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Background/objective: In anterior cruciate ligament ​reconstruction, a tendon graft, anchored by interference screws (IFSs), is frequently used as a replacement for the damaged ligament. Generally, IFSs are classified as being either metallic or polymeric. Metallic screws have sharp threads that lacerate the graft, preventing solid fixation. These constructs are difficult to image ​and can limit bone--screw integration because of the higher stiffness of the screw. Polymeric materials are often a better match to bone's material properties, but lack the strength needed to hold grafts in place. Magnesium (Mg) is a material of great promise for orthopaedic applications. Mg has mechanical properties similar to bone, ability to be seen on magnetic resonance imagings, and promotes bone healing. However, questions still remain regarding the strength of Mg-based screws. Previous ex vivo ​animal experiments found stripping of the screw drive when the full torque was applied to Mg screws during surgery, preventing full insertion and poor graft fixation. The similar design of the Mg screw led to questions regarding the relationship between material properties and design, and the ultimate impact on mechanical behaviour. Thus, the objective of this study was to analyze the stresses in the screw head, a key factor in the stripping mechanism of IFS, then use that information to improve screw design, for this material. Methods: Using finite element analysis, a comparison study of six drive designs (hexagonal, quadrangle, torx, trigonal, trilobe, and turbine) was performed. This was followed by a parametric analysis to determine appropriate drive depth and drive width. Results: It was observed that with a typical torque (2 ​Nm) used for screw insertion during anterior cruciate ligament reconstruction, the maximum von Mises and shear stress values were concentrated in the corners or turns of the drive, which could lead to stripping if the values were greater than the yield stress of Mg (193 ​MPa). With a four-time ​increase in drive depth to be fully driven and a 30% greater drive width, these maximum stress values were significantly decreased by more than 75%. Conclusion: It was concluded that improving the design of a Mg-based screw may increase surgical success rates, by decreasing device failure at insertion. The translational potential of this article: The results of this work have the potential to improve designs of degradable IFSs, allowing for greater torque to be applied and thus greater screw fixation between host bone and the graft. Such a fixation will allow greater integration, better patient healing, and ultimately improved patient outcomes. Keywords: Finite element analysis, Interference screw, Screw design, Screw insertion

Background/Objective: We have previously shown that an extracellular matrix (ECM) bioscaffold derived from porcine small intestine submucosa (SIS) enhanced the healing of a gap injury of the medial collateral ligament as well as the central third defect of the patellar tendon. With the addition of a hydrogel form of SIS, we found that a transected goat anterior cruciate ligament (ACL) could also be healed. The result begs the research question of whether SIS hydrogel has positive effects on ACL fibroblasts (ACLFs) and thus facilitates ACL healing. Methods: In the study, ECM-SIS hydrogel was fabricated from the digestion of decellularised and sterilised sheets of SIS derived from αGal-deficient (GalSafe) pigs. As a comparison, a pure collagen hydrogel was also fabricated from commercial collagen type I solution. The morphometrics of hydrogels was assessed with scanning electron microscopy. The ECM-SIS and collagen hydrogels had similar fibre diameters (0.105 ± 0.010 μm vs. 0.114 ± 0.004 μm), fibre orientation (0.51 ± 0.02 vs. 0.52 ± 0.02), and pore size (0.092 ± 0.012 μm vs. 0.087 ± 0.008 μm). The preservation of bioactive properties of SIS hydrogel was assessed by detecting bioactive molecules sensitive to processing and enzyme digestion, such as growth factors fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta 1 (TGF-β1), with enzyme-linked immunosorbent assay. ACLFs were isolated and expanded in culture from explants of rat ACLs (n = 3). The cells were then seeded on the hydrogels and cultured with 0%, 1%, and 10% foetal bovine serum (FBS) for 3 days and 7 days. Cell attachment was observed using a light microscope and scanning electron microscopy, whereas cell proliferation and matrix production (collagen types I and III) were examined with bromodeoxyuridine assays and reverse transcription-polymerase chain reaction, respectively. Results: The results showed that FGF-2 and TGF-β1 in the SIS hydrogel were preserved by 50% (65.9 ± 26.1 ng/g dry SIS) and 90% (4.4 ± 0.6 ng/g dry SIS) relative to their contents in ECM-SIS sheets, respectively. At Day 3 of culture, ACLFs on the SIS hydrogel were found to proliferate 39%, 31%, and 22% more than those on the pure collagen hydrogel at 0%, 1%, and 10% FBS, respectively (p

Abstract Background Recently, healing of a ruptured anterior cruciate ligament (ACL) is reconsidered. In a previous study, we have shown that the transected ACL can heal after treatment with the triple X locking suture alone or combined with small intestine submucosa (SIS). The first research question of this study was whether the healing ACLs in both groups show histological characteristics that are typical for ligament healing. Secondly, did the combined treatment with SIS lead to improved histological healing, in terms of the morphology of the fibrous synovial layer, the extracellular matrix (ECM), collagen fiber orientation, cellularity, ratio of myofibroblasts, and collagen type 3 staining. The hypothesis was that SIS enhances the healing by the scaffolding effect, endogenous growth factors, and chemoattractants. Methods In the Suture group, the left ACL was transected and sutured with the triple X locking suture repair technique. In the Suture‐SIS group, the left ACL underwent the same procedure with the addition of SIS. The right ACL served as internal control. Standard histology and immunostaining of α‐smooth muscle actin (SMA) and collagen type 3 were used. Results Microscopy showed that the fibrous synovial layer around the ACL was reestablished in both groups. The collagen fibers in the Suture‐SIS group stained denser, were more compactly arranged, and the ECM contained fewer voids and fat vacuoles. Neovasculature running between the collagen fibers was observed in both experimental groups. Collagen type 3 stained less in the Suture‐SIS group. The cellularity in the Suture group, Suture‐SIS group and Control was 1265 ± 1034 per mm2, 954 ± 378 per mm2, 254 ± 92, respectively; 49%, 26% and 20% of the cells stain positive for α‐SMA, respectively. Conclusion The healing ACL in both treated groups showed histological characteristics which are comparable to the spontaneously healing medial collateral ligament and showed that the ACL has a similar intrinsic healing response. Though, no definitive conclusions on the beneficial effects of the SIS scaffold on the healing process can be made.

Background: In double-bundle anterior cruciate ligament reconstruction, overloading either 1 of the 2 grafts should be avoided to decrease the risk of graft failure. Hypothesis: Overloading of the posterolateral graft may occur when it is fixed at 30° of knee flexion because the posterolateral bundle is elongated as the knee approaches extension. Study Design: Controlled laboratory study. Methods: Ten human cadaveric knees were tested at (1) intact, (2) anterior cruciate ligament-deficient, (3) double-bundle anterior cruciate ligament reconstruction with the anteromedial and posterolateral grafts fixed at 60° of flexion and full extension, respectively (fixation 60/FE), and (4) double-bundle anterior cruciate ligament reconstruction with both grafts fixed at 30° of flexion simultaneously (fixation 30/30). Two external loading conditions simulating clinical examinations were used: (1) 134-N anterior tibial load and (2) combined rotatory loads of 10 N·m valgus and 5 N·m internal tibial torques. Data on knee kinematics and in situ forces in the 2 bundles of the intact anterior cruciate ligament and the respective grafts were obtained. Results: In response to 134-N anterior tibial load, knee kinematics and in situ force in the grafts were similar to the intact knee for both fixation protocols. The force in the anteromedial graft for fixation 60/FEwas 34% higher, whereas the posterolateral graft for fixation 30/30 was 46% higher, compared with the intact anteromedial and posterolateral bundles, respectively. In response to combined rotatory loads, the posterolateral graft for fixation 30/30 carried 67% higher load than did the intact posterolateral bundle. Conclusion: Fixation 30/30 overloaded the posterolateral graft, whereas fixation 60/FE overloaded the anteromedial graft. Clinical Relevance: In double-bundle anterior cruciate ligament reconstruction, even though overall forces in the graft are the same as intact anterior cruciate ligament, the force distributions may not be the same as the intact bundles, and overloading of 1 of the 2 grafts may occur. [ABSTRACT FROM AUTHOR]