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Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation
SECTION XIII Soft-Tissue Graft Cortical Fixation
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Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation Chadwick C. Prodromos, MD
INTRODUCTION The Endobutton (EB) is the most widely used femoral fixation device worldwide that is designed specifically for soft tissue grafts. Pioneered by Dr. Thomas Rosenberg and introduced around 1990, it was the first device specifically designed to hold soft tissue grafts. As originally designed, the surgeon would tie a Dacron tape connecting the button to the tendon. This technique was subsequently supplanted by use of the EB-CL (continuous loop), which obviated the need to tie knots. Due to the longevity of the device, there is a much wider body of literature concerning it than any of the other newer, soft tissue–specific devices.
BIOMECHANICS Numerous studies have analyzed the pullout strength and stiffness of this device.1–7 There was much discussion at one point about a so-called bungee effect, in which the device’s fixation on the cortex and not in the tunnel supposedly resulted in lower stiffness. However, it has subsequently been shown that the greater stiffness resulting from cortical anchorage dwarfs the slightly reduced stiffness from the greater length of the construct.7 Also, as described elsewhere in the text, stiffness has no bearing on ultimate stability. This is because the stiffness of all grafts is independent of their mode of fixation once tunnel healing has occurred at about 2 months postoperatively. After this time, load is borne by the healed fibers that connect the graft to the tunnel, not by the device. Because the fixation device is not load bearing after this time, its stiffness is irrelevant. However, even before that time, stiffness is less important because the stiffness represents only elastic deformation of the graft. It is only plastic deformation, not elastic deformation, that will result in greater ultimate clinical laxity. In fact, reduced stiffness, or greater elasticity, in the graft-fixation construct will diminish the forces that tend to displace the fixation device in cyclical loading. This reduction in stiffness diminishes these forces by partially dissipating them in temporary elastic deformation of the graft. Therefore, ultimately, stability may actually be enhanced by protecting the construct from plastic deformation or fixation device slippage while tunnel healing is occurring.
CLINICAL RESULTS In the largest meta-analysis of anterior cruciate ligament reconstruction autografts, the EB-hamstring combination was found to have the highest stability rates of any graft-fixation construct when paired with modern tibial fixation.8–14 Morbidity has been minimal.15–18 In our experience,8 the EB has proven to be extremely reliable. After more than 20 years of continuous use, as well as follow-up of more than 80% of
all implanted EBs, we have experienced a graft failure rate of less than 1% (see Chapter 117). Approximately 86% of grafts have had International Knee Documentation Committee n ormal stability. We have had no hardware complications and no displaced EBs, and we have not had to remove an EB.
SURGICAL TECHNIQUE Principle The EB is a small oval button that anchors the graft against the outer femoral cortex. It is passed up from within, without a second femoral incision.
Materials The EB-CL (continuous loop) is the standard implant. It comes with fabric loops already attached to the EB in 5-mm increments, with 10 mm being the shortest. A standard anterior cruciate ligament tray is used, although a special 4.5-mm drill bit, available only from Smith & Nephew (Andover, Massachusetts), must be used.
Femoral-Tunnel Formation Principles of Femoral-Tunnel Drilling Two femoral tunnels are necessary in sequence with each other, as will be described. We drill the tunnel transtibially although some use the medial portal. A laser-marked, long transtibial guide pin with markings every 2 mm is used to drill the femoral tunnel at a 65-degree coronal angle. It is important to drill the tunnel such that the exit is in the femoral metaphysis rather than the femoral condyle, if possible, so that the tunnel will have adequate length. It has recently become apparent that a femoral-tunnel entry lower down at the 10:30-o’clock position rather than the 11-o’clock position (for a left knee) will improve rotational stability. This lower entry will, however, also result in a shorter tunnel, because the exit will tend to be from the narrower condyle, which is lower down than the wider metaphysis. To compensate for this, the knee needs to be more flexed during drilling to 90 degrees or more in order to redirect the tunnel upward toward the metaphysis. The following is our technique for femoral-tunnel formation and EB fixation.
Notchplasty We always perform a lateral notchplasty, but not roofplasty, of about 3 mm for visualization. All soft tissue should be removed
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from the tunnel so that the over-the-top position can be clearly seen. It should also be probed to make sure the surgeon knows where the back of the notch is.
Basic Technique With the leg hanging free at its usual angle of about 75 degrees, a 1-mm deep indentation is made with the tip of the drill pin at the 10:00-o’clock position, and about 3–4 mm distal to (forward from) the over-the-top position. The tunnel entry point is found in this fashion because visualization is easiest at this degree of knee flexion. We then pull the pin back and make sure the location for the tunnel is satisfactory. The knee is then flexed to around 80–90 degrees. The pin is then reinserted into the indentation, and the tunnel is slowly drilled, taking care to stop when the resistance of cortical bone is reached. This is easily felt if the tunnel is drilled slowly and with a light touch. The cortex will usually be reached at 30–40 mm, as seen on the lasermarked pin.
by more than 9 mm, the guide pin and then the acorn drill bit should be reinserted over the guide pin, and the socket should be drilled a little farther so that it is within 6–9 mm of the total length. If the far wall of the cortex is accidentally violated, this can be easily salvaged with an Xtendobutton, as will be described.
Calculating Endobutton–Continuous Loop Length The socket length is subtracted from the total channel length, and 6 or 7 mm are added for a turning radius. If that number is a multiple of 5, then that is the EB-CL used. If it is not a multiple of 5, then the next-largest number that is a multiple of 5 is selected. For example, if the total channel is 34 mm and the socket is 27 mm, the difference would be 7 mm (7 + 6 = 13). The next-largest number that is a multiple of 5 is 15, so a 15-mm EB-CL is selected. In this case, 34 – 15 = 19, so a 19 mm of graft would be in the femoral tunnel.
Minimum Tunnel Length Our minimum acceptable tunnel length is 30 mm, which when the 15-mm continuous loop length is subtracted, leaves 15 mm of graft in the tunnel. The cortex is 3–5 mm thick. Thus we make sure that the laser pin shows at least 27 mm inserted into the condyle before reaching the femoral cortex, to ensure that the total channel length will be at least 30 mm after drilling through the cortex.
Redrilling If the First Tunnel Is Too Short If the tunnel is less than 27 mm, we withdraw the pin, relax the knee to 75 degrees or so, and make a new pilot indentation slightly higher than the 10:00-o’clock position and/or about 5 mm distal to over-the-top position (i.e., slightly higher and more distal or forward than the original hole). We then redrill the hole. The new tunnel should be significantly longer. The changes in tunnel location yield longer tunnels and will still result in a tunnel in a very acceptable location. If the knee is adequately flexed the first time, however, a second pass will rarely be necessary.
Fig. 63.1. The 4.5-mm drill bit is drilled through the cortex over the previously drilled, laser-marked, long guide pin after the socket has been drilled.
Finishing the Femoral Tunnel Once a satisfactory tunnel has been found, the laser pin is further drilled through the cortex. We observe the laser markings when giving way is achieved, which indicates the pin has burst through the cortex, so we have a good idea of the total channel length. Next, the appropriate acorn reamer is inserted over the pin. This is drilled nearly to the cortex, as measured from the laser pin. If high resistance is felt before the anticipated point is reached, drilling should be stopped to avoid breaking through the opposite cortex. Generally the acorn reamer will be drilled 1–2 mm shorter than the laser pin length indication of where the cortex was reached. The socket will usually be about 6 mm shorter than the total channel length. It must be within 9 mm of the length of the total tunnel, to allow a 15-mm EB-CL to be used. This is because at least 6 mm of extra length is needed to allow a turning radius for the EB as it sits outside the femoral cortex (i.e., 6 + 9 = 15 mm). Once the socket is drilled, the acorn drill bit is withdrawn and a 4.5-mm bit is inserted and drilled through the outer cortex with the guide pin still in place (Fig. 63.1). After the 4.5-mm tunnel is drilled, the guide pin is removed with the 4.5-mm drill bit. Next, the long-depth gauge is used to measure the total channel length (Fig. 63.2). If it exceeds the socket length
Fig. 63.2. The total channel length is measured with the long-depth gauge while viewing the femoral-tunnel entry point arthroscopically.
CHAPTER 63 Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation
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Preparing the Endobutton/Graft Construct The EB-CL is positioned in the holder on the Graftmaster board. The graft is then passed through the fabric loop attached to the EB (Fig. 63.3). A violet #3–0 or 4–0 monofilament absorbable suture is then sewn across the graft (Fig. 63.4) at a distance from the EB that is 2 mm greater than the total channel length, as identified on the Graftmaster board on which the construct is positioned. In the earlier example, the total channel length was 34 mm, so the suture would be placed at 36 mm from the EB. This will provide arthroscopic evidence that the graft has been passed to the proper depth later in the procedure. This area should also be marked with a marking pin. This absorbable colored suture also locks the graft in place, preventing it from sliding on the fabric loop. A #5 suture is then passed through one eyehole, and a #2 suture through the other eyehole of the EB. All four suture ends are then passed through the eye of the long passing pin (Fig. 63.5), and a hemostat is applied to the four suture ends near their tips to lock the graft onto the pin.
arthroscope. The knee should be flexed during this passage to the same degree as when the femoral tunnel was drilled. The pin is then inserted into the femoral tunnel and passed proximalward out through a puncture in the soft tissue, where it is pulled free of the passing sutures (Fig. 63.6). Sometimes the pin must be redirected subtly within the femoral socket before it finds the smaller 4.5-mm tunnel and makes its way into the soft tissue. The two #5 sutures are then grasped with a Kocher clamp. The sutures are wound onto the closed Kocher jaws like a spool. The Kocher clamp with wound sutures is then strongly pulled until the graft can be felt to pass into the femoral socket and become fully seated. The previously inserted violet suture and ink markings on the graft are visualized arthroscopically just outside the femoral-tunnel opening, which confirms that the graft is in proper position. If the graft is not fully seated, the Kocher clamp can be wound like a windlass to pull in the graft. Cycling of the knee may also help.
Passing the Graft
The two #2 sutures are then pulled to flatten the EB on the external femoral surface. After slack is taken up, a slight toggling should be felt (Fig. 63.7). Strong retrograde tension should be applied to the whipstitches as they dangle out the tibial incision while the knee is flexed and extended to make sure the graft cannot be pulled back out of it (Fig. 63.8). We then wrap the sutures around the smooth shank of the tibial screw and hold very strong tension while fully flexing and extending the knee 3 times. This serves to eliminate slack from the graft. This will serve to pull the graft out of the knee if the EB has not been seated; for this reason, this step is very important. We have had the graft withdraw in this fashion 2 or 3 times and have successfully reseated it each time (see the “Troubleshooting” section later in this chapter). We have never had a graft pull out later. However, if this step had been omitted, later loosening could have occurred in these cases. The tibial screw or other tibial fixation method is then tightened.
The long pin with the graft and sutures attached is then passed into the tibial tunnel into the knee, where it is visualized with the
Seating the Endobutton
Removing the Passing Sutures
Fig. 63.3. The prepared graft is passed through the fabric loop until each arm of the graft is the same length.
After the EB is flattened and tibial fixation has been applied, the passing sutures should be pulled out from the EB. The #2 suture should be tried first, making sure that it slides freely (if not, see problem 3 in “Troubleshooting”). If it does slide freely, cut one limb off at skin level, and pull the other end out and discard it. This is repeated with the #5 suture.
Fig. 63.4. The colored absorbable monofilament suture locks the graft to prevent sliding and also marks the entry point for the femoral tunnel.
Fig. 63.5. All four sutures—two #5 and two #2 sutures—are passed through the eye of the long passing pin.
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To ta lc In ha se nn le rti ng on el th le Co ng nn th e sp ct an ion
A
B Fig. 63.6. A and B, The long guide pin is passed into the knee and out through the soft tissue, with the graft construct attached.
Fig. 63.7. The #2 sutures are used to flatten the Endobutton, seating it on the femoral cortex after the graft has been pulled into the socket with the #5 sutures.
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CHAPTER 63 Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation
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Fig. 63.8. Strong retrograde tension fails to dislodge the graft when the knee is cycled once the Endobutton has been properly seated.
TROUBLESHOOTING In this section, we list all the EB problems that we have either encountered or theorized but not encountered. In all cases, the difficulty was dealt with, the surgery was finished with only a minor delay, and a good result was obtained. In over 20 years of continuous use we have never had an EB-related complication, EB failure, or migration. We have never had to remove an EB nor had a graft fail when fixated with an EB.8 Rarely, however, one of the following problems may arise. If the surgeon is prepared, these problems should pose no difficulty. The EB has proven to be remarkably trouble-free over the most extended use of any soft tissue femoral fixation device. PROBLEM 1: WHAT IF THE ENDOBUTTON WILL NOT FLATTEN AND THE GRAFT PULLS BACK THROUGH AND INTO THE KNEE? Cause 1
The total channel length was measured too short, and hence the EB-CL is too short, so it is not emerging outside the femoral cortex where it can be flattened. Comment. This is a rare occurrence that was slightly more likely to happen in the past, when tunnels were placed higher and channels were longer than at present. The lower tunnel placements currently used result in relatively short tunnels, which are easier to measure. Also, initially the long guide pin did not have laser markings. At our urging, Smith and Nephew began fabricating marked guide pins and have now included laser length markings on all long guide pins, which allows the surgeon to closely estimate the femoral-tunnel length while drilling, before measuring with the depth gauge. Remedy. If the EB will not flatten and seat and catch, it should be passed a second time. If it still will not seat, then the femoral tunnel should be remeasured. If a longer measurement is indeed obtained, a longer EB-CL should be attached, and the EB should now flatten and catch appropriately. If the total channel was measured accurately and if the difference between the total channel length and the socket is 8 or 9 mm, such that the turning radius of the EB is only 6 or 7 mm, then the socket should be drilled another 2 or 3 mm if possible. This allows a greater turning radius for the EB of 8–10 mm and should facilitate seating.
Cause 2
The lateral cortex was damaged by the socket reamer, effectively enlarging the 4.5-mm tunnel such that the EB does not hold and falls back into the joint. Comment. If this occurs, you will usually know when you burst through with the socket reamer (or at least suspect it), but it is possible to damage the cortex and not realize it until the EB will not hold. Remedy 1. A second incision of 3 cm in length near the exit of the femoral tunnel can be made. A #5 suture can be substituted for the #2 suture and tied two by two with the other already inserted #5 suture around a 6.5-mm, two-thirds threaded unicortical cancellous screw and washer inserted about 1.5 cm away from the exit of the femoral tunnel. Remedy 2. Currently this problem could be more easily salvaged without a second incision by attaching the larger, recently introduced Xtendobutton to the EB and then passing the graft again. This larger button will hold in a socket-sized larger tunnel up to at least 10 mm. The surgeon should make sure an Xtendobutton is present at surgery, in case it is required. Cause 3
The two passing sutures are tangled. Comment. When the graft is pulled back, the entanglement that prevents the thinner flattening suture from functioning should be clearly visible arthroscopically. Remedy. Separate the #5 and #2 sutures from each other, and pass the graft again without withdrawing the sutures from their exit out of the thigh. PROBLEM 2: WHAT IF THE ENDOBUTTON FLATTENS INITIALLY BUT IS PULLED BACK OUT WHEN THE GRAFT IS TENSIONED? Cause 1
Excessive tensioning pressure was applied to the graft on the tibia, and the EB was pulled back without apparent cause. Comment. We have had this occur on only one occasion for no apparent reason, except that we were probably excessively tensioning the graft during range of motion of the knee prior to Continued
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SECTION XIII Soft-Tissue Graft Cortical Fixation
tying around the tibial screw. There was a palpable “thunk” when it happened, as though a minor knee subluxation had taken place. We then noticed mild slack on the construct and slight withdrawal arthroscopically. Remedy. Repass and flatten the EB. If it holds, as it did during our case, take a radiograph before applying tibial fixation with fluoroscopy to make sure the position is satisfactory. If so, proceed to finish tibial fixation. Nothing further needs to be done, although we would recommend a repeat radiograph at 3, 7, and 14 days postoperatively to verify EB position. Repeat radiographs in our clinic showed no migration, and excellent stability ultimately resulted. Cause/Remedy 2
See Problem 1, Cause 2. PROBLEM 3: WHAT IF THE PASSING SUTURES CANNOT BE PULLED OUT OF THE ENDOBUTTON AFTER FIXATION? Cause
Entanglement or entrapment in soft tissue. Comment. This is less likely to happen if the knee is flexed to the same degree for passing suture removal as during graft passage. Remedy. The surgeon should slide one of the passing sutures a few millimeters to make sure it is free. If it will not slide one way easily, it often will do so in the opposite direction. If it still will not slide, the soft tissue of the thigh should be compressed downward and the ends cut. The recoil of the soft tissue will ensure that the ends retract well below the dermis. We have had this happen once. No sequela occurred as a result of the suture being left in the soft tissue. We prefer this to forcing the suture to come out, which we fear might displace the EB into the tunnel.
PROBLEM 4: WHAT IF THE ENDOBUTTON-CL IS SO LONG THAT THERE IS TOO LITTLE GRAFT IN THE FEMORAL TUNNEL? Cause
Mismeasurement of the tunnel or miscalculation with selection of an EB-CL that is too long. Comment. We have never had this happen, but the surgeon should be prepared in case it does occur. Remedy. Even if there were less graft in the tunnel than we had planned, we would leave it alone if there were at least 15 mm of graft in the tunnel. Studies19,20 and our own experience and that of others have shown this to be adequate. If less than 15 mm were in the tunnel and the fabric loop were visible through the arthroscope, we would recommend cutting the loop arthroscopically and then using the 4.5-mm bit to push the EB outward into the soft tissue. The tunnel would then be remeasured, and another EB-CL of more appropriate length would be used. If the fabric loop were not visible arthroscopically or could not be cut and if less than 15 mm of graft were in the tunnel, we would make a small second incision to either remove the EB or feed it back into the tunnel so that it could be removed from below. We would then remeasure the tunnel and use an appropriately shorter EB so that satisfactory graft remained in the tunnel. PROBLEM 5: WHAT IF THE FAR FEMORAL CORTEX IS BLOWN OUT WITH THE SOCKET REAMER SUCH THAT A 4.5-MM TUNNEL CANNOT BE DRILLED?
See Problem 1, Cause 2. Problem 5 is the same problem, but with earlier recognition that it has occurred.
THE XTENDOBUTTON More recently released, the Xtendobutton is a larger button that attaches to the standard EB (Fig. 63.9), effectively enlarging its profile as described earlier. It can be used routinely to eliminate the need to drill the narrower 4.5-mm tunnel. This larger profile can be used with larger tunnels up to at least a 10-mm tunnel. We still use the smaller 4.5-mm tunnel in conjunction with the larger socket, because we believe the smaller bone removal may be beneficial and because we are comfortable with this technique after 20 years of continuous use. However, it is likely that the use of the Xtendobutton will prove to be just as reliable. Xtendobutton use eliminates the calculations involved with two tunnels, which may facilitate the procedure for the occasional user. As described earlier, the Xtendobutton is of great value if the surgeon penetrates out the far femoral cortex with the larger socket reamer, such that the standard EB is too small to use. Before the introduction of the Xtendobutton, a second incision would have had to be made over the femur for insertion of a femoral screw. The Xtendobutton allows the procedure to be completed in the usual fashion without a second femoral incision (Fig. 63.10).
CONCLUSIONS Stability: Unsurpassed stability rates have been reported using the EB. The bungee effect: The bungee effect is either nonexistent or clinically insignificant. Technique: The most important technical point is to flex the knee to near 90 degrees during femoral-tunnel drilling to ensure a tunnel of at least 30 mm in length. Morbidity: The complication rate has been virtually nonexistent, with only a few reported cases (and none in our experience), despite the highest level of use of any noninterference screw femoral fixation device.
Fig. 63.9. The Xtendobutton fits over the Endobutton so that it is large enough to hold outside a 10-mm femoral tunnel.
Xtendobutton: The Xtendobutton provides salvage without making a femoral incision if the far cortex is blown out. It also simplifies the procedure for the occasional user. Ease of use: The method is straightforward and easily learned. SELECTED READINGS
Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med. 2004;32(3):635–640. Brand Jr B, Weiler A, Caborn DNM, Brown Jr CH, Johnson DL. Graft fixation in cruciate ligament surgery. Am J Sports Med. 2000;28(5):761–774. Cooley VJ, Deffner KT, Rosenberg TD. Quadrupled semitendinosus anterior cruciate ligament reconstruction: 5-year results in patients without meniscus loss. Arthroscopy. 2001;17(8):795–800.
CHAPTER 63 Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation
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A
B Fig. 63.10. A and B, In this revision case, the Xtendobutton was used to anchor the graft on the outside of a 9-mm femoral tunnel.
Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med. 2003;31(4):564–573. Prodromos CC, Han YS, Keller BL, Bolyard RJ. Stability of hamstring anterior cruciate ligament reconstruction at two- to eight-year followup. Arthroscopy. 2005;21(2):138–146. Prodromos CC, Joyce BT, Shi K, Keller BL. A meta-analysis of stability after anterior cruciate ligament reconstruction as a function of hamstring versus patellar-tendon graft and fixation type. Arthroscopy. 2005;21(10):1202–1208. Scheffler SU, Sudkamp NP, Gockenjan A, Hoffmann RF, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: the impact of fixation level and fixation method under cyclic loading. Arthroscopy. 2002;18(3):304–315.
To JT, Howell SM, Hull ML. Contributions of femoral fixation methods to the stiffness of anterior cruciate ligament replacements at implantation. Arthroscopy. 1999;15(4):379–387. Yamazaki S, Yasuda K, Tomita F, Minami A, Tohyama H. The effect of intraosseous graft length on tendon-bone healing in anterior cruciate ligament reconstruction using flexor tendon. Knee Surg Sports Traumatol Arthrosc. 2006;14(11):1086–1093. Zantop T, Brucker P, Bell K, et al. The effect of tunnel-graft length on the primary and secondary stability in ACL reconstruction: a study in a goat model. In: Presented at the 2006 Meeting of the European Society of Sports Traumatology, Knee Surgery, and Arthroscopy. Innsbruck: Australia; 2006.
A complete reference list can be found online at ExpertConsult.com.
REFERENCES
1. Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med. 2004;32(3):635–640. 2. Brand Jr B, Weiler A, Caborn DNM, Brown Jr CH, Johnson DL. Graft fixation in cruciate ligament surgery. Am J Sports Med. 2000;28(5):761–774. 3. Brand Jr J, Hamilton D, Selby D, Pienkowski D, Caborn DN, Johnson DL. Biomechanical comparison of quadriceps tendon fixation with patellar tendon bone plug interference fixation in cruciate ligament reconstruction. Arthroscopy. 2000;16(8):805–812. 4. Brown CH, Wilson DR, Hecker A, et al. Comparison of hamstring and patellar tendon femoral fixation: cyclic load. In: Presented at the 1999 Meeting of the American Orthopaedic Society for Sports Medicine. Traverse City: MI; 1999. 5. Rowden NJ, Sher D, Rogers GJ, Schindhelm K. Anterior cruciate ligament graft fixation: initial comparison of patellar tendon and semitendinosus autografts in young fresh cadavers. Am J Sports Med. 1997;25(4):472–478. 6. Scheffler SU, Sudkamp NP, Gockenjan A, Hoffmann RF, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: the impact of fixation level and fixation method under cyclic loading. Arthroscopy. 2002;18(3):304–315. 7. To JT, Howell SM, Hull ML. Contributions of femoral fixation methods to the stiffness of anterior cruciate ligament replacements at implantation. Arthroscopy. 1999;15(4):379–387. 8. Prodromos CC, Han YS, Keller BL, Bolyard RJ. Stability of hamstring anterior cruciate ligament reconstruction at two- to eight-year follow-up. Arthroscopy. 2005;21(2):138–146. 9. Gobbi A, Mahajan S, Zanazzo M, Tuy B. Patellar tendon versus quadrupled bone-semitendinosus anterior cruciate ligament reconstruction: a prospective clinical investigation in athletes. Arthroscopy. 2003;19(6):592–601. 10. Gobbi A, Tuy B, Mahajan S, Panuncialman I. Quadrupled bonesemitendinosus anterior cruciate ligament reconstruction: a clinical investigation in a group of athletes. Arthroscopy. 2003;19(7):691–699.
11. Cooley VJ, Deffner KT, Rosenberg TD. Quadrupled semitendinosus anterior cruciate ligament reconstruction: 5-year results in patients without meniscus loss. Arthroscopy. 2001;17(8):795–800. 12. Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med. 2003;31(4):564–573. 13. Yasuda K, Kondo E, Ichiyama H, et al. Anatomic reconstruction of the anteromedial and posterolateral bundles of the anterior cruciate ligament using hamstring tendon grafts. Arthroscopy. 2004;20(10): 1015–1025. 14. Prodromos CC, Joyce BT, Shi K, Keller BL. A meta-analysis of stability after anterior cruciate ligament reconstruction as a function of hamstring versus patellar-tendon graft and fixation type. Arthroscopy. 2005;21(10):1202–1208. 15. Karaoglu S, Halici M, Baktir A. An unidentified pitfall of Endobutton use: case report. Knee Surg Sports Traumatol Arthrosc. 2002;10(4): 247–249. 16. Simonian PT, Behr CT, Stechschulte Jr DJ, Wickiewicz TL, Warren RF. Potential pitfall of the Endobutton. Arthroscopy. 1998;14(1): 66–69. 17. Muneta T, Yagishita K, Kurihara Y, Sekiya I. Intra-articular detachment of the Endobutton more than 18 months after anterior cruciate ligament reconstruction. Arthroscopy. 1999;15(7):775–778. 18. Brucker P, Zelle BA, Fu FH. Intraarticular Endobutton displacement in anatomic anterior cruciate ligament double-bundle reconstruction: a case report. Op Tech Orthop. 2005;15:154–157. 19. Zantop T, Brucker P, Bell K, et al. The effect of tunnel-graft length on the primary and secondary stability in ACL reconstruction: a study in a goat model. In: Presented at the 2006 Meeting of the European Society of Sports Traumatology, Knee Surgery, and Arthroscopy. Innsbruck: Australia; 2006. 20. Yamazaki S, Yasuda K, Tomita F, Minami A, Tohyama H. The effect of intraosseous graft length on tendon-bone healing in anterior cruciate ligament reconstruction using flexor tendon. Knee Surg Sports Traumatol Arthrosc. 2006;14(11):1086–1093.
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Endobutton Anterior Cruciate Ligament Reconstruction Femoral Fixation Chadwick C. Prodromos, MD
INTRODUCTION The Endobutton (EB) is the most widely used femoral fixation device worldwide that is designed specifically for soft tissue grafts. Pioneered by Dr. Thomas Rosenberg and introduced around 1990, it was the first device specifically designed to hold soft tissue grafts. As originally designed, the surgeon would tie a Dacron tape connecting the button to the tendon. This technique was subsequently supplanted by use of the EB-CL (continuous loop), which obviated the need to tie knots. Due to the longevity of the device, there is a much wider body of literature concerning it than any of the other newer, soft tissue–specific devices.
BIOMECHANICS Numerous studies have analyzed the pullout strength and stiffness of this device.1–7 There was much discussion at one point about a so-called bungee effect, in which the device’s fixation on the cortex and not in the tunnel supposedly resulted in lower stiffness. However, it has subsequently been shown that the greater stiffness resulting from cortical anchorage dwarfs the slightly reduced stiffness from the greater length of the construct.7 Also, as described elsewhere in the text, stiffness has no bearing on ultimate stability. This is because the stiffness of all grafts is independent of their mode of fixation once tunnel healing has occurred at about 2 months postoperatively. After this time, load is borne by the healed fibers that connect the graft to the tunnel, not by the device. Because the fixation device is not load bearing after this time, its stiffness is irrelevant. However, even before that time, stiffness is less important because the stiffness represents only elastic deformation of the graft. It is only plastic deformation, not elastic deformation, that will result in greater ultimate clinical laxity. In fact, reduced stiffness, or greater elasticity, in the graft-fixation construct will diminish the forces that tend to displace the fixation device in cyclical loading. This reduction in stiffness diminishes these forces by partially dissipating them in temporary elastic deformation of the graft. Therefore, ultimately, stability may actually be enhanced by protecting the construct from plastic deformation or fixation device slippage while tunnel healing is occurring.
CLINICAL RESULTS In the largest meta-analysis of anterior cruciate ligament reconstruction autografts, the EB-hamstring combination was found to have the highest stability rates of any graft-fixation construct when paired with modern tibial fixation.8–14 Morbidity has been minimal.15–18 In our experience,8 the EB has proven to be extremely reliable. After more than 20 years of continuous use, as well as follow-up of more than 80% of
all implanted EBs, we have experienced a graft failure rate of less than 1% (see Chapter 117). Approximately 86% of grafts have had International Knee Documentation Committee n ormal stability. We have had no hardware complications and no displaced EBs, and we have not had to remove an EB.
SURGICAL TECHNIQUE Principle The EB is a small oval button that anchors the graft against the outer femoral cortex. It is passed up from within, without a second femoral incision.
Materials The EB-CL (continuous loop) is the standard implant. It comes with fabric loops already attached to the EB in 5-mm increments, with 10 mm being the shortest. A standard anterior cruciate ligament tray is used, although a special 4.5-mm drill bit, available only from Smith & Nephew (Andover, Massachusetts), must be used.
Femoral-Tunnel Formation Principles of Femoral-Tunnel Drilling Two femoral tunnels are necessary in sequence with each other, as will be described. We drill the tunnel transtibially although some use the medial portal. A laser-marked, long transtibial guide pin with markings every 2 mm is used to drill the femoral tunnel at a 65-degree coronal angle. It is important to drill the tunnel such that the exit is in the femoral metaphysis rather than the femoral condyle, if possible, so that the tunnel will have adequate length. It has recently become apparent that a femoral-tunnel entry lower down at the 10:30-o’clock position rather than the 11-o’clock position (for a left knee) will improve rotational stability. This lower entry will, however, also result in a shorter tunnel, because the exit will tend to be from the narrower condyle, which is lower down than the wider metaphysis. To compensate for this, the knee needs to be more flexed during drilling to 90 degrees or more in order to redirect the tunnel upward toward the metaphysis. The following is our technique for femoral-tunnel formation and EB fixation.
Notchplasty We always perform a lateral notchplasty, but not roofplasty, of about 3 mm for visualization. All soft tissue should be removed
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from the tunnel so that the over-the-top position can be clearly seen. It should also be probed to make sure the surgeon knows where the back of the notch is.
Basic Technique With the leg hanging free at its usual angle of about 75 degrees, a 1-mm deep indentation is made with the tip of the drill pin at the 10:00-o’clock position, and about 3–4 mm distal to (forward from) the over-the-top position. The tunnel entry point is found in this fashion because visualization is easiest at this degree of knee flexion. We then pull the pin back and make sure the location for the tunnel is satisfactory. The knee is then flexed to around 80–90 degrees. The pin is then reinserted into the indentation, and the tunnel is slowly drilled, taking care to stop when the resistance of cortical bone is reached. This is easily felt if the tunnel is drilled slowly and with a light touch. The cortex will usually be reached at 30–40 mm, as seen on the lasermarked pin.
by more than 9 mm, the guide pin and then the acorn drill bit should be reinserted over the guide pin, and the socket should be drilled a little farther so that it is within 6–9 mm of the total length. If the far wall of the cortex is accidentally violated, this can be easily salvaged with an Xtendobutton, as will be described.
Calculating Endobutton–Continuous Loop Length The socket length is subtracted from the total channel length, and 6 or 7 mm are added for a turning radius. If that number is a multiple of 5, then that is the EB-CL used. If it is not a multiple of 5, then the next-largest number that is a multiple of 5 is selected. For example, if the total channel is 34 mm and the socket is 27 mm, the difference would be 7 mm (7 + 6 = 13). The next-largest number that is a multiple of 5 is 15, so a 15-mm EB-CL is selected. In this case, 34 – 15 = 19, so a 19 mm of graft would be in the femoral tunnel.
Minimum Tunnel Length Our minimum acceptable tunnel length is 30 mm, which when the 15-mm continuous loop length is subtracted, leaves 15 mm of graft in the tunnel. The cortex is 3–5 mm thick. Thus we make sure that the laser pin shows at least 27 mm inserted into the condyle before reaching the femoral cortex, to ensure that the total channel length will be at least 30 mm after drilling through the cortex.
Redrilling If the First Tunnel Is Too Short If the tunnel is less than 27 mm, we withdraw the pin, relax the knee to 75 degrees or so, and make a new pilot indentation slightly higher than the 10:00-o’clock position and/or about 5 mm distal to over-the-top position (i.e., slightly higher and more distal or forward than the original hole). We then redrill the hole. The new tunnel should be significantly longer. The changes in tunnel location yield longer tunnels and will still result in a tunnel in a very acceptable location. If the knee is adequately flexed the first time, however, a second pass will rarely be necessary.
Fig. 63.1. The 4.5-mm drill bit is drilled through the cortex over the previously drilled, laser-marked, long guide pin after the socket has been drilled.
Finishing the Femoral Tunnel Once a satisfactory tunnel has been found, the laser pin is further drilled through the cortex. We observe the laser markings when giving way is achieved, which indicates the pin has burst through the cortex, so we have a good idea of the total channel length. Next, the appropriate acorn reamer is inserted over the pin. This is drilled nearly to the cortex, as measured from the laser pin. If high resistance is felt before the anticipated point is reached, drilling should be stopped to avoid breaking through the opposite cortex. Generally the acorn reamer will be drilled 1–2 mm shorter than the laser pin length indication of where the cortex was reached. The socket will usually be about 6 mm shorter than the total channel length. It must be within 9 mm of the length of the total tunnel, to allow a 15-mm EB-CL to be used. This is because at least 6 mm of extra length is needed to allow a turning radius for the EB as it sits outside the femoral cortex (i.e., 6 + 9 = 15 mm). Once the socket is drilled, the acorn drill bit is withdrawn and a 4.5-mm bit is inserted and drilled through the outer cortex with the guide pin still in place (Fig. 63.1). After the 4.5-mm tunnel is drilled, the guide pin is removed with the 4.5-mm drill bit. Next, the long-depth gauge is used to measure the total channel length (Fig. 63.2). If it exceeds the socket length
Fig. 63.2. The total channel length is measured with the long-depth gauge while viewing the femoral-tunnel entry point arthroscopically.
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Preparing the Endobutton/Graft Construct The EB-CL is positioned in the holder on the Graftmaster board. The graft is then passed through the fabric loop attached to the EB (Fig. 63.3). A violet #3–0 or 4–0 monofilament absorbable suture is then sewn across the graft (Fig. 63.4) at a distance from the EB that is 2 mm greater than the total channel length, as identified on the Graftmaster board on which the construct is positioned. In the earlier example, the total channel length was 34 mm, so the suture would be placed at 36 mm from the EB. This will provide arthroscopic evidence that the graft has been passed to the proper depth later in the procedure. This area should also be marked with a marking pin. This absorbable colored suture also locks the graft in place, preventing it from sliding on the fabric loop. A #5 suture is then passed through one eyehole, and a #2 suture through the other eyehole of the EB. All four suture ends are then passed through the eye of the long passing pin (Fig. 63.5), and a hemostat is applied to the four suture ends near their tips to lock the graft onto the pin.
arthroscope. The knee should be flexed during this passage to the same degree as when the femoral tunnel was drilled. The pin is then inserted into the femoral tunnel and passed proximalward out through a puncture in the soft tissue, where it is pulled free of the passing sutures (Fig. 63.6). Sometimes the pin must be redirected subtly within the femoral socket before it finds the smaller 4.5-mm tunnel and makes its way into the soft tissue. The two #5 sutures are then grasped with a Kocher clamp. The sutures are wound onto the closed Kocher jaws like a spool. The Kocher clamp with wound sutures is then strongly pulled until the graft can be felt to pass into the femoral socket and become fully seated. The previously inserted violet suture and ink markings on the graft are visualized arthroscopically just outside the femoral-tunnel opening, which confirms that the graft is in proper position. If the graft is not fully seated, the Kocher clamp can be wound like a windlass to pull in the graft. Cycling of the knee may also help.
Passing the Graft
The two #2 sutures are then pulled to flatten the EB on the external femoral surface. After slack is taken up, a slight toggling should be felt (Fig. 63.7). Strong retrograde tension should be applied to the whipstitches as they dangle out the tibial incision while the knee is flexed and extended to make sure the graft cannot be pulled back out of it (Fig. 63.8). We then wrap the sutures around the smooth shank of the tibial screw and hold very strong tension while fully flexing and extending the knee 3 times. This serves to eliminate slack from the graft. This will serve to pull the graft out of the knee if the EB has not been seated; for this reason, this step is very important. We have had the graft withdraw in this fashion 2 or 3 times and have successfully reseated it each time (see the “Troubleshooting” section later in this chapter). We have never had a graft pull out later. However, if this step had been omitted, later loosening could have occurred in these cases. The tibial screw or other tibial fixation method is then tightened.
The long pin with the graft and sutures attached is then passed into the tibial tunnel into the knee, where it is visualized with the
Seating the Endobutton
Removing the Passing Sutures
Fig. 63.3. The prepared graft is passed through the fabric loop until each arm of the graft is the same length.
After the EB is flattened and tibial fixation has been applied, the passing sutures should be pulled out from the EB. The #2 suture should be tried first, making sure that it slides freely (if not, see problem 3 in “Troubleshooting”). If it does slide freely, cut one limb off at skin level, and pull the other end out and discard it. This is repeated with the #5 suture.
Fig. 63.4. The colored absorbable monofilament suture locks the graft to prevent sliding and also marks the entry point for the femoral tunnel.
Fig. 63.5. All four sutures—two #5 and two #2 sutures—are passed through the eye of the long passing pin.
63
To ta lc In ha se nn le rti ng on el th le Co ng nn th e sp ct an ion
A
B Fig. 63.6. A and B, The long guide pin is passed into the knee and out through the soft tissue, with the graft construct attached.
Fig. 63.7. The #2 sutures are used to flatten the Endobutton, seating it on the femoral cortex after the graft has been pulled into the socket with the #5 sutures.
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Fig. 63.8. Strong retrograde tension fails to dislodge the graft when the knee is cycled once the Endobutton has been properly seated.
TROUBLESHOOTING In this section, we list all the EB problems that we have either encountered or theorized but not encountered. In all cases, the difficulty was dealt with, the surgery was finished with only a minor delay, and a good result was obtained. In over 20 years of continuous use we have never had an EB-related complication, EB failure, or migration. We have never had to remove an EB nor had a graft fail when fixated with an EB.8 Rarely, however, one of the following problems may arise. If the surgeon is prepared, these problems should pose no difficulty. The EB has proven to be remarkably trouble-free over the most extended use of any soft tissue femoral fixation device. PROBLEM 1: WHAT IF THE ENDOBUTTON WILL NOT FLATTEN AND THE GRAFT PULLS BACK THROUGH AND INTO THE KNEE? Cause 1
The total channel length was measured too short, and hence the EB-CL is too short, so it is not emerging outside the femoral cortex where it can be flattened. Comment. This is a rare occurrence that was slightly more likely to happen in the past, when tunnels were placed higher and channels were longer than at present. The lower tunnel placements currently used result in relatively short tunnels, which are easier to measure. Also, initially the long guide pin did not have laser markings. At our urging, Smith and Nephew began fabricating marked guide pins and have now included laser length markings on all long guide pins, which allows the surgeon to closely estimate the femoral-tunnel length while drilling, before measuring with the depth gauge. Remedy. If the EB will not flatten and seat and catch, it should be passed a second time. If it still will not seat, then the femoral tunnel should be remeasured. If a longer measurement is indeed obtained, a longer EB-CL should be attached, and the EB should now flatten and catch appropriately. If the total channel was measured accurately and if the difference between the total channel length and the socket is 8 or 9 mm, such that the turning radius of the EB is only 6 or 7 mm, then the socket should be drilled another 2 or 3 mm if possible. This allows a greater turning radius for the EB of 8–10 mm and should facilitate seating.
Cause 2
The lateral cortex was damaged by the socket reamer, effectively enlarging the 4.5-mm tunnel such that the EB does not hold and falls back into the joint. Comment. If this occurs, you will usually know when you burst through with the socket reamer (or at least suspect it), but it is possible to damage the cortex and not realize it until the EB will not hold. Remedy 1. A second incision of 3 cm in length near the exit of the femoral tunnel can be made. A #5 suture can be substituted for the #2 suture and tied two by two with the other already inserted #5 suture around a 6.5-mm, two-thirds threaded unicortical cancellous screw and washer inserted about 1.5 cm away from the exit of the femoral tunnel. Remedy 2. Currently this problem could be more easily salvaged without a second incision by attaching the larger, recently introduced Xtendobutton to the EB and then passing the graft again. This larger button will hold in a socket-sized larger tunnel up to at least 10 mm. The surgeon should make sure an Xtendobutton is present at surgery, in case it is required. Cause 3
The two passing sutures are tangled. Comment. When the graft is pulled back, the entanglement that prevents the thinner flattening suture from functioning should be clearly visible arthroscopically. Remedy. Separate the #5 and #2 sutures from each other, and pass the graft again without withdrawing the sutures from their exit out of the thigh. PROBLEM 2: WHAT IF THE ENDOBUTTON FLATTENS INITIALLY BUT IS PULLED BACK OUT WHEN THE GRAFT IS TENSIONED? Cause 1
Excessive tensioning pressure was applied to the graft on the tibia, and the EB was pulled back without apparent cause. Comment. We have had this occur on only one occasion for no apparent reason, except that we were probably excessively tensioning the graft during range of motion of the knee prior to Continued
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tying around the tibial screw. There was a palpable “thunk” when it happened, as though a minor knee subluxation had taken place. We then noticed mild slack on the construct and slight withdrawal arthroscopically. Remedy. Repass and flatten the EB. If it holds, as it did during our case, take a radiograph before applying tibial fixation with fluoroscopy to make sure the position is satisfactory. If so, proceed to finish tibial fixation. Nothing further needs to be done, although we would recommend a repeat radiograph at 3, 7, and 14 days postoperatively to verify EB position. Repeat radiographs in our clinic showed no migration, and excellent stability ultimately resulted. Cause/Remedy 2
See Problem 1, Cause 2. PROBLEM 3: WHAT IF THE PASSING SUTURES CANNOT BE PULLED OUT OF THE ENDOBUTTON AFTER FIXATION? Cause
Entanglement or entrapment in soft tissue. Comment. This is less likely to happen if the knee is flexed to the same degree for passing suture removal as during graft passage. Remedy. The surgeon should slide one of the passing sutures a few millimeters to make sure it is free. If it will not slide one way easily, it often will do so in the opposite direction. If it still will not slide, the soft tissue of the thigh should be compressed downward and the ends cut. The recoil of the soft tissue will ensure that the ends retract well below the dermis. We have had this happen once. No sequela occurred as a result of the suture being left in the soft tissue. We prefer this to forcing the suture to come out, which we fear might displace the EB into the tunnel.
PROBLEM 4: WHAT IF THE ENDOBUTTON-CL IS SO LONG THAT THERE IS TOO LITTLE GRAFT IN THE FEMORAL TUNNEL? Cause
Mismeasurement of the tunnel or miscalculation with selection of an EB-CL that is too long. Comment. We have never had this happen, but the surgeon should be prepared in case it does occur. Remedy. Even if there were less graft in the tunnel than we had planned, we would leave it alone if there were at least 15 mm of graft in the tunnel. Studies19,20 and our own experience and that of others have shown this to be adequate. If less than 15 mm were in the tunnel and the fabric loop were visible through the arthroscope, we would recommend cutting the loop arthroscopically and then using the 4.5-mm bit to push the EB outward into the soft tissue. The tunnel would then be remeasured, and another EB-CL of more appropriate length would be used. If the fabric loop were not visible arthroscopically or could not be cut and if less than 15 mm of graft were in the tunnel, we would make a small second incision to either remove the EB or feed it back into the tunnel so that it could be removed from below. We would then remeasure the tunnel and use an appropriately shorter EB so that satisfactory graft remained in the tunnel. PROBLEM 5: WHAT IF THE FAR FEMORAL CORTEX IS BLOWN OUT WITH THE SOCKET REAMER SUCH THAT A 4.5-MM TUNNEL CANNOT BE DRILLED?
See Problem 1, Cause 2. Problem 5 is the same problem, but with earlier recognition that it has occurred.
THE XTENDOBUTTON More recently released, the Xtendobutton is a larger button that attaches to the standard EB (Fig. 63.9), effectively enlarging its profile as described earlier. It can be used routinely to eliminate the need to drill the narrower 4.5-mm tunnel. This larger profile can be used with larger tunnels up to at least a 10-mm tunnel. We still use the smaller 4.5-mm tunnel in conjunction with the larger socket, because we believe the smaller bone removal may be beneficial and because we are comfortable with this technique after 20 years of continuous use. However, it is likely that the use of the Xtendobutton will prove to be just as reliable. Xtendobutton use eliminates the calculations involved with two tunnels, which may facilitate the procedure for the occasional user. As described earlier, the Xtendobutton is of great value if the surgeon penetrates out the far femoral cortex with the larger socket reamer, such that the standard EB is too small to use. Before the introduction of the Xtendobutton, a second incision would have had to be made over the femur for insertion of a femoral screw. The Xtendobutton allows the procedure to be completed in the usual fashion without a second femoral incision (Fig. 63.10).
CONCLUSIONS Stability: Unsurpassed stability rates have been reported using the EB. The bungee effect: The bungee effect is either nonexistent or clinically insignificant. Technique: The most important technical point is to flex the knee to near 90 degrees during femoral-tunnel drilling to ensure a tunnel of at least 30 mm in length. Morbidity: The complication rate has been virtually nonexistent, with only a few reported cases (and none in our experience), despite the highest level of use of any noninterference screw femoral fixation device.
Fig. 63.9. The Xtendobutton fits over the Endobutton so that it is large enough to hold outside a 10-mm femoral tunnel.
Xtendobutton: The Xtendobutton provides salvage without making a femoral incision if the far cortex is blown out. It also simplifies the procedure for the occasional user. Ease of use: The method is straightforward and easily learned. SELECTED READINGS
Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med. 2004;32(3):635–640. Brand Jr B, Weiler A, Caborn DNM, Brown Jr CH, Johnson DL. Graft fixation in cruciate ligament surgery. Am J Sports Med. 2000;28(5):761–774. Cooley VJ, Deffner KT, Rosenberg TD. Quadrupled semitendinosus anterior cruciate ligament reconstruction: 5-year results in patients without meniscus loss. Arthroscopy. 2001;17(8):795–800.
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A
B Fig. 63.10. A and B, In this revision case, the Xtendobutton was used to anchor the graft on the outside of a 9-mm femoral tunnel.
Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med. 2003;31(4):564–573. Prodromos CC, Han YS, Keller BL, Bolyard RJ. Stability of hamstring anterior cruciate ligament reconstruction at two- to eight-year followup. Arthroscopy. 2005;21(2):138–146. Prodromos CC, Joyce BT, Shi K, Keller BL. A meta-analysis of stability after anterior cruciate ligament reconstruction as a function of hamstring versus patellar-tendon graft and fixation type. Arthroscopy. 2005;21(10):1202–1208. Scheffler SU, Sudkamp NP, Gockenjan A, Hoffmann RF, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: the impact of fixation level and fixation method under cyclic loading. Arthroscopy. 2002;18(3):304–315.
To JT, Howell SM, Hull ML. Contributions of femoral fixation methods to the stiffness of anterior cruciate ligament replacements at implantation. Arthroscopy. 1999;15(4):379–387. Yamazaki S, Yasuda K, Tomita F, Minami A, Tohyama H. The effect of intraosseous graft length on tendon-bone healing in anterior cruciate ligament reconstruction using flexor tendon. Knee Surg Sports Traumatol Arthrosc. 2006;14(11):1086–1093. Zantop T, Brucker P, Bell K, et al. The effect of tunnel-graft length on the primary and secondary stability in ACL reconstruction: a study in a goat model. In: Presented at the 2006 Meeting of the European Society of Sports Traumatology, Knee Surgery, and Arthroscopy. Innsbruck: Australia; 2006.
A complete reference list can be found online at ExpertConsult.com.
REFERENCES
1. Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med. 2004;32(3):635–640. 2. Brand Jr B, Weiler A, Caborn DNM, Brown Jr CH, Johnson DL. Graft fixation in cruciate ligament surgery. Am J Sports Med. 2000;28(5):761–774. 3. Brand Jr J, Hamilton D, Selby D, Pienkowski D, Caborn DN, Johnson DL. Biomechanical comparison of quadriceps tendon fixation with patellar tendon bone plug interference fixation in cruciate ligament reconstruction. Arthroscopy. 2000;16(8):805–812. 4. Brown CH, Wilson DR, Hecker A, et al. Comparison of hamstring and patellar tendon femoral fixation: cyclic load. In: Presented at the 1999 Meeting of the American Orthopaedic Society for Sports Medicine. Traverse City: MI; 1999. 5. Rowden NJ, Sher D, Rogers GJ, Schindhelm K. Anterior cruciate ligament graft fixation: initial comparison of patellar tendon and semitendinosus autografts in young fresh cadavers. Am J Sports Med. 1997;25(4):472–478. 6. Scheffler SU, Sudkamp NP, Gockenjan A, Hoffmann RF, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: the impact of fixation level and fixation method under cyclic loading. Arthroscopy. 2002;18(3):304–315. 7. To JT, Howell SM, Hull ML. Contributions of femoral fixation methods to the stiffness of anterior cruciate ligament replacements at implantation. Arthroscopy. 1999;15(4):379–387. 8. Prodromos CC, Han YS, Keller BL, Bolyard RJ. Stability of hamstring anterior cruciate ligament reconstruction at two- to eight-year follow-up. Arthroscopy. 2005;21(2):138–146. 9. Gobbi A, Mahajan S, Zanazzo M, Tuy B. Patellar tendon versus quadrupled bone-semitendinosus anterior cruciate ligament reconstruction: a prospective clinical investigation in athletes. Arthroscopy. 2003;19(6):592–601. 10. Gobbi A, Tuy B, Mahajan S, Panuncialman I. Quadrupled bonesemitendinosus anterior cruciate ligament reconstruction: a clinical investigation in a group of athletes. Arthroscopy. 2003;19(7):691–699.
11. Cooley VJ, Deffner KT, Rosenberg TD. Quadrupled semitendinosus anterior cruciate ligament reconstruction: 5-year results in patients without meniscus loss. Arthroscopy. 2001;17(8):795–800. 12. Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med. 2003;31(4):564–573. 13. Yasuda K, Kondo E, Ichiyama H, et al. Anatomic reconstruction of the anteromedial and posterolateral bundles of the anterior cruciate ligament using hamstring tendon grafts. Arthroscopy. 2004;20(10): 1015–1025. 14. Prodromos CC, Joyce BT, Shi K, Keller BL. A meta-analysis of stability after anterior cruciate ligament reconstruction as a function of hamstring versus patellar-tendon graft and fixation type. Arthroscopy. 2005;21(10):1202–1208. 15. Karaoglu S, Halici M, Baktir A. An unidentified pitfall of Endobutton use: case report. Knee Surg Sports Traumatol Arthrosc. 2002;10(4): 247–249. 16. Simonian PT, Behr CT, Stechschulte Jr DJ, Wickiewicz TL, Warren RF. Potential pitfall of the Endobutton. Arthroscopy. 1998;14(1): 66–69. 17. Muneta T, Yagishita K, Kurihara Y, Sekiya I. Intra-articular detachment of the Endobutton more than 18 months after anterior cruciate ligament reconstruction. Arthroscopy. 1999;15(7):775–778. 18. Brucker P, Zelle BA, Fu FH. Intraarticular Endobutton displacement in anatomic anterior cruciate ligament double-bundle reconstruction: a case report. Op Tech Orthop. 2005;15:154–157. 19. Zantop T, Brucker P, Bell K, et al. The effect of tunnel-graft length on the primary and secondary stability in ACL reconstruction: a study in a goat model. In: Presented at the 2006 Meeting of the European Society of Sports Traumatology, Knee Surgery, and Arthroscopy. Innsbruck: Australia; 2006. 20. Yamazaki S, Yasuda K, Tomita F, Minami A, Tohyama H. The effect of intraosseous graft length on tendon-bone healing in anterior cruciate ligament reconstruction using flexor tendon. Knee Surg Sports Traumatol Arthrosc. 2006;14(11):1086–1093.
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