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
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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