Mechanical analysis of modified femoral neck system in the treatment of osteoporotic femoral neck fractures.

BACKGROUND: Despite the explicit biomechanical advantages associated with FNS, it is currently inconclusive, based on the existing literature, whether Femoral Neck System (FNS) outperforms Cannulated cancellous screws (CSS) in all aspects. Due to variances in bone morphology and bone density between the elderly and young cohorts, additional research is warranted to ascertain whether the benefits of FNS remain applicable to elderly osteoporosis patients. This study aimed to investigate the biomechanical properties of FNS in osteoporotic femoral neck fractures and propose optimization strategies including additional anti-rotation screw. METHODS: The Pauwels type III femoral neck fracture models were reconstructed using finite element numerical techniques. The CSS, FNS, and modified FNS (M-FNS) models were created based on features and parameterization. The various internal fixations were individually assembled with the assigned normal and osteoporotic models. In the static analysis mode, uniform stress loads were imposed on all models. The deformation and stress variations of the femur and internal fixation models were recorded. Simultaneously, descriptions of shear stress and strain energy were also incorporated into the figures. RESULTS: Following bone mass reduction, deformations in CSS, FNS, and M-FNS increased by 47%, 52%, and 40%, respectively. The equivalent stress increments for CSS, FNS, and M-FNS were 3%, 43%, 17%, respectively. Meanwhile, variations in strain energy and shear stress were observed. The strain energy increments for CSS, FNS, and M-FNS were 4%, 76%, and 5%, respectively. The shear stress increments for CSS, FNS, and M-FNS were 4%, 65% and 44%, respectively. Within the osteoporotic model, M-FNS demonstrated the lowest total displacement, shear stress, and strain energy. CONCLUSION: Modified FNS showed better stability in the osteoporotic model (OM). Using FNS alone may not exhibit immediate shear resistance advantages in OM. Concurrently, the addition of one anti-rotation screw can be regarded as a potential optimization choice, ensuring a harmonious alignment with the structural characteristics of FNS.

Biomechanical changes in the proximal femur before and after removal of femoral neck system.

BACKGROUND: As an innovative internal fixation system, FNS (femoral neck system) is increasingly being utilized by surgeons for the treatment of femoral neck fractures. At present, there have been numerous finite element analysis experiments studying the immediate stability of FNS and CSS in treating femoral neck fractures. However, there is scarce mechanical analysis available regarding the effects post internal fixation removal. This study aimed to investigate the alterations in mechanical parameters of the proximal femur before and after the removal of FNS (femoral neck system), and to assess potential distinctions in indicators following the extraction of CSS (Cannulated Screws). METHODS: A proximal femur model was reconstructed using finite element numerical techniques. The models for CSS and FNS were formulated utilizing characteristics and parametric definitions. The internal fixation was combined with a normal proximal femur model to simulate the healing state after fracture surgery. Within the framework of static analysis, consistent stress burdens were applied across the entirety of the models. The total deformation and equivalent stress of the proximal femur were recorded before and after the removal of internal fixation. RESULTS: Under the standing condition, the total deformation of the model before and after removing CSS was 0.99 mm and 1.10 mm, respectively, indicating an increase of 12%. The total deformation of the model before and after removing FNS was 0.65 mm and 0.76 mm, respectively, indicating an increase of 17%. The equivalent stress for CSS and FNS were 55.21 MPa and 250.67 MPa, respectively. The average equivalent stress on the cross-section of the femoral neck before and after removal of CSS was 7.76 MPa and 6.11 MPa, respectively. The average equivalent stress on the cross-section of the femoral neck before and after removal of FNS was 9.89 MPa and 8.79 MPa, respectively. CONCLUSIONS: The retention of internal fixation may contribute to improved stability of the proximal femur. However, there still existed risks of stress concentration in internal fixation and stress shielding in the proximal femur. Compared to CSS, the removal of FNS results in larger bone tunnels and insufficient model stability. Further clinical interventions are recommended to address this issue.

Changes in the femoral trochlear induced with estradiol exposure, an experimental study on rats.

BACKGROUND: It is well known that estrogen is closely related to bone and joint tissue. Findings indicate that estradiol, injected during pregnancy, passes through the placental barrier and reaches the fetuses in utero where it exerts its action. Since trochlea appears well established in the prenatal period, however, whether trochlear dysplasia is related to estradiol exposure has not been confirmed, and the pathological process of estradiol exposure-induced trochlear dysplasia remains unclear. This study aimed to establish an estradiol exposure animal model in fetuses and to analyze the morphology of the femoral trochlear in neonatal rats. METHODS: 30 pregnant Wistar rats provided by the local Animal Center were assigned randomly into three groups, a high dose estradiol injection group, a low dose estradiol injection group and a blank control group. Gross, cross-sectional observation, histological staining measurement and microcomputed tomography of the rat offspring were conducted to evaluate the morphological changes of the femoral trochlea. RESULTS: The incidence of trochlear dysplasia increased with the concentration of estradiol injection. Gross and cross-sectional observation showed a shallower trochlea groove in two groups with estradiol injection. Histological staining measurement indicated that the trochlear sulcus angle and trochlear sulcus depth were significantly different between the two groups with estradiol injection and the blank control group at 0,5 and 10 days after birth. Subchondral bone loss was observed in the two estradiol injection groups by micro-CT, and the bone loss was found to deteriorate over time. CONCLUSION: In this study, estradiol exposure in fetuses had an adverse effect on intrauterine development and could induce trochlear dysplasia and bone loss in rat offspring. In addition, this study also showed that the higher concentration of estradiol injection in pregnant rats, the more incidence of trochlear dysplasia in rat offspring.