Does thread shape affect the fixation strength of the bioabsorbable interference screws for anterior cruciate ligament reconstructions? A biomechanical study

Abstract

BackgroundThe purpose of this study was to compare the biomechanical behaviour of two bioabsorbable interference screws with different geometries.MethodsTwo different pitch (2.5 and 5 mm) bioabsorbable interference screws, both 9 × 30 mm, were tested. Tests were performed with forty bovine digital extensor tendons and skeletally mature porcine tibiae. Two protocols of cyclic tests at 1 Hz were performed: 1000 cycles from 50 to 250 N, and 5000 cycles from 100 to 300 N (n = 10 for each type of test and screw). After the cyclic loading, a final ramp displacement until failure at 0.5 mm/s was applied.ResultsThe stiffness after the cyclic phase of the tests was not statistically different between the two screws (1000th cycle: 2.5 mm pitch 280.3 ± 56.4 N/mm, 5 mm pitch 275.2 ± 65.0 N/mm, P = .965; 5000th cycle: 2.5 mm pitch 281.3 ± 66.4 N/mm, 5 mm pitch 286.1 ± 79.4 N/mm, P = .814). The yield load was not significantly different between the screws (1000 cycle tests: 2.5 mm pitch 482.2 ± 120.2 N, 5 mm pitch 495.9 ± 131.3 N, P = .508; 5000 cycle tests: 2.5 mm pitch 476.4 ± 65.3 N, 5 mm pitch 494.3 ± 39.2 N, P = .391). No correlation was found between the insertion torque and yield load (1000 cycle tests, R2 = 0.013; 5000 cycle tests, R2 = 0.006).ConclusionsThe pitch of bioabsorbable interference screws does not seem to affect fixation strength. Also, the authors recommend not to use insertion torque alone to estimate the fixation strength.

Biomechanical Stability of Third-Generation Adjustable Suture Loop Devices Versus Continuous Loop Button Device for Cortical Fixation of ACL Tendon Grafts

“…Previous studies have shown that the porcine knee anatomy is sufficiently similar to that of the human knee 38 and that porcine flexor tendons possess similar biomechanical properties to human hamstring tendons, 11 making the porcine knee model a setup used frequently to assess biomechanics of orthopaedic implants in knee surgery. 10 , 18 , 19 , 21 A graft diameter of 8 mm was chosen for this study, resembling the typical thickness of a hamstring ACL graft. Considering that some implants failed by damage to the implant-to-bone interface and that bone density in the porcine model is significantly higher in comparison with human specimens, 1 this may have biased the load to failure toward higher values.…”

“…Cyclic loading was performed at a speed of 100 mm/s. Preconditioning was performed with 10 cycles at 250 N. Cyclic loading was performed with 1000 cycles between 0 and 250 N. 18 Subsequently, load to failure was applied at a speed of 25 mm/min. Elongation and load were recorded continuously during all tests.…”

Interference screws manufactured from magnesium display similar primary stability for soft tissue anterior cruciate ligament graft fixation compared to a biocomposite material – a biomechanical study

“…This biomechanical study has several limitations to mention. Previous studies showed that the porcine knee anatomy and ligament biomechanics are adequately similar to humans, making it a frequently used model to assess biomechanical primary stability of orthopedic implants [ 10 , 12 , 17 , 31 ]. However, bone density in the porcine model is significantly higher in comparison to humans [ 1 ].…”

“…The IFS utilized in this study have different geometries, most prominently different thread shapes and thread pitches, which could have possibly influenced the biomechanical properties of the screws. However, both geometries reflect implants currently available in clinical practice, and thread shape was shown not to influence biomechanical properties of interference screws [ 17 ]. The comparisons between the implants are limited to the timepoint zero.…”

“…For testing of the tibial graft-IFS-construct, the following protocol was used: Preconditioning was performed using 10 cycles at 50 N and cyclic loading was performed at a frequency of 0.5 Hz. Then, 1000 cycles with a load from 30 to 250 N per cycle were performed, as previously described [ 17 ]. Subsequently, load to failure testing was performed at a speed of 25 mm/min.…”