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Precision of Tunnel Execution in Navigated Anterior Cruciate Ligament Reconstruction
Precision of Tunnel Execution in Navigated Anterior Cruciate Ligament Reconstruction Jason L. Koh, MD,* and Dukhwan Ko, MD† Anterior cruciate ligament (ACL) reconstruction is one of the most common orthopedic procedures in sports medicine. As the number of ACL reconstructions have increased, ACL revision surgery is increasing. Nonanatomic femoral and tibial tunnel placement is an important cause of failure of ACL reconstruction. Unfortunately, accurate tunnel placement can be difficult with current techniques, even for experienced surgeons. Computer-assisted surgery and navigation system can provide precise information about tunnel location and impingement, and may reduce the rate of revision surgery. The operative technique and the results of ACL reconstruction with navigation are described. Oper Tech Orthop 18:158-165 © 2008 Elsevier Inc. All rights reserved. KEYWORDS anterior cruciate ligament reconstruction, computer-assisted surgery, navigation, tunnel
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nterior cruciate ligament (ACL) reconstruction is one of the most common procedures performed by orthopaedic surgeons. Approximately 175,000 ACL reconstructions are performed annually in the United States, with a cost of more than 1 billion dollars.1,2 In addition, the number of surgeons performing the ACL reconstruction has increased. However, 80% of ACL reconstructions are conducted by orthopaedic surgeons whose experience is limited to fewer than 20 cases in a year.3 For these reasons, numbers of revision surgery are increasing accordingly. Estimates of the rate of revision surgery are as high as 10 –20%, potentially resulting in more than 35,000 revisions a year.1 Most revisions are related to technical errors, primarily tunnel placement.4 Multiple studies have documented that the locations of the femoral and tibial tunnels have significant effects on the knee and that accuracy in tunnel positioning is essential for the success of ACL reconstruction.4-18 The most common error in ACL reconstruction has historically been a femoral tunnel that is too anterior.5,6 Anterior femoral tunnel placement leads to excessive tension on the graft in flexion, resulting in restriction of knee flexion and eventual stretching of the
*Department of Orthopaedic Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL. †Department of Orthopaedic Surgery, School of Medicine, Konkuk University, Chungju, Korea. Address reprint requests to Jason L. Koh, MD, Department of Orthopaedic Surgery, Feinberg School of Medicine, Northwestern University, 676N Saint Clair, 13th Floor, Chicago, IL 60611. E-mail: drjasonkoh@ gmail.com
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graft.5,7 In addition to sagittal positioning of the femoral tunnel, coronal tunnel positioning has been emphasized for rotational stability to prevent the pivot shift phenomenon. An oblique placement of the femoral tunnel near the 10-o’clock position rather than a more vertical placement is important in restoring rotational stability of the knee joint.8,19,20 A tibial tunnel that is too far anterior is associated with impingement on the intercondylar notch.7,10,17,18 This impingement against the roof of the intercondylar notch has been correlated with eventual graft failure11 and the formation of a “Cyclops” lesion.21 Anterior tibial tunnels are associated with significant loss of both flexion and extension.17 Tibial tunnels that are too far posterior may lead to excessive strain in extension, impingement on the posterior cruciate ligament (PCL), and subsequent loss of flexion.5,9,19,22 Excessive medial placement of tibial tunnel may result in impingement on the PCL and has been associated with loss of flexion.17 Excessive lateral placement may cause lateral notch impingement and has been associated with synovitis and laxity.16 Inappropriate tunnel placement result in graft stretching, impingement, loss of motion, increased laxity, synovitis, pain, poor clinical outcome, higher rates of graft failure, revision, and osteoarthritis over time.4-7,9,11-14,16,23 There has been a tremendous focus on improving the accuracy of tunnel position. Unfortunately, accurate tunnel placement remains difficult with current arthroscopic techniques, even for experienced surgeons.6,24-26 The need for increasing accuracy in tunnel placement has led to the application of computer-assisted surgery for ACL reconstruction.
Precision of tunnel execution in navigated ACL
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Surgical Technique Image-Free, Wireless Navigation System and Setup OrthoPilot (B. Braun-Aesculap, Tuttlingen, Germany) (Fig. 1) is an image-free, wireless navigation system that does not require preoperative computed tomography, radiographic data, or intraoperative fluoroscopy. An infrared camera can track the position of markers of the femur, tibia, and pointer used in the surgery to ⬍1 mm and ⬍1° combined with a computer system. Real-time information about knee position, tip of pointer and guide, and anterior translation and rotational stability is provided. The OrthoPilot is designed to be used with any type of graft chosen by the physician.
Setup, Diagnostic Arthroscopy, Graft Preparation, and Notchpalsty The OrthoPilot system is positioned opposite the side of the operative leg, and the camera is positioned approximately 2 meters away. Patient identification and the type and size of the graft are input into the computer. A standard knee arthroscopy is performed, and any intraarticular pathology, such as a meniscal tear, is addressed. Ruptured ACL stump is removed, and if the notch is narrow, notchplasty is performed with shaver or burr. Graft harvest is performed according to the preference of the surgeon or the patient.
Figure 2 Femoral and tibial markers are attached to 2 K-wires inserted into the distal femur and tibia.
Fixation of Reflective Markers After preparation of the graft and notchplasty, two 2.5 mm ⫻ 100 mm K-wires are inserted percutaneously into the distal femur and antero-medial aspect of the tibia, and rigid bodies with reflective markers are secured to the K-wires. These markers are positioned to be recognized by the infrared camera throughout the procedure (Fig. 2).
Registration of Extra-Articular Anatomical Landmarks Once infrared camera recognizes the markers of femur and tibia, begin identifying the anatomical landmarks starting with the tibia. Attach another marker to the straight pointer, and register the following extra-articular landmarks into the computer with a click of a foot pedal (Fig. 3): 1. Tibial tuberosity. 2. Anterior edge of tibia 3. Medial edge and lateral edge of tibial plateau
Kinematics Acquisition Kinematic data on the location of the tibia and femur are acquired with registering the position of the knee in 90° of flexion and extension. The leg is slowly moved from extension to 90° of flexion for the kinematic data acquisition (Fig. 4).
Preoperative Stability Test
Figure 1 The OrthoPilot is an image-free wireless navigation system that does not require preoperative computed tomography, radiographic data, or intraoperative fluoroscopy.
Preoperative knee stability can be assessed by application of manual anterior translation and internal and external forces at a specific angle (usually 30° of flexion). Lachman test anterior translation at 30° of flexion and the degree of internal and external rotation is then measured and recorded (Fig. 5). Additional anteroposterior translation and rotational data also can be collected.
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Figure 3 The (A) tibial tuberosity, (B) anterior edge of the tibia, and (C) medial and (D) lateral edge of the tibial plateau are registered.
Registration of Intra-Articular Anatomical Landmarks Registering intra-articular landmarks are necessary to enable the computation of the tibial exit point and femoral tunnel position. Place the pointer with marker into the anteromedial working portal and register the following intra-articular landmarks (Figs. 6 and 7): 1. Anterior edge of the posterior cruciate ligament on the tibial plateau. 2. Posterior edge of the anterior horn of the lateral meniscus 3. Medial intercondylar eminence 4. Margin of intercondylar notch outlet 5. Margin of ACL femoral footprint 6. 12-o’clock over-the-top position (use hook pointer) 7. Lateral over-the-top position (use hook pointer)
Navigation for Tunnel Placement After registering all the landmarks, navigation of the tibial tunnel location is performed with use of the navigated tibial
drill guide with marker. On the tibial side, the precise location of the tip of tibial guide is identified in relation to the PCL, lateral meniscus, medial tibial eminence, and the location is shown as the percentage of the coronal and sagittal diameters of tibial plateau in real time. The system computes and displays the projection of the femoral notch onto the tibial plateau. Sagittal and coronal angulation of drill guide is also shown on the display (Fig. 8). The surgeon therefore can adjust the tibial drill guide tip to obtain the most ideal location of the tunnel using aforementioned information. The tibial guide pin is drilled, and the tibial exit point is registered. After the tibial tunnel is drilled, the femoral starting point is then evaluated with the pointer for distance from the over-the-top position, on the clock face location. In addition, the isometry and potential impingement (or estimated clearance) of the graft are calculated and displayed in real time (Fig. 9). If correct femoral insertion point cannot be approached with the transtibial guide, one should change to the transportal technique for femoral
Precision of tunnel execution in navigated ACL
Figure 4 Kinematic data are acquired with (A) 90° of flexion, (B) extension, and (C) motion from extension through 90° of flexion. Accurate tracking of the tibia and femur are assessed during kinematic acquisition (D).
Figure 5 Preoperative stability is measured. (A) Initial screen where the knee flexion angle for stability testing is chosen. (B) Dynamic measurement of translation and rotation is shown on the screen.
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Figure 6 Intra-articular landmarks of tibial side are registered. (A) Anterior edge of posterior cruciate ligament, (B) anterior horn of the lateral meniscus, and (C) medial intercondylar eminence.
tunnel drilling. Then, femoral tunnel is drilled at the most appropriate location of the femoral starting point using either method.
Discussion
Postoperative Stability Test
Multiple clinical studies have reported that a high amount of variability of tunnel position exists and these inappropriate tunnel positions have significant effects on the clinical outcome.6,7,10,13,14,16,17 Aglietti et al7 reported in their long-term study of 89 ACL reconstructions that the femoral tunnel was misplaced anterior along the roof of the notch in 10% of the
After graft passage and fixation, postoperative stability is measured with the OrthoPilot by calculating the final anterior translation by a manual maximum anterior force and internal and external rotation of the tibia. These values can be compared with the preoperative knee stability test to assess the quality of the ACL reconstruction (Fig. 10).
Accuracy of Tunnel Placement by Surgeons: Variation of Tunnel Location
Figure 7 Intra-articular landmarks of femoral side are registered. (A) Margin of intercondylar notch outlet, (B) margin of ACL femoral footprint, (C) 12-o’clock over-the-top position, and (D) lateral over-the-top position.
Precision of tunnel execution in navigated ACL
Figure 8 The tip of tibial drill guide is identified in relation to the posterior cruciate ligament and as percentage of sagittal and coronal diameter of tibial plateau. Orientation angle of tibial guide is also shown on the display.
knees and that this positioning significantly increased the rate of graft failure to 62.5%.In another study about tibial tunnel placement and impingement, anterior placement of tibial tunnel (12–23 mm from the anterior edge of the tibia) produced graft impingement and flexion contracture, and stability and knee extension were significantly better when the center of tibial tunnel was 2–3 mm posterior to the center of the normal ACL insertion.10 These 2 studies used an isometer to improve the accuracy of tunnel location, but the authors found that the use of the isometer suggested an inappropriate tunnel location (ie, anterior femoral tunnel placement and variable tibial tunnel placement). Kohn et al24 evaluated drill hole position in ACL reconstruction that was performed during an advanced arthroscopy course. In 24 cadaver knees, inaccurate placement was
Figure 9 Navigation for femoral tunnel shows femoral starting point from the over-the-top position, clock face location, isometric value, potential impingement, and the length of Blumensatt’s line.
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Figure 10 Postoperative knee stability is measured and can be compared with the preoperative test.
found in 50% of the femoral tunnels (12 of 24 knees) and 25% of the tibial tunnels (6 of 24 knees); the notchplasty was insufficient in 25%. Sudhahar et al26 compared expected vs actual tunnel position in 32 patients of ACL reconstruction performed by 2 experienced ACL surgeons. A comparison was made between the positions of the tunnels as perceived by the surgeon intraoperatively with the actual position as shown on the postoperative X-ray. The locations of the tibial tunnels on AP views had a poor correlation (R2 ⫽ 0.14, P ⫽ 0.22), and the tunnels on the lateral views had no correlation (R2 ⫽ 0.07, P ⫽ 0.36), and 4 of 32 tunnels (12.5%) were in very different position to that expected by the surgeon. In a study of tibial guide placement, Harner’s group27 repositioned their tibial guide wires 43% of the time after fluoroscopic evaluation, and they reported it was more difficult to evaluate actual position of tibial tunnel arthroscopically. These authors suggested intraoperative fluoroscopic confirmation of the tibial tunnel position before drilling. However, intraoperative fluoroscopy risks radiation exposure, increases the operative time, and requires additional equipment and staff. In addition, radiographs can be inaccurate in the evaluation of tunnel position.28,29 This high amount of variability in tunnel location, especially sagittal location of tibial tunnels, is likely related to the difficulty in evaluating depth and distance with the standard monocular arthroscope. Three-dimensional intra-articular space filled with water is difficult to evaluate on a 2-dimensional screen, particularly the anteroposterior distance.30 Moreover, the use of soft-tissue landmarks as reference point in conventional technique can lead to misplacement of tibial tunnel, because soft-tissue structures, such as PCL and meniscus, may have variability in positioning. There have been tremendous efforts to improve the accuracy of femoral and tibial tunnels in ACL reconstruction. However, reconstruction with conventional guides still can result in unacceptable graft placement variability. Therefore,
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164 significant interest has been shown in the development of computer-assisted surgery as having potential for improving accurate tunnel placement.
Laboratory Studies With Computer-Assisted Navigation Since computer-assisted surgery (CAS) was applied to the ACL reconstruction, multiple studies have demonstrated that computer-assisted navigation significantly enhances accuracy of femoral and tibial tunnel placement in ACL reconstruction. Picard et al25 and the Pittsburgh group compared the accuracy of tunnel placement between traditional technique and navigation technique by the use of 20 foam knees and 2 surgeons experienced in ACL reconstruction. Distances of the actual tunnel from the ideal tunnel placement were 4.2 ⫾ 1.8 mm (femur) and 4.9 ⫾ 2.3 mm (tibia) with the traditional arthroscopic technique. However, the distances were significantly decreased to 2.7 ⫾ 1.9 mm (femur) and 3.4 ⫾ 2.3 mm (tibia) with the computer-assisted navigation technique. In another study comparing ACL tunnel placement using traditional technique by 4 surgeons and robotic technique, the distribution of intra-articular points for tunnel positions for each 10 foam knees performed by 4 surgeons varied from 2 to 3.4 mm on the tibia and from 2.3 to 4.5 mm on the femur, whereas the distribution by robotic technique was 2.0 mm on the tibia and 2.1 mm on the femur. Variation in surgeon precision of tunnel placement for ACL reconstruction was greater on the femur than the tibia and was correlated with experience, whereas robotic system had more consistent tunnel directions than the surgeon’s tunnels.31 Schep et al32 compared intersurgeon variance of tunnel position in ACL reconstruction using both conventional and CAS in which 3 orthopaedic surgeons with different levels of experience (ie, an experienced surgeon, a fellow-level surgeon, and a resident-level surgeon), each performed 8 virtual tunnel placements with navigation and 4 conventional tunnel placements on fresh-frozen cadaver knees. The 2 lessexperienced surgeons were responsible for 3 cases of impingement when they used a conventional technique. No impingement or elongation was seen when using CAS.
Clinical Results With Computer-Assisted Navigation The improved accuracy of computer-assisted navigation in ACL reconstruction is also documented in many clinical studies.30,33-40 One of the earlier studies investigating the use of CAS in ACL reconstruction was conducted by Klos et al,33 who compared conventional tunnel drilling and fluoroscopic visualization with computer overlay. They reported that graft placement variability was reduced significantly when fluoroscopy and computer assistance were used. The standard deviation of the graft location on the tibia was 6% in conventional group and 3% with fluoroscopy and computer assistance. For femoral side, the standard deviation of the graft location was 9% in conventional group and 3% with fluoroscopy and computer assistance.
Degenhart34 reported 150 ACL reconstructions with the OrthoPilot navigation system in which more precise femoral and tibial tunnel location could be achieved with addition of minimal operating time. Eichhorn35 compared a series of 300 navigated ACL reconstructions with 300 conventional reconstructions. The knees in the navigated group had more desirable radiographic tunnel placement position compared with the knees in the conventional group. In the navigated group, more optimal position of tibial tunnel at 47 ⫾ 5% of anteroposterior dimension and femoral tunnel in the 10- or 2-o’clock placement was seen, as compared with the conventional group where the tibial tunnel was placed more posterior at 50 ⫾ 3% and the femoral tunnel more vertical in the 11- or 1-o’clock placement. In a randomized controlled trial by Plaweski et al,40 30 patients were treated with a conventional technique and 30 patients with a navigation system. There was no significant difference in absolute laxity, but the variability of laxity in the navigated group was significantly less than in the conventional group (P ⫽ 0.0003). A significant difference (P ⫽ 0.03) also was found between the groups in the sagittal position of the tibial tunnel. Distance between the projection of the Blumensaat line on the tibial plateau and the anterior edge of the tibial tunnel was ⫺1.2 (⫺5 to ⫹4) in the conventional group, whereas it was 0.4 (0 to 3) in the navigated group. The anterior border of the tibial tunnel remained at the same level or posterior to the roof of the notch in all cases in the navigated group, suggesting that it is possible to place the tibial tunnel more anteriorly while preventing notch impingement. In our experience comparing 34 manual and 42 navigated ACL reconstructions, the sagittal position of tibial tunnel was noted more anterior and more anatomic in the navigated group compared with the manual group (P ⫽ 0.002). Femoral tunnels were located at 10:30/1:30 on the clock face.38 Computer-assisted navigation systems are now used in more complex cases, such as double-bundle ACL reconstruction or revision ACL surgery, in which more accurate evaluation and precise execution of tunnels is required. Although many studies reported that more accurate tunnel placement was achieved with navigation systems, there are a few reports of clinical outcome data. Long-term, prospective studies comparing functional outcome in conventional and navigated ACL reconstruction are required to determine whether this enhanced accuracy will lead to better long-term results.
Conclusions Accurate tunnel placement is critical to the success of ACL reconstruction. However, surgeons are not accurate as they think they are, and variability of tunnel location can be observed even among experienced surgeons. Computer-assisted navigation systems provide reliable information to surgeons about the precise tunnel location, potential impingement, and isometry during operation. Computer-assisted navigation significantly can enhance accuracy of femoral and tibial tunnel placement in ACL reconstruction.
Precision of tunnel execution in navigated ACL
References 1. Matava M, Boden B: AOSSM institutes multi-center revision ACL study. AOSSM Sports Med Update March-April:5, 2005 2. Griffin LY, Agel J, Albohm MJ, et al: Noncontact anterior cruciate ligament injuries: Risk factors and prevention strategies. J Am Acad Orthop Surg 8:141-150, 2000 3. Eichhorn J, Girdano N: Computerassistierte rekonstruktion des vorderen kreuzbandes mit dem navigations system. Arthroskopie 18:2426, 2005 4. Getelman MH, Friedman MJ: Revision anterior cruciate ligament reconstruction surgery. J Am Acad Orthop Surg 7:189-198, 1999 5. Allen CR, Giffin JR, Harner CD: Revision anterior cruciate ligament reconstruction. Orthop Clin North Am 34:79-98, 2003 6. Sommer C, Friederich NF, Muller W: Improperly placed anterior cruciate ligament grafts: Correlation between radiological parameters and clinical results. Knee Surg Sports Traumatol Arthrosc 8:207-213, 2000 7. Aglietti P, Buzzi R, Giron F, et al: Arthroscopic-assisted anterior cruciate ligament reconstruction with the central third patellar tendon. A 5-8-year follow-up. Knee Surg Sports Traumatol Arthrosc 5:138-144, 1997 8. Loh JC, Fukuda Y, Tsuda E, et al: Knee stability and graft function following anterior cruciate ligament reconstruction: Comparison between 11 o’clock and 10 o’clock femoral tunnel placement. 2002 Richard O’Connor Award Paper. Arthroscopy 19:297-304, 2003 9. Carson EW, Simonian PT, Wickiewicz TL, et al: Revision anterior cruciate ligament reconstruction. Instr Course Lect 47:361-368, 1998 10. Howell SM, Clark JA: Tibial tunnel placement in anterior cruciate ligament reconstructions and graft impingement. Clin Orthop Relat Res 187-195, 1992 11. Howell SM, Taylor MA: Failure of reconstruction of the anterior cruciate ligament due to impingement by the intercondylar roof. J Bone Jt Surg Am 75:1044-1055, 1993 12. Howell SM, Wallace MP, Hull ML, et al: Evaluation of the singleincision arthroscopic technique for anterior cruciate ligament replacement. A study of tibial tunnel placement, intraoperative graft tension, and stability. Am J Sports Med 27:284-293, 1999 13. Ikeda H, Muneta T, Niga S, et al: The long-term effects of tibial drill hole position on the outcome of anterior cruciate ligament reconstruction. Arthroscopy 15:287-291, 1999 14. Khalfayan EE, Sharkey PF, Alexander AH, et al: The relationship between tunnel placement and clinical results after anterior cruciate ligament reconstruction. Am J Sports Med 24:335-341, 1996 15. Markolf KL, Hame S, Hunter DM, et al: Effects of femoral tunnel placement on knee laxity and forces in an anterior cruciate ligament graft. J Orthop Res 20:1016-1024, 2002 16. Muneta T, Yamamoto H, Ishibashi T, et al: The effects of tibial tunnel placement and roofplasty on reconstructed anterior cruciate ligament knees. Arthroscopy 11:57-62, 1995 17. Romano VM, Graf BK, Keene JS, et al: Anterior cruciate ligament reconstruction. The effect of tibial tunnel placement on range of motion. Am J Sports Med 21:415-418, 1993 18. Yaru NC, Daniel DM, Penner D: The effect of tibial attachment site on graft impingement in an anterior cruciate ligament reconstruction. Am J Sports Med 20:217-220, 1992 19. Lee MC, Seong SC, Lee S, et al: Vertical femoral tunnel placement results in rotational knee laxity after anterior cruciate ligament reconstruction. Arthroscopy 23:771-778, 2007 20. Scopp JM, Jasper LE, Belkoff SM, et al: The effect of oblique femoral tunnel placement on rotational constraint of the knee reconstructed using patellar tendon autografts. Arthroscopy 20:294-299, 2004
165 21. Jackson DW, Schaefer RK: Cyclops syndrome: Loss of extension following intra-articular anterior cruciate ligament reconstruction. Arthroscopy 6:171-178, 1990 22. Fineberg MS, Zarins B, Sherman OH: Practical considerations in anterior cruciate ligament replacement surgery. Arthroscopy 16:715-724, 2000 23. Boden B, Migaud H, Gougeon F, et al: Effect of graft position on laxity after anterior cruciate ligament reconstruction. Stress radiography in 90 knees 2-5 years after autograft. Acta Orthop Belg 62:2-7, 1996 24. Kohn D, Busche T, Carls J: Drill hole position in endoscopic anterior cruciate ligament reconstruction. Results of an advanced arthroscopy course. Knee Surg Sports Traumatol Arthrosc 6:S13-S15, 1998 (suppl 1) 25. 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 Aid Surg 6:279-289, 2001 26. Sudhahar TA, Glasgow MM, Donell ST: Comparison of expected vs. actual tunnel position in anterior cruciate ligament reconstruction. Knee 11:15-18, 2004 27. Cha PS, West RV, Harner CD: The Results of Using Intraoperative Fluoroscopy for Ideal Tibial tunnel position During Anterior Cruciate Ligament Reconstruction: Proceeding of the 11th ESSKA Congress and 4th World Congress on Sports Trauma. Athens, Greece, 2004 28. Cole J, Brand JC, Jr, Caborn DN, et al: Radiographic analysis of femoral tunnel position in anterior cruciate ligament reconstruction. Am J Knee Surg 13:218-222, 2000 29. Klos TV, Harman MK, Habets RJ, et al: Locating femoral graft placement from lateral radiographs in anterior cruciate ligament reconstruction: A comparison of 3 methods of measuring radiographic images. Arthroscopy 16:499-504, 2000 30. Koh J: Computer-assisted navigation and anterior cruciate ligament reconstruction: Accuracy and outcomes. Orthopedics 28:s1283-s1287, 2005 31. Burkart A, Debski RE, McMahon PJ, et al: Precision of ACL tunnel placement using traditional and robotic techniques. Comput Aid Surg 6:270-278, 2001 32. Schep NW, Stavenuiter MH, Diekerhof CH, et al: Intersurgeon variance in computer-assisted planning of anterior cruciate ligament reconstruction. Arthroscopy 21:942-947, 2005 33. Klos TV, Habets RJ, Banks AZ, et al: Computer assistance in arthroscopic anterior cruciate ligament reconstruction. Clin Orthop Relat Res 65-69, 1998 34. Degenhart M: Computer-navigated ACL reconstruction with the OrthoPilot. Surg Technol Int 12:245-251, 2004 35. Eichhorn J: Three years of experience with computer navigation-assisted positioning of drilling tunnels in anterior cruciate ligament replacement (SS-67). Arthroscopy 20:31-32, 2004 36. Hart R, Krejzla J, Svab P, et al: Outcomes after conventional versus computer-navigated anterior cruciate ligament reconstruction. Arthroscopy 24:569-578, 2008 37. Hiraoka H, Kuribayashi S, Fukuda A, et al: Endoscopic anterior cruciate ligament reconstruction using a computer-assisted fluoroscopic navigation system. J Orthop Sci 11:159-166, 2006 38. Kodali P, Yang S, Koh J: Computer-assisted surgery for anterior cruciate ligament reconstruction. Sports Med Arthrosc 16:67-76, 2008 39. Mauch F, Apic G, Becker U, et al: Differences in the placement of the tibial tunnel during reconstruction of the anterior cruciate ligament with and without computer-assisted navigation. Am J Sports Med 35: 1824-1832, 2007 40. 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
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nterior cruciate ligament (ACL) reconstruction is one of the most common procedures performed by orthopaedic surgeons. Approximately 175,000 ACL reconstructions are performed annually in the United States, with a cost of more than 1 billion dollars.1,2 In addition, the number of surgeons performing the ACL reconstruction has increased. However, 80% of ACL reconstructions are conducted by orthopaedic surgeons whose experience is limited to fewer than 20 cases in a year.3 For these reasons, numbers of revision surgery are increasing accordingly. Estimates of the rate of revision surgery are as high as 10 –20%, potentially resulting in more than 35,000 revisions a year.1 Most revisions are related to technical errors, primarily tunnel placement.4 Multiple studies have documented that the locations of the femoral and tibial tunnels have significant effects on the knee and that accuracy in tunnel positioning is essential for the success of ACL reconstruction.4-18 The most common error in ACL reconstruction has historically been a femoral tunnel that is too anterior.5,6 Anterior femoral tunnel placement leads to excessive tension on the graft in flexion, resulting in restriction of knee flexion and eventual stretching of the
*Department of Orthopaedic Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL. †Department of Orthopaedic Surgery, School of Medicine, Konkuk University, Chungju, Korea. Address reprint requests to Jason L. Koh, MD, Department of Orthopaedic Surgery, Feinberg School of Medicine, Northwestern University, 676N Saint Clair, 13th Floor, Chicago, IL 60611. E-mail: drjasonkoh@ gmail.com
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graft.5,7 In addition to sagittal positioning of the femoral tunnel, coronal tunnel positioning has been emphasized for rotational stability to prevent the pivot shift phenomenon. An oblique placement of the femoral tunnel near the 10-o’clock position rather than a more vertical placement is important in restoring rotational stability of the knee joint.8,19,20 A tibial tunnel that is too far anterior is associated with impingement on the intercondylar notch.7,10,17,18 This impingement against the roof of the intercondylar notch has been correlated with eventual graft failure11 and the formation of a “Cyclops” lesion.21 Anterior tibial tunnels are associated with significant loss of both flexion and extension.17 Tibial tunnels that are too far posterior may lead to excessive strain in extension, impingement on the posterior cruciate ligament (PCL), and subsequent loss of flexion.5,9,19,22 Excessive medial placement of tibial tunnel may result in impingement on the PCL and has been associated with loss of flexion.17 Excessive lateral placement may cause lateral notch impingement and has been associated with synovitis and laxity.16 Inappropriate tunnel placement result in graft stretching, impingement, loss of motion, increased laxity, synovitis, pain, poor clinical outcome, higher rates of graft failure, revision, and osteoarthritis over time.4-7,9,11-14,16,23 There has been a tremendous focus on improving the accuracy of tunnel position. Unfortunately, accurate tunnel placement remains difficult with current arthroscopic techniques, even for experienced surgeons.6,24-26 The need for increasing accuracy in tunnel placement has led to the application of computer-assisted surgery for ACL reconstruction.
Precision of tunnel execution in navigated ACL
159
Surgical Technique Image-Free, Wireless Navigation System and Setup OrthoPilot (B. Braun-Aesculap, Tuttlingen, Germany) (Fig. 1) is an image-free, wireless navigation system that does not require preoperative computed tomography, radiographic data, or intraoperative fluoroscopy. An infrared camera can track the position of markers of the femur, tibia, and pointer used in the surgery to ⬍1 mm and ⬍1° combined with a computer system. Real-time information about knee position, tip of pointer and guide, and anterior translation and rotational stability is provided. The OrthoPilot is designed to be used with any type of graft chosen by the physician.
Setup, Diagnostic Arthroscopy, Graft Preparation, and Notchpalsty The OrthoPilot system is positioned opposite the side of the operative leg, and the camera is positioned approximately 2 meters away. Patient identification and the type and size of the graft are input into the computer. A standard knee arthroscopy is performed, and any intraarticular pathology, such as a meniscal tear, is addressed. Ruptured ACL stump is removed, and if the notch is narrow, notchplasty is performed with shaver or burr. Graft harvest is performed according to the preference of the surgeon or the patient.
Figure 2 Femoral and tibial markers are attached to 2 K-wires inserted into the distal femur and tibia.
Fixation of Reflective Markers After preparation of the graft and notchplasty, two 2.5 mm ⫻ 100 mm K-wires are inserted percutaneously into the distal femur and antero-medial aspect of the tibia, and rigid bodies with reflective markers are secured to the K-wires. These markers are positioned to be recognized by the infrared camera throughout the procedure (Fig. 2).
Registration of Extra-Articular Anatomical Landmarks Once infrared camera recognizes the markers of femur and tibia, begin identifying the anatomical landmarks starting with the tibia. Attach another marker to the straight pointer, and register the following extra-articular landmarks into the computer with a click of a foot pedal (Fig. 3): 1. Tibial tuberosity. 2. Anterior edge of tibia 3. Medial edge and lateral edge of tibial plateau
Kinematics Acquisition Kinematic data on the location of the tibia and femur are acquired with registering the position of the knee in 90° of flexion and extension. The leg is slowly moved from extension to 90° of flexion for the kinematic data acquisition (Fig. 4).
Preoperative Stability Test
Figure 1 The OrthoPilot is an image-free wireless navigation system that does not require preoperative computed tomography, radiographic data, or intraoperative fluoroscopy.
Preoperative knee stability can be assessed by application of manual anterior translation and internal and external forces at a specific angle (usually 30° of flexion). Lachman test anterior translation at 30° of flexion and the degree of internal and external rotation is then measured and recorded (Fig. 5). Additional anteroposterior translation and rotational data also can be collected.
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Figure 3 The (A) tibial tuberosity, (B) anterior edge of the tibia, and (C) medial and (D) lateral edge of the tibial plateau are registered.
Registration of Intra-Articular Anatomical Landmarks Registering intra-articular landmarks are necessary to enable the computation of the tibial exit point and femoral tunnel position. Place the pointer with marker into the anteromedial working portal and register the following intra-articular landmarks (Figs. 6 and 7): 1. Anterior edge of the posterior cruciate ligament on the tibial plateau. 2. Posterior edge of the anterior horn of the lateral meniscus 3. Medial intercondylar eminence 4. Margin of intercondylar notch outlet 5. Margin of ACL femoral footprint 6. 12-o’clock over-the-top position (use hook pointer) 7. Lateral over-the-top position (use hook pointer)
Navigation for Tunnel Placement After registering all the landmarks, navigation of the tibial tunnel location is performed with use of the navigated tibial
drill guide with marker. On the tibial side, the precise location of the tip of tibial guide is identified in relation to the PCL, lateral meniscus, medial tibial eminence, and the location is shown as the percentage of the coronal and sagittal diameters of tibial plateau in real time. The system computes and displays the projection of the femoral notch onto the tibial plateau. Sagittal and coronal angulation of drill guide is also shown on the display (Fig. 8). The surgeon therefore can adjust the tibial drill guide tip to obtain the most ideal location of the tunnel using aforementioned information. The tibial guide pin is drilled, and the tibial exit point is registered. After the tibial tunnel is drilled, the femoral starting point is then evaluated with the pointer for distance from the over-the-top position, on the clock face location. In addition, the isometry and potential impingement (or estimated clearance) of the graft are calculated and displayed in real time (Fig. 9). If correct femoral insertion point cannot be approached with the transtibial guide, one should change to the transportal technique for femoral
Precision of tunnel execution in navigated ACL
Figure 4 Kinematic data are acquired with (A) 90° of flexion, (B) extension, and (C) motion from extension through 90° of flexion. Accurate tracking of the tibia and femur are assessed during kinematic acquisition (D).
Figure 5 Preoperative stability is measured. (A) Initial screen where the knee flexion angle for stability testing is chosen. (B) Dynamic measurement of translation and rotation is shown on the screen.
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Figure 6 Intra-articular landmarks of tibial side are registered. (A) Anterior edge of posterior cruciate ligament, (B) anterior horn of the lateral meniscus, and (C) medial intercondylar eminence.
tunnel drilling. Then, femoral tunnel is drilled at the most appropriate location of the femoral starting point using either method.
Discussion
Postoperative Stability Test
Multiple clinical studies have reported that a high amount of variability of tunnel position exists and these inappropriate tunnel positions have significant effects on the clinical outcome.6,7,10,13,14,16,17 Aglietti et al7 reported in their long-term study of 89 ACL reconstructions that the femoral tunnel was misplaced anterior along the roof of the notch in 10% of the
After graft passage and fixation, postoperative stability is measured with the OrthoPilot by calculating the final anterior translation by a manual maximum anterior force and internal and external rotation of the tibia. These values can be compared with the preoperative knee stability test to assess the quality of the ACL reconstruction (Fig. 10).
Accuracy of Tunnel Placement by Surgeons: Variation of Tunnel Location
Figure 7 Intra-articular landmarks of femoral side are registered. (A) Margin of intercondylar notch outlet, (B) margin of ACL femoral footprint, (C) 12-o’clock over-the-top position, and (D) lateral over-the-top position.
Precision of tunnel execution in navigated ACL
Figure 8 The tip of tibial drill guide is identified in relation to the posterior cruciate ligament and as percentage of sagittal and coronal diameter of tibial plateau. Orientation angle of tibial guide is also shown on the display.
knees and that this positioning significantly increased the rate of graft failure to 62.5%.In another study about tibial tunnel placement and impingement, anterior placement of tibial tunnel (12–23 mm from the anterior edge of the tibia) produced graft impingement and flexion contracture, and stability and knee extension were significantly better when the center of tibial tunnel was 2–3 mm posterior to the center of the normal ACL insertion.10 These 2 studies used an isometer to improve the accuracy of tunnel location, but the authors found that the use of the isometer suggested an inappropriate tunnel location (ie, anterior femoral tunnel placement and variable tibial tunnel placement). Kohn et al24 evaluated drill hole position in ACL reconstruction that was performed during an advanced arthroscopy course. In 24 cadaver knees, inaccurate placement was
Figure 9 Navigation for femoral tunnel shows femoral starting point from the over-the-top position, clock face location, isometric value, potential impingement, and the length of Blumensatt’s line.
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Figure 10 Postoperative knee stability is measured and can be compared with the preoperative test.
found in 50% of the femoral tunnels (12 of 24 knees) and 25% of the tibial tunnels (6 of 24 knees); the notchplasty was insufficient in 25%. Sudhahar et al26 compared expected vs actual tunnel position in 32 patients of ACL reconstruction performed by 2 experienced ACL surgeons. A comparison was made between the positions of the tunnels as perceived by the surgeon intraoperatively with the actual position as shown on the postoperative X-ray. The locations of the tibial tunnels on AP views had a poor correlation (R2 ⫽ 0.14, P ⫽ 0.22), and the tunnels on the lateral views had no correlation (R2 ⫽ 0.07, P ⫽ 0.36), and 4 of 32 tunnels (12.5%) were in very different position to that expected by the surgeon. In a study of tibial guide placement, Harner’s group27 repositioned their tibial guide wires 43% of the time after fluoroscopic evaluation, and they reported it was more difficult to evaluate actual position of tibial tunnel arthroscopically. These authors suggested intraoperative fluoroscopic confirmation of the tibial tunnel position before drilling. However, intraoperative fluoroscopy risks radiation exposure, increases the operative time, and requires additional equipment and staff. In addition, radiographs can be inaccurate in the evaluation of tunnel position.28,29 This high amount of variability in tunnel location, especially sagittal location of tibial tunnels, is likely related to the difficulty in evaluating depth and distance with the standard monocular arthroscope. Three-dimensional intra-articular space filled with water is difficult to evaluate on a 2-dimensional screen, particularly the anteroposterior distance.30 Moreover, the use of soft-tissue landmarks as reference point in conventional technique can lead to misplacement of tibial tunnel, because soft-tissue structures, such as PCL and meniscus, may have variability in positioning. There have been tremendous efforts to improve the accuracy of femoral and tibial tunnels in ACL reconstruction. However, reconstruction with conventional guides still can result in unacceptable graft placement variability. Therefore,
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164 significant interest has been shown in the development of computer-assisted surgery as having potential for improving accurate tunnel placement.
Laboratory Studies With Computer-Assisted Navigation Since computer-assisted surgery (CAS) was applied to the ACL reconstruction, multiple studies have demonstrated that computer-assisted navigation significantly enhances accuracy of femoral and tibial tunnel placement in ACL reconstruction. Picard et al25 and the Pittsburgh group compared the accuracy of tunnel placement between traditional technique and navigation technique by the use of 20 foam knees and 2 surgeons experienced in ACL reconstruction. Distances of the actual tunnel from the ideal tunnel placement were 4.2 ⫾ 1.8 mm (femur) and 4.9 ⫾ 2.3 mm (tibia) with the traditional arthroscopic technique. However, the distances were significantly decreased to 2.7 ⫾ 1.9 mm (femur) and 3.4 ⫾ 2.3 mm (tibia) with the computer-assisted navigation technique. In another study comparing ACL tunnel placement using traditional technique by 4 surgeons and robotic technique, the distribution of intra-articular points for tunnel positions for each 10 foam knees performed by 4 surgeons varied from 2 to 3.4 mm on the tibia and from 2.3 to 4.5 mm on the femur, whereas the distribution by robotic technique was 2.0 mm on the tibia and 2.1 mm on the femur. Variation in surgeon precision of tunnel placement for ACL reconstruction was greater on the femur than the tibia and was correlated with experience, whereas robotic system had more consistent tunnel directions than the surgeon’s tunnels.31 Schep et al32 compared intersurgeon variance of tunnel position in ACL reconstruction using both conventional and CAS in which 3 orthopaedic surgeons with different levels of experience (ie, an experienced surgeon, a fellow-level surgeon, and a resident-level surgeon), each performed 8 virtual tunnel placements with navigation and 4 conventional tunnel placements on fresh-frozen cadaver knees. The 2 lessexperienced surgeons were responsible for 3 cases of impingement when they used a conventional technique. No impingement or elongation was seen when using CAS.
Clinical Results With Computer-Assisted Navigation The improved accuracy of computer-assisted navigation in ACL reconstruction is also documented in many clinical studies.30,33-40 One of the earlier studies investigating the use of CAS in ACL reconstruction was conducted by Klos et al,33 who compared conventional tunnel drilling and fluoroscopic visualization with computer overlay. They reported that graft placement variability was reduced significantly when fluoroscopy and computer assistance were used. The standard deviation of the graft location on the tibia was 6% in conventional group and 3% with fluoroscopy and computer assistance. For femoral side, the standard deviation of the graft location was 9% in conventional group and 3% with fluoroscopy and computer assistance.
Degenhart34 reported 150 ACL reconstructions with the OrthoPilot navigation system in which more precise femoral and tibial tunnel location could be achieved with addition of minimal operating time. Eichhorn35 compared a series of 300 navigated ACL reconstructions with 300 conventional reconstructions. The knees in the navigated group had more desirable radiographic tunnel placement position compared with the knees in the conventional group. In the navigated group, more optimal position of tibial tunnel at 47 ⫾ 5% of anteroposterior dimension and femoral tunnel in the 10- or 2-o’clock placement was seen, as compared with the conventional group where the tibial tunnel was placed more posterior at 50 ⫾ 3% and the femoral tunnel more vertical in the 11- or 1-o’clock placement. In a randomized controlled trial by Plaweski et al,40 30 patients were treated with a conventional technique and 30 patients with a navigation system. There was no significant difference in absolute laxity, but the variability of laxity in the navigated group was significantly less than in the conventional group (P ⫽ 0.0003). A significant difference (P ⫽ 0.03) also was found between the groups in the sagittal position of the tibial tunnel. Distance between the projection of the Blumensaat line on the tibial plateau and the anterior edge of the tibial tunnel was ⫺1.2 (⫺5 to ⫹4) in the conventional group, whereas it was 0.4 (0 to 3) in the navigated group. The anterior border of the tibial tunnel remained at the same level or posterior to the roof of the notch in all cases in the navigated group, suggesting that it is possible to place the tibial tunnel more anteriorly while preventing notch impingement. In our experience comparing 34 manual and 42 navigated ACL reconstructions, the sagittal position of tibial tunnel was noted more anterior and more anatomic in the navigated group compared with the manual group (P ⫽ 0.002). Femoral tunnels were located at 10:30/1:30 on the clock face.38 Computer-assisted navigation systems are now used in more complex cases, such as double-bundle ACL reconstruction or revision ACL surgery, in which more accurate evaluation and precise execution of tunnels is required. Although many studies reported that more accurate tunnel placement was achieved with navigation systems, there are a few reports of clinical outcome data. Long-term, prospective studies comparing functional outcome in conventional and navigated ACL reconstruction are required to determine whether this enhanced accuracy will lead to better long-term results.
Conclusions Accurate tunnel placement is critical to the success of ACL reconstruction. However, surgeons are not accurate as they think they are, and variability of tunnel location can be observed even among experienced surgeons. Computer-assisted navigation systems provide reliable information to surgeons about the precise tunnel location, potential impingement, and isometry during operation. Computer-assisted navigation significantly can enhance accuracy of femoral and tibial tunnel placement in ACL reconstruction.
Precision of tunnel execution in navigated ACL
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