Abstract
Introduction The method of graft fixation is critical in anterior cruciate ligament (ACL) reconstruction surgery. Success of surgery is totally dependent on the ability of the implant to secure the graft inside the bone tunnel until complete graft integration. The principle of EndoButton is based on the cortical suspension of the graft. The Cross-Pin is based on graft expansion. The aim of this study was to evaluate the biomechanical performance of EndoButton and Bio Cross-Pin to fix the hamstring graft at femoral side of porcine knee joints and evaluate whether they are able to support of loading applied on graft during immediate post-operative tasks. Methods Fourteen ACL reconstructions were carried out in porcine femurs fixing superficial flexor tendons with Titanium EndoButton (n = 7) and with 6 × 50 mm HA/PLLA Bio Cross-Pin (n = 7). A cyclic loading test was applied with 50-250 N of tensile force at 1 Hz for 1000 cycles. The displacement was measured at 20, 100, 500 and 1000 load cycles to quantify the slippage of the graft during the test. Single-cycle load-to-failure test was performed at 50 N/mm to measure fixation strength. Results The laxity during cyclic loading and the displacement to failure during single-cycle test were lower for the Bio Cross-Pin fixation (8.21 ± 1.72 mm) than the EndoButton (11.20 ± 2.00 mm). The Bio Cross-Pin (112.22 ± 21.20 N.mm–1) was significantly stiffer than the EndoButton fixation (60.50 ±10.38 N.mm–1). There was no significant difference between Bio Cross-Pin (failure loading: 758.29 ± 188.05 N; yield loading: 713.67 ± 192.56 N) and EndoButton strength (failure loading: 672.52 ± 66.56 N; yield loading: 599.91 ± 59.64 N). Both are able to support the immediate post-operative loading applied (445 N). Conclusion The results obtained in this experiment indicate that the Bio Cross-Pin technique promote stiffer fixation during cyclic loading as compared with EndoButton. Both techniques are able to support the immediate post-operative loading applied.
Highlights
The method of graft fixation is critical in anterior cruciate ligament (ACL) reconstruction surgery
The anterior cruciate ligament (ACL) replacement with hamstring graft has been widely performed with positive results
The use of the autograft instead of an artificial graft was preferred to mimic the clinical practice of use a graft retrieved from the patient. These grafts were fixed to the femurs by the two fixation techniques: Titanium EndoButton linked with 30 mm polyurethane Endotape (n = 7) and by Bio Cross-Pin HA/PLLA 70 30 6 × 50 mm (n = 7) (Figure 2)
Summary
The method of graft fixation is critical in anterior cruciate ligament (ACL) reconstruction surgery. Both techniques are able to support the immediate post-operative loading applied. The four-stranded hamstrings have higher strength and stiffness than patellar tendon (Hamner et al, 1999), the integration into the bone is delayed due to the lack of bone block (Blickenstaff et al, 1997; Rodeo et al, 1993; Weiler et al, 2002a, b) This factor makes the early postoperative period a critical time for successful surgery (Becker et al, 2001; Brown et al, 1996; Wilson et al, 1999). The slippage impairs the integration and ligamentization process (Rodeo et al, 1993, 2006)
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