LETTERS TO THE EDITOR
539
Fig 2. Lateral radiograph and CT image of the lateral condyle and lateral wall of the notch with medial condyle removed. On the radiograph (left), the centrum of the anteromedial bundle (green cross), posterolateral bundle (blue cross), and the whole ACL attachment (black cross) are marked. The white line marks the proximal-to-distal length of the radiograph at the site of the midattachment site, and the red line indicates the distance from the proximal projection of the bone on the radiograph to the centrum of the ACL. The proportion of the red line to the white line is 43%dconsistent with the findings in the article. On the CT image (right), a tunnel has been drilled in the centrum of the ACL insertion (confirmed on grid measurements, which are not shown). The solid white line represents the lateral side wall of the notch seen arthroscopically, and the solid red line the distance from the proximal border of the notch side wall to the center of the tunnel. The proportion of red to white is 50%. The dashed white line indicates a distance similar to that drawn on the lateral radiograph, and the dashed red line the distance from the projection of the posterior condyle to the same center of the tunnel; this measures 43%.
Note: The authors report the following potential conflict of interest or source of funding in relation to this article: T.S. receives support from Zimmer UK; A.G. receives support from Arthrex; and J.R. receives support from Smith & Nephew. Ó 2014 by the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2014.02.004
References 1. Piefer JW, Pflugner TR, Hwang MD, Lubowitz JH. Anterior cruciate ligament femoral footprint anatomy: Systematic review of the 21st century literature. Arthroscopy 2012;28: 872-881. 2. Bird J, Carmont MR, Dhillon M, et al. Validation of a new technique to determine midbundle femoral tunnel position in anterior cruciate ligament reconstruction using 3dimensional computed tomography analysis. Arthroscopy 2011;27:1259-1267.
Authors’ Reply We very much appreciate the work and interest in ACL femoral footprint anatomy of Bird et al.1 and the thought-provoking letter from Dr. Spalding et al. The authors suggest a valid point, and we regret that their
important article1 was published after the time of our systematic search of the literature.2 Before we comment further, we first wish to again acknowledge the seminal work of Kaseta et al.3 who, to our knowledge, first described the concept and method of defining the proximal-to-distal distance of the anatomic centrum of the ACL femoral footprint. “This reference was not included in our results, using the study search methods tested, but is recommended as invaluable reading for students of ACL femoral anatomy.”2 Next, reviewing Fig 2 of Dr. Spalding’s letter, it does appear that the center is at 50% when measured on the lateral side wall of the notch of the computed tomographic (CT) image. Unfortunately, CT scans show only the bone, and the location of the articular cartilage margin can only be inferred. Review of the letter’s Fig 2 raises significant doubt in our minds as to whether the white arrowheads that the authors superimposed on the CT image correspond to the arthroscopic landmarks we describe, which are the “articular margins (arthroscopically visualized osteochondral junctions)” of the lateral wall of the femoral intercondylar notch.2 As we wrote, “our translational research goal is to describe arthroscopically useful, surgically relevant landmarks for practicing ACL surgeons who operate without routine use of fluoroscopy or open surgical dissection.”
540
LETTERS TO THE EDITOR
In addition, we did note in our article, as the letter writers emphasize, “Because we derive the percent proximal-to-distal distance using radiographic landmarks, we clarify that the measurements are of the bony notch wall, without consideration of the articular cartilage (which is not visible on radiographs).”2 At any rate, returning to the letter writers’ Fig 2, specifically the white arrowheads that the authors assertively superimposed on the CT image, our impression is that proximally (on the right), the tip of the arrow is very much on the proximal (right) side of a ridge (which we may only speculate as representative of the proximal articular margin), whereas distally (on the left), the tip of the arrow is very much also on the proximal (right) side of a ridge (which we may only speculate as representative of the distal articular margin). Although this language may be confusing, readers who are passionate about ACL anatomy could review the preceding sentence while viewing the figure in question, in which case we believe that our point will be clear. In addition, what is clear is that if the arrows were centered in the middle of the proximal and distal ridges noted on the CT image, the result would be closer to 43%. Furthermore, the figure in question represents only a single scan of a single patient. The results in other patients may vary. Finally, viewing the red arrow on the figure, it is not 100% clear as to the location of the ACL footprint centrum because the scan seems to illustrate a femoral socket that may or may not be entirely anatomic and may or may not entirely correspond to the lateral radiographic image in all planes. However, to be fair, we admire Dr. Spalding et al. and know them to be clever and devoted researchers. We are happy to compromise and to thoughtfully consider that pending additional research, perhaps the correct answer lies somewhere between 43% and 50% of the proximal-to-distal distance of the arthroscopically visualized osteochondral junctions. In our clinical experience, the proximal-to-distal distance generally measures approximately 26 mm; 43% of 26 mm is 11.2 mm and 50% of 26 mm is 13 mm. Therefore, the good news is that our findings are in agreement within a margin of less than 2 mm. Bearing in mind that surgeons are human, and a surgeon’s ability to place a guide pin is imperfect in both precision and accuracy,4,5 it is evident that we are in agreement to an extent that may exceed clinical exactitude. In addition, although anatomy is vital, it is important to remember that we are discussing placement of a relatively small (and proverbial) “needle” in a rather large “haystack,” bearing in mind that the ACL femoral footprint is large, with an area described to be approximately 136 mm2.6,7
Next, ACL surgeons trying to make the decision as to whether to place the ACL femoral footprint at the 50% versus the 43% proximal-to-distal position should thoughtfully consider the well-respected work of Cross et al.8 These authors concluded that there is “no difference in the time-zero biomechanical stability between an anatomic anteromedial and anatomic central single-bundle ACL reconstruction. Given the current debate on the best anatomic ACL reconstruction technique, anatomic socket position in either the anteromedial or central locations provides similar time-zero biomechanics.” Again bearing in mind imperfect surgical precision and accuracy, surgeons should remember that if 43% is too proximal, this would be closer to the anteromedial femoral ACL centrum, which results in similar biomechanics. However, if 50% is too distal, this would be closer to the posterolateral bundle centrum, which may be biomechanically less favorable than anteromedial or central positioning. Thus, we suggest that pending additional research, surgeons trying to make the decision about where to place the ACL femoral centrum would be advised to aim for a proximal-to-distal distance of less than 50%. Moreover, it is important to remember that compared with where we once placed our ACL femoral sockets using endoscopic aimers,9,10 our results are considerably more anatomic1-3,6-8 than in the 1990s, and in this context, as previously, the results of Dr. Spalding’s group and our group are more similar than different. Finally, in the era of anatomic single-bundle ACL reconstruction, our impression is that our surgical outcomes11 have never been better, and our results seem to continue to improve. However, our improved ACL results in the 21st century may be multifactorial, because in addition to changes in ACL femoral socket placement,2 we have altered our ACL tibial socket placement,12 our ACL surgical technique,13 our ACL graft fixation technique,13 and our ACL patient rehabilitation and return to play guidelines,14 have limited our use of allograft tissue in younger patients,15 and have augmented ACL hamstring autografts with allograft tissue (in patients of all ages) when autograft diameter is less than 8.5 mm diameter.16,17 In summary, we believe that Spalding et al. suggest a valid point, yet our opinion is that pending additional research, surgeons trying to make the decision about where to place the ACL femoral centrum would be advised to aim for a proximal-to-distal distance of less than the 50% distance Dr. Spalding’s group suggests. Furthermore, we suggest that the findings of Dr. Spalding’s group1 and our group2 are more similar than different. Finally, we remind surgeons that many factors determine ACL surgical outcome, and that “Understanding ACL research requires patience and persistence.”18
LETTERS TO THE EDITOR
James H. Lubowitz, M.D. Taos, New Mexico www.newmexicokneesurgery.com Michael Hwang, M.D. Jason Piefer, M.D. Ryan Pflugner, M.D. Ó 2014 by the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2014.02.003
References 1. Bird J, Carmont MR, Dhillon M, et al. Validation of a new technique to determine midbundle femoral tunnel position in anterior cruciate ligament reconstruction using 3dimensional computed tomography analysis. Arthroscopy 2011;27:1259-1267. 2. Piefer JW, Pflugner TR, Hwang MD, Lubowitz JH. Anterior cruciate ligament femoral footprint anatomy: Systematic review of the 21st century literature. Arthroscopy 2012;28:872-881. 3. Kaseta MK, DeFrate LE, Charnock BL, Sullivan RT, Garrett WE. Reconstruction technique affects femoral tunnel placement in ACL reconstruction. Clin Orthop Relat Res 2008;466:1467-1474. 4. Lubowitz J, Konicek J. A 3.5-mm-diameter anterior cruciate ligament tibial retrograde socket drilling pin is more accurate than a 2.4-mm-diameter pin. Arthroscopy 2011;26:666-671. 5. Rossi M, Lubowitz J, Provencher M, Poehling G. Precision versus accuracy: A case for common sense. Arthroscopy 2012;28:1043-1044. 6. Lubowitz J, Akhavan S, Waterman B, Aalami-Harandi A, Konicek J. Technique for creating the anterior cruciate ligament femoral socket: Optimizing femoral footprint anatomic restoration using outside-in drilling. Arthroscopy 2013;29:522-528. 7. Hensler D, Working ZM, Illingworth KD, Thorhauer ED, Tashman S, Fu FH. Medial portal drilling: Effects on the femoral tunnel aperture morphology during anterior cruciate ligament reconstruction. J Bone Joint Surg Am 2011;93:2063-2071.
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8. Cross MB, Musahl V, Bedi A, et al. Anteromedial versus central single-bundle graft position: Which anatomic graft position to choose? Knee Surg Sports Traumatol Arthrosc 2012;20:1276-1281. 9. McGuire DA, Hendricks SD, Grinstead GL. Use of an endoscopic aimer for femoral tunnel placement in anterior cruciate ligament reconstruction. Arthroscopy 1996;12:26-31. 10. Morgan CD, Kalman VR, Grawl DM. Isometry testing for anterior cruciate ligament reconstruction revisited. Arthroscopy 1995;11:647-659. 11. Lubowitz J, Schwartzberg R, Smith P. Randomized controlled trial comparing all-inside anterior cruciate ligament reconstruction technique with anterior cruciate ligament reconstruction with a full tibial tunnel. Arthroscopy 2013;29:1195-1200. 12. Hwang MD, Piefer JW, Lubowitz JH. Anterior cruciate ligament tibial footprint anatomy: Systematic review of the 21st century literature. Arthroscopy 2012;28:728-734. 13. Lubowitz J, Ahmad C, Anderson K. All-inside anterior cruciate ligament graft-link technique: Secondgeneration, no-incision anterior cruciate ligament reconstruction. Arthroscopy 2011;26:717-727. 14. Tokish J, Kozlowski E. Return to play after ACL reconstruction. In: Bach B, Provencher M, eds. ACL Surgery: How to get it right the first time and what to do when you don’t. Thorofare, NJ: Slack, 2010. 15. Kaeding CC, Aros B, Pedroza A, et al. Allograft versus autograft anterior cruciate ligament reconstruction: Predictors of failure from a MOON prospective longitudinal cohort. Sports Health 2011;3:73-81. 16. Mariscalco MW, Flanigan DC, Mitchell J, et al. The influence of hamstring autograft size on patient-reported outcomes and risk of revision after anterior cruciate ligament reconstruction: A Multicenter Orthopaedic Outcomes Network (MOON) Cohort Study. Arthroscopy 2013;29:1948-1953. 17. Magnussen RA, Lawrence JT, West RL, Toth AP, Taylor DC, Garrett WE. Graft size and patient age are predictors of early revision after anterior cruciate ligament reconstruction with hamstring autograft. Arthroscopy 2012;28:526-531. 18. Lubowitz J, Poehling G. Understanding ACL research requires patience and persistence. Arthroscopy 2010;26: 869-871.
539
Fig 2. Lateral radiograph and CT image of the lateral condyle and lateral wall of the notch with medial condyle removed. On the radiograph (left), the centrum of the anteromedial bundle (green cross), posterolateral bundle (blue cross), and the whole ACL attachment (black cross) are marked. The white line marks the proximal-to-distal length of the radiograph at the site of the midattachment site, and the red line indicates the distance from the proximal projection of the bone on the radiograph to the centrum of the ACL. The proportion of the red line to the white line is 43%dconsistent with the findings in the article. On the CT image (right), a tunnel has been drilled in the centrum of the ACL insertion (confirmed on grid measurements, which are not shown). The solid white line represents the lateral side wall of the notch seen arthroscopically, and the solid red line the distance from the proximal border of the notch side wall to the center of the tunnel. The proportion of red to white is 50%. The dashed white line indicates a distance similar to that drawn on the lateral radiograph, and the dashed red line the distance from the projection of the posterior condyle to the same center of the tunnel; this measures 43%.
Note: The authors report the following potential conflict of interest or source of funding in relation to this article: T.S. receives support from Zimmer UK; A.G. receives support from Arthrex; and J.R. receives support from Smith & Nephew. Ó 2014 by the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2014.02.004
References 1. Piefer JW, Pflugner TR, Hwang MD, Lubowitz JH. Anterior cruciate ligament femoral footprint anatomy: Systematic review of the 21st century literature. Arthroscopy 2012;28: 872-881. 2. Bird J, Carmont MR, Dhillon M, et al. Validation of a new technique to determine midbundle femoral tunnel position in anterior cruciate ligament reconstruction using 3dimensional computed tomography analysis. Arthroscopy 2011;27:1259-1267.
Authors’ Reply We very much appreciate the work and interest in ACL femoral footprint anatomy of Bird et al.1 and the thought-provoking letter from Dr. Spalding et al. The authors suggest a valid point, and we regret that their
important article1 was published after the time of our systematic search of the literature.2 Before we comment further, we first wish to again acknowledge the seminal work of Kaseta et al.3 who, to our knowledge, first described the concept and method of defining the proximal-to-distal distance of the anatomic centrum of the ACL femoral footprint. “This reference was not included in our results, using the study search methods tested, but is recommended as invaluable reading for students of ACL femoral anatomy.”2 Next, reviewing Fig 2 of Dr. Spalding’s letter, it does appear that the center is at 50% when measured on the lateral side wall of the notch of the computed tomographic (CT) image. Unfortunately, CT scans show only the bone, and the location of the articular cartilage margin can only be inferred. Review of the letter’s Fig 2 raises significant doubt in our minds as to whether the white arrowheads that the authors superimposed on the CT image correspond to the arthroscopic landmarks we describe, which are the “articular margins (arthroscopically visualized osteochondral junctions)” of the lateral wall of the femoral intercondylar notch.2 As we wrote, “our translational research goal is to describe arthroscopically useful, surgically relevant landmarks for practicing ACL surgeons who operate without routine use of fluoroscopy or open surgical dissection.”
540
LETTERS TO THE EDITOR
In addition, we did note in our article, as the letter writers emphasize, “Because we derive the percent proximal-to-distal distance using radiographic landmarks, we clarify that the measurements are of the bony notch wall, without consideration of the articular cartilage (which is not visible on radiographs).”2 At any rate, returning to the letter writers’ Fig 2, specifically the white arrowheads that the authors assertively superimposed on the CT image, our impression is that proximally (on the right), the tip of the arrow is very much on the proximal (right) side of a ridge (which we may only speculate as representative of the proximal articular margin), whereas distally (on the left), the tip of the arrow is very much also on the proximal (right) side of a ridge (which we may only speculate as representative of the distal articular margin). Although this language may be confusing, readers who are passionate about ACL anatomy could review the preceding sentence while viewing the figure in question, in which case we believe that our point will be clear. In addition, what is clear is that if the arrows were centered in the middle of the proximal and distal ridges noted on the CT image, the result would be closer to 43%. Furthermore, the figure in question represents only a single scan of a single patient. The results in other patients may vary. Finally, viewing the red arrow on the figure, it is not 100% clear as to the location of the ACL footprint centrum because the scan seems to illustrate a femoral socket that may or may not be entirely anatomic and may or may not entirely correspond to the lateral radiographic image in all planes. However, to be fair, we admire Dr. Spalding et al. and know them to be clever and devoted researchers. We are happy to compromise and to thoughtfully consider that pending additional research, perhaps the correct answer lies somewhere between 43% and 50% of the proximal-to-distal distance of the arthroscopically visualized osteochondral junctions. In our clinical experience, the proximal-to-distal distance generally measures approximately 26 mm; 43% of 26 mm is 11.2 mm and 50% of 26 mm is 13 mm. Therefore, the good news is that our findings are in agreement within a margin of less than 2 mm. Bearing in mind that surgeons are human, and a surgeon’s ability to place a guide pin is imperfect in both precision and accuracy,4,5 it is evident that we are in agreement to an extent that may exceed clinical exactitude. In addition, although anatomy is vital, it is important to remember that we are discussing placement of a relatively small (and proverbial) “needle” in a rather large “haystack,” bearing in mind that the ACL femoral footprint is large, with an area described to be approximately 136 mm2.6,7
Next, ACL surgeons trying to make the decision as to whether to place the ACL femoral footprint at the 50% versus the 43% proximal-to-distal position should thoughtfully consider the well-respected work of Cross et al.8 These authors concluded that there is “no difference in the time-zero biomechanical stability between an anatomic anteromedial and anatomic central single-bundle ACL reconstruction. Given the current debate on the best anatomic ACL reconstruction technique, anatomic socket position in either the anteromedial or central locations provides similar time-zero biomechanics.” Again bearing in mind imperfect surgical precision and accuracy, surgeons should remember that if 43% is too proximal, this would be closer to the anteromedial femoral ACL centrum, which results in similar biomechanics. However, if 50% is too distal, this would be closer to the posterolateral bundle centrum, which may be biomechanically less favorable than anteromedial or central positioning. Thus, we suggest that pending additional research, surgeons trying to make the decision about where to place the ACL femoral centrum would be advised to aim for a proximal-to-distal distance of less than 50%. Moreover, it is important to remember that compared with where we once placed our ACL femoral sockets using endoscopic aimers,9,10 our results are considerably more anatomic1-3,6-8 than in the 1990s, and in this context, as previously, the results of Dr. Spalding’s group and our group are more similar than different. Finally, in the era of anatomic single-bundle ACL reconstruction, our impression is that our surgical outcomes11 have never been better, and our results seem to continue to improve. However, our improved ACL results in the 21st century may be multifactorial, because in addition to changes in ACL femoral socket placement,2 we have altered our ACL tibial socket placement,12 our ACL surgical technique,13 our ACL graft fixation technique,13 and our ACL patient rehabilitation and return to play guidelines,14 have limited our use of allograft tissue in younger patients,15 and have augmented ACL hamstring autografts with allograft tissue (in patients of all ages) when autograft diameter is less than 8.5 mm diameter.16,17 In summary, we believe that Spalding et al. suggest a valid point, yet our opinion is that pending additional research, surgeons trying to make the decision about where to place the ACL femoral centrum would be advised to aim for a proximal-to-distal distance of less than the 50% distance Dr. Spalding’s group suggests. Furthermore, we suggest that the findings of Dr. Spalding’s group1 and our group2 are more similar than different. Finally, we remind surgeons that many factors determine ACL surgical outcome, and that “Understanding ACL research requires patience and persistence.”18
LETTERS TO THE EDITOR
James H. Lubowitz, M.D. Taos, New Mexico www.newmexicokneesurgery.com Michael Hwang, M.D. Jason Piefer, M.D. Ryan Pflugner, M.D. Ó 2014 by the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2014.02.003
References 1. Bird J, Carmont MR, Dhillon M, et al. Validation of a new technique to determine midbundle femoral tunnel position in anterior cruciate ligament reconstruction using 3dimensional computed tomography analysis. Arthroscopy 2011;27:1259-1267. 2. Piefer JW, Pflugner TR, Hwang MD, Lubowitz JH. Anterior cruciate ligament femoral footprint anatomy: Systematic review of the 21st century literature. Arthroscopy 2012;28:872-881. 3. Kaseta MK, DeFrate LE, Charnock BL, Sullivan RT, Garrett WE. Reconstruction technique affects femoral tunnel placement in ACL reconstruction. Clin Orthop Relat Res 2008;466:1467-1474. 4. Lubowitz J, Konicek J. A 3.5-mm-diameter anterior cruciate ligament tibial retrograde socket drilling pin is more accurate than a 2.4-mm-diameter pin. Arthroscopy 2011;26:666-671. 5. Rossi M, Lubowitz J, Provencher M, Poehling G. Precision versus accuracy: A case for common sense. Arthroscopy 2012;28:1043-1044. 6. Lubowitz J, Akhavan S, Waterman B, Aalami-Harandi A, Konicek J. Technique for creating the anterior cruciate ligament femoral socket: Optimizing femoral footprint anatomic restoration using outside-in drilling. Arthroscopy 2013;29:522-528. 7. Hensler D, Working ZM, Illingworth KD, Thorhauer ED, Tashman S, Fu FH. Medial portal drilling: Effects on the femoral tunnel aperture morphology during anterior cruciate ligament reconstruction. J Bone Joint Surg Am 2011;93:2063-2071.
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8. Cross MB, Musahl V, Bedi A, et al. Anteromedial versus central single-bundle graft position: Which anatomic graft position to choose? Knee Surg Sports Traumatol Arthrosc 2012;20:1276-1281. 9. McGuire DA, Hendricks SD, Grinstead GL. Use of an endoscopic aimer for femoral tunnel placement in anterior cruciate ligament reconstruction. Arthroscopy 1996;12:26-31. 10. Morgan CD, Kalman VR, Grawl DM. Isometry testing for anterior cruciate ligament reconstruction revisited. Arthroscopy 1995;11:647-659. 11. Lubowitz J, Schwartzberg R, Smith P. Randomized controlled trial comparing all-inside anterior cruciate ligament reconstruction technique with anterior cruciate ligament reconstruction with a full tibial tunnel. Arthroscopy 2013;29:1195-1200. 12. Hwang MD, Piefer JW, Lubowitz JH. Anterior cruciate ligament tibial footprint anatomy: Systematic review of the 21st century literature. Arthroscopy 2012;28:728-734. 13. Lubowitz J, Ahmad C, Anderson K. All-inside anterior cruciate ligament graft-link technique: Secondgeneration, no-incision anterior cruciate ligament reconstruction. Arthroscopy 2011;26:717-727. 14. Tokish J, Kozlowski E. Return to play after ACL reconstruction. In: Bach B, Provencher M, eds. ACL Surgery: How to get it right the first time and what to do when you don’t. Thorofare, NJ: Slack, 2010. 15. Kaeding CC, Aros B, Pedroza A, et al. Allograft versus autograft anterior cruciate ligament reconstruction: Predictors of failure from a MOON prospective longitudinal cohort. Sports Health 2011;3:73-81. 16. Mariscalco MW, Flanigan DC, Mitchell J, et al. The influence of hamstring autograft size on patient-reported outcomes and risk of revision after anterior cruciate ligament reconstruction: A Multicenter Orthopaedic Outcomes Network (MOON) Cohort Study. Arthroscopy 2013;29:1948-1953. 17. Magnussen RA, Lawrence JT, West RL, Toth AP, Taylor DC, Garrett WE. Graft size and patient age are predictors of early revision after anterior cruciate ligament reconstruction with hamstring autograft. Arthroscopy 2012;28:526-531. 18. Lubowitz J, Poehling G. Understanding ACL research requires patience and persistence. Arthroscopy 2010;26: 869-871.
