Biomechanical comparison of the femoral neck system versus InterTan nail and three cannulated screws for unstable Pauwels type III femoral neck fracture

Abstract

Background There are a variety of internal fixation methods for unstable femoral neck fractures (FNFs), but the best method is still unclear. Femoral neck system (FNS) is a dynamic angular stabilization system with cross screws, and is a new internal fixation implant designed for minimally invasive fixation of FNFs. In this study, we conducted a biomechanical comparison of FNS, InterTan nail and three cannulated screws for the treatment of Pauwels III FNFs and investigate the biomechanical properties of FNS. Methods A total of 18 left artificial femurs were selected and randomly divide into Group A (fixation with FNS), Group B (fixation with InterTan nail) and Group C (fixation with three cannulated screws), with 6 specimens in each group. After creating Pauwels type III FNF models, the specimens in each were tested with non-destructive quasi-static tests, including torsion, A-P bending and axial compression tests. The average slope of the linear load–deformation curve obtained from quasi-static tests defines the initial torsional stiffness, A-P bending stiffness, and axial compression stiffness. After cyclic loading test was applied, the overall deformation of models and local deformation of implant holes in each group were assessed. The overall deformation was estimated as the displacement recorded by the software of the mechanical testing apparatus. Local deformation was defined as interfragmental displacement. Data were analyzed by one-way analysis of variance (ANOVA) followed by Bonferroni post hoc test using the SPSS software (version 24.0, IBM, New York, NY, USA). Correlation analysis was performed using Pearson’s correlation analysis. Results Group B exhibited significantly higher axial stiffness and A-P bending stiffness than the other two groups (P < 0.01), while Group A had significantly higher axial stiffness and A-P bending stiffness than Group C (P < 0.01). Groups A and B exhibited significantly higher torsional stiffness than Group C (P < 0.01), no statistical significance was observed between Groups A and B (P > 0.05). Group B exhibited significantly lower overall and local deformations than the other two groups (P < 0.01), while Group A had significantly lower overall and local deformations than Group C (P < 0.01). Correlation analysis revealed positive correlation between axial stiffness and A-P bending stiffness (r = 0.925, P < 0.01), torsional stiffness (r = 0.727, P < 0.01), between torsional stiffness and A-P bending stiffness; negative correlation between overall, local deformations and axial stiffness (r = − 0.889, − 0.901, respectively, both P < 0.01), and positive correlation between the two deformations (r = − 0.978, P < 0.01). Conclusion For fixation of unstable FNFs, InterTan nail showed the highest axial stiffness and A-P bending stiffness, followed by FNS, and then three cannulated screws. Torsional stiffness of FNS was comparable to that of the InterTan nail. FNS, as a novel minimally invasive implant, can create good mechanical environment for the healing of unstable FNFs. Clinical studies are needed to confirm the potential advantages of FNS observed in this biomechanical study.

Biomechanical evaluation of two modified intramedullary fixation system for treating unstable femoral neck fractures: A finite element analysis

“…Rupprecht et al reported that compared with CSs and DHS, InterTan nail was more powerful for treating Pauwels type III femoral neck fractures ( Rupprecht et al, 2011 ). Wang et al conducted a biomechanical comparison of FNS, InterTan nail and three CSs for the treatment of Pauwels III femoral neck fractures ( Wang et al, 2022 ). Based on their results, InterTan nail showed the highest axial stiffness and anteroposterior (AP) bending stiffness, followed by FNS, and then three CSs.…”

“…Finite element analysis is a computer simulation method, which has been widely used to study implants for unstable femoral neck fractures ( Peng et al, 2020 ; Zeng et al, 2020 ; Wang et al, 2022 ). It could evaluate the biomechanical properties of different implants by testing the stress and displacement data.…”

“…In this way, the implants will bear relatively large compression and bending stress. Three CSs transfer torque through the interaction between the screws and the cancellous bones based on the “three-point support principle” ( Wang et al, 2022 ). It should be emphasized that our modified IFNS is similar to classical FNS in design, but the difference is that we shorten the overall moment.…”

“…As such, the lack of model validation might be justified to some extent. Many other scholars also applied the same method to simulate bones and implants with acceptable outcomes ( Peng et al, 2020 ; Zeng et al, 2020 ; Wang et al, 2022 ). We will add the cadaver experiment in the further research, and finally apply the two modified implants to patients with unstable femoral neck fractures.…”

Evaluation of a Locking Autocompression Screw Model in Pauwels Type-3 Femoral Neck Fracture: In Vitro Analysis

“…The main strength of our study is that stress distribution was better in X-PIN+P than DHS or DHS+P and, thus, was apparently superior to implants developed to treat the difficult condition of P3 FNF in young adults. Although we have not compared the X-PIN and X-PIN+P with the more contemporary implants such as the Synthes Femoral Neck System, the Rotationally Stable Screw-Anchor (RoSA) and the InterTan nail, biomechanical studies have shown that both mean axial stiffness and mean torsional stiffness of these implants were comparable to that of the DHS, especially when fractures were stabilized using the sliding hip screw system with a blade [ 35 , 36 , 37 ].…”