Biomechanical Comparison of Cross-Pin and Endobutton-CL Femoral Fixation of a Flexor Tendon Graft for Anterior Cruciate Ligament Reconstruction—A Porcine Femur-Graft-Tibia Complex Study

doi:10.1016/j.jss.2009.01.015

Journal of Surgical Research

Volume 161, Issue 2, 15 June 2010, Pages 282-287

https://doi.org/10.1016/j.jss.2009.01.015 Get rights and content

Background

A stable fixation of the graft is imperative for early aggressive rehabilitation after anterior cruciate ligament (ACL) reconstruction. The suspension devices such as Endobutton-CL and Cross-pin system are common techniques of femoral fixation for the hamstring tendon graft and provide superior initial biomechanical properties than the screws system. It remains unclear how such implants perform under cyclic loading and initial pull-out strength.

Materials and Methods

Cross-pin and Endobutton-CL femoral fixation devices were tested for initial fixation strength in porcine knee joints by cyclic loads following a load-to-failure test. The Cross-pin and Endobutton-CL were used for femoral fixation of a porcine profundus flexor digitorum tendon autograft in 20 porcine knees. Ten specimens of femoral-graft-tibia complex in each group were loaded cyclically to between 0 and 150 N at 1 Hz for 1000 cycles following a load-to-failure test at a rate of 150 mm/min.

Results

The amount of total femur-graft-tibia complex graft displacement was significantly lower in the Cross-pin fixation group (5.37 ± 0.28 mm) than in Endobutton-CL fixation group (6.08 ± 0.61 mm: P < 0.05). There were no significant differences in the maximal failure load, yield load, and stiffness between the Cross-pin and Endobutton-CL fixation groups.

Conclusions

This biomechanical study reveals that the Endobutton-CL and Cross-pin femoral fixation devices have an equally strong and safe fixation for ACL reconstruction. However, the Cross-pin fixation has significantly less displacement of femur-graft-tibia complex than that of Endobutton-CL fixation in response to the cyclic loading test. It indicates that the Cross-pin fixation is more suitable for early aggressive rehabilitation following ACL reconstruction.

Introduction

The reconstruction of a torn anterior cruciate ligament using the hamstring tendon graft has become a popular surgical procedure in recent years. A stable fixation of the graft is imperative for early aggressive rehabilitation to minimize quadriceps atrophy and restrictions in the range of motion postoperatively. However, initial graft fixation strength remains the weakest link following anterior cruciate ligament (ACL) reconstruction with the hamstring tendon graft before bony incorporation of the graft [1]. Many devices for soft tissue tendon fixation have been developed to facilitate initial graft fixation, including Cross-pin (TransFix, Arthrex, Germany), Endobutton-CL (a titanium button with a 20-mm continuous polyester loop, Acufex; Smith and Nephew, Andover, MA), Endopearl, Biotransfix pin, interference screw and Bioscrew etc 2, 3, 4, 5. Using interference screw fixation of the tendon graft may cause problems such as divergent screw placement, laceration of sutures or grafts by screw threads, and increasing difficulty of revision surgery in the presence of screws [2]. The use of suspension devices such as Endobutton-CL and Cross-pin system may help avoid these problems. Both fixations are common techniques of femoral fixation for the hamstring tendon graft during endoscopic ACL reconstruction 2, 4, 5, 6, and provide superior initial biomechanical properties than the screws system 3, 7, 8.

The Endobutton-CL provides secure femoral fixation for a quadrupled graft utilizing a titanium button and a polyester loop. The polyester loop serves to connect the hamstring graft to the titanium button as well as increase the length of the entire graft construct. For cross-pin fixation technique, the tendon graft is wrapped 180° and tensioned around the pin at the proximal end of the femoral tunnel. It remains unclear how these devices perform in response to cyclic loading; in addition, the initial fixation strength following ACL reconstruction using a hamstring tendon graft is not known. Our hypothesis is that the Endobutton-CL has relatively greater distance between the points of fixation associated with the tendon graft and the elastic behavior of the polyester loop, which could create significant elongation and laxity of the graft tissue within the femoral bone tunnel under cyclic tensile loading. The purpose of this biomechanical study was to evaluate the initial fixation strength of a porcine profundus flexor digitorum tendon autograft and displacement of femur-graft-tibia complex (FGTC) using the Endobutton-CL and Cross-pin system.

Section snippets

Study Design

Twenty soft-tissue-free porcine knees were used for ACL reconstruction. A single folded profundus flexor digitorum tendon autograft was secured in the femoral tunnel using either the Cross-pin (TransFix, 3.5 mm in diameter and 35 mm in length) or Endobutton-CL with a 20-mm continuous polyester loop (Fig. 1). After the graft was well fixed in the femoral side, pretension of the graft with 89N for 5 min was applied by a tensiometer (Graft Master, Smith and Nephew, MA) mounted in a custom-made rod

Statistics

All results are expressed as mean ± standard deviations. The displacement, maximal failure load, yield load, and stiffness were statistically compared using the Students t-test. The level of significance was set at 0.05.

Results

The amount of total displacements of the isolated porcine ACL (3.69 ± 0.17 mm) were significantly lower than in the Cross-pin (5.37 ± 0.28 mm) and Endobutton-CL groups (6.08 ± 0.61mm) (P < 0.05 for both comparisons). As shown in Fig. 2 and Table 1, all techniques demonstrated the greatest portion of their overall displacement during the first 100 cycles (Cross-pin 47%, Endobutton-CL 58%). The displacement of FGTC for Cross-pin group was significantly less than for Endobutton-CL group in

Discussion

The hamstring tendon has become a popular replacement graft for ACL reconstruction. However, the major concern for the hamstring tendon graft is not its strength but its fixation technique [5]. The ideal technique for hamstring tendon remains controversial. In clinical practice, using the Cross-pin or Endobutton-CL in the femoral side and a Bioscrew with screw posts in the tibia side for fixation of the hamstring tendon graft is a common technique for ACL reconstruction 4, 6, 9, 10, 11.

Conclusion

This biomechanical study reveals that the Endobutton-CL and Cross-pin femoral fixation devices have an equally strong and safe fixation of flexor digital tendon for ACL reconstruction. Both devices provide a secure fixation, however, the Cross-pin fixation has significantly less displacement of FGTC than that of Endobutton-CL fixation in response to the cyclic loading test. It indicates that the Cross-pin fixation is more suitable for early aggressive rehabilitation following ACL reconstruction.

Acknowledgment

This study was supported by The Chen-Han Foundation for Education.

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Cited by (29)

Biomechanical effects of cross-pin's diameter in reconstruction of anterior cruciate ligament – A specific case study via finite element analysis
2022, Injury
Citation Excerpt :
At the tibial fixation area, the interference screw has been widely used in securing the graft inside the bone tunnel to replace the torn ACL as shown in previous studies [4], where it demonstrated higher pull-out stiffness as compared to the cortical button in a previous experiment work by Fogel et al. [5]. Meanwhile, a suspension device such as the cross-pin was superior to the interference screw [6] and cortical button [7] as a femoral graft fixation, since it exerted lower displacement with higher load failure. To be specific, a study by Espejo-Baena et al. [6] focussing on a comparative analysis between four different fixations.
For anterior cruciate ligament reconstruction (ACL-R), one of the crucial aspects of treatment is the fixator selection that could provide initial graft fixation post-operatively. Literature on biomechanical stabilities of different sizes of fixators as femoral graft fixation is limited. Therefore, this study aims to analyse the influence of different diameters of cross-pins on the stability of graft fixations after ACL-R via finite element analysis (FEA). In the methodology, three-dimensional (3D) models of three different diameters of cross-pins were developed, of which anterior tibial loads (ATL) were applied onto the tibia. From the findings, the cross-pin with a smaller diameter (4 mm) provided optimum stability than larger diameter cross-pins, whereby it demonstrated acceptable stresses at the fixators (both cross-pin and interference screw) with a different percentage of 28%, while the stresses at the corresponding bones were favourable for osseointegration to occur. Besides, the strains of the knee joint with 4 mm diameter cross-pin were also superior in providing a good biomechanical environment for bone healing, while the recorded strain values at fixators were comparable with a larger diameter of cross-pins without being inferior in terms of deformation. To conclude, the cross-pin with 4 mm diameter depicted the best biomechanical aspects in graft fixation for ACL-R since it allows better assistance for the osseointegration process and can minimise the possibility of the breakage and migration of fixators. This study is not only useful for medical surgeons to justify their choices of pin diameter to treat patients, but also for researchers to conduct future studies.
The interposition of soft tissue between the cortical button and femoral lateral cortex significantly increases button migration but does not negatively affect knee stability and clinical outcome
2020, Knee
In clinical practice, soft tissue interposition may occur during femoral graft fixation. Soft tissue interposition between the lateral femoral cortex and the cortical button may affect graft tension and related longitudinal graft motion in the tunnel. We aimed to investigate the effect of soft tissue interposition on button migration and clinical outcomes in anatomical single-bundle anterior cruciate ligament reconstruction.
Eighty-four patients aged 18–40 years, who underwent anatomical single-bundle anterior cruciate ligament reconstruction with quadruple hamstring autograft were included. Patients were divided into two groups as Group 1 (n = 32) with soft tissue interposition between the cortical button and cortex, and Group 2 (n = 52) without soft tissue interposition. At the one-year follow-up visit, the anteroposterior knee stability of the patients was evaluated using the Lachman test and KT-2000 arthrometer, and rotational stability was assessed with the pivot shift test. The Lysholm knee score was used to evaluate the functional outcome of the patients. Relationship between tissue interposition and clinical outcome, and button migration was examined.
Button migration was observed in 12 patients in Group 1 (37.5%) and two patients (3.84%) in Group 2 (p < 0.001). However, no significant difference was observed between patients with and without tissue interposition or those with and without button migration regarding knee stability parameters and clinical outcome (p < 0.05).
Postoperative tissue interposition is found to be associated with cortical button migration during the follow-up. However, it does not affect the clinical outcome.
Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model
2016, Arthroscopy - Journal of Arthroscopic and Related Surgery
To evaluate and compare two adjustable femoral cortical suspensory fixation devices used for anterior cruciate ligament reconstruction through a novel, direct computed tomography (CT) analysis metric and biomechanical laxity testing in a matched cadaveric human knee study.
Anterior cruciate ligament reconstructions with bovine tendon grafts were performed using two adjustable femoral cortical suspensory fixation devices (RigidLoop Adjustable [DePuy Synthes Mitek, Raynham, MA] and TightRope [Arthrex, Naples, FL]) in 12 knees (6 matched pairs). A mechanical testing series was used to determine each knee's laxity in the intact condition. After reconstruction, each specimen was again tested for laxity and also imaged with CT. The laxity testing and CT imaging were then repeated after 1,000 cycles of anteroposterior loading on each knee to compare changes in laxity for the two fixation devices and to visualize changes in button-to-graft distance migration through a three-dimensional CT imaging method.
No significant differences were found between the two fixation groups' laxity measures after reconstruction (all P values ≥ .620) or after cycling (all P values ≥ .211) at any flexion angle. In addition, no significant differences were found between the two groups regarding button-to-graft distance migration (P = .773; mean, 0.61 ± 0.6 mm [95% confidence interval, −0.1 to 1.3 mm] in RigidLoop Adjustable group and 0.53 ± 0.6 mm [95% confidence interval, −0.1 to 1.2 mm] in TightRope group).
There were no significant differences between the two femoral cortical suspensory adjustable-loop devices regarding laxity outcomes or loop displacement as measured by button-to-graft distance migration.
Use of either of the adjustable-loop cortical suspensory devices in our analysis would appear to produce similar, acceptable laxity outcomes and minimal effects in terms of device-related loop displacement.
Clinical and functional outcomes after anterior cruciate ligament reconstruction using cortical button fixation versus transfemoral suspensory fixation: A systematic review of randomized controlled trials
2014, Arthroscopy - Journal of Arthroscopic and Related Surgery
Citation Excerpt :
Biomechanical studies have shown superior mechanical properties using extratunnel fixation over intratunnel devices. Several studies have also compared different extratunnel fixation devices without showing clinically relevant differences between them in terms of structural properties under load-to-failure or cyclic loading conditions.6-9,18 Clinical studies seem to suggest increased femoral tunnel widening in the cortical button group.13,19,20
To compare clinical and functional outcomes after anterior cruciate ligament (ACL) reconstruction using cortical button versus transfemoral suspensory fixation.
This systematic review was conducted following the Cochrane handbook guidelines and PROSPERO registration. Only Level I and II randomized controlled trials comparing cortical button and transfemoral suspensory fixation in hamstring ACL reconstruction were included. A literature search was performed using electronic databases. The methodologic quality of included studies was assessed using The Cochrane Collaboration's risk-of-bias tool. All outcomes reported by each study were evaluated. Primary outcome measures were postoperative International Knee Documentation Committee (IKDC) and Lysholm knee scores. Statistical analysis was performed using RevMan software (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen). Dichotomous data were reported as risk ratio and 95% confidence intervals. Heterogeneity was assessed using I².
Five studies involving 317 patients were included. The mean follow-up period was 21.7 ± 7.0 months (range, 12 to 38 months). The mean age of participants was 26.7 ± 1.89 years (range, 16 to 48 years). The Lysholm score, Tegner activity score, and IKDC score were compiled. Clinical assessment was performed by Lachman testing, assessment of side-to-side differences on KT-1000 (MEDmetric, San Diego, CA) testing, and measurements of thigh atrophy, as well as imaging (radiography and computed tomography) to assess for femoral tunnel widening. Pooled statistical analysis was possible only for postoperative IKDC and Lysholm scores. No significant differences were found between the cortical button and transfemoral fixation groups. Included studies did not report differences in clinical outcomes between the 2 groups. Radiographic results suggest increased femoral tunnel widening in the cortical button group. However, tunnel widening was not found to affect clinical results.
The present evidence suggests that there are no short- to medium-term differences in knee-specific outcome measures between patients treated with cortical button femoral graft fixation and those treated with suspensory transfemoral fixation when undergoing ACL reconstruction. In addition, radiologic evidence of tunnel widening does not seem to affect short- to medium-term clinical outcomes.
Level II, systematic review of Level I and II studies.
Improvement of primary stability in ACL reconstruction by mesh augmentation of an established method of free tendon graft fixation. A biomechanical study on a porcine model
2013, Knee
Citation Excerpt :
To simulate a moderate level of activity in the early rehabilitation period we chose a loading regime from 20 to 150 N as Milano et al. did [24]. In several biomechanical studies the displacement rate is described with 150 mm/min [35,36] or 200 mm/min [13,14,17] but there is still no common sense. Perhaps it would have been better to choose a displacement rate of 200 mm/min for a better comparison of our results to other studies.
The aim of the present study was to compare primary stability in ACL reconstruction and ultimate load to failure of a mesh augmented hamstring tendon graft fixed with two cross pins to established hamstrings and bone-patellar-tendon-bone (BTB) graft fixation methods.
Forty fresh porcine femora were divided into four groups: (A): BTB graft fixed with two RigidFix® pins, (B): hamstring tendon graft fixed with a Milagro® interference screw, (C): hamstring tendon graft fixed with two RigidFix® pins, and (D): hamstring tendon graft augmented with Ultrapro® mesh fixed with two RigidFix® pins. Each graft underwent cyclic loading in tension and load to failure. Elastic and plastic displacements were measured by 3-dimensional digital image correlation. Groups were compared by one-way ANOVA and Tukey–Kramer post-hoc tests.
After 1000 cycles, the mean plastic displacement was lowest in the BTB graft (p < 0.001). Plastic displacement was significantly lower in the mesh augmented group compared to the plain hamstring graft and the Milagro screw group (p < 0.05). Load to failure was highest in the mesh-augmented group; significant to the hamstring tendon (p = 0.023).
Although the BTB-graft represented the most stable construct against plastic displacement in our study, mesh augmentation of free tendon grafts significantly increased primary stability and reduced plastic displacement of femoral cross pin fixation. This new augmentation device may better protect the hamstrings graft from secondary elongation during postoperative rehabilitation.
Mesh augmentation seems to be an effective technique to stabilise free hamstring tendon autografts during postoperative rehabilitation with significant reduction of graft slippage.
Anterior cruciate ligament reconstruction in a rabbit model using canine small intestinal submucosa and autologous platelet-rich plasma
2012, Journal of Surgical Research
Citation Excerpt :
After surgery, knee pain will likely persist in patients who undergo this type of reconstruction owing to insufficient strength of the knee stabilizing muscles [2]. Using interference screw fixation of tendon grafts can cause problems such as divergent screw placement, laceration of sutures or grafts by the screw threads, or increased difficulty of revision surgery by the presence of screws [3]. To overcome these problems, various synthetic, allograft, and xenograft materials have been used in ACL reconstruction surgery [4,5].
The bone–ligament interface is the main point of failure after anterior cruciate ligament reconstruction. Synthetic ligament materials have problems such as a greater failure rate of the bone–ligament insertion than autografts. Small intestinal submucosa (SIS) is a biologic scaffold that has been used to repair musculoskeletal tissue and has been shown to promote cell migration and enhance collagen fiber regeneration. Autologous platelet-rich plasma (PRP) has also been investigated as a potential promoter of tendon healing. We investigated SIS and PRP as biomaterials that might strengthen the bone–tunnel interface and improve tendon structure formation.
Anterior cruciate ligament grafts were formed of braid-twist canine SIS. These canine SIS ligament grafts were used for anterior cruciate ligament reconstruction in 20 New Zealand white rabbits. The rabbits were divided into 2 treatment groups. In 1 group (SIS group; n = 10), we only implanted the canine SIS grafts. In the second group (PRP group; n = 10), we applied autologous PRP to the surgical area after implantation of canine SIS grafts. We determined the cytokine level of the autologous PRP using a transforming growth factor-β1 enzyme-linked immunosorbent assay kit. At 1 and 4 wk after surgery, magnetic resonance imaging was performed to evaluate the grafts. The femur–graft–tibia complex was assessed histologically and biomechanically at 8 wk after surgery.
At 1 wk after surgery, the magnetic resonance imaging scans of the PRP group showed high signal-intensity lesions. In biomechanical tests, the SIS group had a significantly greater maximum load, maximum stress, and ultimate load and strain than the PRP group. The histologic findings of the PRP group revealed a greater cellular response, fibrotic tissue regeneration around the graft, broad chondrocyte cell infiltration, and collagen fibers that were loosely attached to the bone.
The PRP group had significantly lower tension load values than the SIS group, and there was greater cellular response in a broad area around the grafts of the rabbits in the PRP group compared with those in the SIS group. The early inflammatory responses around the canine SIS grafts in the PRP group and the altered cytokine or growth factor concentration in the intra-articular capsule of the rabbits in PRP group might explain their relatively low tensile strength results.

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MusculoskeletalBiomechanical Comparison of Cross-Pin and Endobutton-CL Femoral Fixation of a Flexor Tendon Graft for Anterior Cruciate Ligament Reconstruction—A Porcine Femur-Graft-Tibia Complex Study

Background

Materials and Methods

Results

Conclusions

Introduction

Section snippets

Study Design

Statistics

Results

Discussion

Conclusion

Acknowledgment

Arthroscopy

Arthroscopy

Arthroscopy

Arthroscopy

Arthroscopy

J Orthop Sci

Arthroscopy

Arthroscopy

Arthroscopy

Graft fixation in cruciate ligament reconstruction

Am J Sports Med

Musculoskeletal
Biomechanical Comparison of Cross-Pin and Endobutton-CL Femoral Fixation of a Flexor Tendon Graft for Anterior Cruciate Ligament Reconstruction—A Porcine Femur-Graft-Tibia Complex Study