Biomechanical comparison of anterior cruciate ligament reconstruction fixation methods and implications on clinical outcomes

Introduction

Anterior cruciate ligament (ACL) injury is one of the most common knee injuries encountered in orthopaedic surgery, typically occurring during non-contact sport participation, specifically with cutting and pivoting exercises (1). Therefore, ACL reconstruction (ACLR) is a common orthopaedic surgical procedure performed to restore the native function of the ACL and provide translational and rotatory stability of the knee (2,3). The incidence of primary and revision ACLR is increasing annually, with an estimated 80,000 to 100,000 people in the United States undergoing this procedure per year (1,4), with revision rates between 4.1% and 13.3% of all primary ACLRs (5,6).

There are multiple reconstruction techniques with the goal of restoring rotational and translational knee stability and function (2,7). There is a myriad of technical challenges to consider during ACLR that impact clinical outcomes including graft selection, tunnel positioning, graft tensioning, fixation methods, and healing properties (1,2,8,9). In addition to a wide array of fixation methods, several devices have also been developed for graft fixation (1). The different types of fixation methods in ACLR are typically categorized into compression, suspension, post, or hybrid fixation (10,11). Regardless of the implant chosen for fixation, secure fixation is paramount to avoid displacement of the graft and allow for graft integration into the bone tunnel, which typically occurs around three months after surgery (2). Therefore, the biomechanical properties of these implants are particularly important in facilitating early post-operative rehabilitation after ACLR that is necessary for a successful clinical outcome, while also withstanding the shear and tensile forces to avoid displacement and early graft failure during graft osseointegration (12).

The overall reported ACL graft rupture rate at longer than 10-year follow-up was 6.2%, with 10.3% clinical failure (13). While many different factors can lead to ACLR failure, graft fixation is one important factor. Currently, there is no consensus on the optimal graft fixation technique. The reasons for lack of consensus may be attributed to several factors including but not limited to different types of ACLR grafts used, surgeon preference, industry influence/competition, lack of evidence-based recommendations from clinical outcomes studies, and variations in the reported biomechanical effectiveness for different fixation types. Therefore, it is important for surgeons to understand the reported advantages and disadvantages of using different ACLR fixation types based on biomechanics and clinical outcomes. Therefore, the purpose of this review was to highlight the unique advantages and disadvantages of each type of graft fixation method and provide perspective on the role that the available biomechanical properties play in optimizing fixation strategies based on reported clinical outcomes.

Compression fixation

One commonly used method of securing a graft both in the femur and tibia during ACLR is interference screw (IFS) fixation, which employs a compression technique. IFSs have a long history of successful outcomes with a reproducible technique that involves placing a screw in the tunnel to compress the graft against the cancellous tunnel wall (7,14,15). There are different types of IFS fixation to include metallic (often titanium), polyetheretherketone (PEEK), or bioabsorbable screws. Advantages and disadvantages of IFS types can be seen in Table 1. Historically, metal screws were used in up to 1 in 10 ACLR in adolescents and young adults (16), but they have decreased in popularity due to the higher rate of clinical sequalae, and consequence of projection artifact on magnetic resonance imaging (MRI). As such, newer bioabsorbable materials have been utilized to allow for superior post-operative MRI assessment and to allow for gradual resorption with bone replacement and less likelihood of graft injury during time of insertion (15). While bioabsorbable screws have demonstrated good clinical outcomes (17-22) and are MRI compatible, they are rarely completely replaced by bone or absorbed by the body, can cause hyperinflammation and cystic changes, and may be predisposed to breakage, migration and osteolysis (19,23). PEEK screws, on the other hand, are non-bioresorbable and MRI compatible. The product is biocompatible and demonstrates appropriate strength for ACLR (15).

In a randomized controlled trial, Shumborski et al. (15) compared PEEK and titanium IFS fixation among 133 adult patients who were randomized to either PEEK or titanium IFS fixation during primary ACLR with 4-strand hamstring tendon autograft. Authors reported no differences in ACLR re-rupture rate as well as subjective or objective clinical outcomes (P>0.05). The authors also noted that post-operative MRI evaluation of the ACLR graft was improved in the PEEK group due to less artifact than titanium IFS. The absence of metal artifact on MRI, modulus of elasticity similar to human bone, biological compatibility, and equivalent clinical outcomes suggest that PEEK implants may be an excellent choice of ACLR graft fixation. Shen et al. (19) compared bioabsorbable and metallic IFS fixation in a meta-analysis of 10 randomized controlled trials comprising 790 patients undergoing single-bundle ACLR. When tested biomechanically with a KT-1000/-2000 arthrometer, there were no statistically significant differences between bioabsorbable and metallic screw fixation (P>0.05). Also, there were no significant differences in infection or knee joint instability, which has been corroborated by other recent studies (24,25). Other biomechanical studies comparing metal and bioabsorbable IFS fixation of a soft tissue graft found no differences in ultimate load to failure or construct stiffness (17,18). Similarly, Drogset et al. (21) found no significant differences in functional outcomes between bioabsorbable and metal IFS fixation in their prospective randomized study utilizing bone-patellar tendon-bone (BTB) autograft for ACLR.

The utilization of compression fixation specifically in the setting of all-soft tissue grafts has become a point of concern as surgeons questioned whether IFSs would provide adequate fixation without risking injury to the graft at time of insertion. To further investigate this concern, Brand et al. (26) found that bioabsorbable screws were comparable or superior to titanium screws for IFS fixation with respect to load-to-failure for soft tissue grafts and that the bioabsorbable implant produced less screw thread-induced laceration of the soft tissue graft during testing. Another study also concluded that either screw could be used effectively (17). In another biomechanical study, Kruppa et al. (27) examined force exerted across soft tissue grafts that were secured with a tibial IFS. Authors reported that the graft force decreased substantially over the first twenty-four hours after fixation and that this diminished force was not affected by screw diameter or length. As a result, the authors concluded that IFS fixation for all-soft tissue grafts may lead to early postoperative laxity following ACLR in the clinical setting. This finding was confirmed in additional studies that demonstrated graft slippage and weakened biomechanical properties of the soft tissue graft after fixation of all-soft tissue grafts with IFS (11,28). Contrary to these findings, Micucci et al. (29) showed no significant differences in ultimate fixation strength or graft slippage of multiple tested IFSs of varying diameter in the fixation of soft tissue grafts for ACLR. Studies commenting on compression fixation can be seen in Table 2.

Suspensory fixation

Suspensory fixation of an ACLR graft is another commonly used technique that typically involves the use of an extra-cortical bone plug on the femur, tibia, or both that is connected to the graft by suture. Studies examining suspensory fixation are highlighted in Table 3. The development of suspensory fixation has led to a more minimally invasive approach such as utilizing an all-inside ACLR technique (21). In the realm of suspensory fixation, fixed-loop devices (FLDs) and adjustable-loop devices (ALDs) are both commercially available. In FLDs, the graft is attached to a suture loop that is connected to a button that is flipped against cortical bone. In ALDs, the graft is secured to an adjustable loop of suture and a button such that the tension in the construct can be set after flipping the button against the cortex (30). FLDs keep the graft on tension by connecting it at a constant length to the cortical button to maintain the interface between the graft and the bone for healing (31). Multiple studies have found that FLDs have been associated with a higher load-to-failure (30-32). The disadvantage of FLDs include the potential for inaccurate graft and tunnel measurements leading to graft laxity and poor osseointegration as FLDs are a set length and cannot be adjusted once implanted. Newer ALDs have a one-way locking system that allows for customization of the tension in the construct, theoretically improving graft incorporation by minimizing micromotion (31).

In a systematic review comparing FLDs and ALDs, Onggo et al. (31) reported superior biomechanical graft properties in FLDs including higher graft stiffness and higher ultimate load-to-failure. It is important to note that the authors found biomechanical improvement with re-tensioning of ALDs after tibial fixation as per manufacturer instructions and that both constructs possessed the necessary biomechanical strength of a native ACL. Despite the differences in biomechanical properties, there were no significant differences in clinical outcomes, ACLR re-rupture rates, or radiographic evaluation between the two implants. Other biomechanical studies comparing ALDs and FLDs demonstrated no differences in device elongation when cycled on an Instron machine. This is clinically relevant as graft/construct elongation will produce laxity and resultant clinical failure (33,34).

While suspensory fixation can be used with either bony or all-soft tissue grafts, biomechanical comparison of femoral cortical suspension in all-soft tissue grafts noted significant differences between FLDs and ALDs (33-36). FLDs had less cyclic displacement when compared with ALDs (35,36). Petre et al. (36) also biomechanically compared suspension devices in soft tissue grafts in a porcine model looking at ultimate load to failure, stiffness, and displacement. They found that all devices tested had the necessary physiologic biomechanical properties with regard to displacement, failure strength, and stiffness for initial fixation in ACLR when compared to the native ACL. This study did note that FLDs allowed less initial and cyclic displacement but attributed this difference in initial displacement to the critical step of re-tensioning the ALDs after cycling the knee and fixing the tibial side. ALDs have been shown to possess the physiologic strength necessary to be used in ACLR when cyclically tested in vitro and compared to the native knee (36,37).

Post fixation

Post fixation is another method of ACLR, which is usually a metal screw, with or without a washer, or a cross pin that acts as a stable, inflexible point of fixation in the bone separate from the tunnel aperture that acts as a point of fixation for the graft. Post methods of fixation allow for cortical fixation of the graft to the bone often through the use of sutures as an intermediary (12). Table 4 depicts the studies that include post fixation. When analyzing tibial sided graft fixation techniques, Weiss et al. (12) compared IFS fixation, screw-post and washer fixation, and screw-post and washer fixation with an additional IFS in an ACLR animal model. In their analysis, the hybrid fixation of a post and IFS yielded significantly higher final stiffness and higher yield load than the other fixation methods. In addition, the post only group was found to be biomechanically superior to the IFS cohort. Another comparison study on cross-pin fixation, IFS, and suspensory fixation found the cross-pin to have optimal stability regarding stress and strain at the femoral fixation site (38). In a systematic review on the effect of fixation methods on clinical outcomes, Speziali et al. (39) reported a failure rate of 17.3% when a cross-pin was used on the femoral side, which is in contrast to 5.8% with suspensory fixation (39). Suture anchors have also been used as a post fixation, with one cadaveric study demonstrating that suture anchor fixation with suture tape augmentation restored normal knee kinematics (40). There were no significant differences when compared to traditional BTB reconstruction and suspensory fixation alone.

Hybrid/adjunct fixation

A combination of fixation techniques, or hybrid fixation, is another method of securing a graft during ACLR (Table 5). Throughout the evolution of ACLR, hybrid fixation techniques have gained popularity, specifically when considering IFS fixation in isolation with concern of graft slippage with parallel fixation in a different plane (2). As such, hybrid fixation methods have been explored to determine if adjunct fixation improves graft stiffness and increase the fixation strength of the construct. Specifically, hybrid fixation has been used to address concerns with tibial fixation, as the tibia has lower bone density than the femur, and the graft is subject to slippage with parallel fixation (2,7,12). Multiple studies have found that suspensory fixation combined with an IFS fixation is biomechanically superior to suspensory fixation alone (41,42). In a porcine model, Walsh et al. (42) demonstrated that soft tissue grafts fixed with an IFS and suspensory cortical button were able to withstand higher initial and ultimate loads to failure. Similarly, hybrid fixation of an IFS with a post has also been shown to be biomechanically superior (12).

Suture anchors are reliable backup fixation in the tibia as well. Biomechanical analysis of these implants reveals that they possess equivalent pull out strength when compared to a traditional bicortical post implant and are a viable option for ACLR tibial hybrid fixation (43). Cyclic testing of suture anchors demonstrates that the tension set with these anchors at the time of insertion remains constant (44). Transosseous tunnels using only suture have also been described as a backup tibial fixation combined with IFSs, as have staple fixation (45-47).

Staple fixation has more recently been described as an adjuvant to another method of fixation through cortical anchoring of the graft loop parallel to the tibial tunnel in the longitudinal position. This method is indicated for patients with good cortical bone stock and is often reserved for patients with open physes (48). Gerich et al. (49) described its use in cases where a bone block protrudes out of the tibial tunnel. Stiffness of the construct was significantly higher with the use of a surgical staple than with an IFS and they concluded that staple fixation is comparable. Contrary to these finding, Teo et al. (47) compared solitary IFS with an IFS and backup surgical staple and found that there was no biomechanical advantage and that the supplementary fixation may not benefit the construct.

Comparison of fixation methods

Due to the high technical demands of ACLR with significant clinical implications for graft failure, the biomechanical properties of overall graft fixation by compression, suspensory, post and hybrid fixation techniques have been compared throughout the literature. The major biomechanical advantages and disadvantages of these fixation methods are highlighted in Table 6. While each method of graft fixation possesses its own advantages and disadvantages, there is no clear superior fixation technique from a biomechanical perspective when performed technically correct. However, one study suggests that graft tension levels close to 90 N and graft fixation at a 30-degree knee-flexion angle are recommended to achieving overall satisfactory clinical outcomes (2).

Comparison of IFS compression fixation and suspensory fixation techniques have been evaluated extensively in the biomechanical and clinical literature. Overall, biomechanical implications on clinical decision making for ACLR soft tissue graft fixation has remained a challenge, and biomechanical studies have yet to account for the “windshield-wiper” effect leading to higher risk of tunnel widening observed for suspensory devices. Prior research has demonstrated that tunnel osteolysis or widening occurs no matter what graft type (i.e., bone or soft tissue) or fixation method is used and is a reported natural phenomenon. However, there is higher risk of tunnel osteolysis due to this windshield-wiper effect when using soft-tissue grafts and suspensory fixation devices where the graft is not fixed directly in the closed socket tunnel (50). Furthermore, heterogenous suspensory devices have been compared to IFS fixation which has led to inconsistent conclusions in the literature. Mayr et al. (51) noted that grafts fixed with tibial ALDs resulted in higher graft elongation but had higher ultimate failure loads in comparison with those fixed with IFSs at time zero. In contrast, a recent biomechanical study reported that tibial and femoral fixation with three unique adjustable-loop suspensory devices demonstrated higher ultimate failure loads and lower graft elongation when compared to a construct with femoral fixed-loop suspensory fixation and tibial IFS fixation (52). Contrary to these findings, other studies have found that the fixation method biomechanical properties are similar between groups with no definitive clinical impact (53,54).

Studies have also compared IFS, suspensory, post, and cross-pin fixation for ACLR. Ma et al. (55) compared the three modes of fixation with a hamstring ACLR and found no significant differences in clinical outcomes among IFS, suspensory, or post fixation with at least 2 years of follow-up. Cyclic load testing showed similar amounts of graft displacement across all tested types of femoral fixation (56). Specifically examining femoral-sided fixation, one study found that cross-pin was found to have optimum stability with regard to stress and strain (38). This is in contrast to another study that found it to be biomechanically inferior to suspensory fixation (57).

Strengths and limitations

This review provides the most comprehensive and thorough presentation of the available literature in terms of available ACLR fixation methods based on known biomechanical properties and related clinical outcomes. This review gives surgeons a comprehensive presentation of the advantages and disadvantages of the various fixation methods necessary to provide a patient-specific approach to ACLR, though it was not without limitations. This review was limited by the heterogeneity of the current available literature. Comparison studies combined different methods of fixation and with inconsistent reporting of similar outcomes. Biomechanical testing, when performed, was not performed in the same manner across all studies and different outcome measures were used across these models to assess graft success (i.e., load to failure, cyclic loading, graft stiffness, etc.) Because an ACL graft can be successfully secured with any of the above listed categories of fixation or a combination of methods, it is difficult to provide consistent and direct comparisons. Finally, there was a paucity of studies with high-level evidence, thus lowering the overall level of evidence presented.

Conclusions

There remains no clear consensus on the optimal ACLR graft fixation technique or implants when comparing compression, suspensory, post and hybrid fixation methods. The lack of consensus suggests that the ideal fixation method should likely be individualized based on patient-specific factors and demands, patient expectations and desired outcomes, as well as surgeon experience with the goal of restoring anatomic ACL position and function. By having a thorough understanding of the biomechanical properties and associated clinical outcomes of the various described ACLR fixation methods, the advantages and disadvantages of each fixation method can be used to determine the optimal ACLR fixation method based on an individualized approach.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Joint, for the series “Implications of Graft Choice in ACL Reconstruction”. The article has undergone external peer review.

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-22-52/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-22-52/coif). The series “Implications of Graft Choice in ACL Reconstruction” was commissioned by the editorial office without any funding or sponsorship. NND served as the unpaid Guest Editor for the special series. EM reports a family member employed by MedInc of Texas (Arthrex Inc.) and reports being a board/committee member for Arthroscopy Association of North America. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of Defense or the US Government. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Zeng C, Lei G, Gao S, et al. Methods and devices for graft fixation in anterior cruciate ligament reconstruction. Cochrane Database Syst Rev 2018;2018:CD010730. [Crossref]
2. Pereira VL, Medeiros JV, Nunes GRS, et al. Tibial-graft fixation methods on anterior cruciate ligament reconstructions: a literature review. Knee Surg Relat Res 2021;33:7. [Crossref] [PubMed]
3. Yanke A, Ellman MB, Sherman SL, et al. Graft-Tunnel Mismatch in Bone-Tendon-Bone ACL Reconstruction: Prevention and Treatment. Techniques in Orthopaedics 2012;27. [Crossref]
4. Herzog MM, Marshall SW, Lund JL, et al. Trends in Incidence of ACL Reconstruction and Concomitant Procedures Among Commercially Insured Individuals in the United States, 2002-2014. Sports Health 2018;10:523-31. [Crossref] [PubMed]
5. Lind M, Menhert F, Pedersen AB. Incidence and outcome after revision anterior cruciate ligament reconstruction: results from the Danish registry for knee ligament reconstructions. Am J Sports Med 2012;40:1551-7. [Crossref] [PubMed]
6. van Eck CF, Schkrohowsky JG, Working ZM, et al. Prospective analysis of failure rate and predictors of failure after anatomic anterior cruciate ligament reconstruction with allograft. Am J Sports Med 2012;40:800-7. [Crossref] [PubMed]
7. Brand J Jr, Weiler A, Caborn DN, et al. Graft fixation in cruciate ligament reconstruction. Am J Sports Med 2000;28:761-74. [Crossref] [PubMed]
8. Lubowitz JH. Anatomic ACL reconstruction produces greater graft length change during knee range-of-motion than transtibial technique. Knee Surg Sports Traumatol Arthrosc 2014;22:1190-5. [Crossref] [PubMed]
9. Gadikota HR, Sim JA, Hosseini A, et al. The relationship between femoral tunnels created by the transtibial, anteromedial portal, and outside-in techniques and the anterior cruciate ligament footprint. Am J Sports Med 2012;40:882-8. [Crossref] [PubMed]
10. Steiner ME, Hecker AT, Brown CH Jr, et al. Anterior cruciate ligament graft fixation. Comparison of hamstring and patellar tendon grafts. Am J Sports Med 1994;22:240-6; discussion 246-7. [Crossref] [PubMed]
11. Scheffler SU, Südkamp NP, Göckenjan A, et al. 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;18:304-15. [Crossref] [PubMed]
12. Weiss FP, Possoli FAA, Costa IZ, et al. Fixation of the Anterior Ligament Graft at the Tibial Pole: Biomechanical Analysis of Three Methods. Rev Bras Ortop (Sao Paulo) 2019;54:697-702. [PubMed]
13. Crawford SN, Waterman BR, Lubowitz JH. Long-term failure of anterior cruciate ligament reconstruction. Arthroscopy 2013;29:1566-71. [Crossref] [PubMed]
14. Bourke HE, Gordon DJ, Salmon LJ, et al. The outcome at 15 years of endoscopic anterior cruciate ligament reconstruction using hamstring tendon autograft for 'isolated' anterior cruciate ligament rupture. J Bone Joint Surg Br 2012;94:630-7. [Crossref] [PubMed]
15. Shumborski S, Heath E, Salmon LJ, et al. A Randomized Controlled Trial of PEEK Versus Titanium Interference Screws for Anterior Cruciate Ligament Reconstruction With 2-Year Follow-up. Am J Sports Med 2019;47:2386-93. [Crossref] [PubMed]
16. Kramer DE, Kalish LA, Kocher MS, et al. Complications of Bioabsorbable Tibial Interference Screws After Anterior Cruciate Ligament Reconstruction in Pediatric and Adolescent Athletes. Orthop J Sports Med 2020;8:2325967120904010. [Crossref] [PubMed]
17. Laxdal G, Kartus J, Eriksson BI, et al. Biodegradable and metallic interference screws in anterior cruciate ligament reconstruction surgery using hamstring tendon grafts: prospective randomized study of radiographic results and clinical outcome. Am J Sports Med 2006;34:1574-80. [Crossref] [PubMed]
18. Kaeding C, Farr J, Kavanaugh T, et al. A prospective randomized comparison of bioabsorbable and titanium anterior cruciate ligament interference screws. Arthroscopy 2005;21:147-51. [Crossref] [PubMed]
19. Shen C, Jiang SD, Jiang LS, et al. Bioabsorbable versus metallic interference screw fixation in anterior cruciate ligament reconstruction: a meta-analysis of randomized controlled trials. Arthroscopy 2010;26:705-13. [Crossref] [PubMed]
20. Myers P, Logan M, Stokes A, et al. Bioabsorbable versus titanium interference screws with hamstring autograft in anterior cruciate ligament reconstruction: a prospective randomized trial with 2-year follow-up. Arthroscopy 2008;24:817-23. [Crossref] [PubMed]
21. Drogset JO, Straume LG, Bjørkmo I, et al. A prospective randomized study of ACL-reconstructions using bone-patellar tendon-bone grafts fixed with bioabsorbable or metal interference screws. Knee Surg Sports Traumatol Arthrosc 2011;19:753-9. [Crossref] [PubMed]
22. Kousa P, Järvinen TLN, Kannus P, et al. Initial Fixation Strength of Bioabsorbable and Titanium Interference Screws in Anterior Cruciate Ligament Reconstruction: Biomechanical Evaluation by Single Cycle and Cyclic Loading. Am J Sports Med 2001;29:420-5. [Crossref] [PubMed]
23. Xu B, Yin Y, Zhu Y, et al. Comparison of Bioabsorbable and Metallic Interference Screws for Graft Fixation During ACL Reconstruction: A Meta-analysis of Randomized Controlled Trials. Orthop J Sports Med 2021;9:23259671211021577. [Crossref] [PubMed]
24. Benedetto KP, Fellinger M, Lim TE, et al. A new bioabsorbable interference screw: preliminary results of a prospective, multicenter, randomized clinical trial. Arthroscopy 2000;16:41-8. [Crossref] [PubMed]
25. Arama Y, Salmon LJ, Sri-Ram K, et al. Bioabsorbable Versus Titanium Screws in Anterior Cruciate Ligament Reconstruction Using Hamstring Autograft: A Prospective, Blinded, Randomized Controlled Trial With 5-Year Follow-up. Am J Sports Med 2015;43:1893-901. [Crossref] [PubMed]
26. Brand JC Jr, Nyland J, Caborn DN, et al. Soft-tissue interference fixation: bioabsorbable screw versus metal screw. Arthroscopy 2005;21:911-6. [Crossref] [PubMed]
27. Kruppa P, Flies A, Wulsten D, et al. Significant Loss of ACL Graft Force With Tibial-Sided Soft Tissue Interference Screw Fixation Over 24 Hours: A Biomechanical Study. Orthop J Sports Med 2020;8:2325967120916437. [Crossref] [PubMed]
28. Sawyer GA, Anderson BC, Paller D, et al. Effect of interference screw fixation on ACL graft tensile strength. J Knee Surg 2013;26:155-9. [PubMed]
29. Micucci CJ, Frank DA, Kompel J, et al. The effect of interference screw diameter on fixation of soft-tissue grafts in anterior cruciate ligament reconstruction. Arthroscopy 2010;26:1105-10. [Crossref] [PubMed]
30. Houck DA, Kraeutler MJ, McCarty EC, et al. Fixed- Versus Adjustable-Loop Femoral Cortical Suspension Devices for Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis of Biomechanical Studies. Orthop J Sports Med 2018;6:2325967118801762. [Crossref] [PubMed]
31. Onggo JR, Nambiar M, Pai V. Fixed- Versus Adjustable-Loop Devices for Femoral Fixation in Anterior Cruciate Ligament Reconstruction: A Systematic Review. Arthroscopy 2019;35:2484-98. [Crossref] [PubMed]
32. Eguchi A, Ochi M, Adachi N, et al. Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: comparison of the fixed-length loop device versus the adjustable-length loop device. Knee 2014;21:743-8. [Crossref] [PubMed]
33. Smith PA, Piepenbrink M, Smith SK, et al. Adjustable- Versus Fixed-Loop Devices for Femoral Fixation in ACL Reconstruction: An In Vitro Full-Construct Biomechanical Study of Surgical Technique-Based Tibial Fixation and Graft Preparation. Orthop J Sports Med 2018;6:2325967118768743. [Crossref] [PubMed]
34. Singh S, Ramos-Pascual S, Czerbak K, et al. Biomechanical testing of fixed and adjustable femoral cortical suspension devices for ACL reconstruction under high loads and extended cyclic loading. J Exp Orthop 2020;7:27. [Crossref] [PubMed]
35. Johnson JS, Smith SD, LaPrade CM, et al. A biomechanical comparison of femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction under high loads. Am J Sports Med 2015;43:154-60. [Crossref] [PubMed]
36. Petre BM, Smith SD, Jansson KS, et al. Femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction: a comparative biomechanical study. Am J Sports Med 2013;41:416-22. [Crossref] [PubMed]
37. Barrow AE, Pilia M, Guda T, et al. Femoral suspension devices for anterior cruciate ligament reconstruction: do adjustable loops lengthen? Am J Sports Med 2014;42:343-9. [Crossref] [PubMed]
38. Zainal Abidin NA, Abdul Wahab AH, Abdul Rahim RA, et al. Biomechanical analysis of three different types of fixators for anterior cruciate ligament reconstruction via finite element method: a patient-specific study. Med Biol Eng Comput 2021;59:1945-60. [Crossref] [PubMed]
39. Speziali A, Delcogliano M, Tei M, et al. Fixation techniques for the anterior cruciate ligament reconstruction: early follow-up. A systematic review of level I and II therapeutic studies. Musculoskelet Surg 2014;98:179-87. [Crossref] [PubMed]
40. Muench LN, Berthold DP, Archambault S, et al. Anterior cruciate ligament (ACL) repair using cortical or anchor fixation with suture tape augmentation vs ACL reconstruction: A comparative biomechanical analysis. Knee 2022;34:76-88. [Crossref] [PubMed]
41. Oh YH, Namkoong S, Strauss EJ, et al. Hybrid femoral fixation of soft-tissue grafts in anterior cruciate ligament reconstruction using the EndoButton CL and bioabsorbable interference screws: a biomechanical study. Arthroscopy 2006;22:1218-24. [Crossref] [PubMed]
42. Walsh MP, Wijdicks CA, Parker JB, et al. A comparison between a retrograde interference screw, suture button, and combined fixation on the tibial side in an all-inside anterior cruciate ligament reconstruction: a biomechanical study in a porcine model. Am J Sports Med 2009;37:160-7. [Crossref] [PubMed]
43. Verioti CA, Sardelli MC, Nguyen T. Evaluation of 3 Fixation Devices for Tibial-Sided Anterior Cruciate Ligament Graft Backup Fixation. Am J Orthop (Belle Mead NJ) 2015;44:E225-30. [PubMed]
44. Athiviraham A, Lee CS, Smith PA, et al. Self-Tensioning Feature of Knotless Suture Anchor Provides Reproducible Knotless Fixation Independent of Initial Tension. Orthop J Sports Med 2021;9:2325967121991593. [Crossref] [PubMed]
45. Eisen SH, Davidson PA, Rivenburgh DW. Supplemental tibial fixation for anterior cruciate ligament reconstruction. Arthroscopy 2008;24:1078-80. [Crossref] [PubMed]
46. Carulli C, Matassi F, Soderi S, et al. Resorbable screw and sheath versus resorbable interference screw and staples for ACL reconstruction: a comparison of two tibial fixation methods. Knee Surg Sports Traumatol Arthrosc 2017;25:1264-71. [Crossref] [PubMed]
47. Teo WW, Yeoh CS, Wee TH. Tibial fixation in anterior cruciate ligament reconstruction. J Orthop Surg (Hong Kong) 2017;25:2309499017699743. [Crossref] [PubMed]
48. Diego AL, Stemberg Martins V, Dias LJA, et al. Anatomic Outside-In Reconstruction of the Anterior Cruciate Ligament Using Femoral Fixation with Metallic Interference Screw and Surgical Staples (Agrafe) in the Tibia: An Effective Low-Cost Technique. Open Orthop J 2017;11:1154-64. [Crossref] [PubMed]
49. Gerich TG, Cassim A, Lattermann C, et al. Pullout strength of tibial graft fixation in anterior cruciate ligament replacement with a patellar tendon graft: interference screw versus staple fixation in human knees. Knee Surg Sports Traumatol Arthrosc 1997;5:84-8. [Crossref] [PubMed]
50. Monaco E, Fabbri M, Redler A, et al. Anterior cruciate ligament reconstruction is associated with greater tibial tunnel widening when using a bioabsorbable screw compared to an all-inside technique with suspensory fixation. Knee Surg Sports Traumatol Arthrosc 2019;27:2577-84. [Crossref] [PubMed]
51. Mayr R, Heinrichs CH, Eichinger M, et al. Biomechanical comparison of 2 anterior cruciate ligament graft preparation techniques for tibial fixation: adjustable-length loop cortical button or interference screw. Am J Sports Med 2015;43:1380-5. [Crossref] [PubMed]
52. Vertullo CJ, Piepenbrink M, Smith PA, et al. Biomechanical Testing of Three Alternative Quadrupled Tendon Graft Constructs With Adjustable Loop Suspensory Fixation for Anterior Cruciate Ligament Reconstruction Compared With Four-Strand Grafts Fixed With Screws and Femoral Fixed Loop Devices. Am J Sports Med 2019;47:828-36. [Crossref] [PubMed]
53. Greif DN, Shallop BJ, Allegra PR, et al. A Comparison of Two-Year Anterior Cruciate Ligament Reconstruction Clinical Outcomes Using All-Soft Tissue Quadriceps Tendon Autograft With Femoral/Tibial Cortical Suspensory Fixation Versus Tibial Interference Screw Fixation. Arthroscopy 2022;38:881-91. [Crossref] [PubMed]
54. Smith PA, Stannard JP, Pfeiffer FM, et al. Suspensory Versus Interference Screw Fixation for Arthroscopic Anterior Cruciate Ligament Reconstruction in a Translational Large-Animal Model. Arthroscopy 2016;32:1086-97. [Crossref] [PubMed]
55. Ma CB, Francis K, Towers J, et al. Hamstring anterior cruciate ligament reconstruction: a comparison of bioabsorbable interference screw and endobutton-post fixation. Arthroscopy 2004;20:122-8. [Crossref] [PubMed]
56. Kousa P, Järvinen TL, Vihavainen M, et al. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part I: femoral site. Am J Sports Med 2003;31:174-81. [Crossref] [PubMed]
57. Ahmad CS, Gardner TR, Groh M, et al. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med 2004;32:635-40. [Crossref] [PubMed]