 to 30 mm.
Graft Fixation and Recording of the Postoperative Knee Kinematics Both AMB and PLB grafts are introduced through the tibial tunnel to the femoral tunnel with the use of a passing pin. The grafts are secured on the femur by flipping the suture plates and on the tibia by tying the Ethibond sutures to the suture mini discs (B/Braun AESCULAP, Tuttlingen, Germany) applying 40 N of the initial tension at 15° of knee
Figure 4 The arthroscopic view (A) and the navigation monitor screen (B) during the registration of the anterior outlet of the intercondylar notch.
femoral tunnels is also navigated using the transtibial femoral pointer with the instrument transmitter. The transtibial femoral pointer is aimed at the 10:30-o’clock position for the AMB tunnel (Fig. 7A), and the point, which is on the virtual vertical line drawn from the contact point between the lateral femoral condyle and the tibial plateau at 90° of knee flexion and 5 to 8 mm from the edge of the joint cartilage for the PLB.20 The “clock” position, the distance from the over-thetop position, and the deviation of the isometry are shown on the navigation monitor screen (Fig. 7B). The area with potential intercondylar roof or wall impingement is displayed as a red segment of the curve line in the right-bottom field of the screen. In addition, the femoral tunnel position in the sagittal plane is represented as the combination of the superior-inferior and deep-shallow descriptions in nomenclature mapping.18 Those values were 18.3 ⫾ 14.7% and 17.4 ⫾ 8.7%
Figure 5 The arthroscopic view (A) and the navigation monitor screen (B) during the registration of the 12 o’clock over-the-top position.
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Future of Navigated ACL Reconstruction The concept of double-bundle ACL reconstruction is to restore the function of the normal ACL by replicating the anatomy of the anteromedial and posterolateral bundles. Although several surgical techniques to determine the tunnel potion have been recommended, it is still controversial. Since the femoral footprint of the posterolateral bundle is far from the over-the-top position, it is not suitable to define the tunnel position of the posterolateral bundle using the o’clock position. Recently, the resident’s ridge, which is observed to be located anterior to the femoral footprint under arthroscopic view, is recommended as a bony landmark for the femoral tunnel placement of the posterolateral bundle.22 FurFigure 6 The navigation monitor screen for the tibial tunnel placement. The curved line turned to red indicates that the registered position of the tibial tunnel has potential intercondylar roof impingement of the graft.
flexion. The postoperative knee kinematics is recorded in the same manner it was recorded before reconstruction.
Potential Risk of Inaccurate Navigation It is indispensable for the correct and precise navigation that the transmitters keep their position and orientation throughout the entire navigation process. The displacement of the passive transmitter caused by bending or loosening of the fixation wires contributes to the misreading of the 3-dimensional position of the instruments and the knee joint and possible error in the resulting tunnel position data. The fixation elements should be fastened immediately above the skin to obtain maximum stability. The insertion position of the fixation wires should be changed when excessive skin traction occurs in any flexion angles between full extension to 90°. To minimize incautious rough hitting of the transmitters with the surgeon’s hands or surgical instruments, the transmitters are fixated to the tibia and the femur just before the procedures for the tunnel placement. If there are any discrepancies in the tunnel position between the arthroscopic view and the navigation descriptions, the surgeons should check whether the transmitters are fixed securely on the patient and the surgical instrument. The description of the tunnel position provided by the navigation system is reliable when the extra- and intraarticular anatomical landmarks are correctly registered.21 Inadequate registration of the landmarks, however, leads to misconstruction of the 3-dimensional coordinates of the knee joint. For correct registration of the extra-articular landmarks, the bony landmarks are carefully palpated, and the tip of the pointer is stabilized by the opposite surgeon’s hand and pressed to the skin on the appropriate position to compensate for the thickness of the overlying soft tissue (Fig. 1). Severely obese patients in whom it is difficult to palpate the extra-articular landmarks, especially the medial and lateral edges of the tibial plateau, should be excluded.
Figure 7 The arthroscopic view (A) and the navigation monitor screen (B) during the femoral tunnel placement. The area with potential intercondylar roof or wall impingement is displayed as a red segment of the curved line in the right-bottom field of the screen.
E. Tsuda and Y. Ishibashi
170 ther anatomical studies of the ACL footprint may provide new anatomical landmarks to be registered for more accurate and consistent placement of the tunnels in navigated doublebundle ACL reconstruction. Another advantage of computer navigation in ACL reconstruction is ability to accurately assess the real-time knee kinematics intraoperatively. Limited quantitative techniques to measure the in vivo kinematics of the ACL-reconstructed knees are available. The measurement of knee laxity under not only the simple uniplanar load but also more complex multi-planar load in the navigation system help understanding of the biomechanical characteristics of single- and multibundle grafts transplanted in different reconstruction techniques.
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