Hybrid Tibial Fixation for Anterior Cruciate Ligament Reconstruction With Achilles Tendon Allograft

Original Article With Video Illustration

Hybrid Tibial Fixation for Anterior Cruciate Ligament Reconstruction With Achilles Tendon Allograft Jung Ho Noh, M.D., Ph.D., Bo Gyu Yang, M.D., Seung Rim Yi, M.D., Ph.D., Young Hak Roh, M.D., and Jun Suk Lee, M.D.

Purpose: To compare clinical outcomes of tibial fixation between a biodegradable interference screw only and a biodegradable interference screw supplemented by a post-tie using a washer screw in single-bundle anterior cruciate ligament (ACL) reconstruction with 2-strand free tendon Achilles allograft in active young men. Methods: A prospective study was performed in 80 subjects who underwent single-bundle ACL reconstruction. A 2-strand free tendon Achilles allograft fixed with an EndoButton (Smith & Nephew, Andover, MA) in the femoral tunnel and with a Bio-Interference screw (Arthrex, Naples, FL) in the tibial tunnel was used in group I. Supplementary fixation was performed with a post-tie using a washer screw in group II. The Lachman test, pivot-shift test, International Knee Documentation Committee classification, Lysholm score, range of knee motion, and side-to-side difference were evaluated preoperatively and at the last follow-up. The Tegner activity scale was evaluated before injury and at the last follow-up. The 1-leg hop test was assessed at the last follow-up. Results: Of the patients, 36 in group I and 35 in group II could be followed up for at least 2 years. At the last follow-up, 7 patients in group I and 1 in group II showed a 2⫹ or 3⫹ on the Lachman test (P ⫽ .027). The mean side-to-side difference was 2.9 ⫾ 2.3 mm in group I and 1.4 ⫾ 1.6 mm in group II at the last follow-up (P ⫽ .002). The other clinical outcomes were not significantly different between the 2 groups. Conclusions: Supplementary tibial fixation with a post-tie in ACL reconstruction using 2-strand free tendon Achilles allograft was more effective than a biodegradable interference screw only in restoration of the anterior stability of the tibia. Level of Evidence: Level II, randomized controlled trial.

B

one–patellar tendon– bone and hamstring tendon are widely used as autografts for anterior cruciate ligament (ACL) reconstruction; however, allografts also have been used because of concerns over morbidity at the donor site. In the past, the outcomes of bone-to-bone fixation were better than those of soft tissue–to– bone fixation. However, the outcomes of ACL reconstruction using soft tissue graft have been improved with the development of

technology and technique of fixation through biomechanical studies.1-3 Pullout strength at the metaphyseal bone in the proximal tibia has been reported to be less than that in the distal femur.4 The reasons are that the bony structure of the tibial metaphysis is less dense than that of the femoral metaphysis and that the direction of pullout force of the graft is parallel to the tibial tunnel whereas it is usually angled to the femoral tunnel.5 Many authors

From the Kangwon National University Hospital (J.H.N.), Chuncheon; National Police Hospital (B.G.Y., S.R.Y., J.S.L.), Seoul; and Department of Orthopaedic Surgery, Gil Medical Center, Gachon Medical School, Gachon University (Y.H.R.), Incheon, South Korea. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received September 30, 2011; accepted March 12, 2012. Address correspondence to Young Hak Roh, M.D., Department of Orthopaedic Surgery, Gil Medical Center, Gachon Medical School, Gachon University, 1198 Kuwol-dong, Namdong-gu, Incheon 405-760, South Korea. E-mail: [email protected] © 2012 by the Arthroscopy Association of North America 0749-8063/11624/$36.00 http://dx.doi.org/10.1016/j.arthro.2012.03.012

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TIBIAL FIXATION FOR ACL RECONSTRUCTION agree that the fixation strength of interference screws is affected by bone density. The softer cancellous bone in the tibia impairs the grip of fixation devices that primarily engage cancellous bone, such as the interference screw.6 There have been several studies that compared the fixation strength between an interference screw only and an interference screw with supplementation.7-9 Most of the studies were conducted with porcine or bovine bone, which is generally denser than human bone, and showed no differences. However, most studies using human cadaveric bone showed that the fixation strength of the interference screw was disappointing.9,10 There may be an issue that the human cadavers were mostly old or sometimes had chronic disease that reduced the bone density. Hill et al.11 reported that supplementary fixation improved the outcomes of ACL reconstruction with hamstring tendon fixed with an interference screw in the tibial tunnel in female patients. However, most ACL injuries occur during active sports; therefore, most ACL-injured patients are active and young, and men are predominant. These characteristics are considerably different from those of the subjects in previous cadaveric studies. Poor fixation may increase the chance of residual laxity and often leads to unsatisfactory outcomes after surgery. Theoretically, sufficient stiffness of graft fixation allows early mobilization with less residual laxity. In the tibial tunnel, soft-tissue grafts are usually fixed with interference screws, and staples or spiked washer screws are often used for supplementary fixation on the tibial cortex to improve stiffness of the graft construct.12-14 The purpose of this study was to compare the clinical outcomes of tibial fixation in ACL reconstruction using 2-strand free tendon Achilles allograft in active young men with a biodegradable interference screw only (group I) versus a biodegradable interference screw supplemented by a post-tie with a washer screw (group II). The hypothesis of this study was that supplementary tibial fixation would provide better clinical outcomes and improved stability compared with a biodegradable interference screw only. METHODS A prospective, randomized, comparative study was conducted with the approval of the ethics committee of our institution during July 2008 to May 2009. The subjects underwent ACL reconstruction with a 2-strand free tendon Achilles allograft fixed with an EndoButton CL (Smith & Nephew, Andover, MA) in the femoral tunnel and Bio-Interference screw (Ar-

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threx, Naples, FL) in the tibial tunnel. Subjects who had medial collateral ligament injury that was treated conservatively or meniscus tear that was managed by partial meniscectomy were included. We excluded female subjects; subjects aged older than 45 years; and subjects who had meniscus repair, subtotal or total meniscectomy, other ligament injuries that required surgical treatment other than the ACL, any injury on the ipsilateral leg other than the knee, previous injury on either leg, and full-thickness cartilage damage that required microfracture, multiple drilling, osteochondral autograft, or autogenous chondrocyte implantation. A total of 118 subjects were diagnosed with ACL rupture, and 31 subjects were excluded. Among the subjects who met the inclusion criteria, 7 refused to participate in the study. The subjects were grouped by computer-generated randomization: 40 in group I and 40 in group II. Eighty subjects were recruited and provided informed consent to undergo surgery and for study inclusion. All the subjects were diagnosed by physical examination and magnetic resonance imaging, with confirmation by arthroscopy. The Lachman test and pivot-shift test were conducted with patients under anesthesia before reconstruction. Fresh-frozen Achilles allograft was thawed at room temperature. After removal of a calcaneal bone block, the tendinous allograft was split along the tendon fibers to obtain a proper-sized graft. Then, the allograft was folded into 2 strands and trimmed to fit the 9-mm tunnel. The allograft was looped into a 2-strand graft, and its length was set to be 9.5 to 10.5 cm depending on the length of the tibial tunnel. The thickness of the graft was 9 mm. Whipstitches of approximately 2.5 to 3 cm were placed using No. 2 Ethibond (Ethicon, Somerville, NJ) at each free end of the graft (Video 1, available at www.arthroscopyjournal.org). By use of a single-bundle reconstruction technique, the tibial tunnel was made at the footprint or 7 mm anterior to the posterior cruciate ligament and the femoral tunnel was made at the 10:30 or 1:30 clock position through the anteromedial portal with knee flexion greater than 120° (Video 2, available at www.arthroscopyjournal.org). The size of the reamer for the femoral and tibial tunnels was 9 mm, which was the same as the thickness of the graft. Twenty-five to thirty millimeters of the graft was inserted in the femoral tunnel and was fixed with an EndoButton CL. Before tibial fixation, the knee was moved through its full range of motion under maximal manual load 20 times for pre-tensioning. Tibial fixation was conducted with knee flexion of 20° and with maximal manual tension. In group I

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tibial fixation was conducted with a 10 ⫻ 28 –mm Bio-interference screw. The 35-mm Bio-interference screw may provide more stable fixation than the 28-mm Bio-interference screw15; however, the 35-mm Bio-interference screw is seldomly available in Korea. Therefore the 28-mm Bio-interference screw was chosen for this study. In group II a 4.5-mm bicortical screw with a washer was inserted into the drill hole 1.5 cm distal to the anterior aperture of the tibial tunnel. Two sutures hanging on 1 free end of the strand were tied with sutures on the other free end around the washer screw. Tibial tunnel fixation was conducted with a 8 ⫻ 28 –mm Bio-interference screw after use of a post-tie. Postoperative Rehabilitation Quadriceps strengthening exercise was performed immediately after surgery, partial weight bearing was allowed on the third day, and full weight bearing was allowed as tolerated. Continuous passive motion exercise was begun on the second postoperative day, and up to 90° of flexion was allowed until the fourteenth day, 120° of flexion until the sixth week, and full range of motion afterward. After 12 weeks, jogging and stationary bicycling were allowed. After 6 months, subjects were allowed to participate in competitive sports except for those that might involve strong contact with other players, such as football or soccer, or those that might impose strong external forces on the subjects’ knee, such as skiing or snowboarding. All kinds of exercises were allowed after 9 months. Assessment of Outcomes The Lachman test and pivot-shift test were graded according to the International Knee Documentation Committee (IKDC) 2000 criteria and were evaluated preoperatively and at the last follow-up by 2 orthopaedic surgeons who were not involved in the surgical procedures. The IKDC classification and Lysholm score were evaluated preoperatively and at the last follow-up. Range of motion of the injured knee was compared with that of the uninjured knee at the last follow-up. The Tegner activity scale was evaluated before injury and at the last follow-up. Stress radiographs were taken with both knees at flexion of 30° and loaded to 150 N using a Telos stress device (Austin & Associates, Fallston, MD) preoperatively and at the last follow-up. The side-to-side difference (SSD) was measured by 2 orthopaedic surgeons using a picture archiving and communication system (GE

Healthcare, Chicago, IL). The 1-leg hop test was performed at the last follow-up; the maximal distance out of 3 trials was adopted and analyzed as a percentage of that of the uninjured leg. Statistical Analysis The sample size was calculated to be 35 subjects in each group with a power of 80% and a significance level of .05 to detect a difference of 5 points in Lysholm score between the 2 groups. Statistical analyses of the differences in continuous variables between the 2 groups were performed with the unpaired Student t test and differences in categorical variables with the Mann-Whitney U test, ␹2 test, and Wilcoxon signed rank test. Interobserver and intraobserver reliability were assessed by intraclass correlation coefficient (ICC) with the respective 95% confidence intervals. SPSS software (version 17.0; SPSS, Chicago, IL) was used for statistical analyses. The minimum level of significance was .05. RESULTS Seventy-one subjects could be followed up for at least 2 years. Seven subjects were lost to follow-up, one subject had a tibial shaft fracture due to a traffic accident, and one subject had reinjury to the same knee while playing soccer, and they were excluded from the analysis. Demographics of the subjects are presented in Table 1. Interobserver ICCs for the Lachman test, pivot-shift test, and SSD were over 0.8, and the intraobserver ICC for SSD was 0.948. In all subjects the preoperative Lachman test showed a grade of 2 or 3. At the last follow-up, 29 subjects (80.6%) in group I and 34 (97.1%) in group II showed a grade of 0 or 1 and 7 (19.4%) in group I and 1 (2.9%) in group II showed a grade of 2 on the Lachman test (P ⫽ .027). Preoperatively, 11 subjects (30.6%) in group I and 10 (28.6%) in group II showed a grade of 1 and 25 (69.4%) in group I and 25 (71.4%) in group II showed a grade of 2 or 3 on the pivot-shift test. At the last follow-up, 4 subjects (11.1%) in group I and 1 (2.9%) in group II showed a grade of 2 on the pivot-shift test (P ⫽ .174). None of the subjects showed a grade of 3 on the Lachman test or pivot-shift test at the last follow-up. All subjects showed a grade of C or D according to the IKDC classification preoperatively. At the last follow-up, 29 subjects (80.6%) in group I and 33 (94.3%) in group II showed a grade of A or B and 7 (19.4%) in group I and 2 (5.7%) in group II showed a grade of C according to the IKDC classifi-

TIBIAL FIXATION FOR ACL RECONSTRUCTION TABLE 1.

Variables Median age (range) (yr) Laterality (right/ left) Mean body mass index (kg/m2) Mean period from injury to operation (wk) Mean follow-up period (mo) Mechanism of injury Sports Fall down Traffic accident Unknown

Demographics

Group II (Bio-Interference Screw With Group I Post-Tie Using (Bio-Interference Washer Screw) P Screw) (n ⫽ 36) (n ⫽ 35) Value 23 (19-45)

22 (19-45)

.382*

18:18

16:19

.718†

23.8 ⫾ 2.6

23.6 ⫾ 2.2

.844‡

8.5 ⫾ 9.7

7.0 ⫾ 8.6

.441‡

30.9 ⫾ 2.3

30.9 ⫾ 2.4

.923‡

29 5 1 1

25 7 3 0

.455†

*Mann-Whitney U test. †␹2 Test. ‡Student t test.

cation (P ⫽ .082) (Table 2). None of the subjects showed an IKDC grade of D at the last follow-up. The median Lysholm score was 59 (range, 44 to 78) in group I and 56 (range, 44 to 80) in group II preoperatively (P ⫽ .673), and it was 91 (range, 80 to 100) in group I and 95 (range, 85 to 100) in group II at the last follow-up (P ⫽ .163) (Table 3). One subject in group I showed limitation of motion of 5° compared with the other knee. The median score on the Tegner activity scale was 7 (range, 5 to 9) in both groups before injury (P ⫽ .289), and it was 6 (range, 4 to 8) in group I and 6 (range, 4 to 9) in group II at the last follow-up (P ⫽ .369) (Table 4). The mean SSD measured with the Telos stress device was 9.7 ⫾ 4.0 mm in group I and 9.9 ⫾ 3.9 mm in group II preoperatively (P ⫽ .613), and it was 2.9 ⫾ 2.3 mm in group I and 1.4 ⫾ 1.6 mm in group II at the last follow-up (P ⫽ .002) (Table 5). The mean value on the 1-leg hop test was 88.5% ⫾ 5.7% in group I and 90.4% ⫾ 5.0% in group II compared with the other knee at the last follow-up (P ⫽ .127). No subjects in group II have complained about skin irritation or tenderness at the site of supplementary fixation during follow-up. No other complications

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were observed during the follow-up period in either group. DISCUSSION The results of this study showed that the outcomes of supplementary fixation with a post-tie in addition to a biodegradable interference screw in the tibial tunnel were significantly better than those of a biodegradable interference screw only with regard to the restoration of the anterior stability of the tibia in terms of the Lachman test (negative or 1⫹ v 2⫹ or 3⫹) and SSD. Other clinical outcomes in group II were also superior to those in group I, though this was not statistically significant. Fixation methods in ACL reconstruction are largely divided into 3 categories: compression (e.g., metal or biodegradable interference screw), expansion (e.g., Rigidfix [DePuy Mitek, Raynham, MA]), and suspension (e.g., EndoButton, EndoPearl [Linvatec, Largo, FL], Transfix [Arthrex, Naples, FL], or Bone mulch [Biomet, Warsaw, IN]). Metal and biodegradable interference screws are widely used for soft tissue–to– bone fixation as well as bone-to-bone fixation in ACL reconstruction. However, the results of soft tissue–to– bone fixation with metal or biodegradable interference screws have been shown to be not very promising in many studies.11,16,17 Although the fixation strength with an outside-in technique may be better to some extent, the fixation strength in the tibial tunnel is less than that in the femoral tunnel, and it may not be enough to bear stress, given that the normal daily load in the intact ACL is approximately 450 N.18,19 Magen TABLE 2.

Lachman Test, Pivot-Shift Test, and IKDC Classification at Last Follow-up

Lachman test Negative 1⫹ 2⫹ 3⫹ Pivot-shift test Negative 1⫹ 2⫹ 3⫹ IKDC classification A B C D

Group I

Group II

20 (55.6%) 9 (25.0%) 7 (19.4%) 0 (0%)

28 (80.0%) 6 (17.1%) 1 (2.9%) 0 (0%)

24 (66.7%) 8 (22.2%) 4 (11.1%) 0 (0%)

30 (85.7%) 4 (11.4%) 1 (2.9%) 0 (0%)

17 (47.2%) 12 (33.3%) 7 (19.4%) 0 (0%)

26 (74.3%) 7 (20.0%) 2 (5.7%) 0 (0%)

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J. H. NOH ET AL. TABLE 3.

Lysholm Score

Preoperative

Median Lysholm score (range)

Last Follow-up

Group I

Group II

P Value

Group I

Group II

P Value

59 (44-78)

56 (44-80)

.673*

91 (80-100)

95 (85-100)

.163*

*Mann-Whitney U test.

et al.10 reported that the failure load of interference screws, which was 350 N, was not sufficient in the tibia. Wang et al.20 reported that the graft slipped by about 7 mm under a 400-N load in a study of the fixation strength of biodegradable interference screws in the tibial tunnel. Weimann et al.21 reported graft slippage of 4.1 mm after 1,000 cyclic loads of 250 N. In addition to interference screw fixation in the tibial tunnel, augmentation with staples or spiked washers is often conducted because of its less secure fixation.12,14 Walz et al.22 stated that supplementary fixation with interference screws in tibias with low bone density was helpful to prevent graft slippage. Nagarkatti et al.23 showed that augmenting soft-tissue fixation on the tibial side with an anchor composed of a polylactic acid ball or cortical bone disk significantly increased the stiffness of the construct. However, Au et al.24 reported that the hybrid fixation of an EndoButton and an interference screw was not a loadsharing construct. They reported an increase in ultimate load but not in stiffness. Their findings support the idea that under loads below yield load, it is the first line of fixation that endures the entire tensile load. In this study, the tibial end of the graft was fixed with a post-tie first and interference screw afterward. This technique helps create tension for the 2 fixations equally, and the load-sharing effect between first-line fixation (interference screw) and second-line fixation (post-tie) will be more attainable. Lee et al.7 reported that supplementary fixation with a staple or PushLock screw (Arthrex) did not increase the structural strength and stiffness of the soft-tissue graft fixation with a biodegradable interference screw

TABLE 4.

in the porcine knee. However, this finding may not be applied to the clinical situation, and the fixation strength of interference screws is greater in the porcine knee because it is denser than the human knee. Moreover, bone mineral density in the proximal tibia decreases after ACL injury.25 Hill et al.11 reported that supplementary tibial fixation in female patients yielded significantly improved clinical outcomes after ACL reconstruction with hamstring autograft. Bailey et al.26 reported that the properties of interference screw fixation for soft-tissue graft in the porcine tibia were overestimated compared with the young human tibia. Our study showed that supplementary fixation was helpful even in active young men who had relatively denser bone. Hill et al. reported that supplementary staple fixation on the tibia was effective to lower anterior displacement of the tibia. The tensile strength of No. 2 Ethibond, which is about 120 to 130 N,27 is relatively less than the stress to the ACL that occurs during activities of daily living. Miller et al.28 reported that the failure loads of Orthocord (DePuy Mitek), FiberWire (Arthrex), and MaxBraid (Biomet, Warsaw, IN) were superior to the failure load of Ethibond in a mechanical study of suture material. More secure fixation may be achieved if these materials are used instead of Ethibond. However, the total number of sutures at the end of each strand is 4, and the post-tie shares load with the interference screw; therefore, we do not think this would be an issue. Five to ten millimeters of the tibial end of the graft was left out of the tunnel to prevent cutting of the suture by the sharp margin of the tibial tunnel entrance. Further studies are needed to clarify whether

Tegner Activity Scale Preinjury

Median score on Tegner activity scale (range) *Mann-Whitney U test. †Wilcoxon signed rank test.

Last Follow-up

Group I

Group II

P Value

Group I

Group II

P Value

7 (5-9)

7 (5-9)

.289*

6 (4-8)

6 (4-9)

.369†

TIBIAL FIXATION FOR ACL RECONSTRUCTION TABLE 5.

SSD Measured With Telos Stress Device

Preoperative

Mean SSD (mm)

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Last Follow-up

Group I

Group II

P Value

Group I

Group II

P Value

9.7 ⫾ 4.0

9.9 ⫾ 3.9

.613*

2.9 ⫾ 2.3

1.4 ⫾ 1.6

.002*

*Student t test.

this method helps prevent rupture of suture material. A screw with no thread within around 5 mm of its head was used, and post-tie fixation was performed after insertion of the threaded portion of the screw into the bone to prevent suture cutting by the thread of the screw. On the basis of the results of this study showing that the anterior stability of the tibia has been better restored in group II than in group I, the null hypothesis has been accepted. This study had a few limitations. The follow-up period was short, and we did not distinguish between the femoral side and tibial side as the cause of residual laxity. The graft was fixed with an EndoButton on the femoral side to minimize slippage; however, further study would be needed to identify whether the residual laxity during follow-up is due to tibial side slippage or not. Another limitation was that the diameters of the interference screws were not identical in the 2 groups. When the graft is fixed with an interference screw only in the tibial tunnel, the diameter of the interference screw used is usually the same as or 1 mm larger than that of the tibial tunnel, as was the case in group I. We used interference screws 1 mm smaller in diameter than that of the tibial tunnel in group II. There has been a debate regarding whether the greater diameter of the interference screw yields greater fixation strength in the tibial tunnel. Micucci et al.29 reported that the interference screw diameter did not affect the fixation strength in their bovine tibial study. Namkoong et al.30 also reported that no increase in graft fixation strength was observed when increasing the interference screw diameter beyond 3 mm of the tunnel diameter. In the case of fixation with an interference screw with a large diameter, the graft often twists around the interference screw in the tibial tunnel during insertion of the interference screw, which may adversely affect the clinical outcomes. Although the difference in the diameter of the interference screw did not affect the fixation strength and outcomes significantly, there might be a concern about an intervention bias.

CONCLUSIONS Supplementary tibial fixation with a post-tie in ACL reconstruction using 2-strand free tendon Achilles allograft was more effective than a biodegradable interference screw only in restoration of the anterior stability of the tibia. Acknowledgment: The authors thank Wonjoo Jung for editorial assistance. REFERENCES 1. Sajovic M, Strahovnik A, Dernovsek MZ, Skaza K. Quality of life and clinical outcome comparison of semitendinosus and gracilis tendon versus patellar tendon autografts for anterior cruciate ligament reconstruction: An 11-year follow-up of a randomized controlled trial. Am J Sports Med 2011;39:21612169. 2. Leal-Blanquet J, Alentorn-Geli E, Tuneu J, Valentí JR, Maestro A. Anterior cruciate ligament reconstruction: A multicenter prospective cohort study evaluating 3 different grafts using same bone drilling method. Clin J Sport Med 2011;21: 294-300. 3. Holm I, Oiestad BE, Risberg MA, Aune AK. No difference in knee function or prevalence of osteoarthritis after reconstruction of the anterior cruciate ligament with 4-strand hamstring autograft versus patellar tendon-bone autograft: A randomized study with 10-year follow-up. Am J Sports Med 2010;38:448454. 4. Scheffler SU, Südkamp NP, Göckenjan 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;18:304-315. 5. Beattie KA, Boulos P, Duryea J, et al. The relationships between bone mineral density in the spine, hip, distal femur and proximal tibia and medial minimum joint space width in the knees of healthy females. Osteoarthritis Cartilage 2005; 13:872-878. 6. Corry IS, Webb JM, Clingeleffer AJ, Pinczewski LA. Arthroscopic reconstruction of the anterior cruciate ligament. A comparison of patellar tendon autograft and four-strand hamstring tendon autograft. Am J Sports Med 1999;27: 444-454. 7. Lee JJ, Otarodifard K, Jun BJ, McGarry MH, Hatch GF, Lee TQ. Is supplementary fixation necessary in anterior cruciate ligament reconstructions? Am J Sports Med 2011;39:360365. 8. John A, Stanley R, Nilsson K, Field J. Augmentation of tibial fixation of soft-tissue grafts in anterior cruciate ligament reconstruction. Arthroscopy 2007;23:1193-1197.

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