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Radiographic Results of Femoral Tunnel Drilling Through the Anteromedial Portal in Anterior Cruciate Ligament Reconstruction
Radiographic Results of Femoral Tunnel Drilling Through the Anteromedial Portal in Anterior Cruciate Ligament Reconstruction Anup Ajit Shah, M.D., Andy Brien, M.D., and Walter Richard Lowe, M.D.
Purpose: The goal of this study was to determine the femoral tunnel position by use of the head of a metallic femoral interference screw as a reference marker. In addition, we present postoperative films from an anatomically placed single-bundle anterior cruciate ligament with femoral interference screw fixation using the anteromedial portal drilling technique. Methods: Two surgeons evaluated 43 random postoperative radiographs in patients who underwent anterior cruciate ligament reconstruction by a single surgeon. Four measurements were taken on lateral knee radiographs with superimposed condyles for each patient. These included the total sagittal diameter of the lateral condyle measured along the Blumensaat line (A1), the maximum intercondylar height from the Blumensaat line to the condyle edge along the center of the screw head (B1), the distance from the center of the screw head to the most dorsal contour of the lateral condyle (A2), and the distance from the center of the screw head to the Blumensaat line (B2). The latter 2 values were then expressed as percentages of the lengths A1 and B1. From the anteroposterior (AP) films, the angle between the axis of the screw and anatomic axis of the femur was determined. Results: The center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height. The axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Conclusions: The mean center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height. The mean axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Furthermore, we have described the appearance of a lateral radiograph with this technique. Level of Evidence: Level III, diagnostic study.
A
pproximately 75,000 to 100,000 anterior cruciate ligament (ACL) reconstructions are performed every year in the United States.1,2 The increased incidence of ACL reconstructions reflects the growing participation in sports activities by the general population. Whereas graft selection, graft fixation, and surgical technique in this population are highly controversial, orthopaedic surgeons agree that accurate
From the Department of Orthopaedic Surgery, Baylor College of Medicine, Houston, Texas, U.S.A. The authors report no conflict of interest. Received July 23, 2009; accepted May 6, 2010. Address correspondence and reprint requests to Anup Ajit Shah, M.D., Department of Orthopaedic Surgery, Baylor College of Medicine, 6620 Main St, 13th Floor, Houston, TX 77030, U.S.A. E-mail: [email protected] © 2010 by the Arthroscopy Association of North America 0749-8063/9438/$36.00 doi:10.1016/j.arthro.2010.05.007
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femoral tunnel placement is paramount for successful ACL reconstruction. The anatomy of the femoral insertion site of the ACL has been studied extensively. Recently, ACL reconstruction with the anteromedial portal drilling technique and reconstruction of both bundles of the ACL in an attempt to anatomically re-create the native ligament has gained popularity. It has been shown that anteromedial portal drilling places the graft in a more anatomic position and that double-bundle reconstruction restores rotational stability in a cadaveric study.3,4 However, few studies suggest superior clinical outcomes with double-bundle reconstruction.5-7 Regardless of the decision to use a single- versus doublebundle technique, surgeons must be able to evaluate femoral tunnel position from plain radiography, especially in patients with symptomatic instability and in revision cases. The position of the femoral tunnel and therefore the graft is critical to functional outcome. A
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 26, No 12 (December), 2010: pp 1586-1592
ACL FEMORAL DRILLING THROUGH AM PORTAL graft placed in a nonanatomic and nonisometric position can restrict motion or stretch, leading to knee instability. Several studies have reported on the difficulties of identifying the femoral tunnel position with plain radiography during postoperative evaluation.8-10 As more ACL reconstructions are being performed, increasing numbers of patients are being seen for recurrent instability and decreased motion. In these patients the cause of failure must be determined, and graft position must be identified. The purpose of this study was to report our radiographic findings, specifically to determine the femoral tunnel position relative to the head of a metallic femoral interference screw and present postoperative films from an anatomically placed single-bundle ACL with femoral interference screw fixation using the anteromedial portal drilling technique. We hypothesized that femoral tunnel placement would be more anatomic with this technique. In addition, we believed that screw placement and orientation on postoperative radiographs could accurately determine placement of the femoral tunnel.
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Postoperative radiographs from 43 consecutive ACLreconstructed patients were evaluated. Exclusion criteria included all modes of femoral fixation other than metal interference screws, patients with multiligament knee reconstructions, and poor-quality films. All patients had a single-bundle ACL reconstruction by the senior surgeon with either bone-patellar tendon-bone autograft or Achilles tendon allograft with metal interference screw for femoral fixation.
the tunnel was drilled to 11 mm with a cannulated drill. The femoral tunnel was drilled through the anteromedial portal with the knee flexed to 120°. An awl was used to mark the center of the ACL insertion by use of the lateral bifurcate ridge if clearly identified or the center of the remaining ACL fibers as a landmark at 90° of flexion. This was confirmed with anteromedial portal site viewing. Subsequently, the femoral guide pin was placed at this site with the use of an “over-the-top” offset with the knee in 120° of flexion. A 10-mm half reamer was drilled to a depth of 25 mm at the anatomic footprint. The bone plug portion of the Achilles tendon allograft or bone-tendon-bone (prepared during the case to a size of 10 ⫻ 20 mm) was then inserted into the femoral tunnel by use of a series of passing sutures and fixed with a cannulated metal femoral interference screw (Arthrex, Naples, FL) measuring 7 ⫻ 20 mm. The bone plug was rotated so that the graft was oriented to mimic the anteromedial and posterolateral bundles. The screw was placed on the cancellous portion of the bone plug that faced anterior, lateral, and superior. The screw was placed at the bone-joint interface. Tibial fixation was performed with the Biomet WasherLoc system (Biomet, Warsaw, IN), an interference screw, or a post depending on the type of graft used. The graft was fixed with manual tension on it, with the knee in 20° of flexion. No posterior drawer stress was placed during fixation. Postoperative treatment included the use of a hinged knee brace for 2 months and a continuous passive motion machine for 1 week after surgery. The brace was open to 90° and increased as swelling subsided. Patients ambulated with crutches and were allowed to bear weight as tolerated. Almost all patients discontinued using crutches within 2 weeks.
Surgical Technique and Tunnel Placement
Radiographic Evaluation
The same surgical technique was used in all patients. Before surgery, all patients were examined under anesthesia to confirm the preoperative diagnosis made by physical examination and imaging. Arthroscopic ACL reconstruction was performed with either bone–patellar tendon– bone autograft or Achilles tendon allografts. After diagnostic arthroscopy, meniscal and chondral pathology was addressed. Initially, the native ACL tibial stump was debrided. The tibial drill guide was placed at the center of the footprint, and the tibial tunnel was drilled with a guide pin. The tibial drill hole was placed medially between the tibial tuberosity and pes tendon insertion site, and
Plain films were taken at 2 months (anteroposterior [AP], 30° flexion lateral, and extension lateral). The films were found to be satisfactory with more than 90% overlap of the condyles on the lateral film and less than 30% overlap of the fibular head and proximal tibia on the AP film. Two surgeons (neither of whom was the operating surgeon) evaluated a total of 43 radiographs. The head of the metallic screw was used as a reference point that was flush with the tunnel opening correlating with the mouth of the tunnel. Radiographic analysis of the ACL insertion on the femoral side was performed according to the quadrant method described by Bernard et al.11 and Bernard and
METHODS
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Hertel.12 This is a manual method that they described for analyzing the center of the ACL on traditional lateral radiographs. Four measurements were taken on lateral knee flexion and extension views with superimposed condyles for each patient, similar to those described by Bernard et al.,11 Bernard and Hertel,12 and Giron et al.13 These included the total sagittal diameter of the lateral condyle measured along the Blumensaat line (A1), the maximum intercondylar height from the Blumensaat line to the condyle edge along the center of the screw head (B1), the distance from the center of the screw head to the most dorsal contour of the lateral condyle (A2), and the distance from the center of the screw head to the Blumensaat line (B2). The latter 2 values were then expressed as percentages of the lengths A1 and B1: Blumensaat line percent and condylar height percent, respectively (Fig 1). From the AP films, the angle between the axis of the screw and anatomic axis of the femur was determined (Fig 2). Analysis of interobserver reliability was performed for the A1, A2, B1, and B2 measurements by use of the method proposed by Bland and Altman,14 and the 95% limits of agreement are reported. Each of the 2 observers made each measurement twice. Because the difference between the 2 measurements was not more than 1 mm, only the mean measurement was recorded. RESULTS The evaluated radiographic films were found to be adequate. Ranges of measurements from both exam-
FIGURE 1. Sagittal diameter and intercondylar height measurements from lateral radiograph. BL, Blumensaat line; CH, condylar height.
FIGURE 2.
Coronal angle measurement on AP film.
iners for all 4 measurements and ratio calculation were as follows: A1, 42.0 to 64.7 mm; A2, 11.0 to 25.4 mm; A2/A1 ⫻100, 18.3% to 41.6%; B1, 23.0 to 32.4 mm; B2, 1.6 to 13.0 mm; B2/B1 ⫻100, 5.8% to 42.5%, and axis of screw, 30° to 57°. The mean center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height (Fig 3). The mean axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Interobserver agreement was established by use of the analysis proposed by Bland and Altman14 by reporting the limits of agreement. This method evaluates the difference between the repeated measurements and gives 95% limits of agreement. This is the range of differences that 95% of the measures fell between. Table 1 shows the agreement data between both observers. The measurement differences were calculated as “observer 1” and “observer 2,” and a negative difference meant that measurements by observer 2 were larger than those by observer 1. In the case of B2 and the B2/B1 ratio, the mean difference was significantly different from 0, which indicates that measurements by observer 2 were consistently and significantly higher than those by observer 1. These limits of agreement indicate the range of difference (not absolute and not percentages) that includes 95% of the measure-
ACL FEMORAL DRILLING THROUGH AM PORTAL
FIGURE 3. Center of screw head by use of quadrant method (black, screw head; red, center of ACL footprint according to data from Bernard and Hertel12).
ments; therefore, they provide information about the spread of the data. For the A1 measurement, the difference between both observers was approximately ⫾ 1.6% (after evaluation of the range and mean A1 measurement). However, the B2 measurement difference was found to be approximately ⫾50%, which resulted in poor agreement between the measurements of the B2:B1 ratio. However, the mean distance of B2 was found to be 7 mm, and any difference in measurement between the 2 observers would be evaluated as having poor agreement because a larger percent difference would be seen. Although the differences between the 2 observers’ measurements were statistically significant when compared with the mean value, the differences would only be clinically significant if there was a large variation in tunnel placement. The mean differences for the A1 measurement ranged from ⫺3.12 to 2.61 mm. For the B2 measurement, the mean differences ranged from ⫺3.97 to 1.81 mm, which is very similar. It should be noted that for the B2 measurement, 1 observer consistently measured higher values than the other observer, which may indicate the possibility of observer bias in this single measurement. DISCUSSION The primary findings of this study show femoral tunnel placement at the center of the ACL insertion
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site according to Bernard and Hertel.12 By use of the anteromedial technique with metallic femoral interference screw fixation, placement of the femoral tunnel can be confirmed with plain radiographs postoperatively. Inaccurate femoral tunnel placement is thought to be the most common technical error in ACL reconstruction,15 and its consequences are well known.16-18 Some of the potential problems include loss of motion, notch impingement, and eventual graft failure. Slight variations in tunnel position can have a profound effect on knee function because the femoral attachment is closer to the rotational center of the knee. It was shown recently that drilling through the anteromedial portal is more precise and places the tunnel closer to the anatomic femoral insertion of the ACL when compared with the transtibial technique.3 Placement of the femoral tunnel in a more horizontal position or closer to the 10-o’clock position has been shown to more effectively resist rotatory loads and result in less anterior tibial translation.19 In addition, knee kinematics in this type of reconstruction have been shown to be similar to those in an intact knee.16 The purpose of our study was to determine femoral tunnel placement by use of radiographic films with the head of a metal interference screw as a reference point and describe the postoperative image of an anatomically reconstructed single-bundle ACL. Several prior studies have evaluated tunnel position using plain radiographs and computed tomography. Some authors reported difficulty in identifying the bone tunnels on plain films because of poor-quality radiographs, poor technique, and/or contrast issues.8-10,20 For certain indications, Hoser et al.8 recommend computed tomography because of poor tunnel visibility and inaccurate tunnel projection with plain radiographs. However, exposure to higher doses of radiation and the cost of the scan have limited its application. Milankov and Miljkovic21 created a positioning device for precise femoral tunnel drilling to decrease TABLE 1.
Agreement Data Between Both Observers
Measure
Mean Difference
Limits of Agreement
A1 A2 A2/A1 (%) B1 B2 B2/B1 (%) Degrees from anatomic axis (°)
⫺0.25 0.05 0.23 ⫺0.22 ⫺1.08 ⫺3.86 ⫺0.64
⫺3.12 to 2.61 ⫺2.71 to 2.82 ⫺4.47 to 4.94 ⫺3.7 to 3.26 ⫺3.97 to 1.81 ⫺13.52 to 5.81 ⫺5.35 to 4.06
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FIGURE 4. Femoral ACL footprint and screw placement according to data from several authors.9,11,22
wide variations in femoral tunnel placement among surgeons. In their study they used a positioning device based on preoperative radiographic measurements according to Bernard and Hertel.12 They adjusted the device to place the center of a single-bundle ACL reconstruction at approximately 25% of the sagittal diameter and at 25% of the height of the lateral femoral condyle. Satisfactory placement of the graft was confirmed on postoperative radiographs; however, this device has not gained popularity. Bernard and Hertel12 found the center of the femoral ACL attachment to be 24.8% of the distance of the Blumensaat line and 28.5% of the height of the
lateral femoral condyle from the Blumensaat line (Fig 3). They have described this as being in the inferior and distal part of the most posterior and superior quadrant when using the quadrant method on a lateral film. Lintner et al.9 showed that the femoral insertion occupied the upper 59% and posterior 32% of the intercondylar notch on lateral radiographs. In their study they found the superior-most part of the insertion at the level of the intercondylar notch on lateral films. Recently, Zantop et al.22 described the femoral insertions of the anteromedial and posterolateral bundles according to the technique of Bernard and Hertel. They found the center of the anteromedial bundle to be 18.5% of the sagittal diameter and 22.3% of the height of the lateral femoral condyle. The center of the posterolateral bundle was found to be 29.3% of the sagittal diameter and 53.6% of the height of the lateral femoral condyle. It can be inferred that the lateral bifurcate ridge described by Shen et al.23 lies between the 2 centers of each bundle described by Zantop et al. In our study remnants of the native ACL, the lateral bifurcate ridge, and/or resident’s ridge were identified, and the tunnel was drilled in hyperflexion to fill the majority of the native ACL footprint. When evaluated postoperatively, the location of the screw was found at approximately 31% and 25% of the Blumensaat line and the condylar height, respectively, when the quadrant method was applied. Figure 4 depicts the center of the screw head and its relation to the described ACL insertion site from other studies. When the figure is rotated 90° clockwise, one can better appreciate the anatomy when viewed with the arthroscope from the anteromedial portal site in a flexed knee position. Figure 5 shows the screw anterior to the posteriorly positioned graft.
FIGURE 5. Plain film and arthroscopic view of lateral femoral condyle showing tunnel and screw orientation in flexion according to data from several authors.9,11,22
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FIGURE 6. Postoperative lateral knee films from transtibial and anteromedial drilling techniques. Red circle shows the location of the femoral tunnel.
Figure 6 depicts the difference in postoperative images after ACL reconstruction with transtibial and anteromedial drilling techniques. The obliquity of the screw is perhaps the most obvious difference; however, when studied in detail, the tunnel can be identified from the lucency seen just inferior and posterior to the screw head. Another obvious difference is the location of the screw. With the transtibial technique, the screw is often above the Blumensaat line, whereas the screw is well below the line with the anteromedial portal drilling technique. We believe that this image represents anatomic placement of the femoral tunnel in ACL reconstruction and is the radiograph surgeons should keep in mind when evaluating femoral tunnel placement. The position of the ACL graft is critical to the success of the reconstruction. Identifying femoral tunnel position with plain radiography can assist with preoperative planning and is an objective and costeffective method of determining graft position. In the coronal plane, femoral tunnels were placed approximately 43° from the anatomic axis of the femur. This is similar to Dargel et al.,24 who found approximately 50° of angulation with the anteromedial technique compared with a more vertical tunnel with the transtibial technique. Some limitations of the study should be acknowledged. First, the graft cannot be visualized with plain radiographs. We have assumed graft position based on the orientation of the screw and graft in the tunnel during fixation. However, meticulous surgical technique and images during arthroscopy can confirm this orientation. Second, because this was a retrospective study, the technique of obtaining radiographs was not controlled. Radiographs were taken by different technicians at different locations. Third, tibial tunnel
placement is also a point of controversy; however, it has been shown that femoral tunnel placement is more important for restoring rotational stability. Lastly, we have addressed the possibility of bias in the B2 measurement because 1 observer consistently measured higher values than the other observer. However, we do not believe this is clinically significant. Despite these limitations, we believe our study adds valuable information regarding the radiographic findings after ACL reconstruction through the anteromedial portal. CONCLUSIONS The mean center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height. The mean axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Furthermore, we have described the appearance of a lateral radiograph with this technique. Acknowledgment: The authors thank Dr. Philip Noble for his assistance with the statistical analysis portion of this study.
REFERENCES 1. Brown CH Jr, Carson EW. Revision anterior cruciate ligament surgery. Clin Sports Med 1999;18:109-171. 2. Harner CD, Giffin JR, Dunteman RC, Annunziata CC, Friedman MJ. Evaluation and treatment of recurrent instability after anterior cruciate ligament reconstruction. Instr Course Lect 2001;50:463-474. 3. Gavriilidis I, Motsis E, Pakos E, Georgoulis A, Mitsionis G, Xenakis T. Transtibial versus anteromedial portal of the femoral tunnel in ACL reconstruction: A cadaver study. Knee 2008;15:364-367.
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4. Tashman S, Collon D, Anderson K, Kolowich P, Anderst W. Abnormal rotational knee motion during running after anterior cruciate ligament reconstruction. Am J Sports Med 2004;32: 975-983. 5. Siebold R, Dehler C, Ellert T. Prospective randomized comparison of double bundle vs single bundle anterior cruciate ligament reconstruction. Arthroscopy 2008;24:137-145. 6. Yagi M, Kuroda R, Nagamune K, Yoshiya S, Kurosaka M. Double bundle ACL reconstruction can improve rotation stability. Clin Orthop Relat Res 2007;454:108-113. 7. Yasuda K, Kondo E, Ichiyama H, Tanabe Y, Tohyama H. Clinical evaluation of anatomic double bundle anterior cruciate ligament reconstruction procedure using hamstring tendon grafts: Comparisons among 3 different procedures. Arthroscopy 2006;22:240-251. 8. Hoser C, Tecklengurg K, Kuenzel KH, Fink C. Postoperative evaluation of femoral tunnel position in ACL reconstruction: Plain radiography vs computer tomography. Knee Surg Sports Traumatol Arthrosc 2005;13:256-262. 9. Lintner DM, Dewitt SE, Moseley JB. Radiographic evaluation of native anterior cruciate ligament attachments and graft placement for reconstruction. Am J Sports Med 1996;15:539-542. 10. Khalfayan EE, Sharkey PF, Alexander AL, Bruckner JD, Bynum EB. The relationship between tunnel placement and clinical results after anterior cruciate ligament reconstruction. Am J Sports Med 1996;24:335-341. 11. Bernard M, Hertel P, Hornung H, Cierpinski T. Femoral insertion of the ACL: Radiographic quadrant method. Am J Knee Surg 1997;10:14-21. 12. Bernard M, Hertel P. Intraoperative and postoperative insertion control of anterior cruciate ligament-plasty: A radiologic measuring method (quadrant method). Unfallchirurg 1996;99: 332-340 (in German). 13. Giron F, Buzzi R, Aglietti P. Femoral tunnel position in anterior cruciate ligament reconstruction using three techniques. A cadaver study. Arthroscopy 1999;15:75-76. 14. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307-310.
15. Topliss C, Webb J. An audit of tunnel position in anterior cruciate ligament reconstruction. Knee 2001;8:59-63. 16. Musahl V, Plakseychuk A, VanScyoc A, et al. Varying femoral tunnels between the anatomical footprint and isometric positions. Effect on kinematics of the anterior cruciate ligament-reconstructed knee. Am J Sports Med 2005; 33:712-718. 17. Amis AA, Jakob RP. Anterior cruciate ligament graft positioning, tensioning, and twisting. Knee Surg Sports Traumatol Arthrosc 1998;6:S2-S12 (Suppl 1). 18. Irrgang JJ, Harner CD. Loss of motion following knee ligament reconstruction. Sports Med 1995;19:150-159. 19. Loh JC, Fukuda Y, Tsuda E, Steadman RJ, Fu FH, Woo S. Knee stability and graft function following anterior cruciate ligament reconstruction: Comparison between 11 o’clock and 10 o’clock femoral tunnel placement. Arthroscopy 2003;19: 297-304. 20. Sommer C, Friederich NF, Muller W. Improperly placed anterior cruciate ligament grafts: Correlation between radiological parameters and clinical results. Knee Surg Sports Traumatol Arthrosc 2000;8:207-213. 21. Milankov M, Miljkovic N. A new positioning device for precise femoral insertion of the anterior cruciate ligament autograft. Knee Surg Sports Traumatol Arthrosc 2000;8:149153. 22. Zantop T, Wellmann M, Fu FH, Peterson W. Tunnel positioning of anteromedial and posterolateral bundles in anatomic cruciate ligament reconstruction. Anatomic and radiographic findings. Am J Sports Med 2008;36:65-72. 23. Shen W, Forsythe B, Ingham SM, Honkamp NJ, Fu FH. Application of the anatomic double bundle reconstruction concept to revision and augmentation anterior cruciate ligament surgeries. J Bone Joint Surg Am 2008;90:20-34 (Suppl 4). 24. Dargel J, Schmidt-Wiethoff R, Fischer S. Femoral bone tunnel placement using the transtibial tunnel or the anteromedial portal in ACL reconstruction: A radiographic evaluation. Knee Surg Sports Traumatol Arthrosc 2009;17:220-227.
Purpose: The goal of this study was to determine the femoral tunnel position by use of the head of a metallic femoral interference screw as a reference marker. In addition, we present postoperative films from an anatomically placed single-bundle anterior cruciate ligament with femoral interference screw fixation using the anteromedial portal drilling technique. Methods: Two surgeons evaluated 43 random postoperative radiographs in patients who underwent anterior cruciate ligament reconstruction by a single surgeon. Four measurements were taken on lateral knee radiographs with superimposed condyles for each patient. These included the total sagittal diameter of the lateral condyle measured along the Blumensaat line (A1), the maximum intercondylar height from the Blumensaat line to the condyle edge along the center of the screw head (B1), the distance from the center of the screw head to the most dorsal contour of the lateral condyle (A2), and the distance from the center of the screw head to the Blumensaat line (B2). The latter 2 values were then expressed as percentages of the lengths A1 and B1. From the anteroposterior (AP) films, the angle between the axis of the screw and anatomic axis of the femur was determined. Results: The center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height. The axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Conclusions: The mean center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height. The mean axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Furthermore, we have described the appearance of a lateral radiograph with this technique. Level of Evidence: Level III, diagnostic study.
A
pproximately 75,000 to 100,000 anterior cruciate ligament (ACL) reconstructions are performed every year in the United States.1,2 The increased incidence of ACL reconstructions reflects the growing participation in sports activities by the general population. Whereas graft selection, graft fixation, and surgical technique in this population are highly controversial, orthopaedic surgeons agree that accurate
From the Department of Orthopaedic Surgery, Baylor College of Medicine, Houston, Texas, U.S.A. The authors report no conflict of interest. Received July 23, 2009; accepted May 6, 2010. Address correspondence and reprint requests to Anup Ajit Shah, M.D., Department of Orthopaedic Surgery, Baylor College of Medicine, 6620 Main St, 13th Floor, Houston, TX 77030, U.S.A. E-mail: [email protected] © 2010 by the Arthroscopy Association of North America 0749-8063/9438/$36.00 doi:10.1016/j.arthro.2010.05.007
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femoral tunnel placement is paramount for successful ACL reconstruction. The anatomy of the femoral insertion site of the ACL has been studied extensively. Recently, ACL reconstruction with the anteromedial portal drilling technique and reconstruction of both bundles of the ACL in an attempt to anatomically re-create the native ligament has gained popularity. It has been shown that anteromedial portal drilling places the graft in a more anatomic position and that double-bundle reconstruction restores rotational stability in a cadaveric study.3,4 However, few studies suggest superior clinical outcomes with double-bundle reconstruction.5-7 Regardless of the decision to use a single- versus doublebundle technique, surgeons must be able to evaluate femoral tunnel position from plain radiography, especially in patients with symptomatic instability and in revision cases. The position of the femoral tunnel and therefore the graft is critical to functional outcome. A
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 26, No 12 (December), 2010: pp 1586-1592
ACL FEMORAL DRILLING THROUGH AM PORTAL graft placed in a nonanatomic and nonisometric position can restrict motion or stretch, leading to knee instability. Several studies have reported on the difficulties of identifying the femoral tunnel position with plain radiography during postoperative evaluation.8-10 As more ACL reconstructions are being performed, increasing numbers of patients are being seen for recurrent instability and decreased motion. In these patients the cause of failure must be determined, and graft position must be identified. The purpose of this study was to report our radiographic findings, specifically to determine the femoral tunnel position relative to the head of a metallic femoral interference screw and present postoperative films from an anatomically placed single-bundle ACL with femoral interference screw fixation using the anteromedial portal drilling technique. We hypothesized that femoral tunnel placement would be more anatomic with this technique. In addition, we believed that screw placement and orientation on postoperative radiographs could accurately determine placement of the femoral tunnel.
1587
Postoperative radiographs from 43 consecutive ACLreconstructed patients were evaluated. Exclusion criteria included all modes of femoral fixation other than metal interference screws, patients with multiligament knee reconstructions, and poor-quality films. All patients had a single-bundle ACL reconstruction by the senior surgeon with either bone-patellar tendon-bone autograft or Achilles tendon allograft with metal interference screw for femoral fixation.
the tunnel was drilled to 11 mm with a cannulated drill. The femoral tunnel was drilled through the anteromedial portal with the knee flexed to 120°. An awl was used to mark the center of the ACL insertion by use of the lateral bifurcate ridge if clearly identified or the center of the remaining ACL fibers as a landmark at 90° of flexion. This was confirmed with anteromedial portal site viewing. Subsequently, the femoral guide pin was placed at this site with the use of an “over-the-top” offset with the knee in 120° of flexion. A 10-mm half reamer was drilled to a depth of 25 mm at the anatomic footprint. The bone plug portion of the Achilles tendon allograft or bone-tendon-bone (prepared during the case to a size of 10 ⫻ 20 mm) was then inserted into the femoral tunnel by use of a series of passing sutures and fixed with a cannulated metal femoral interference screw (Arthrex, Naples, FL) measuring 7 ⫻ 20 mm. The bone plug was rotated so that the graft was oriented to mimic the anteromedial and posterolateral bundles. The screw was placed on the cancellous portion of the bone plug that faced anterior, lateral, and superior. The screw was placed at the bone-joint interface. Tibial fixation was performed with the Biomet WasherLoc system (Biomet, Warsaw, IN), an interference screw, or a post depending on the type of graft used. The graft was fixed with manual tension on it, with the knee in 20° of flexion. No posterior drawer stress was placed during fixation. Postoperative treatment included the use of a hinged knee brace for 2 months and a continuous passive motion machine for 1 week after surgery. The brace was open to 90° and increased as swelling subsided. Patients ambulated with crutches and were allowed to bear weight as tolerated. Almost all patients discontinued using crutches within 2 weeks.
Surgical Technique and Tunnel Placement
Radiographic Evaluation
The same surgical technique was used in all patients. Before surgery, all patients were examined under anesthesia to confirm the preoperative diagnosis made by physical examination and imaging. Arthroscopic ACL reconstruction was performed with either bone–patellar tendon– bone autograft or Achilles tendon allografts. After diagnostic arthroscopy, meniscal and chondral pathology was addressed. Initially, the native ACL tibial stump was debrided. The tibial drill guide was placed at the center of the footprint, and the tibial tunnel was drilled with a guide pin. The tibial drill hole was placed medially between the tibial tuberosity and pes tendon insertion site, and
Plain films were taken at 2 months (anteroposterior [AP], 30° flexion lateral, and extension lateral). The films were found to be satisfactory with more than 90% overlap of the condyles on the lateral film and less than 30% overlap of the fibular head and proximal tibia on the AP film. Two surgeons (neither of whom was the operating surgeon) evaluated a total of 43 radiographs. The head of the metallic screw was used as a reference point that was flush with the tunnel opening correlating with the mouth of the tunnel. Radiographic analysis of the ACL insertion on the femoral side was performed according to the quadrant method described by Bernard et al.11 and Bernard and
METHODS
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A. A. SHAH ET AL.
Hertel.12 This is a manual method that they described for analyzing the center of the ACL on traditional lateral radiographs. Four measurements were taken on lateral knee flexion and extension views with superimposed condyles for each patient, similar to those described by Bernard et al.,11 Bernard and Hertel,12 and Giron et al.13 These included the total sagittal diameter of the lateral condyle measured along the Blumensaat line (A1), the maximum intercondylar height from the Blumensaat line to the condyle edge along the center of the screw head (B1), the distance from the center of the screw head to the most dorsal contour of the lateral condyle (A2), and the distance from the center of the screw head to the Blumensaat line (B2). The latter 2 values were then expressed as percentages of the lengths A1 and B1: Blumensaat line percent and condylar height percent, respectively (Fig 1). From the AP films, the angle between the axis of the screw and anatomic axis of the femur was determined (Fig 2). Analysis of interobserver reliability was performed for the A1, A2, B1, and B2 measurements by use of the method proposed by Bland and Altman,14 and the 95% limits of agreement are reported. Each of the 2 observers made each measurement twice. Because the difference between the 2 measurements was not more than 1 mm, only the mean measurement was recorded. RESULTS The evaluated radiographic films were found to be adequate. Ranges of measurements from both exam-
FIGURE 1. Sagittal diameter and intercondylar height measurements from lateral radiograph. BL, Blumensaat line; CH, condylar height.
FIGURE 2.
Coronal angle measurement on AP film.
iners for all 4 measurements and ratio calculation were as follows: A1, 42.0 to 64.7 mm; A2, 11.0 to 25.4 mm; A2/A1 ⫻100, 18.3% to 41.6%; B1, 23.0 to 32.4 mm; B2, 1.6 to 13.0 mm; B2/B1 ⫻100, 5.8% to 42.5%, and axis of screw, 30° to 57°. The mean center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height (Fig 3). The mean axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Interobserver agreement was established by use of the analysis proposed by Bland and Altman14 by reporting the limits of agreement. This method evaluates the difference between the repeated measurements and gives 95% limits of agreement. This is the range of differences that 95% of the measures fell between. Table 1 shows the agreement data between both observers. The measurement differences were calculated as “observer 1” and “observer 2,” and a negative difference meant that measurements by observer 2 were larger than those by observer 1. In the case of B2 and the B2/B1 ratio, the mean difference was significantly different from 0, which indicates that measurements by observer 2 were consistently and significantly higher than those by observer 1. These limits of agreement indicate the range of difference (not absolute and not percentages) that includes 95% of the measure-
ACL FEMORAL DRILLING THROUGH AM PORTAL
FIGURE 3. Center of screw head by use of quadrant method (black, screw head; red, center of ACL footprint according to data from Bernard and Hertel12).
ments; therefore, they provide information about the spread of the data. For the A1 measurement, the difference between both observers was approximately ⫾ 1.6% (after evaluation of the range and mean A1 measurement). However, the B2 measurement difference was found to be approximately ⫾50%, which resulted in poor agreement between the measurements of the B2:B1 ratio. However, the mean distance of B2 was found to be 7 mm, and any difference in measurement between the 2 observers would be evaluated as having poor agreement because a larger percent difference would be seen. Although the differences between the 2 observers’ measurements were statistically significant when compared with the mean value, the differences would only be clinically significant if there was a large variation in tunnel placement. The mean differences for the A1 measurement ranged from ⫺3.12 to 2.61 mm. For the B2 measurement, the mean differences ranged from ⫺3.97 to 1.81 mm, which is very similar. It should be noted that for the B2 measurement, 1 observer consistently measured higher values than the other observer, which may indicate the possibility of observer bias in this single measurement. DISCUSSION The primary findings of this study show femoral tunnel placement at the center of the ACL insertion
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site according to Bernard and Hertel.12 By use of the anteromedial technique with metallic femoral interference screw fixation, placement of the femoral tunnel can be confirmed with plain radiographs postoperatively. Inaccurate femoral tunnel placement is thought to be the most common technical error in ACL reconstruction,15 and its consequences are well known.16-18 Some of the potential problems include loss of motion, notch impingement, and eventual graft failure. Slight variations in tunnel position can have a profound effect on knee function because the femoral attachment is closer to the rotational center of the knee. It was shown recently that drilling through the anteromedial portal is more precise and places the tunnel closer to the anatomic femoral insertion of the ACL when compared with the transtibial technique.3 Placement of the femoral tunnel in a more horizontal position or closer to the 10-o’clock position has been shown to more effectively resist rotatory loads and result in less anterior tibial translation.19 In addition, knee kinematics in this type of reconstruction have been shown to be similar to those in an intact knee.16 The purpose of our study was to determine femoral tunnel placement by use of radiographic films with the head of a metal interference screw as a reference point and describe the postoperative image of an anatomically reconstructed single-bundle ACL. Several prior studies have evaluated tunnel position using plain radiographs and computed tomography. Some authors reported difficulty in identifying the bone tunnels on plain films because of poor-quality radiographs, poor technique, and/or contrast issues.8-10,20 For certain indications, Hoser et al.8 recommend computed tomography because of poor tunnel visibility and inaccurate tunnel projection with plain radiographs. However, exposure to higher doses of radiation and the cost of the scan have limited its application. Milankov and Miljkovic21 created a positioning device for precise femoral tunnel drilling to decrease TABLE 1.
Agreement Data Between Both Observers
Measure
Mean Difference
Limits of Agreement
A1 A2 A2/A1 (%) B1 B2 B2/B1 (%) Degrees from anatomic axis (°)
⫺0.25 0.05 0.23 ⫺0.22 ⫺1.08 ⫺3.86 ⫺0.64
⫺3.12 to 2.61 ⫺2.71 to 2.82 ⫺4.47 to 4.94 ⫺3.7 to 3.26 ⫺3.97 to 1.81 ⫺13.52 to 5.81 ⫺5.35 to 4.06
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FIGURE 4. Femoral ACL footprint and screw placement according to data from several authors.9,11,22
wide variations in femoral tunnel placement among surgeons. In their study they used a positioning device based on preoperative radiographic measurements according to Bernard and Hertel.12 They adjusted the device to place the center of a single-bundle ACL reconstruction at approximately 25% of the sagittal diameter and at 25% of the height of the lateral femoral condyle. Satisfactory placement of the graft was confirmed on postoperative radiographs; however, this device has not gained popularity. Bernard and Hertel12 found the center of the femoral ACL attachment to be 24.8% of the distance of the Blumensaat line and 28.5% of the height of the
lateral femoral condyle from the Blumensaat line (Fig 3). They have described this as being in the inferior and distal part of the most posterior and superior quadrant when using the quadrant method on a lateral film. Lintner et al.9 showed that the femoral insertion occupied the upper 59% and posterior 32% of the intercondylar notch on lateral radiographs. In their study they found the superior-most part of the insertion at the level of the intercondylar notch on lateral films. Recently, Zantop et al.22 described the femoral insertions of the anteromedial and posterolateral bundles according to the technique of Bernard and Hertel. They found the center of the anteromedial bundle to be 18.5% of the sagittal diameter and 22.3% of the height of the lateral femoral condyle. The center of the posterolateral bundle was found to be 29.3% of the sagittal diameter and 53.6% of the height of the lateral femoral condyle. It can be inferred that the lateral bifurcate ridge described by Shen et al.23 lies between the 2 centers of each bundle described by Zantop et al. In our study remnants of the native ACL, the lateral bifurcate ridge, and/or resident’s ridge were identified, and the tunnel was drilled in hyperflexion to fill the majority of the native ACL footprint. When evaluated postoperatively, the location of the screw was found at approximately 31% and 25% of the Blumensaat line and the condylar height, respectively, when the quadrant method was applied. Figure 4 depicts the center of the screw head and its relation to the described ACL insertion site from other studies. When the figure is rotated 90° clockwise, one can better appreciate the anatomy when viewed with the arthroscope from the anteromedial portal site in a flexed knee position. Figure 5 shows the screw anterior to the posteriorly positioned graft.
FIGURE 5. Plain film and arthroscopic view of lateral femoral condyle showing tunnel and screw orientation in flexion according to data from several authors.9,11,22
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FIGURE 6. Postoperative lateral knee films from transtibial and anteromedial drilling techniques. Red circle shows the location of the femoral tunnel.
Figure 6 depicts the difference in postoperative images after ACL reconstruction with transtibial and anteromedial drilling techniques. The obliquity of the screw is perhaps the most obvious difference; however, when studied in detail, the tunnel can be identified from the lucency seen just inferior and posterior to the screw head. Another obvious difference is the location of the screw. With the transtibial technique, the screw is often above the Blumensaat line, whereas the screw is well below the line with the anteromedial portal drilling technique. We believe that this image represents anatomic placement of the femoral tunnel in ACL reconstruction and is the radiograph surgeons should keep in mind when evaluating femoral tunnel placement. The position of the ACL graft is critical to the success of the reconstruction. Identifying femoral tunnel position with plain radiography can assist with preoperative planning and is an objective and costeffective method of determining graft position. In the coronal plane, femoral tunnels were placed approximately 43° from the anatomic axis of the femur. This is similar to Dargel et al.,24 who found approximately 50° of angulation with the anteromedial technique compared with a more vertical tunnel with the transtibial technique. Some limitations of the study should be acknowledged. First, the graft cannot be visualized with plain radiographs. We have assumed graft position based on the orientation of the screw and graft in the tunnel during fixation. However, meticulous surgical technique and images during arthroscopy can confirm this orientation. Second, because this was a retrospective study, the technique of obtaining radiographs was not controlled. Radiographs were taken by different technicians at different locations. Third, tibial tunnel
placement is also a point of controversy; however, it has been shown that femoral tunnel placement is more important for restoring rotational stability. Lastly, we have addressed the possibility of bias in the B2 measurement because 1 observer consistently measured higher values than the other observer. However, we do not believe this is clinically significant. Despite these limitations, we believe our study adds valuable information regarding the radiographic findings after ACL reconstruction through the anteromedial portal. CONCLUSIONS The mean center of the screw head was 31.3% of the Blumensaat line and 24.8% of the condylar height. The mean axis of the screw was found to be 43° from the anatomic axis of the femur on the AP radiographs. Furthermore, we have described the appearance of a lateral radiograph with this technique. Acknowledgment: The authors thank Dr. Philip Noble for his assistance with the statistical analysis portion of this study.
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