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Anterior Cruciate Ligament Reconstruction Femoral Tunnel Characteristics Using an Accessory Medial Portal Versus Traditional Transtibial Drilling
Anterior Cruciate Ligament Reconstruction Femoral Tunnel Characteristics Using an Accessory Medial Portal Versus Traditional Transtibial Drilling Marc Tompkins, M.D., Christopher T. Cosgrove, B.S., Matthew D. Milewski, M.D., Stephen F. Brockmeier, M.D., Joseph M. Hart, Ph.D., and Mark D. Miller, M.D.
Purpose: To evaluate anterior cruciate ligament femoral tunnel characteristics using an accessory medial (AM) portal and transtibial (TT) drilling. Methods: Ten matched pairs of cadaveric knees underwent arthroscopic AM portal or TT femoral drilling with 8-mm reamers. All knees underwent computed tomography scanning and were evaluated for tunnel aperture area, shape as described by the length of the long and short axes, location of the tunnel relative to the anterior and inferior aspects of the articular surface with the knee in extension, tunnel angle in the coronal and axial planes, and tunnel length. Results: The femoral tunnel aperture area was 50.5 4.8 mm2 for AM portal drilling and 51.9 4.6 mm2 for TT drilling (P ¼ .5). The femoral tunnel aperture long axis was 8.5 1.1 mm for AM portal drilling and 9.2 1.3 mm for TT drilling (P ¼ .2), and the short axis was 8.0 0.5 mm for AM portal drilling and 8.0 0.5 mm for TT drilling (P ¼ .8). The femoral tunnel aperture was 5.0 1.4 mm from the anterior wall for AM portal drilling and 9.9 1.7 mm for TT drilling (P < .001), and it was 7.6 2.4 mm from the inferior articular surface for AM portal drilling and 8.9 2.2 mm for TT drilling (P ¼ .2). The femoral tunnel orientation in the coronal plane was 42.1 4.8 for AM portal drilling and 60.9 6.7 for TT drilling (P < .001), and the orientation in the axial plane was 20.9 4.4 for AM portal drilling and 22.7 13.5 for TT drilling (P ¼ .7). The femoral tunnel length was 35.6 2.8 mm for AM portal drilling and 40.3 7.9 mm for TT drilling (P ¼ .1). Conclusions: The use of an AM portal creates a tunnel more anterior and more horizontal than tunnels created by a TT technique. Clinical Relevance: The femoral tunnel characteristics may have an effect on the strain placed on the graft, the graft bending angle, whether enough graft can be placed into the tunnel, and, ultimately, the ability of the body to fully heal the graft.
A
s anterior cruciate ligament (ACL) reconstruction surgery has evolved, emphasis has recently been placed on more anatomic reconstructions.1 This has been described using both single- and double-bundle techniques.2,3 In either case the concept is to place the ACL graft in a more anatomic location on both the tibia From the Department of Orthopaedic Surgery, University of Minnesota (M.T.), Minneapolis, Minnesota; Elite Sports Medicine (M.D. Milewski), Connecticut Children's Medical Center, Hartford, Connecticut; and the Department of Orthopaedic Surgery, University of Virginia (C.T.C., S.F.B., J.M.H., M.D.M), Charlottesville, Virginia, U.S.A. The authors report the following potential conflict of interest or source of funding in relation to this article: UVA Medical Student Summer Research Project Stipend. The cadavers used for this study were donated by the International Institute for the Advancement of Medicine, Jessup, Pennsylvania. Received March 17, 2012; accepted October 29, 2012. Address correspondence to Marc Tompkins, M.D., Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Ave S, Suite R200, Minneapolis, MN 55454, U.S.A. E-mail: [email protected] Ó 2013 by the Arthroscopy Association of North America 0749-8063/12179/$36.00 http://dx.doi.org/10.1016/j.arthro.2012.10.030
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and femur. The result on the femoral side is that the graft is being placed lower, more distal, on the wall of the lateral femoral condyle within the notch, which also places the graft in a more horizontal orientation.4 The tunnel is also slightly more anterior than is typical with a transtibial (TT) technique using an over-the-top guide. It is believed that a horizontal graft, in contrast to a more vertical graft, provides better rotational control, in addition to providing anterior-to-posterior translational stability.5,6 One technique that is being used to perform ACL reconstructions with a greater focus on the anatomy, and that has gained popularity in recent years, is independent femoral tunnel drilling through an anteromedial portal.7 This was first described over a decade ago, using a traditional anteromedial parapatellar arthroscopy portal.8,9 However, the use of an accessory medial (AM) portal for femoral tunnel drilling has also been described, which allows for the arthroscope to be placed in the anteromedial portal, providing better visualization of the ACL footprint than with
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anterolateral viewing.10 It is not known what effect an AM portal has on the femoral tunnel characteristics relative to femoral tunnel drilling using a more traditional TT technique. These characteristics include aperture area and shape, distance of the aperture from the articular surface, orientation of the tunnel within the lateral femoral condyle, and tunnel length and volume. The purpose of this study was to compare femoral tunnel characteristics after AM portal drilling versus a traditional TT drilling technique. The null hypothesis was that femoral tunnel characteristics including tunnel aperture, tunnel lengths, tunnel location on the lateral wall, and tunnel orientation within the lateral femoral condyle would be the same for both techniques.
Methods We used 10 matched pairs of fresh-frozen cadaveric knees (N ¼ 20 knees) for this study (mean age, 74.9 11.3 years). We randomized each pair to receive arthroscopic TT drilling on 1 side and an arthroscopic AM portal approach on the other side. There was equal representation of right and left knees for each group. Reconstruction Technique Medial and lateral parapatellar arthroscopic portals were made following standard technique with portals placed close to the patellar tendon. For the TT group, the ACL was debrided with a shaver and a standard notchplasty was carried out to visualize the over-thetop position in the posterior aspect of the lateral femoral condyle. The notchplasty was carried out in such a way that the least amount of bone and footprint was removed until the posterior wall of the lateral femoral condyle could be adequately viewed with the arthroscope in the lateral portal. The tibial tunnel was then drilled. With a view of the stump at the tibial ACL footprint, an Acufex external tibial tunnel drill guide (Smith & Nephew Endoscopy, Andover, MA) was set at 55 and placed so that the guide pin entered the knee in the center of the tibial ACL stump. Externally, this was placed immediately anterior to the fibers of the superficial medial collateral ligament, with care taken not to violate any medial collateral ligament fibers. An 8-mm tunnel was drilled over the guidewire with a barrel reamer; 8 mm was chosen because this is a common diameter for 4-strand hamstring grafts.11 Replication of a hamstring reconstruction was chosen because over 70% of respondents at Symposium BB during the American Academy of Orthopaedic Surgeons 2011 Annual Meeting stated that their graft of choice for primary ACL reconstruction is a quadrupled hamstring autograft; this has also been suggested in a recent Arthroscopy article.12 Next, a 7-mm TT offset guide (Arthrex, Naples, FL) was introduced and placed over the posterior aspect of the lateral femoral condyle, and
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a Beath pin was advanced through the lateral femoral condyle. In each specimen the surgeon attempted to move the offset guide as far down the lateral wall as the tibial tunnel would allow, in an attempt to place the Beath pin as close to the native ACL footprint as possible. Techniques used to help facilitate this placement included rotating the TT offset guide and adding varus stress to the knee. The Beath pin was then overdrilled with an 8-mm acorn reamer. Care was taken to push or oscillate the reamer through the tibial tunnel rather than running it to reduce the risk of widening the tibial tunnel or aperture. When the anatomic tibial tunnel did not allow the offset guide to reach the posterior aspect of the lateral femoral condyle, the tibial tunnel was reamed additionally, but as minimally as feasible, until it was possible to appropriately place the offset guide. This was necessary in 3 of the knees undergoing TT drilling. All of these steps were accomplished with the knee in 80 to 90 of flexion. For the AM portal group, a shaver was used to debride the ACL stump through a traditional anteromedial portal as described earlier. A short cuff of tissue was left intact at the femoral and tibial ACL footprints, for visual evaluation of the footprint, as described for the “footprint” method.13 The arthroscope was then moved to the anteromedial portal to allow direct visualization of the entire footprint. An 18-gauge spinal needle was inserted into the joint to identify an acceptable location for an AM portal with access to the center of the footprint. The AM portal was placed more medial and distal than the traditional anteromedial portal, approximately 1 to 2 cm medial and 5 mm distal to the standard anteromedial portal. A microfracture awl was used to create a pilot hole at the center of the footprint. A Beath needle was then introduced into the pilot hole and left in place while the knee was maximally hyperflexed (mean, 130.2 5.8 ). The Beath needle was advanced through the lateral femoral condyle, and the flexion angle was recorded. An EndoButton drill bit (Smith & Nephew Endoscopy) was introduced over the Beath needle. Both instruments were removed, and the depth of the tunnel was measured with a depth gauge, followed by reinsertion of the Beath needle. The Beath needle was overdrilled with an 8-mm reamer, which was advanced to within 5 mm of the lateral cortex. The tibial tunnel was then drilled independently in the same manner as in the TT technique. All reconstructions were performed by the 2 senior surgeons, with each surgeon performing 5 reconstructions for both techniques. Computed Tomography Technique and Image Processing After the procedures, all knees underwent computed tomography scanning (SOMATOM Definition; Siemens,
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Erlangen, Germany) at 80 keV by use of bone algorithms. We scanned with a 0.625-mm detector configuration and constructed prospective axial images at 0.625 mm with 50% slice overlap. Multiplanar reformatted 2-dimensional images were created at a slice thickness of 1 mm with a slice interval of 1 mm from this axial data set on a clinical workstation (Carestream PACS, Client Suite v10.2; Carestream Health, Rochester, NY). All measurements were performed with the Carestream PACS Client and were carried out in conjunction with a sports medicine fellowshipetrained orthopaedic surgeon. For aperture area and the long- and short-axis distance of the aperture, the reformatted 3-dimensional reconstruction images were rotated such that they were oriented parallel to the intra-articular aperture (Fig 1). The aperture area was calculated with a region-ofinterest tool and freehand, manual tracings, and the long and short axes were measured with a distance tool. The distances to the anterior and inferior articular surfaces were measured with a distance tool by use of 3-dimensional reconstructions in the sagittal plane (Fig 1). The distance to the anterior wall was measured from the anterior edge of the femoral tunnel aperture, and the distance from the articular surface was measured from the inferior edge of the femoral tunnel aperture. Both of these measurements were performed with the knee in extension; however, the directions described pertain to the knee being in 90 of flexion as would be seen during knee arthroscopy (Fig 1). Tunnel angles were obtained with Cobb angle measurements. The tunnel angle in the coronal plane was measured relative to the tibial plateau, and the angle in the axial plane was measured relative to the
posterior condylar axis; both measurements were performed with the knee in extension (Figs 2 and 3). The tunnel length was obtained by counting the number of slices (1 mm each on the 2-dimensional reconstruction) starting at the aperture until reaching the lateral cortex of the femur. This was doublechecked by rotating the reformatted images such that they were oriented perpendicular to the tunnel in the coronal plane (Fig 2). Volume (v) was calculated with the formula for a cylinder: v ¼ p r2 height, where r is radius and height equals tunnel length. The area was calculated as described earlier; this was calculated every 5 mm, and the average was used in the volume formula.4 Statistical Analysis Independent-samples t tests were used to compare the following measurements between the 2 drilling techniques: femoral aperture area (in square millimeters), femoral aperture long and short axes (in millimeters), femoral aperture distances (anterior and inferior) from the articular surface (in millimeters), tunnel angle in the coronal and axial planes (in degrees), femoral tunnel length (in millimeters), and femoral tunnel volume (in cubic millimeters). Tests were considered statistically significant if the P values were .05 or less.
Results The femoral tunnel orientation in the coronal plane was more horizontal for the AM portal technique than for the TT technique. The femoral tunnel aperture was closer to the anterior articular surface for the AM portal technique than for the TT technique. There was not Fig 1. (A) The 3-dimensional reconstruction has been rotated in such a way that the aperture can be viewed en fosse, allowing for freehand measurement of the femoral tunnel aperture area (black outline). (B) The 3-dimensional reconstruction has been rotated in such a way that the aperture can be viewed en fosse, allowing for measurement of the femoral tunnel aperture long and short axes (arrows). (C) A 3-dimensional reconstruction in the sagittal plane allowing measurement from the anterior edge of the femoral tunnel aperture to the anterior wall (long arrow), as well as from the inferior edge of the femoral tunnel aperture to the inferior articular surface (short arrow). It should be noted that the directions described pertain to the knee being in 90 of flexion as would be seen during knee arthroscopy.
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FEMORAL TUNNEL CHARACTERISTICS
Fig 2. (A) The femoral tunnel angle in the coronal plane was measured relative to the tibial plateau. (B) The femoral tunnel length (arrow) was calculated by rotating the tunnel into view in the coronal plane. It should be noted that the exit point of the tunnel for the AM reconstruction is just above the lateral femoral epicondyle.
a significant difference between AM portal and TT techniques for aperture area, aperture long axis, aperture short axis, distance from the inferior articular surface, orientation in the axial plane, tunnel length, and tunnel volume. Table 1 presents femoral tunnel characteristics.
Discussion This study shows that the use of an AM portal for femoral tunnel drilling creates different tunnel characteristics than TT femoral tunnel drilling, even when one is attempting to place the TT tunnel in an anatomic position on the femur. The use of an AM portal resulted in a tunnel aperture position that is more anterior within the notch and a femoral tunnel that is more horizontal. We believe that this tunnel aperture placement should mean that the tunnel is placed in a more anatomic position, because the femoral footprint anatomy was
used to guide the tunnel placement. If so, previous studies have shown that a more anatomic placement will create more normal knee kinematics in both anterior-toposterior translation and rotation.14-16 The more horizontal position relative to the TT tunnel could also help rotational stability, especially in the early phases of healing until graft incorporation.15,17,18 The femoral tunnel characteristics may have an effect on the strain placed on the graft, the graft bending angle, whether enough graft can be placed into the tunnel, and ultimately, the ability of the body to fully heal the graft.19-24 It is unclear what effect a more anterior aperture and a more horizontal tunnel may have on the previously mentioned parameters, but these likely will change graft strain and graft bending angle. Further study will be needed in both cadaveric and clinical models to assess whether these changes in tunnel characteristics will result in clinically measurable differences in laxity or patients’ feelings of stability. This study is unique in evaluating femoral tunnels after the use of an AM portal, which is in a different location than more traditional anteromedial portals, for independent femoral tunnel drilling. This builds on similar Table 1. Femoral Tunnel Characteristics Variable
Fig 3. The femoral tunnel angle in the axial plane was measured relative to the posterior condylar axis.
Aperture area (mm2) Aperture long axis (mm) Aperture short axis (mm) Aperture from anterior articular surface (mm) Aperture from inferior articular surface (mm) Tunnel orientation in coronal plane ( ) Tunnel orientation in axial plane ( ) Tunnel length (mm) Tunnel volume (mm3)
AM Portal 50.5 8.5 8.0 5.0
4.8 1.1 0.5 1.4
TT 51.9 9.2 8.0 9.9
P Value 4.6 1.3 0.5 1.7
.5 .2 .8 <.001*
7.6 2.4
8.9 2.2
42.1 4.8
60.9 6.7
20.9 4.4
22.7 13.5
.7
35.6 2.8 1659 177
40.3 7.9 1829 369
.1 .2
*Statistically significant (P < .05).
.2 <.001*
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studies that have used more traditional anteromedial portals for independent femoral tunnel drilling.4,18,25 In addition, this study evaluates the orientation of the tunnels within the lateral femoral condyle, which has not previously been reported. Though not statistically significant, there is also a trend toward a smaller and more circular tunnel aperture, a tunnel lower on the lateral wall, and tunnels that are shorter but of adequate length by use of an AM portal.24 Because the most important healing point for the graft within the tunnel is at the aperture, the larger size and more elliptical shape in the TT femoral tunnels could have important ramifications on graft incorporation or tunnel widening.26-30 On the other hand, a more elliptical aperture may mean a more gentle turn of the graft into the tunnel and therefore less strain on the graft in the early phases of healing. Though also not statistically significant, the tunnel length trended toward being shorter when an AM portal was used (4.7 mm shorter). With a mean length of greater than 35 mm, however, this tunnel is likely still of adequate length for clinical utility.24 In the axial plane, the AM portal tunnels were generally oriented toward the lateral femoral epicondyle and therefore the greatest width of bone within the lateral femoral condyle. This likely accounts for the adequate length of the tunnels as compared with previous studies showing shortened tunnels with a standard anteromedial portal.19,25 One concern from this orientation of the femoral tunnel would be that the epicondyle and therefore the lateral collateral ligament would be violated; however, this was not the case because the tunnels exited the lateral femoral condyle just superior to the epicondyle in the coronal plane (Fig 2). Further study will be needed in both cadaveric and clinical models to more precisely identify what is an adequate tunnel length for clinical success. A shorter femoral tunnel translates to lower volume. It is unclear what significance this might have, but these volume values may serve as a reference for future studies evaluating the femoral tunnel in ACL reconstruction. Recently, a similar study was performed comparing femoral tunnels created through an anteromedial portal versus TT drilling.4 The emphasis of that study was on comparing the more horizontal tunnel created by an anteromedial portal with that from TT drilling. There was not, however, a stated emphasis placed on creating an anatomic starting point for the tunnel as was performed in our study. We wished to directly compare some of the data from our study with that study; however, the previous study was performed with 10-mm drill bits, making it difficult to directly compare most of the measurements. In general, the trends for aperture size and shape were similar. Interestingly, it would appear that both the TT tunnel and the AM
portal tunnel in our study started lower on the lateral wall, likely resulting in a more horizontal tunnel in the coronal plane than their counterparts from the previous study. In addition, it is important to note that the tunnel length was greater in our study, especially when one compares the AM tunnels from our study with the anteromedial tunnels from the previous study. Both of these findings likely result from the emphasis placed on an anatomic starting point in our study. Because we know that tunnel length is important and other previous studies have shown that more horizontal tunnels increase rotational stability of the knee, these findings emphasize the value of focusing on an anatomic reconstruction.5,6 Future studies should compare the femoral tunnel characteristics created by an AM portal versus a traditional anteromedial portal. Future studies should also be carried out to radiographically follow up ACL reconstruction patients and evaluate the effects of various tunnel characteristics on the incorporation of the graft or on tunnel widening. One recent study with radiographic follow-up performed at 1 year did not show significant differences, but there was a trend toward greater tunnel widening in the TT group versus femoral tunnel drilling through an anteromedial portal.31 In addition, these changes in the femoral tunnel resulting from different reconstruction techniques should be followed clinically to assess whether there is any clinical significance. Another area of recent interest in the literature, and related to the tunnel characteristics, has been graft bending angles.20,23 The effect that different aperture size and shape, tunnel location, and tunnel angle has on graft bending angles and therefore graft strain will also be important to follow. Limitations Limitations of this study include the fact that it is a cadaveric study. The cadavers ages were older than most patients undergoing ACL reconstruction, so it is probable that the femoral tunnel bone quality was more osteopenic than the normal ACL reconstruction population, which could affect some of the femoral tunnel characteristics. The radiographic review was not blinded to the technique being evaluated because of the complex radiographic analysis. Ideally, we would like to compare a traditional anteromedial portal approach with an AM approach; however, as a first step, we believed that it was important to compare the AM approach with a TT approach, because the TT approach is more traditional and continues to be performed by many orthopaedic surgeons.
Conclusions The use of an AM portal creates a tunnel more anterior and more horizontal than tunnels created by a TT technique.
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Acknowledgment The authors thank Winston Evatt, Carmen Spitzer, Jamie Weathersbee, and Rick Stewart for their time and assistance in scanning the cadaveric specimens.
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18.
References 1. Kopf S, Musahl V, Tashman S, et al. A systematic review of the femoral origin and tibial insertion morphology of the ACL. Knee Surg Sports Traumatol Arthrosc 2009;17:213-219. 2. Buoncristiani AM, Tjoumakaris FP, Starman JS, et al. Anatomic double-bundle anterior cruciate ligament reconstruction. Arthroscopy 2006;22:1000-1006. 3. Steiner M. Anatomic single-bundle ACL reconstruction. Sports Med Arthrosc 2009;17:247-251. 4. Miller CD, Gerdeman AC, Hart JM, et al. A comparison of 2 drilling techniques on the femoral tunnel for anterior cruciate ligament reconstruction. Arthroscopy 2011;27: 372-379. 5. Steiner ME, Battaglia TC, Heming JF, et al. Independent drilling outperforms conventional transtibial drilling in anterior cruciate ligament reconstruction. Am J Sports Med 2009;37:1912-1919. 6. Seon JK, Park SJ, Lee KB, et al. In vivo stability and clinical comparison of anterior cruciate ligament reconstruction using low or high femoral tunnel positions. Am J Sports Med 2011;39:127-133. 7. Harner CD, Honkamp NJ, Ranawat AS. Anteromedial portal technique for creating the anterior cruciate ligament femoral tunnel. Arthroscopy 2008;24:113-115. 8. Corry IS, Webb JM, Clingeleffer AJ, et al. Arthroscopic reconstruction of the anterior cruciate ligament. A comparison of patellar tendon autograft and four-strand hamstring tendon autograft. Am J Sports Med 1999;27:444-454. 9. Otto D, Pinczewski LA, Clingeleffer A, et al. Five-year results of single-incision arthroscopic anterior cruciate ligament reconstruction with patellar tendon autograft. Am J Sports Med 1998;26:181-188. 10. Pombo MW, Shen W, Fu FH. Anatomic double-bundle anterior cruciate ligament reconstruction: Where are we today? Arthroscopy 2008;24:1168-1177. 11. Treme G, Diduch DR, Billante MJ, et al. Hamstring graft size prediction: A prospective clinical evaluation. Am J Sports Med 2008;36:2204-2209. 12. Zantop T, Kubo S, Petersen W, et al. Current techniques in anatomic anterior cruciate ligament reconstruction. Arthroscopy 2007;23:938-947. 13. Bedi A, Altchek DW. The “footprint” anterior cruciate ligament technique: An anatomic approach to anterior cruciate ligament reconstruction. Arthroscopy 2009;25: 1128-1138. 14. 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 2002;20:1016-1024. 15. Bedi A, Musahl V, Steuber V, et al. Transtibial versus anteromedial portal reaming in anterior cruciate ligament reconstruction: An anatomic and biomechanical evaluation of surgical technique. Arthroscopy 2011;27:380-390. 16. Abebe ES, Utturkar GM, Taylor DC, et al. The effects of femoral graft placement on in vivo knee kinematics after
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anterior cruciate ligament reconstruction. J Biomech 2011;44:924-929. 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 2004;20:294-299. Illingworth KD, Hensler D, Working ZM, et al. A simple evaluation of anterior cruciate ligament femoral tunnel position: The inclination angle and femoral tunnel angle. Am J Sports Med 2011;39:2611-2618. Bedi A, Raphael B, Maderazo A, et al. Transtibial versus anteromedial portal drilling for anterior cruciate ligament reconstruction: A cadaveric study of femoral tunnel length and obliquity. Arthroscopy 2010;26:342-350. Hantes ME, Zachos VC, Liantsis A, et al. Differences in graft orientation using the transtibial and anteromedial portal technique in anterior cruciate ligament reconstruction: A magnetic resonance imaging study. Knee Surg Sports Traumatol Arthrosc 2009;17:880-886. Kopf S, Martin DE, Tashman S, et al. Effect of tibial drill angles on bone tunnel aperture during anterior cruciate ligament reconstruction. J Bone Joint Surg Am 2010;92:871-881. Lubowitz JH, Konicek J. Anterior cruciate ligament femoral tunnel length: Cadaveric analysis comparing anteromedial portal versus outside-in technique. Arthroscopy 2010;26:1357-1362. Nishimoto K, Kuroda R, Mizuno K, et al. Analysis of the graft bending angle at the femoral tunnel aperture in anatomic double bundle anterior cruciate ligament reconstruction: A comparison of the transtibial and the far anteromedial portal technique. Knee Surg Sports Traumatol Arthrosc 2009;17:270-276. Zantop T, Ferretti M, Bell KM, et al. Effect of tunnel-graft length on the biomechanics of anterior cruciate ligamentreconstructed knees: Intra-articular study in a goat model. Am J Sports Med 2008;36:2158-2166. Golish SR, Baumfeld JA, Schoderbek RJ, et al. The effect of femoral tunnel starting position on tunnel length in anterior cruciate ligament reconstruction: A cadaveric study. Arthroscopy 2007;23:1187-1192. Cain EL Jr, Clancy WG Jr. Anatomic endoscopic anterior cruciate ligament reconstruction with patella tendon autograft. Orthop Clin North Am 2002;33:717-725. Clancy WG Jr. Intra-articular reconstruction of the anterior cruciate ligament. Orthop Clin North Am 1985;16:181-189. Silva A, Sampaio R, Pinto E. Femoral tunnel enlargement after anatomic ACL reconstruction: A biological problem? Knee Surg Sports Traumatol Arthrosc 2010;18:1189-1194. L’Insalata JC, Klatt B, Fu FH, et al. Tunnel expansion following anterior cruciate ligament reconstruction: A comparison of hamstring and patellar tendon autografts. Knee Surg Sports Traumatol Arthrosc 1997;5:234-238. Chhabra A, Kline AJ, Nilles KM, et al. Tunnel expansion after anterior cruciate ligament reconstruction with autogenous hamstrings: A comparison of the medial portal and transtibial techniques. Arthroscopy 2006;22: 1107-1112. Xu Y, Ao Y, Wang J, et al. Relation of tunnel enlargement and tunnel placement after single-bundle anterior cruciate ligament reconstruction. Arthroscopy 2011;27: 923-932.
Purpose: To evaluate anterior cruciate ligament femoral tunnel characteristics using an accessory medial (AM) portal and transtibial (TT) drilling. Methods: Ten matched pairs of cadaveric knees underwent arthroscopic AM portal or TT femoral drilling with 8-mm reamers. All knees underwent computed tomography scanning and were evaluated for tunnel aperture area, shape as described by the length of the long and short axes, location of the tunnel relative to the anterior and inferior aspects of the articular surface with the knee in extension, tunnel angle in the coronal and axial planes, and tunnel length. Results: The femoral tunnel aperture area was 50.5 4.8 mm2 for AM portal drilling and 51.9 4.6 mm2 for TT drilling (P ¼ .5). The femoral tunnel aperture long axis was 8.5 1.1 mm for AM portal drilling and 9.2 1.3 mm for TT drilling (P ¼ .2), and the short axis was 8.0 0.5 mm for AM portal drilling and 8.0 0.5 mm for TT drilling (P ¼ .8). The femoral tunnel aperture was 5.0 1.4 mm from the anterior wall for AM portal drilling and 9.9 1.7 mm for TT drilling (P < .001), and it was 7.6 2.4 mm from the inferior articular surface for AM portal drilling and 8.9 2.2 mm for TT drilling (P ¼ .2). The femoral tunnel orientation in the coronal plane was 42.1 4.8 for AM portal drilling and 60.9 6.7 for TT drilling (P < .001), and the orientation in the axial plane was 20.9 4.4 for AM portal drilling and 22.7 13.5 for TT drilling (P ¼ .7). The femoral tunnel length was 35.6 2.8 mm for AM portal drilling and 40.3 7.9 mm for TT drilling (P ¼ .1). Conclusions: The use of an AM portal creates a tunnel more anterior and more horizontal than tunnels created by a TT technique. Clinical Relevance: The femoral tunnel characteristics may have an effect on the strain placed on the graft, the graft bending angle, whether enough graft can be placed into the tunnel, and, ultimately, the ability of the body to fully heal the graft.
A
s anterior cruciate ligament (ACL) reconstruction surgery has evolved, emphasis has recently been placed on more anatomic reconstructions.1 This has been described using both single- and double-bundle techniques.2,3 In either case the concept is to place the ACL graft in a more anatomic location on both the tibia From the Department of Orthopaedic Surgery, University of Minnesota (M.T.), Minneapolis, Minnesota; Elite Sports Medicine (M.D. Milewski), Connecticut Children's Medical Center, Hartford, Connecticut; and the Department of Orthopaedic Surgery, University of Virginia (C.T.C., S.F.B., J.M.H., M.D.M), Charlottesville, Virginia, U.S.A. The authors report the following potential conflict of interest or source of funding in relation to this article: UVA Medical Student Summer Research Project Stipend. The cadavers used for this study were donated by the International Institute for the Advancement of Medicine, Jessup, Pennsylvania. Received March 17, 2012; accepted October 29, 2012. Address correspondence to Marc Tompkins, M.D., Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Ave S, Suite R200, Minneapolis, MN 55454, U.S.A. E-mail: [email protected] Ó 2013 by the Arthroscopy Association of North America 0749-8063/12179/$36.00 http://dx.doi.org/10.1016/j.arthro.2012.10.030
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and femur. The result on the femoral side is that the graft is being placed lower, more distal, on the wall of the lateral femoral condyle within the notch, which also places the graft in a more horizontal orientation.4 The tunnel is also slightly more anterior than is typical with a transtibial (TT) technique using an over-the-top guide. It is believed that a horizontal graft, in contrast to a more vertical graft, provides better rotational control, in addition to providing anterior-to-posterior translational stability.5,6 One technique that is being used to perform ACL reconstructions with a greater focus on the anatomy, and that has gained popularity in recent years, is independent femoral tunnel drilling through an anteromedial portal.7 This was first described over a decade ago, using a traditional anteromedial parapatellar arthroscopy portal.8,9 However, the use of an accessory medial (AM) portal for femoral tunnel drilling has also been described, which allows for the arthroscope to be placed in the anteromedial portal, providing better visualization of the ACL footprint than with
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anterolateral viewing.10 It is not known what effect an AM portal has on the femoral tunnel characteristics relative to femoral tunnel drilling using a more traditional TT technique. These characteristics include aperture area and shape, distance of the aperture from the articular surface, orientation of the tunnel within the lateral femoral condyle, and tunnel length and volume. The purpose of this study was to compare femoral tunnel characteristics after AM portal drilling versus a traditional TT drilling technique. The null hypothesis was that femoral tunnel characteristics including tunnel aperture, tunnel lengths, tunnel location on the lateral wall, and tunnel orientation within the lateral femoral condyle would be the same for both techniques.
Methods We used 10 matched pairs of fresh-frozen cadaveric knees (N ¼ 20 knees) for this study (mean age, 74.9 11.3 years). We randomized each pair to receive arthroscopic TT drilling on 1 side and an arthroscopic AM portal approach on the other side. There was equal representation of right and left knees for each group. Reconstruction Technique Medial and lateral parapatellar arthroscopic portals were made following standard technique with portals placed close to the patellar tendon. For the TT group, the ACL was debrided with a shaver and a standard notchplasty was carried out to visualize the over-thetop position in the posterior aspect of the lateral femoral condyle. The notchplasty was carried out in such a way that the least amount of bone and footprint was removed until the posterior wall of the lateral femoral condyle could be adequately viewed with the arthroscope in the lateral portal. The tibial tunnel was then drilled. With a view of the stump at the tibial ACL footprint, an Acufex external tibial tunnel drill guide (Smith & Nephew Endoscopy, Andover, MA) was set at 55 and placed so that the guide pin entered the knee in the center of the tibial ACL stump. Externally, this was placed immediately anterior to the fibers of the superficial medial collateral ligament, with care taken not to violate any medial collateral ligament fibers. An 8-mm tunnel was drilled over the guidewire with a barrel reamer; 8 mm was chosen because this is a common diameter for 4-strand hamstring grafts.11 Replication of a hamstring reconstruction was chosen because over 70% of respondents at Symposium BB during the American Academy of Orthopaedic Surgeons 2011 Annual Meeting stated that their graft of choice for primary ACL reconstruction is a quadrupled hamstring autograft; this has also been suggested in a recent Arthroscopy article.12 Next, a 7-mm TT offset guide (Arthrex, Naples, FL) was introduced and placed over the posterior aspect of the lateral femoral condyle, and
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a Beath pin was advanced through the lateral femoral condyle. In each specimen the surgeon attempted to move the offset guide as far down the lateral wall as the tibial tunnel would allow, in an attempt to place the Beath pin as close to the native ACL footprint as possible. Techniques used to help facilitate this placement included rotating the TT offset guide and adding varus stress to the knee. The Beath pin was then overdrilled with an 8-mm acorn reamer. Care was taken to push or oscillate the reamer through the tibial tunnel rather than running it to reduce the risk of widening the tibial tunnel or aperture. When the anatomic tibial tunnel did not allow the offset guide to reach the posterior aspect of the lateral femoral condyle, the tibial tunnel was reamed additionally, but as minimally as feasible, until it was possible to appropriately place the offset guide. This was necessary in 3 of the knees undergoing TT drilling. All of these steps were accomplished with the knee in 80 to 90 of flexion. For the AM portal group, a shaver was used to debride the ACL stump through a traditional anteromedial portal as described earlier. A short cuff of tissue was left intact at the femoral and tibial ACL footprints, for visual evaluation of the footprint, as described for the “footprint” method.13 The arthroscope was then moved to the anteromedial portal to allow direct visualization of the entire footprint. An 18-gauge spinal needle was inserted into the joint to identify an acceptable location for an AM portal with access to the center of the footprint. The AM portal was placed more medial and distal than the traditional anteromedial portal, approximately 1 to 2 cm medial and 5 mm distal to the standard anteromedial portal. A microfracture awl was used to create a pilot hole at the center of the footprint. A Beath needle was then introduced into the pilot hole and left in place while the knee was maximally hyperflexed (mean, 130.2 5.8 ). The Beath needle was advanced through the lateral femoral condyle, and the flexion angle was recorded. An EndoButton drill bit (Smith & Nephew Endoscopy) was introduced over the Beath needle. Both instruments were removed, and the depth of the tunnel was measured with a depth gauge, followed by reinsertion of the Beath needle. The Beath needle was overdrilled with an 8-mm reamer, which was advanced to within 5 mm of the lateral cortex. The tibial tunnel was then drilled independently in the same manner as in the TT technique. All reconstructions were performed by the 2 senior surgeons, with each surgeon performing 5 reconstructions for both techniques. Computed Tomography Technique and Image Processing After the procedures, all knees underwent computed tomography scanning (SOMATOM Definition; Siemens,
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Erlangen, Germany) at 80 keV by use of bone algorithms. We scanned with a 0.625-mm detector configuration and constructed prospective axial images at 0.625 mm with 50% slice overlap. Multiplanar reformatted 2-dimensional images were created at a slice thickness of 1 mm with a slice interval of 1 mm from this axial data set on a clinical workstation (Carestream PACS, Client Suite v10.2; Carestream Health, Rochester, NY). All measurements were performed with the Carestream PACS Client and were carried out in conjunction with a sports medicine fellowshipetrained orthopaedic surgeon. For aperture area and the long- and short-axis distance of the aperture, the reformatted 3-dimensional reconstruction images were rotated such that they were oriented parallel to the intra-articular aperture (Fig 1). The aperture area was calculated with a region-ofinterest tool and freehand, manual tracings, and the long and short axes were measured with a distance tool. The distances to the anterior and inferior articular surfaces were measured with a distance tool by use of 3-dimensional reconstructions in the sagittal plane (Fig 1). The distance to the anterior wall was measured from the anterior edge of the femoral tunnel aperture, and the distance from the articular surface was measured from the inferior edge of the femoral tunnel aperture. Both of these measurements were performed with the knee in extension; however, the directions described pertain to the knee being in 90 of flexion as would be seen during knee arthroscopy (Fig 1). Tunnel angles were obtained with Cobb angle measurements. The tunnel angle in the coronal plane was measured relative to the tibial plateau, and the angle in the axial plane was measured relative to the
posterior condylar axis; both measurements were performed with the knee in extension (Figs 2 and 3). The tunnel length was obtained by counting the number of slices (1 mm each on the 2-dimensional reconstruction) starting at the aperture until reaching the lateral cortex of the femur. This was doublechecked by rotating the reformatted images such that they were oriented perpendicular to the tunnel in the coronal plane (Fig 2). Volume (v) was calculated with the formula for a cylinder: v ¼ p r2 height, where r is radius and height equals tunnel length. The area was calculated as described earlier; this was calculated every 5 mm, and the average was used in the volume formula.4 Statistical Analysis Independent-samples t tests were used to compare the following measurements between the 2 drilling techniques: femoral aperture area (in square millimeters), femoral aperture long and short axes (in millimeters), femoral aperture distances (anterior and inferior) from the articular surface (in millimeters), tunnel angle in the coronal and axial planes (in degrees), femoral tunnel length (in millimeters), and femoral tunnel volume (in cubic millimeters). Tests were considered statistically significant if the P values were .05 or less.
Results The femoral tunnel orientation in the coronal plane was more horizontal for the AM portal technique than for the TT technique. The femoral tunnel aperture was closer to the anterior articular surface for the AM portal technique than for the TT technique. There was not Fig 1. (A) The 3-dimensional reconstruction has been rotated in such a way that the aperture can be viewed en fosse, allowing for freehand measurement of the femoral tunnel aperture area (black outline). (B) The 3-dimensional reconstruction has been rotated in such a way that the aperture can be viewed en fosse, allowing for measurement of the femoral tunnel aperture long and short axes (arrows). (C) A 3-dimensional reconstruction in the sagittal plane allowing measurement from the anterior edge of the femoral tunnel aperture to the anterior wall (long arrow), as well as from the inferior edge of the femoral tunnel aperture to the inferior articular surface (short arrow). It should be noted that the directions described pertain to the knee being in 90 of flexion as would be seen during knee arthroscopy.
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FEMORAL TUNNEL CHARACTERISTICS
Fig 2. (A) The femoral tunnel angle in the coronal plane was measured relative to the tibial plateau. (B) The femoral tunnel length (arrow) was calculated by rotating the tunnel into view in the coronal plane. It should be noted that the exit point of the tunnel for the AM reconstruction is just above the lateral femoral epicondyle.
a significant difference between AM portal and TT techniques for aperture area, aperture long axis, aperture short axis, distance from the inferior articular surface, orientation in the axial plane, tunnel length, and tunnel volume. Table 1 presents femoral tunnel characteristics.
Discussion This study shows that the use of an AM portal for femoral tunnel drilling creates different tunnel characteristics than TT femoral tunnel drilling, even when one is attempting to place the TT tunnel in an anatomic position on the femur. The use of an AM portal resulted in a tunnel aperture position that is more anterior within the notch and a femoral tunnel that is more horizontal. We believe that this tunnel aperture placement should mean that the tunnel is placed in a more anatomic position, because the femoral footprint anatomy was
used to guide the tunnel placement. If so, previous studies have shown that a more anatomic placement will create more normal knee kinematics in both anterior-toposterior translation and rotation.14-16 The more horizontal position relative to the TT tunnel could also help rotational stability, especially in the early phases of healing until graft incorporation.15,17,18 The femoral tunnel characteristics may have an effect on the strain placed on the graft, the graft bending angle, whether enough graft can be placed into the tunnel, and ultimately, the ability of the body to fully heal the graft.19-24 It is unclear what effect a more anterior aperture and a more horizontal tunnel may have on the previously mentioned parameters, but these likely will change graft strain and graft bending angle. Further study will be needed in both cadaveric and clinical models to assess whether these changes in tunnel characteristics will result in clinically measurable differences in laxity or patients’ feelings of stability. This study is unique in evaluating femoral tunnels after the use of an AM portal, which is in a different location than more traditional anteromedial portals, for independent femoral tunnel drilling. This builds on similar Table 1. Femoral Tunnel Characteristics Variable
Fig 3. The femoral tunnel angle in the axial plane was measured relative to the posterior condylar axis.
Aperture area (mm2) Aperture long axis (mm) Aperture short axis (mm) Aperture from anterior articular surface (mm) Aperture from inferior articular surface (mm) Tunnel orientation in coronal plane ( ) Tunnel orientation in axial plane ( ) Tunnel length (mm) Tunnel volume (mm3)
AM Portal 50.5 8.5 8.0 5.0
4.8 1.1 0.5 1.4
TT 51.9 9.2 8.0 9.9
P Value 4.6 1.3 0.5 1.7
.5 .2 .8 <.001*
7.6 2.4
8.9 2.2
42.1 4.8
60.9 6.7
20.9 4.4
22.7 13.5
.7
35.6 2.8 1659 177
40.3 7.9 1829 369
.1 .2
*Statistically significant (P < .05).
.2 <.001*
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studies that have used more traditional anteromedial portals for independent femoral tunnel drilling.4,18,25 In addition, this study evaluates the orientation of the tunnels within the lateral femoral condyle, which has not previously been reported. Though not statistically significant, there is also a trend toward a smaller and more circular tunnel aperture, a tunnel lower on the lateral wall, and tunnels that are shorter but of adequate length by use of an AM portal.24 Because the most important healing point for the graft within the tunnel is at the aperture, the larger size and more elliptical shape in the TT femoral tunnels could have important ramifications on graft incorporation or tunnel widening.26-30 On the other hand, a more elliptical aperture may mean a more gentle turn of the graft into the tunnel and therefore less strain on the graft in the early phases of healing. Though also not statistically significant, the tunnel length trended toward being shorter when an AM portal was used (4.7 mm shorter). With a mean length of greater than 35 mm, however, this tunnel is likely still of adequate length for clinical utility.24 In the axial plane, the AM portal tunnels were generally oriented toward the lateral femoral epicondyle and therefore the greatest width of bone within the lateral femoral condyle. This likely accounts for the adequate length of the tunnels as compared with previous studies showing shortened tunnels with a standard anteromedial portal.19,25 One concern from this orientation of the femoral tunnel would be that the epicondyle and therefore the lateral collateral ligament would be violated; however, this was not the case because the tunnels exited the lateral femoral condyle just superior to the epicondyle in the coronal plane (Fig 2). Further study will be needed in both cadaveric and clinical models to more precisely identify what is an adequate tunnel length for clinical success. A shorter femoral tunnel translates to lower volume. It is unclear what significance this might have, but these volume values may serve as a reference for future studies evaluating the femoral tunnel in ACL reconstruction. Recently, a similar study was performed comparing femoral tunnels created through an anteromedial portal versus TT drilling.4 The emphasis of that study was on comparing the more horizontal tunnel created by an anteromedial portal with that from TT drilling. There was not, however, a stated emphasis placed on creating an anatomic starting point for the tunnel as was performed in our study. We wished to directly compare some of the data from our study with that study; however, the previous study was performed with 10-mm drill bits, making it difficult to directly compare most of the measurements. In general, the trends for aperture size and shape were similar. Interestingly, it would appear that both the TT tunnel and the AM
portal tunnel in our study started lower on the lateral wall, likely resulting in a more horizontal tunnel in the coronal plane than their counterparts from the previous study. In addition, it is important to note that the tunnel length was greater in our study, especially when one compares the AM tunnels from our study with the anteromedial tunnels from the previous study. Both of these findings likely result from the emphasis placed on an anatomic starting point in our study. Because we know that tunnel length is important and other previous studies have shown that more horizontal tunnels increase rotational stability of the knee, these findings emphasize the value of focusing on an anatomic reconstruction.5,6 Future studies should compare the femoral tunnel characteristics created by an AM portal versus a traditional anteromedial portal. Future studies should also be carried out to radiographically follow up ACL reconstruction patients and evaluate the effects of various tunnel characteristics on the incorporation of the graft or on tunnel widening. One recent study with radiographic follow-up performed at 1 year did not show significant differences, but there was a trend toward greater tunnel widening in the TT group versus femoral tunnel drilling through an anteromedial portal.31 In addition, these changes in the femoral tunnel resulting from different reconstruction techniques should be followed clinically to assess whether there is any clinical significance. Another area of recent interest in the literature, and related to the tunnel characteristics, has been graft bending angles.20,23 The effect that different aperture size and shape, tunnel location, and tunnel angle has on graft bending angles and therefore graft strain will also be important to follow. Limitations Limitations of this study include the fact that it is a cadaveric study. The cadavers ages were older than most patients undergoing ACL reconstruction, so it is probable that the femoral tunnel bone quality was more osteopenic than the normal ACL reconstruction population, which could affect some of the femoral tunnel characteristics. The radiographic review was not blinded to the technique being evaluated because of the complex radiographic analysis. Ideally, we would like to compare a traditional anteromedial portal approach with an AM approach; however, as a first step, we believed that it was important to compare the AM approach with a TT approach, because the TT approach is more traditional and continues to be performed by many orthopaedic surgeons.
Conclusions The use of an AM portal creates a tunnel more anterior and more horizontal than tunnels created by a TT technique.
FEMORAL TUNNEL CHARACTERISTICS
Acknowledgment The authors thank Winston Evatt, Carmen Spitzer, Jamie Weathersbee, and Rick Stewart for their time and assistance in scanning the cadaveric specimens.
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