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Transtibial Tunnel Drilling of the Femoral Tunnel for Anatomic Single-Bundle Anterior Cruciate Ligament Reconstruction
SECTION IX Principles of Tunnel Formation
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41
Transtibial Tunnel Drilling of the Femoral Tunnel for Anatomic Single-Bundle Anterior Cruciate Ligament Reconstruction Chadwick C. Prodromos, MD
INTRODUCTION
Decreased Graft Abrasion at the Femoral Outlet
Drilling the femoral tunnel via the tibial tunnel (transtibial tunnel drilling or TTTD) has been the standard technique since the early days of anterior cruciate ligament reconstruction (ACLR) and has produced excellent results with both hamstring and patellar tendon grafts.1–3 The groundbreaking work of Stephen Howell4 showed that a coronal angle of 65 degrees is optimal, and this has been universally felt to be easily achievable with TTTD. More recently there has been a trend toward transmedial portal drilling (TMPD) of the femoral tunnel. This trend started in response to the transient trend toward double-bundle reconstruction, which necessitated placing one of the tunnels far down on the wall of the femoral intercondylar notch, which cannot be done transtibially. While meta-analyses5,6 have shown marginally overall better results from double-bundle ACLR, other reports have shown no difference,7 and morbidity and surgical difficulty have been recognized to be greater with double-bundle. Thus most orthopaedic surgeons have now reverted to anatomic single-bundle reconstruction,8 placing the femoral tunnel in the middle of the femoral footprint of the anterior cruciate ligament (ACL), instead of at the bottom. Additionally, a recent landmark paper9 from the lab of Andrew Amis has shown that “66% to 84% of the resistance to tibial anterior drawer arose from the ACL fibers at the central-proximal area of the femoral attachment…corresponding to the anteromedial bundle…The central area resisted 82% to 90% of the anterior drawer force; …and the posterior fan-like area, 11% to 15%.” These findings from arguably the world’s leader in studies of this kind argue powerfully in favor of the easier traditional transtibial drilling of the femoral tunnel rather than the more difficult medial portal technique, since there is now excellent anatomical and biomechanical evidence that drilling near the bottom of the femoral wall is unnecessary and indeed not physiologic.
One of the original perceived advantages of TTTD is that the graft has a relatively straight course as it enters the femoral tunnel. The tibial and femoral tunnels are essentially colinear with the TTTD technique. This decreases abrasion of the graft at the femoral outlet since the graft is not bent around its entrance point.
TRANS FEMORAL TUNNEL DISADVANTAGES Difficult Knee Flexion Angle In TMPD, drilling must be done with the knee hyperflexed to over 110 degrees. Such hyperflexion provides both reduced visibility and a view that is unfamiliar to most orthopaedic surgeons as they search for femoral footprint landmarks. Such hyperflexion can also be difficult to maintain in lower extremities of large girth, which has become increasingly common in patients.
Shorter Femoral Tunnel Length TMPD has the further disadvantage that it tends to produce shorter femoral tunnels,10 which may be too short for proper fixation with buttons or cross-pins.11
Increased Graft Femoral Tunnel Abrasion TMPD causes the graft to enter the femoral tunnel at a significant angle, since the femoral tunnel is drilled at a different angle (i.e., more horizontally) than the tibial tunnel. This angle subjects the graft to greater abrasive stresses than are seen with TTTD.
TRANSTIBIAL FEMORAL TUNNEL DRILLING ADVANTAGES
TRANSTIBIAL FEMORAL TUNNEL DRILLING TECHNIQUE
Comfortable Knee Flexion Angle
TTTD is not difficult. The only caution is to make sure the graft is not too vertical, with a femoral entry point too high in the notch. The generic steps of proper TTTD are described as follows. The clinical pearls that enable an appropriate coronal graft angle are bold:
TTTD can be carried out with the knee flexed to its natural position of roughly 70 degrees as routine arthroscopy is conducted. This technique and the intra-articular view provided are familiar to most orthopaedic surgeons.
Adequate Tunnel Length TTTD drilling routinely allows femoral tunnels of at least 3 cm in length.10
1. Tibial Guide: Select a commercially available tibial guide. All of the major device companies offer these, and any are suitable for TTTD. 2. Placing the Tibial Incision: This is the most important step because it dictates the tibial tunnel entry point. The
167
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SECTION IX Principles of Tunnel Formation
tibial tunnel entry point dictates tunnel angle and femoral tunnel entry point possibilities. The vertical or oblique incision should be placed toward the mid- or posterior tibia just anterior to the attachment of the medial collateral ligament. The entry point should be sufficiently posterior and the tip of the drill guide held simultaneously within the tibial footprint of the anatomic attachment of the ACL, so that it results in a sufficiently oblique tibial tunnel of about 65 degrees in the coronal plane.4 This will allow direction of the long guide pin to a suitable femoral entry point at about 10:30/1:30 o’clock in the notch within the middle of the femoral ACL footprint. CAUTION: If the entry point on the tibia is not posterior, then the tibial tunnel will be more vertical and will direct the guide pin to an entry point in the notch that is too high. This will produce a vertical graft and predispose to failure. For hamstring harvest the same incision can easily be used to harvest the hamstring and drill the tibial tunnel. However, it is important to realize that the harvest incision for the BTB graft is, in general, too far anterior to allow drilling through it for the tibial tunnel, unless the incision is sufficiently long to allow soft tissue to be moved posteromedially on the tibia. 3. Drilling the Tibial Tunnel: This should be drilled in the usual fashion, with a point-to-point guide. 4. Femoral Wallplasty: We believe it is imperative to perform a limited notch lateral (3 mm) wallplasty and also remove all soft tissue from the femoral attachment of the ACL so that the proper entry point can be easily visualized. This is performed with the arthroscope in the lateral portal and the shaver and burr in the medial portal. If visualization is difficult, a 70degree scope may be used to better see around the lateral femoral chondyle (LFC) to the femoral ACL attachment. 5. Drilling the Femoral Tunnel: A long guide pin is passed through the tibial tunnel, and the tip is placed in the middle of the anatomic attachment of the ACL on the femur. If step 2 (listed previously) was properly executed, the tip of the pin should find this point easily. We prefer not to use guides, which can impair visualization, and instead bring the tip of the guide pin all the way proximally to the over-the-top position and then walk it back sufficiently to allow a tunnel to be drilled that will not break out the proximal cortex. This point is at 10:30/1:30 o’clock. Sometimes knee flexion needs to be slightly decreased to help just the tip (2 mm) of the guide pin to insert at the proper point. The knee can then be flexed a few degrees for the drilling of the tunnel. The guide pin is then overdrilled with the appropriate diameter reamer. We typically hold the knee in about 80 degrees of knee flexion (a little more than the 70 degrees or so that it finds on its own from gravity). If the knee is held a little flexed for drilling, this position must be maintained by an assistant until the guide pin is removed to avoid guide pin bending or breakage. 6. Finishing the Femoral Tunnel: From this point forward, steps will vary depending on the guide system used.
CONCLUSIONS The author and countless other experienced ACL surgeons have used the TTTD technique for decades with reliably excellent results. It is easy to place the femoral tunnel in exactly the right location with appropriate coronal plane obliquity for anatomic single-bundle ACLR. TTTD also avoids the hardship and potential errors of placing the tunnel in a hyperflexed knee. It reduces the likelihood of short tunnels and graft abrasion The transient fascination with double-bundle techniques has apparently caused some to forget the ease and excellent results of using TTTD. TTTD was only questioned because it could not fill the bottom of the footprint, which is now both from clinical studies and the work of Amis, seen by most as unnecessary and perhaps undesirable. The only advantage of TMPD is for the rapidly shrinking group of surgeons who use double-bundle repair routinely. And even there we have found an outside-in guide to be preferable for the lower tunnel when we use doublebundle repairs for revisions. SELECTED READINGS
Ahldén M, Sernert N, Karlsson J, Kartus J. A prospective randomized study comparing double- and single-bundle techniques for anterior cruciate ligament reconstruction. Am J Sports Med. 2013;41(11): 2484–2491. Björnsson H, Desai N, Musahl V, et al. Is double-bundle anterior cruciate ligament reconstruction superior to single-bundle? A comprehensive systematic review. Knee Surg Sports Traumatol Arthrosc. 2015;23(3):696–739. Gelber P, Reina F, Torres R, Monllau J. Effect of femoral tunnel length on the safety of anterior cruciate ligament graft fixation using cross-pin technique: a cadaveric study. Am J Sports Med. 2010;38(9):1877–1884. Gerdeman A, Hart J, Bennett C, Golish S, Gaskin C, Miller M. A comparison of 2 drilling techniques on the femoral tunnel for anterior cruciate ligament reconstruction. Arthroscopy. 2011;27(3):372–379. Haro M, Riff A, Bach BJ. Tips for successful transtibial anterior cruciate ligament reconstruction. J Knee Surg. 2014;27(5):331–342. Howell S, Gittins M, Gottlieb J, Traina S, Zoellner T. The relationship between the angle of the tibial tunnel in the coronal plane and loss of flexion and anterior laxity after anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29(5):567–574. Kawaguchi Y, Kondo E, Takeda R, Akita K, Yasuda K, Amis A. The role of fibers in the femoral attachment of the anterior cruciate ligament in resisting tibial displacement. Arthroscopy. 2015;31(3):435–444. Li Y, Ning G, Wu Q, et al. Single-bundle or double-bundle for anterior cruciate ligament reconstruction: a meta-analysis. Knee. 2014;21(1):28–37. Massey P, Tjoumakaris F, Bernstein J. Eminence-based medicine versus evidence-based medicine: is anterior cruciate ligament reconstruction optimally performed with the double-bundle technique? Phys Sportsmed. 2013;41(1):102–106. Prodromos C, Han Y, Keller B, Bolyard R. Stability results of hamstring anterior cruciate ligament reconstruction at 2- to 8-year follow-up. Arthroscopy. 2005;21(2):138–146. Rue J, Ghodadra N, Lewis P, Bach BJ. Femoral and tibial tunnel position using a transtibial drilled anterior cruciate ligament reconstruction technique. J Knee Surg. 2008;21(3):246–249.
A complete reference list can be found online at ExpertConsult.com.
REFERENCES
1. Prodromos C, Han Y, Keller B, Bolyard R. Stability results of hamstring anterior cruciate ligament reconstruction at 2- to 8-year follow-up. Arthroscopy. 2005;21(2):138–146. 2. Haro M, Riff A, Bach BJ. Tips for successful transtibial anterior cruciate ligament reconstruction. J Knee Surg. 2014;27(5):331–342. 3. Rue J, Ghodadra N, Lewis P, Bach BJ. Femoral and tibial tunnel position using a transtibial drilled anterior cruciate ligament reconstruction technique. J Knee Surg. 2008;21(3):246–249. 4. Howell S, Gittins M, Gottlieb J, Traina S, Zoellner T. The relationship between the angle of the tibial tunnel in the coronal plane and loss of flexion and anterior laxity after anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29(5):567–574. 5. Björnsson H, Desai N, Musahl V, et al. Is double-bundle anterior cruciate ligament reconstruction superior to single-bundle? A comprehensive systematic review. Knee Surg Sports Traumatol Arthrosc. 2015;23(3):696–739. 6. Li Y, Ning G, Wu Q, et al. Single-bundle or double-bundle for anterior cruciate ligament reconstruction: a meta-analysis. Knee. 2014;21(1):28–37.
7. Ahldén M, Sernert N, Karlsson J, Kartus J. A prospective randomized study comparing double- and single-bundle techniques for anterior cruciate ligament reconstruction. Am J Sports Med. 2013;41(11): 2484–2491. 8. Massey P, Tjoumakaris F, Bernstein J. Eminence-based medicine versus evidence-based medicine: is anterior cruciate ligament reconstruction optimally performed with the double-bundle technique? Phys Sportsmed. 2013;41(1):102–106. 9. Kawaguchi Y, Kondo E, Takeda R, Akita K, Yasuda K, Amis A. The role of fibers in the femoral attachment of the anterior cruciate ligament in resisting tibial displacement. Arthroscopy. 2015;31(3): 435–444. 10. Gerdeman A, Hart J, Bennett C, Golish S, Gaskin C, Miller M. A comparison of 2 drilling techniques on the femoral tunnel for anterior cruciate ligament reconstruction. Arthroscopy. 2011;27(3):372–379. 11. Gelber P, Reina F, Torres R, Monllau J. Effect of femoral tunnel length on the safety of anterior cruciate ligament graft fixation using cross-pin technique: a cadaveric study. Am J Sports Med. 2010;38(9):1877–1884.
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41
Transtibial Tunnel Drilling of the Femoral Tunnel for Anatomic Single-Bundle Anterior Cruciate Ligament Reconstruction Chadwick C. Prodromos, MD
INTRODUCTION
Decreased Graft Abrasion at the Femoral Outlet
Drilling the femoral tunnel via the tibial tunnel (transtibial tunnel drilling or TTTD) has been the standard technique since the early days of anterior cruciate ligament reconstruction (ACLR) and has produced excellent results with both hamstring and patellar tendon grafts.1–3 The groundbreaking work of Stephen Howell4 showed that a coronal angle of 65 degrees is optimal, and this has been universally felt to be easily achievable with TTTD. More recently there has been a trend toward transmedial portal drilling (TMPD) of the femoral tunnel. This trend started in response to the transient trend toward double-bundle reconstruction, which necessitated placing one of the tunnels far down on the wall of the femoral intercondylar notch, which cannot be done transtibially. While meta-analyses5,6 have shown marginally overall better results from double-bundle ACLR, other reports have shown no difference,7 and morbidity and surgical difficulty have been recognized to be greater with double-bundle. Thus most orthopaedic surgeons have now reverted to anatomic single-bundle reconstruction,8 placing the femoral tunnel in the middle of the femoral footprint of the anterior cruciate ligament (ACL), instead of at the bottom. Additionally, a recent landmark paper9 from the lab of Andrew Amis has shown that “66% to 84% of the resistance to tibial anterior drawer arose from the ACL fibers at the central-proximal area of the femoral attachment…corresponding to the anteromedial bundle…The central area resisted 82% to 90% of the anterior drawer force; …and the posterior fan-like area, 11% to 15%.” These findings from arguably the world’s leader in studies of this kind argue powerfully in favor of the easier traditional transtibial drilling of the femoral tunnel rather than the more difficult medial portal technique, since there is now excellent anatomical and biomechanical evidence that drilling near the bottom of the femoral wall is unnecessary and indeed not physiologic.
One of the original perceived advantages of TTTD is that the graft has a relatively straight course as it enters the femoral tunnel. The tibial and femoral tunnels are essentially colinear with the TTTD technique. This decreases abrasion of the graft at the femoral outlet since the graft is not bent around its entrance point.
TRANS FEMORAL TUNNEL DISADVANTAGES Difficult Knee Flexion Angle In TMPD, drilling must be done with the knee hyperflexed to over 110 degrees. Such hyperflexion provides both reduced visibility and a view that is unfamiliar to most orthopaedic surgeons as they search for femoral footprint landmarks. Such hyperflexion can also be difficult to maintain in lower extremities of large girth, which has become increasingly common in patients.
Shorter Femoral Tunnel Length TMPD has the further disadvantage that it tends to produce shorter femoral tunnels,10 which may be too short for proper fixation with buttons or cross-pins.11
Increased Graft Femoral Tunnel Abrasion TMPD causes the graft to enter the femoral tunnel at a significant angle, since the femoral tunnel is drilled at a different angle (i.e., more horizontally) than the tibial tunnel. This angle subjects the graft to greater abrasive stresses than are seen with TTTD.
TRANSTIBIAL FEMORAL TUNNEL DRILLING ADVANTAGES
TRANSTIBIAL FEMORAL TUNNEL DRILLING TECHNIQUE
Comfortable Knee Flexion Angle
TTTD is not difficult. The only caution is to make sure the graft is not too vertical, with a femoral entry point too high in the notch. The generic steps of proper TTTD are described as follows. The clinical pearls that enable an appropriate coronal graft angle are bold:
TTTD can be carried out with the knee flexed to its natural position of roughly 70 degrees as routine arthroscopy is conducted. This technique and the intra-articular view provided are familiar to most orthopaedic surgeons.
Adequate Tunnel Length TTTD drilling routinely allows femoral tunnels of at least 3 cm in length.10
1. Tibial Guide: Select a commercially available tibial guide. All of the major device companies offer these, and any are suitable for TTTD. 2. Placing the Tibial Incision: This is the most important step because it dictates the tibial tunnel entry point. The
167
168
SECTION IX Principles of Tunnel Formation
tibial tunnel entry point dictates tunnel angle and femoral tunnel entry point possibilities. The vertical or oblique incision should be placed toward the mid- or posterior tibia just anterior to the attachment of the medial collateral ligament. The entry point should be sufficiently posterior and the tip of the drill guide held simultaneously within the tibial footprint of the anatomic attachment of the ACL, so that it results in a sufficiently oblique tibial tunnel of about 65 degrees in the coronal plane.4 This will allow direction of the long guide pin to a suitable femoral entry point at about 10:30/1:30 o’clock in the notch within the middle of the femoral ACL footprint. CAUTION: If the entry point on the tibia is not posterior, then the tibial tunnel will be more vertical and will direct the guide pin to an entry point in the notch that is too high. This will produce a vertical graft and predispose to failure. For hamstring harvest the same incision can easily be used to harvest the hamstring and drill the tibial tunnel. However, it is important to realize that the harvest incision for the BTB graft is, in general, too far anterior to allow drilling through it for the tibial tunnel, unless the incision is sufficiently long to allow soft tissue to be moved posteromedially on the tibia. 3. Drilling the Tibial Tunnel: This should be drilled in the usual fashion, with a point-to-point guide. 4. Femoral Wallplasty: We believe it is imperative to perform a limited notch lateral (3 mm) wallplasty and also remove all soft tissue from the femoral attachment of the ACL so that the proper entry point can be easily visualized. This is performed with the arthroscope in the lateral portal and the shaver and burr in the medial portal. If visualization is difficult, a 70degree scope may be used to better see around the lateral femoral chondyle (LFC) to the femoral ACL attachment. 5. Drilling the Femoral Tunnel: A long guide pin is passed through the tibial tunnel, and the tip is placed in the middle of the anatomic attachment of the ACL on the femur. If step 2 (listed previously) was properly executed, the tip of the pin should find this point easily. We prefer not to use guides, which can impair visualization, and instead bring the tip of the guide pin all the way proximally to the over-the-top position and then walk it back sufficiently to allow a tunnel to be drilled that will not break out the proximal cortex. This point is at 10:30/1:30 o’clock. Sometimes knee flexion needs to be slightly decreased to help just the tip (2 mm) of the guide pin to insert at the proper point. The knee can then be flexed a few degrees for the drilling of the tunnel. The guide pin is then overdrilled with the appropriate diameter reamer. We typically hold the knee in about 80 degrees of knee flexion (a little more than the 70 degrees or so that it finds on its own from gravity). If the knee is held a little flexed for drilling, this position must be maintained by an assistant until the guide pin is removed to avoid guide pin bending or breakage. 6. Finishing the Femoral Tunnel: From this point forward, steps will vary depending on the guide system used.
CONCLUSIONS The author and countless other experienced ACL surgeons have used the TTTD technique for decades with reliably excellent results. It is easy to place the femoral tunnel in exactly the right location with appropriate coronal plane obliquity for anatomic single-bundle ACLR. TTTD also avoids the hardship and potential errors of placing the tunnel in a hyperflexed knee. It reduces the likelihood of short tunnels and graft abrasion The transient fascination with double-bundle techniques has apparently caused some to forget the ease and excellent results of using TTTD. TTTD was only questioned because it could not fill the bottom of the footprint, which is now both from clinical studies and the work of Amis, seen by most as unnecessary and perhaps undesirable. The only advantage of TMPD is for the rapidly shrinking group of surgeons who use double-bundle repair routinely. And even there we have found an outside-in guide to be preferable for the lower tunnel when we use doublebundle repairs for revisions. SELECTED READINGS
Ahldén M, Sernert N, Karlsson J, Kartus J. A prospective randomized study comparing double- and single-bundle techniques for anterior cruciate ligament reconstruction. Am J Sports Med. 2013;41(11): 2484–2491. Björnsson H, Desai N, Musahl V, et al. Is double-bundle anterior cruciate ligament reconstruction superior to single-bundle? A comprehensive systematic review. Knee Surg Sports Traumatol Arthrosc. 2015;23(3):696–739. Gelber P, Reina F, Torres R, Monllau J. Effect of femoral tunnel length on the safety of anterior cruciate ligament graft fixation using cross-pin technique: a cadaveric study. Am J Sports Med. 2010;38(9):1877–1884. Gerdeman A, Hart J, Bennett C, Golish S, Gaskin C, Miller M. A comparison of 2 drilling techniques on the femoral tunnel for anterior cruciate ligament reconstruction. Arthroscopy. 2011;27(3):372–379. Haro M, Riff A, Bach BJ. Tips for successful transtibial anterior cruciate ligament reconstruction. J Knee Surg. 2014;27(5):331–342. Howell S, Gittins M, Gottlieb J, Traina S, Zoellner T. The relationship between the angle of the tibial tunnel in the coronal plane and loss of flexion and anterior laxity after anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29(5):567–574. Kawaguchi Y, Kondo E, Takeda R, Akita K, Yasuda K, Amis A. The role of fibers in the femoral attachment of the anterior cruciate ligament in resisting tibial displacement. Arthroscopy. 2015;31(3):435–444. Li Y, Ning G, Wu Q, et al. Single-bundle or double-bundle for anterior cruciate ligament reconstruction: a meta-analysis. Knee. 2014;21(1):28–37. Massey P, Tjoumakaris F, Bernstein J. Eminence-based medicine versus evidence-based medicine: is anterior cruciate ligament reconstruction optimally performed with the double-bundle technique? Phys Sportsmed. 2013;41(1):102–106. Prodromos C, Han Y, Keller B, Bolyard R. Stability results of hamstring anterior cruciate ligament reconstruction at 2- to 8-year follow-up. Arthroscopy. 2005;21(2):138–146. Rue J, Ghodadra N, Lewis P, Bach BJ. Femoral and tibial tunnel position using a transtibial drilled anterior cruciate ligament reconstruction technique. J Knee Surg. 2008;21(3):246–249.
A complete reference list can be found online at ExpertConsult.com.
REFERENCES
1. Prodromos C, Han Y, Keller B, Bolyard R. Stability results of hamstring anterior cruciate ligament reconstruction at 2- to 8-year follow-up. Arthroscopy. 2005;21(2):138–146. 2. Haro M, Riff A, Bach BJ. Tips for successful transtibial anterior cruciate ligament reconstruction. J Knee Surg. 2014;27(5):331–342. 3. Rue J, Ghodadra N, Lewis P, Bach BJ. Femoral and tibial tunnel position using a transtibial drilled anterior cruciate ligament reconstruction technique. J Knee Surg. 2008;21(3):246–249. 4. Howell S, Gittins M, Gottlieb J, Traina S, Zoellner T. The relationship between the angle of the tibial tunnel in the coronal plane and loss of flexion and anterior laxity after anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29(5):567–574. 5. Björnsson H, Desai N, Musahl V, et al. Is double-bundle anterior cruciate ligament reconstruction superior to single-bundle? A comprehensive systematic review. Knee Surg Sports Traumatol Arthrosc. 2015;23(3):696–739. 6. Li Y, Ning G, Wu Q, et al. Single-bundle or double-bundle for anterior cruciate ligament reconstruction: a meta-analysis. Knee. 2014;21(1):28–37.
7. Ahldén M, Sernert N, Karlsson J, Kartus J. A prospective randomized study comparing double- and single-bundle techniques for anterior cruciate ligament reconstruction. Am J Sports Med. 2013;41(11): 2484–2491. 8. Massey P, Tjoumakaris F, Bernstein J. Eminence-based medicine versus evidence-based medicine: is anterior cruciate ligament reconstruction optimally performed with the double-bundle technique? Phys Sportsmed. 2013;41(1):102–106. 9. Kawaguchi Y, Kondo E, Takeda R, Akita K, Yasuda K, Amis A. The role of fibers in the femoral attachment of the anterior cruciate ligament in resisting tibial displacement. Arthroscopy. 2015;31(3): 435–444. 10. Gerdeman A, Hart J, Bennett C, Golish S, Gaskin C, Miller M. A comparison of 2 drilling techniques on the femoral tunnel for anterior cruciate ligament reconstruction. Arthroscopy. 2011;27(3):372–379. 11. Gelber P, Reina F, Torres R, Monllau J. Effect of femoral tunnel length on the safety of anterior cruciate ligament graft fixation using cross-pin technique: a cadaveric study. Am J Sports Med. 2010;38(9):1877–1884.
168.e1