[Biomechanical characteristics of retinaculum in the treatment of femoral neck fractures].

OBJECTIVE: To investigate the biomechanical characteristics of retinaculum in the treatment of femoral neck fractures. METHODS: The CT data of a 75-year-old female volunteer was processed by software to construct an intact femur model and femoral neck fracture model fixed with three cannulated screws, which were divided into models with retinaculum or not. The Von-Mises stress distribution and displacement were compared to analyze the stability differences between the different models to study the mechanical characteristics of the retinaculum in the treatment of femoral neck fractures. RESULTS: In the intact femur, the most obvious displacement appeared in the weight-bearing area of the femoral head, with retinaculum 0.381 37 mm, and without retinaculum 0.381 68 mm. The most concentrated part of the Von-Mises stress distribution was located in the medial and inferior part of the femoral neck, with retinaculum 11.80 MPa, without retinaculum 11.91 MPa. In the femoral neck fracture fixed with three cannulated screws model, the most obvious position of displacement also appeared in the weight-bearing area of the femoral head, with retinaculum 0.457 27 mm, without retinaculum 0.458 63 mm. The most concentrated part of the Von-Mises located at the medical and inferior part of the femoral neck, with retinaculum 59.22 MPa, without retinaculum 59.14 MPa. For the cannulated screws, the Von-Mises force peaks all appeared in the posterior and superior screw, with retinaculum 107.48 MPa, without retinaculum 110.84 MPa. Among the three screws, the Von-Mises stress of the anterior-superior screw was the smallest, which was 67.88 MPa vs 68.76 MPa in the retinaculum and non-retinaculum groups, respectively. CONCLUSION: The complete retinaculum has little effect on the stability of intact femur and femoral neck fractures with anatomical reduction after internal fixation, and cannot effectively improve the stability of the fracture end after the fracture.

[Surgical treatment for ipsilateral femoral neck and shaft fracture].

OBJECTIVE: To retrospectively analyze efficacy of single structure internal fixation and double structure internal fixation in the treatment of ipsilateral femoral shaft and neck fracture, and analyze their indications. METHODS: From June 2015 to December 2020, 21 patients with ipsilateral femoral shaft and femoral neck fracture were treated, including 14 males and 7 females, aged 23 to 69 years old with an average of(38.1±12.9) years old. According to different femoral shaft fracture sites, some patients were fixed with cephalomedullary implant for both femoral neck and the femoral shaft(single structure, InterTan or PFNA Ⅱ), some patients were fixed with cannulated screws for the femoral neck and a retrograde locking nail for the femoral shaft (dual structure), and postoperative function and complications were recorded during follow-up. In 10 cases of single-structure fixation, the femoral necks were all basicervical fractures, and the femoral shaft fractures were located in the proximal isthmus;11 cases were double-structure fixation, 9 cases in 11 were basal type of femoral neck, 2 cases in 11 were neck type, and the femoral shaft fractures were located in the isthmus and the distal isthmus. RESULTS: All patients were followed up for 12 to 27 months. No femoral head necrosis, deformity, delay or nonunion occurred in the patients with single-structure fixation, and no delayed union or nonunion occurred in femoral shaft fractures;At the final follow-up, Harris score of patients with single-structure fixation was 91.8±4.1, with 8 cases were excellent and 2 cases were good. The fractures of patients with dual-structure fixation achieved good union without femoral head necrosis, except 1 case of femoral shaft fracture had delayed union;At the final follow-up, Harris score of patients with dual-structure fixation was 92.4±5.9, 7 cases were excellent, 3 cases were good, and 1 case was fair. CONCLUSION: Good reduction and fixation is the key to the treatment of such fractures. Both the single-structure fixation and the dual-structure fixation are good methods, and it should be selected according to the locations of femoral shaft and femoral neck fractures. Single-structure fixation is a good choice for femoral shaft fractures located at the proximal isthmus and basal femoral neck fractures. For isthmus and distal femoral shaft fractures combined with ipsilateral femoral neck fractures, dual-structure fixation is recommended.

Biomechanical and finite element study of drilling sites for benign lesions in femoral head and neck with curettage, bone-grafting and internal fixation.

Objective: To evaluate the influence of drilling sites for benign lesions in femoral head and neck with curettage, bone-grafting and internal fixation. Methods: Twelve paired formalin-fixed human cadaveric femora were grouped randomly into 2 groups of 6 pairs each, which were group 1 and group 2, and one of each pair of femora was grouped randomly to drill an oval-shaped hole in the anterior femoral neck, and the contralateral femur was assigned to drill an oval-shaped hole in the lateral of the proximal femur. Group 1 femora were simulated the operation of curettage, bone-grafting and internal fixation, and group 2 femora were simulated the operation of curettage. Besides, finite element models corresponding to mechanical testing were simulated according to one of the twelve femora, then finite element analysis were done. Wilcoxon signed-rank test was used for statistical analysis, with a p value < 0.05 indicating statistical significance. Results: The simulated operation of curettage decreased the axial stiffness and torsional stiffness of the intact proximal femur significantly, while there was no statistical difference on the degree of the decline between different drilling sites. Although the simulated operation of bone-grafting and internal fixation in different drilling sites increased the axial stiffness and torsional stiffness, only in the case of implanting bones and internal fixation for the lateral cortical drilled hole increased the axial stiffness greatly and made a statistical difference, even more stiff than the intact proximal femur model. Conclusion: Compared with drilling in the anterior femoral neck, a bigger stability could be obtained after drilling in the lateral proximal femur for benign lesions in femoral head and neck with curettage, bone-grafting and internal fixation.