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Tibial tunnel bone grafting: a new technique for dealing with graft- tunnel mismatch in endoscopic anterior cruciate ligament reconstruction
Technical Note
Tibial Tunnel Bone Grafting: A New Technique for Dealing With Graft-Tunnel Mismatch in Endoscopic Anterior Cruciate Ligament Reconstruction Bradley L. Fowler, M.D., and Vincent J. DiStefano, M.D.
Summary: A problem that is frequently encountered during endoscopic anterior cruciate ligament reconstruction bone–patellar tendon–bone autograft is that the graft is often too long and protrudes from the tibial tunnel. If less than 20 mm of the bone plug remains in the tibial tunnel, interference screw fixation cannot safely be used, and an alternate form of fixation may have to be employed. A simple technique has been developed to deal with this problem. The technique involves bone-grafting the tibial tunnel with a cancellous core of bone that is removed while creating the tibial tunnel. This not only makes it possible to safely use interference screw fixation in all cases, but it also makes it possible to place the point of graft fixation very near the anatomic anterior cruciate ligament insertion site. Key Words: Endoscopic—ACL reconstruction—Graft-tunnel mismatch—Bone grafting.
D
espite its current popularity, endoscopic anterior cruciate ligament (ACL) reconstruction using bone–patellar tendon–bone autograft remains a technically difficult operation. Part of the difficulty encountered during this operation stems from the fact that the length of the graft does not necessarily match the length of the tunnel into which it is supposed to fit, and the graft often protrudes from the tibial tunnel. Shaffer et al.1 have termed this graft-tunnel mismatch. This occurs because of the great amount of anatomic variation that exists between the length of the patellar tendon and the intra-articular distance between the ACL origin and insertion sites. The length of the patellar tendon has been measured from 40 to 63 mm From Mountain View Orthopedics and Sports Medicine, Klamath Falls, Oregon (B.L.F.); and the Department of Orthopedic Surgery, The Graduate Hospital, Philadelphia, Pennsylvania (V.J.D.), U.S.A. Address correspondence and reprint requests to Bradley L. Fowler, M.D., 2301 Mt. View Blvd., Klamath Falls, OR 97601, U.S.A. r 1998 by the Arthroscopy Association of North America 0749-8063/98/1402-1512$3.00/0
224
and the intra-articular distance has been reported to range from 18 to 40 mm.2-4 If a patient has a relatively long patellar tendon and/or ashort intra-articular distance, then there is going to be graft-tunnel mismatch. When it occurs, and less than 20 mm of the tibial bone plug remains within the tibial tunnel, proper interference screw fixation cannot be accomplished and an alternate, less secure form of fixation may have to be used to anchor the tibial end of the graft. Currently described methods for dealing with grafttunnel mismatch include using a more vertical, thus longer, tibial tunnel; recessing the graft up into the femur; flipping the tibial bone plug onto the tendinous portion of the graft; using alternative fixation on the tibia; or simply using a different graft source altogether. While using a slightly more vertical tibial tunnel than was standard for the two-incision technique is advisable, there is a limit to how vertical and how long a tibial tunnel can be made. If the tunnel is made too vertically (⬎60°), access to the over-the-top position is impaired, and there may be some difficulty
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 14, No 2 (March), 1998: pp 224–228
TIBIAL TUNNEL BONE GRAFTING in placing the femoral tunnel as posterior as it needs to be. Shaffer et al.1 have described a technique where the femoral bone plug is recessed up into the femur. Although this technique is effective in getting the tibial bone plug up into the tunnel so that interference screw fixation can be used, the advantage of having the bone-tendon interface right at the femoral tunnel opening is lost. With the femoral bone plug recessed, nonphysiological motion, or ‘‘windshield-wipering,’’ can occur between the tendon and femoral tunnel, which may compromise the graft.5 Morgan et al.5 have dealt with graft-tunnel mismatch by flipping the tibial bone plug onto the tendinous portion of the graft, thus shortening the graft. With this technique, the length of the graft can be modified so that interference screw fixation can be placed very near the anatomic insertion site of the ACL, deep within the tibial tunnel. Another option is simply to use an alternative form of fixation on the tibia when graft-tunnel mismatch occurs. Other options for fixation include stapling the tibial bone plug into a trough on the anterior tibia, placing a cortical screw through the bone plug, or tying the lead sutures over a post.6-8 Unfortunately, none of these forms of fixation supply the initial pullout strength as an interference screw, and, therefore, postoperative rehabilitation protocols may have to be altered. A new and simple technique has been developed to deal with graft-tunnel mismatch. This technique involves bone-grafting the proximal end of the tibial tunnel with a trephined core of bone that is harvested from the tibial tunnel using a coring reamer (Arthrex; Naples, FL). By securing an appropriate length of this cored bone to the graft just above the tibial bone plug, the entire length of the tibial tunnel can be filled with bone when the graft is pulled up into the joint. This not only makes interference screw fixation possible in all cases, it creates a press-fit for the tendon within the tunnel, and it moves the graft fixation closer to the anatomic ACL insertion site. OPERATIVE TECHNIQUE Arthroscopic examination of the knee is performed in the usual fashion, and associated meniscal and articular cartilage injuries are cared for. The remnants of the ruptured ACL are debrided, a notchplasty is performed if indicated, and the over-the-top point is identified on the femur. The center of the prospective femoral tunnel, which should be placed as far posteri-
225
orly as possible, is determined and marked. The bone-tendon-bone graft is now harvested from the central one third of the patellar tendon using the standard technique. The bone blocks should be approximately 25-mm long and 10-mm thick. The length of each component of the graft, as well as its entire length, is measured and recorded. The bone blocks are shaped with a rongeur and sized so that they pass snugly through 9- to 11-mm sizing tubes. Lead sutures are placed in the bone blocks, and the graft is then preconditioned by placing it under 8 to 10 lb of tension while the tunnels are prepared. The tibial tunnel is now prepared. Using a tibial tunnel guide that is set between 50° and 60°, a guide pin is placed centrally into the posterior half of the ACL tibial stump, according to the guidelines described by Jackson and Gasser.9 Great care should be taken so that only one pass is made with the guide pin, because multiple holes make using the coring reamer much more difficult. Once the guide pin is in the proper position, the outer cortex of the tibia is reamed with a standard cannulated reamer, which is the same size as the coring reamer to be used. We suggest that a coring reamer that is 2-mm smaller than the desired size of the tibial tunnel be used, as the smaller core of bone will fit better on the graft. The guide pin is now exchanged for a collared guide pin over which the coring reamer is passed. Care should be taken not to advance the reamer too forcefully, as this may cause eccentric reaming with respect to the guide pin. The coring reamer should be passed all the way up into the joint and should be visualized to spin freely to ensure that all soft tissue attachments have been severed. The reamer is now removed from the joint and a cored cancellous bone plug the length of the tibial tunnel is obtained from within the reamer. The tibial tunnel can now be enlarged to its desired size by using a tunnel dilator over a guide pin. If necessary, fine adjustments can be made in the placement of the tibial tunnel by reaming over an eccentrically placed guide pin that is anchored in the femoral notch. The femoral tunnel is now addressed. With the knee flexed to 90°, a long Beath pin is passed up through the tibial tunnel, into the previously marked location for the femoral tunnel, and out the anterolateral thigh. Over this guide pin, a calibrated reamer is placed into the knee and the intra-articular distance and the tibial tunnel length are measured. The femoral tunnel is then reamed to the desired depth, and the composite length of both tunnels and the intra-articular distance is measured. If the length of both tunnels plus the intra-
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articular distance is less than the length of the graft, the tibial tunnel should be bone-grafted. The amount of bone required to fill the tibial tunnel is calculated by subtracting the intra-articular distance from the length of the tendinous portion of the graft (Fig 1). This amount of the cored bone is then secured to the tendon, just above the tibial bone plug, so that when the graft is pulled up into the joint, the tibial tunnel is completely filled with bone. The cored bone is attached to the graft with a No. 2 Ethibond suture (Ethicon; Somerville, NJ). Using a Keith needle, the suture is passed down through the center of the core, through the transverse hole at the base of the tibial bone plug, and back up through the core (Fig 2). The suture ends are now passed down through the tendon, wrapped around either side of the tendon, and tied to one another right at the superior end of the core. Suturing the graft in this fashion secures the core of bone at both ends so that migration cannot occur during placement of the graft (Fig 3). The core of bone can be further secured with circumferential sutures; however, we have not found this to be necessary. The entire graft is now passed through the appropriate sizing tube, and the graft trimmed as necessary. The graft can now be pulled up into the joint and the femoral bone plug seated into the femoral tunnel. While the graft is seated, the tibial end should be rotated 90° away from the lateral wall of the notch to help prevent lateral wall impingement and perhaps increase biomechanical strength of the graft.10 With the graft fully seated, the bone-tendon interface should be flush with the inner wall of the notch on the femoral side, and the cored-bone graft should be flush with the
A
B
C
FIGURE 2. (A) The bone graft is secured by passing a No. 2 Ethibond suture on a Keith needle through the tendon, down through the center of the core. (B) The suture is then passed across the base of the tibial bone block and back up through the core. (C) The suture is then passed through the tendon, and the suture ends are wrapped around and tied to one another at the base of the graft.
FIGURE 1. The length of the bone graft required to fill the tibial tunnel is calculated by subtracting the intra-articular distance from the length of the tendinous portion of the graft.
floor of the notch on the tibial side. The femoral bone plug is now fixated with an interference screw in the usual fashion. The tibial side is fixated with an 8 or 9 ⫻ 30 mm interference screw. By using a long interference screw, purchase can be obtained in both the cored bone graft and the tibial bone plug, and the screw does not have to be buried deep within the tibial tunnel (Fig 4). The graft is now inspected to insure that there is no impingement in either extension or flexion, and the knee is examined for stability. If bone is protruding
TIBIAL TUNNEL BONE GRAFTING
FIGURE 3. The final graft construct which is ready for placement in the knee.
from the tibial tunnel, this is removed with an osteotome. Along with the remainder of the cored bone, this can be used for bone grafting the defects in the patella and tibial tubercle. The wound is now closed in a routine fashion. DISCUSSION Graft-tunnel mismatch is a problem frequently encountered during endoscopic ACL reconstruction. Some of the currently described techniques for dealing with this complication include using a more vertical tibial tunnel, recessing the graft up into the femur, and using an alternate form of fixation on the tibia. Although these techniques may make it possible to fixate either end of a long graft, they fail to address two potentially important issues. The first is the proximity of the fixation of the graft to the anatomic ACL origin and insertion sites. If our goal is to reconstruct the ACL as accurately as possible, it makes intuitive sense to fixate the graft as close as possible to where the original ACL was anchored. Indeed, several authors have concluded
227
that the stability of an ACL graft is compromised as the fixation of the graft is moved further away from the anatomic origin and insertion.5,11,12 The second issue is that, as the tibial bone plug is displaced further distal on the tibia, more of the tibial tunnel is occupied only by the tendinous portion of the graft. Even when the tibial bone plug is flush with the distal opening of a 50-mm tibial tunnel, at least 25 mm of the proximal end of the tunnel is occupied only by the tendinous portion of the graft. This creates the potential for motion, as the average cross-sectional area of a 10-mm patellar tendon graft is less than half that of a 10-mm tunnel.10 This nonphysiological motion between the tendon and the tunnel puts abnormal stresses on the graft and may contribute to graft failure.5,13 Rodeo et al.14 have shown that tendons that are tightly fit will heal into bone tunnels with the creation of Sharpey’s fibers. van Rens et al.15 have also shown that iliotibial band grafts will heal securely into bone tunnels when they are tightly fixated with a cancellous bone peg. However, little is known about the type of healing that occurs between a tendon and bone tunnel when there is not a tight fit and motion exists. Addressing these same concerns, Morgan et al.5,13 have described two techniques. One involves using a semitendinosus graft that is triple-wrapped around bone plugs that are harvested with a coring reamer. When the graft is prepared, the bone plugs can be set apart the same distance as the intra-articular distance so that the tendinous portion of the graft is essentially made to be the same length as the ACL that is being replaced. The graft is then fixated very near the anatomic ACL origin and insertion sites with interfer-
FIGURE 4. Bone grafting the tibial tunnel makes interference screw fixation possible, even when the graft is too long and a tibial bone block is protruding. With a long interference screw (30-mm), the graft can be fixated very close to the anatomic ACL insertion site.
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ence screws. Interference screw fixation with cancellous bone plugs, such as this, has been shown to have a pullout strength of 354 N compared with a pull-out strength of 663 N with cortical bone plugs in a porcine model.16 The second technique involves flipping the tibial bone plug onto the tendinous portion of the graft, thus shortening the graft. This graft can similarly be fixated very near the tibial insertion site with an interference screw placed deep within the tibial tunnel. Our technique accomplishes the same objectives as the techniques described by Morgan et al., but with a graft that is very easy to prepare and one that is biomechanically superior to a hamstring tendon construct.10,17,18 This technique also achieves near anatomic fixation of the graft, but does not require placement of an interference screw deep within the tibial tunnel, which could be problematic in a revision situation. Although biomechanical studies would be required to determine the exact pullout strength of this construct, it should be safe to assume that the pullout strength is somewhere between that of a cancellous bone plug and a cortical bone plug alone that have individually been fixated with an interference screw. Given this, the initial fixation strength of a bonegrafted tibial tunnel with an interference screw is better than that of other fixation options and is adequate to begin aggressive early rehabilitation.
CONCLUSION Despite precautions to avoid it, graft-tunnel mismatch with a protruding tibial bone plug is an inevitability in a certain number of cases. Bone grafting the tibial tunnel with a cancellous bone plug harvested with a coring reamer is a simple and effective technique for dealing with this complication. Filling the tibial tunnel with bone also has the potential advantages of reducing motion between the tendon and the tunnel, improving the healing of the graft to the tunnel, and allowing for more anatomic fixation of the tibial end of the graft. Acknowledgment: The authors express their gratitude for the art work created by Judy Johnson.
REFERENCES 1. Shaffer B, Gow W, Tibone JE. Graft tunnel mismatch in endoscopic anterior cruciate ligament reconstruction: A new technique of intraarticular measurement and modified graft harvesting. Arthroscopy 1993;9:633-646. 2. Ellison AE, Berg EE. Embryology, anatomy, and function of the anterior cruciate ligament. Orthop Clin North Am 1985; 16:3. 3. Kennedy JC, Weinberg HW, Wilson AS. The anatomy and function of the anterior cruciate ligament: as determined by clinical and morphological studies. J Bone Joint Surg Am 1974;56:223-225. 4. Norwood LA, Cross MJ. Anterior cruciate ligament: functional anatomy of its bundles in rotatory instabilities. Am J Sports Med 1979;7:23-26. 5. Morgan CD, Kalman VR, Grawl DM. Isometry testing for anterior cruciate reconstruction revisited. Arthroscopy 1995;11: 647-659. 6. Burks R. Practical considerations in cruciate graft fixation. Op Tech Orthop 1992;2:71-75. 7. Butler DL. Evaluation of fixation methods in cruciate ligament replacement. Instr Course Lect 1987;36:173-178. 8. Kurosaka M, Yoshiya S, Andrish JT. A biomechanical comparison of different surgical techniques of graft fixation in anterior cruciate ligament reconstruction. Am J Sports Med 1987;15:225229. 9. Jackson DW, Gasser SI. Tibial tunnel placement in ACL reconstruction. Arthroscopy 1994;10:124-131. 10. Cooper DE, Deng XH, Burstein AL, Warren RF. The strength of the central third patellar tendon graft. Am J Sports Med 1993;21:818-824. 11. O’Connor JS, Zavutsky A. Anterior cruciate ligament function in the normal knee. In: Jackson DW, ed. The anterior cruciate ligament: Current and future concepts. New York: Raven, 1993:39-52. 12. Ishibashi Y, Rudy TW, Kim HS, Fu FH, Woo SL-Y. The effect of the ACL graft fixation level on knee stability. Arthroscopy 1997;13:177-182. 13. Morgan C. Bone-hamstring-bone autograft for ACL reconstruction. Presented at the Arthroscopic Surgery Meeting, Scottsdale, AZ, January 1994. 14. Rodeo SA, Arnoczky SP, Torzilli PA, et al. Tendon healing in a bone tunnel. J Bone and Joint Surg Am 1993;75:1795-1803. 15. van Rens TJG, Van den Berg AF, Huisker R, Kuypers W. Substitution of the anterior cruciate ligament: A long-term histologic and biomechanical study with autogenous pedicled grafts of the iliotibial band in dogs. Arthroscopy 1986;2:139154. 16. Liu SH, Kabo JM, Osti L. Biomechanics of two types of bone-tendon-bone graft for ACL reconstruction. J Bone Joint Surg Br 1995;77:232-235. 17. Noyes FR, Butler DL, Grood ES, et al. Biomechanical analysis of human ligament grafts used in knee ligament repairs and reconstructions. J Bone Joint Surg Am 1984;66:344-352. 18. Steiner ME, Hecker AT, Brown CH, Hayes WL. Anterior cruciate ligament graft fixation: Comparison of hamstring and patellar tendon grafts. Am J Sports Med 1994;22:240-247.
Tibial Tunnel Bone Grafting: A New Technique for Dealing With Graft-Tunnel Mismatch in Endoscopic Anterior Cruciate Ligament Reconstruction Bradley L. Fowler, M.D., and Vincent J. DiStefano, M.D.
Summary: A problem that is frequently encountered during endoscopic anterior cruciate ligament reconstruction bone–patellar tendon–bone autograft is that the graft is often too long and protrudes from the tibial tunnel. If less than 20 mm of the bone plug remains in the tibial tunnel, interference screw fixation cannot safely be used, and an alternate form of fixation may have to be employed. A simple technique has been developed to deal with this problem. The technique involves bone-grafting the tibial tunnel with a cancellous core of bone that is removed while creating the tibial tunnel. This not only makes it possible to safely use interference screw fixation in all cases, but it also makes it possible to place the point of graft fixation very near the anatomic anterior cruciate ligament insertion site. Key Words: Endoscopic—ACL reconstruction—Graft-tunnel mismatch—Bone grafting.
D
espite its current popularity, endoscopic anterior cruciate ligament (ACL) reconstruction using bone–patellar tendon–bone autograft remains a technically difficult operation. Part of the difficulty encountered during this operation stems from the fact that the length of the graft does not necessarily match the length of the tunnel into which it is supposed to fit, and the graft often protrudes from the tibial tunnel. Shaffer et al.1 have termed this graft-tunnel mismatch. This occurs because of the great amount of anatomic variation that exists between the length of the patellar tendon and the intra-articular distance between the ACL origin and insertion sites. The length of the patellar tendon has been measured from 40 to 63 mm From Mountain View Orthopedics and Sports Medicine, Klamath Falls, Oregon (B.L.F.); and the Department of Orthopedic Surgery, The Graduate Hospital, Philadelphia, Pennsylvania (V.J.D.), U.S.A. Address correspondence and reprint requests to Bradley L. Fowler, M.D., 2301 Mt. View Blvd., Klamath Falls, OR 97601, U.S.A. r 1998 by the Arthroscopy Association of North America 0749-8063/98/1402-1512$3.00/0
224
and the intra-articular distance has been reported to range from 18 to 40 mm.2-4 If a patient has a relatively long patellar tendon and/or ashort intra-articular distance, then there is going to be graft-tunnel mismatch. When it occurs, and less than 20 mm of the tibial bone plug remains within the tibial tunnel, proper interference screw fixation cannot be accomplished and an alternate, less secure form of fixation may have to be used to anchor the tibial end of the graft. Currently described methods for dealing with grafttunnel mismatch include using a more vertical, thus longer, tibial tunnel; recessing the graft up into the femur; flipping the tibial bone plug onto the tendinous portion of the graft; using alternative fixation on the tibia; or simply using a different graft source altogether. While using a slightly more vertical tibial tunnel than was standard for the two-incision technique is advisable, there is a limit to how vertical and how long a tibial tunnel can be made. If the tunnel is made too vertically (⬎60°), access to the over-the-top position is impaired, and there may be some difficulty
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 14, No 2 (March), 1998: pp 224–228
TIBIAL TUNNEL BONE GRAFTING in placing the femoral tunnel as posterior as it needs to be. Shaffer et al.1 have described a technique where the femoral bone plug is recessed up into the femur. Although this technique is effective in getting the tibial bone plug up into the tunnel so that interference screw fixation can be used, the advantage of having the bone-tendon interface right at the femoral tunnel opening is lost. With the femoral bone plug recessed, nonphysiological motion, or ‘‘windshield-wipering,’’ can occur between the tendon and femoral tunnel, which may compromise the graft.5 Morgan et al.5 have dealt with graft-tunnel mismatch by flipping the tibial bone plug onto the tendinous portion of the graft, thus shortening the graft. With this technique, the length of the graft can be modified so that interference screw fixation can be placed very near the anatomic insertion site of the ACL, deep within the tibial tunnel. Another option is simply to use an alternative form of fixation on the tibia when graft-tunnel mismatch occurs. Other options for fixation include stapling the tibial bone plug into a trough on the anterior tibia, placing a cortical screw through the bone plug, or tying the lead sutures over a post.6-8 Unfortunately, none of these forms of fixation supply the initial pullout strength as an interference screw, and, therefore, postoperative rehabilitation protocols may have to be altered. A new and simple technique has been developed to deal with graft-tunnel mismatch. This technique involves bone-grafting the proximal end of the tibial tunnel with a trephined core of bone that is harvested from the tibial tunnel using a coring reamer (Arthrex; Naples, FL). By securing an appropriate length of this cored bone to the graft just above the tibial bone plug, the entire length of the tibial tunnel can be filled with bone when the graft is pulled up into the joint. This not only makes interference screw fixation possible in all cases, it creates a press-fit for the tendon within the tunnel, and it moves the graft fixation closer to the anatomic ACL insertion site. OPERATIVE TECHNIQUE Arthroscopic examination of the knee is performed in the usual fashion, and associated meniscal and articular cartilage injuries are cared for. The remnants of the ruptured ACL are debrided, a notchplasty is performed if indicated, and the over-the-top point is identified on the femur. The center of the prospective femoral tunnel, which should be placed as far posteri-
225
orly as possible, is determined and marked. The bone-tendon-bone graft is now harvested from the central one third of the patellar tendon using the standard technique. The bone blocks should be approximately 25-mm long and 10-mm thick. The length of each component of the graft, as well as its entire length, is measured and recorded. The bone blocks are shaped with a rongeur and sized so that they pass snugly through 9- to 11-mm sizing tubes. Lead sutures are placed in the bone blocks, and the graft is then preconditioned by placing it under 8 to 10 lb of tension while the tunnels are prepared. The tibial tunnel is now prepared. Using a tibial tunnel guide that is set between 50° and 60°, a guide pin is placed centrally into the posterior half of the ACL tibial stump, according to the guidelines described by Jackson and Gasser.9 Great care should be taken so that only one pass is made with the guide pin, because multiple holes make using the coring reamer much more difficult. Once the guide pin is in the proper position, the outer cortex of the tibia is reamed with a standard cannulated reamer, which is the same size as the coring reamer to be used. We suggest that a coring reamer that is 2-mm smaller than the desired size of the tibial tunnel be used, as the smaller core of bone will fit better on the graft. The guide pin is now exchanged for a collared guide pin over which the coring reamer is passed. Care should be taken not to advance the reamer too forcefully, as this may cause eccentric reaming with respect to the guide pin. The coring reamer should be passed all the way up into the joint and should be visualized to spin freely to ensure that all soft tissue attachments have been severed. The reamer is now removed from the joint and a cored cancellous bone plug the length of the tibial tunnel is obtained from within the reamer. The tibial tunnel can now be enlarged to its desired size by using a tunnel dilator over a guide pin. If necessary, fine adjustments can be made in the placement of the tibial tunnel by reaming over an eccentrically placed guide pin that is anchored in the femoral notch. The femoral tunnel is now addressed. With the knee flexed to 90°, a long Beath pin is passed up through the tibial tunnel, into the previously marked location for the femoral tunnel, and out the anterolateral thigh. Over this guide pin, a calibrated reamer is placed into the knee and the intra-articular distance and the tibial tunnel length are measured. The femoral tunnel is then reamed to the desired depth, and the composite length of both tunnels and the intra-articular distance is measured. If the length of both tunnels plus the intra-
226
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articular distance is less than the length of the graft, the tibial tunnel should be bone-grafted. The amount of bone required to fill the tibial tunnel is calculated by subtracting the intra-articular distance from the length of the tendinous portion of the graft (Fig 1). This amount of the cored bone is then secured to the tendon, just above the tibial bone plug, so that when the graft is pulled up into the joint, the tibial tunnel is completely filled with bone. The cored bone is attached to the graft with a No. 2 Ethibond suture (Ethicon; Somerville, NJ). Using a Keith needle, the suture is passed down through the center of the core, through the transverse hole at the base of the tibial bone plug, and back up through the core (Fig 2). The suture ends are now passed down through the tendon, wrapped around either side of the tendon, and tied to one another right at the superior end of the core. Suturing the graft in this fashion secures the core of bone at both ends so that migration cannot occur during placement of the graft (Fig 3). The core of bone can be further secured with circumferential sutures; however, we have not found this to be necessary. The entire graft is now passed through the appropriate sizing tube, and the graft trimmed as necessary. The graft can now be pulled up into the joint and the femoral bone plug seated into the femoral tunnel. While the graft is seated, the tibial end should be rotated 90° away from the lateral wall of the notch to help prevent lateral wall impingement and perhaps increase biomechanical strength of the graft.10 With the graft fully seated, the bone-tendon interface should be flush with the inner wall of the notch on the femoral side, and the cored-bone graft should be flush with the
A
B
C
FIGURE 2. (A) The bone graft is secured by passing a No. 2 Ethibond suture on a Keith needle through the tendon, down through the center of the core. (B) The suture is then passed across the base of the tibial bone block and back up through the core. (C) The suture is then passed through the tendon, and the suture ends are wrapped around and tied to one another at the base of the graft.
FIGURE 1. The length of the bone graft required to fill the tibial tunnel is calculated by subtracting the intra-articular distance from the length of the tendinous portion of the graft.
floor of the notch on the tibial side. The femoral bone plug is now fixated with an interference screw in the usual fashion. The tibial side is fixated with an 8 or 9 ⫻ 30 mm interference screw. By using a long interference screw, purchase can be obtained in both the cored bone graft and the tibial bone plug, and the screw does not have to be buried deep within the tibial tunnel (Fig 4). The graft is now inspected to insure that there is no impingement in either extension or flexion, and the knee is examined for stability. If bone is protruding
TIBIAL TUNNEL BONE GRAFTING
FIGURE 3. The final graft construct which is ready for placement in the knee.
from the tibial tunnel, this is removed with an osteotome. Along with the remainder of the cored bone, this can be used for bone grafting the defects in the patella and tibial tubercle. The wound is now closed in a routine fashion. DISCUSSION Graft-tunnel mismatch is a problem frequently encountered during endoscopic ACL reconstruction. Some of the currently described techniques for dealing with this complication include using a more vertical tibial tunnel, recessing the graft up into the femur, and using an alternate form of fixation on the tibia. Although these techniques may make it possible to fixate either end of a long graft, they fail to address two potentially important issues. The first is the proximity of the fixation of the graft to the anatomic ACL origin and insertion sites. If our goal is to reconstruct the ACL as accurately as possible, it makes intuitive sense to fixate the graft as close as possible to where the original ACL was anchored. Indeed, several authors have concluded
227
that the stability of an ACL graft is compromised as the fixation of the graft is moved further away from the anatomic origin and insertion.5,11,12 The second issue is that, as the tibial bone plug is displaced further distal on the tibia, more of the tibial tunnel is occupied only by the tendinous portion of the graft. Even when the tibial bone plug is flush with the distal opening of a 50-mm tibial tunnel, at least 25 mm of the proximal end of the tunnel is occupied only by the tendinous portion of the graft. This creates the potential for motion, as the average cross-sectional area of a 10-mm patellar tendon graft is less than half that of a 10-mm tunnel.10 This nonphysiological motion between the tendon and the tunnel puts abnormal stresses on the graft and may contribute to graft failure.5,13 Rodeo et al.14 have shown that tendons that are tightly fit will heal into bone tunnels with the creation of Sharpey’s fibers. van Rens et al.15 have also shown that iliotibial band grafts will heal securely into bone tunnels when they are tightly fixated with a cancellous bone peg. However, little is known about the type of healing that occurs between a tendon and bone tunnel when there is not a tight fit and motion exists. Addressing these same concerns, Morgan et al.5,13 have described two techniques. One involves using a semitendinosus graft that is triple-wrapped around bone plugs that are harvested with a coring reamer. When the graft is prepared, the bone plugs can be set apart the same distance as the intra-articular distance so that the tendinous portion of the graft is essentially made to be the same length as the ACL that is being replaced. The graft is then fixated very near the anatomic ACL origin and insertion sites with interfer-
FIGURE 4. Bone grafting the tibial tunnel makes interference screw fixation possible, even when the graft is too long and a tibial bone block is protruding. With a long interference screw (30-mm), the graft can be fixated very close to the anatomic ACL insertion site.
228
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ence screws. Interference screw fixation with cancellous bone plugs, such as this, has been shown to have a pullout strength of 354 N compared with a pull-out strength of 663 N with cortical bone plugs in a porcine model.16 The second technique involves flipping the tibial bone plug onto the tendinous portion of the graft, thus shortening the graft. This graft can similarly be fixated very near the tibial insertion site with an interference screw placed deep within the tibial tunnel. Our technique accomplishes the same objectives as the techniques described by Morgan et al., but with a graft that is very easy to prepare and one that is biomechanically superior to a hamstring tendon construct.10,17,18 This technique also achieves near anatomic fixation of the graft, but does not require placement of an interference screw deep within the tibial tunnel, which could be problematic in a revision situation. Although biomechanical studies would be required to determine the exact pullout strength of this construct, it should be safe to assume that the pullout strength is somewhere between that of a cancellous bone plug and a cortical bone plug alone that have individually been fixated with an interference screw. Given this, the initial fixation strength of a bonegrafted tibial tunnel with an interference screw is better than that of other fixation options and is adequate to begin aggressive early rehabilitation.
CONCLUSION Despite precautions to avoid it, graft-tunnel mismatch with a protruding tibial bone plug is an inevitability in a certain number of cases. Bone grafting the tibial tunnel with a cancellous bone plug harvested with a coring reamer is a simple and effective technique for dealing with this complication. Filling the tibial tunnel with bone also has the potential advantages of reducing motion between the tendon and the tunnel, improving the healing of the graft to the tunnel, and allowing for more anatomic fixation of the tibial end of the graft. Acknowledgment: The authors express their gratitude for the art work created by Judy Johnson.
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