Background: The transforming growth factor-beta (TGF-β) signaling pathway is an important pathway associated with the pathogenesis of osteoarthritis (OA). This study was to investigate the involvement of circRNAs in the TGF-β signaling pathway. Methods: Cell Counting Kit-8 (CCK-8) assay and 5-ethynyl-2′-deoxyuridine (EdU) assay were used to detect the proliferation of primary mouse chondrocytes (PMCs). RNA-sequencing together with bioinformatics analysis were used to systematically clarify TGF-β1 induced alternations of circRNAs in PMCs. The regulatory and functional role of circPhf21a was examined in PMCs. Downstream targets of circPhf21a were explored by RNA-sequencing after overexpression of circPhf21a and verified by RT-qPCR in PMCs. Finally, the role and mechanism of circPhf21a in OA were explored in mouse models. Results: We found that TGF-β1 promoted the proliferation of PMCs. Meanwhile, RT-qPCR and western blotting indicated that TGF-β1 promoted extracellular matrix (ECM) anabolism. RNA-sequencing revealed that a total of 36 circRNAs were differentially expressed between PMCs treated with and without TGF-β1. Of these, circPhf21a was significantly decreased by TGF-β1. Furthermore, circPhf21a knockdown promoted the proliferation and ECM synthesis of PMCs, whereas overexpression of circPhf21a showed the opposite effects. Mechanically, the expression profiles of the mRNAs revealed that Vegfa may be the target of circPhf21a. Additionally, we found that circPhf21a was significantly upregulated in the mouse OA model, and inhibition of circPhf21a significantly relieved the progression of OA. Conclusions: Our results found that TGF-β1 promoted the proliferation and ECM synthesis of PMCs via the circPhf21a-Vegfa axis, which may provide novel therapeutic targets for OA treatment.

This study aims to assess the biomechanical performance of the 7.3 mm fully threaded off-axis screw (7.3-FTOS) configuration in stabilizing vertical femoral neck fractures (FNSs), comparing its effectiveness with other fixation methods. A vertical FNF model with an 80° Pauwels angle was simulated and stabilized using four internal fixation constructs: Three inverted cannulated compression screws (ICCS), 7.3 mm partially threaded off-axis screw (7.3-PTOS), 4.5 mm fully threaded off-axis screw (4.5-FTOS), and 7.3-FTOS. The fracture fixation models were developed, refined, and optimized using Geomagic for 3D reconstruction and surface smoothing, and SolidWorks for parametric modeling. Comparative finite element analysis was then conducted using Ansys to assess the biomechanical behavior of each fixation method. The maximum femoral displacements for ICCS, 7.3-PTOS, 4.5-FTOS and 7.3-FTOS were 10.40 mm, 8.08 mm, 7.71 mm, and 7.15 mm, respectively. The peak internal fixation displacements were 9.76 mm, 7.55 mm, 7.25 mm, and 6.78 mm, respectively. The maximum gap displacement measured 2.73 mm, 1.19 mm, 0.94 mm, and 0.55 mm, respectively. The maximum displacement along the Z-axis, representing the shear force direction, was recorded as 2.93 mm, 2.69 mm, 2.66 mm, and 2.63 mm, respectively. The peak von Mises stress (VMS) values in the distal femur were 218.04 MPa, 121.99 MPa, 123.42 MPa, and 113.86 MPa, respectively. The peak VMS values of the internal fixation constructs were 10.40 mm, 8.08 mm, 7.71 mm, and 7.15 mm, respectively. Finite element analysis results revealed that 7.3-FTOS configuration exhibited superior resistance to shear and rotational forces in vertical FNFs compared to ICCS, 7.3-PTOS, and 4.5-FTOS, demonstrating enhanced mechanical performance. These findings establish a foundation for advancing experimental investigations and potential future clinical translation.