Triangular Mechanical Structure of the Proximal Femur

Abstract

Objective The mechanical high modulus structure of the proximal femur could guide clinical surgical treatment and instrument design of proximal femoral fractures. The purpose of this study is to analyze and verify the mechanical structure of the proximal femur. Methods A total of 375 patients with intertrochanteric fractures were imaged using computed tomography (CT) scans. Patients were grouped according to age and sex. Cortical and medullary cavity parameters (cortical thickness [CTh], cortical mean density [CM], upper‐lower diameter length [ULL], and medial‐lateral diameter length [MLL]) were measured at eight planes. Six proximal femoral finite element models of different sexes and ages were constructed. To verify the measurement results, Abaqus was used to implement the force load to describe the von Mises stress distribution, and the maximum von Mises stress values of each wall of the proximal femur were compared. Results The CTh values of the lower and upper walls were higher than those of the anterior and posterior walls of the femoral neck (p < 0.05). The CM values of the lower and upper walls were higher than those of the anterior and posterior walls of the subcephalic and middle femoral neck (p < 0.05). The ULL value gradually increased from the subcephalic region to the bottom (p < 0.05). The CTh and CM values of the medial and lateral walls were higher than those of the anterior and posterior walls in the femoral trochanteric region (p < 0.05). The MLL value decreased gradually from the plane 20 mm above the upper edge to that 20 mm below the vertex of the femoral lesser trochanter (p < 0.05). The von Mises stress was concentrated on the upper and lower walls of the femoral neck and on the medial and lateral walls of the femoral trochanteric region. The maximum von Mises stress values of the upper and lower walls were higher than those of the anterior and posterior walls of the femoral neck. The maximum von Mises stress values of the medial and lateral walls were higher than those of the anterior and posterior walls in the femoral trochanteric region, except for the plane 20 mm above the upper edge of the femoral lesser trochanter. Conclusion The bone mass of the proximal femur presented a triangular high‐modulus distribution, which bore the main stress of the proximal femur. The triangular mechanical structure provides a guideline for the surgical strategy and instrument design of the proximal femur.

Proximal femoral bionic nail—a novel internal fixation system for the treatment of femoral neck fractures: a finite element analysis

“…As our results show, the maximum principal stress of the PFBN is 17.25% of the DHS and 52.12% of the CS, while the minimum principal stress is 74.65% of the DHS and 50.45% of the CS. The cross structure is designed to facilitate the transfer of compression and tension forces between screws, thereby reducing stress concentration on individual screws and mitigating postoperative complications related to proximal femoral plates ( Augat et al, 2019 ; Xu et al, 2022 ). Finally, the PFBN is a centrally fixed internal fixation, which reduces the lever arm and stress concentration of the implant.…”

“…The unique biomechanics comes from the special anatomy of the proximal femur, where joint forces are transformed into compression and tension forces through a significant bending moment and conveyed through the trabecular system in compression and tension ( Aminian et al, 2007 ; Stiehl et al, 2007 ). The design concepts of CSs and DHSs are inherently incongruent with the anatomical structure and mechanics of the proximal femur, resulting in instability and stress concentration, leading to a high incidence of postoperative complications ( Aminian et al, 2007 ; Johnson et al, 2017 ; Tianye et al, 2019 ; Fan et al, 2021 ; Xu et al, 2022 ). Furthermore, an attempt has also been made to increase the anti-compression force by adding additional screws and medial femoral support plates based on CSs and DHSs ( Mir and Collinge, 2015 ; Zhuang et al, 2019 ; Li et al, 2023 ).…”

“…However, these improvements increase tissue damage and overlook the design for anti-tension force, resulting in stress distribution, plate fractures, and limiting clinical application ( Teng et al, 2022 ; Huang et al, 2023 ; Nan et al, 2023 ). Therefore, our team was the first to propose the concept of triangular-supported fixation (TSF) and design the proximal femoral bionic nail (PFBN) based on the triangular structure and mechanics characters of the proximal femur ( Ding et al, 2022b ; Xu et al, 2022 ). The key to TSF lies in the addition of support screws, creating a crossover structure that mimics the compression and tension trabeculae of the proximal femur, thus improving stress distribution and stability, which has been shown to be effective in intertrochanteric fractures ( Ding et al, 2022a ; Wang et al, 2022a ; Wang et al, 2022b ; Zhao et al, 2023 ).…”

From Koch’s Bone Biomechanical Analysis to Contemporary Proximal Femur Fracture Management

“…Its borders are made up of the three main compressive and tensile trabeculae; the primary compressive trabeculae which are vertically oriented from the medial femoral head, the principal tensile trabeculae from the inferior aspect of the fovea to the greater trochanter, and lastly the secondary compressive trabeculae from greater to LT [20]. Studies on the proximal femur have found that the thickest cortex is found at the upper wall of the femoral neck, as well as the medial and lateral walls of the trochanteric area, with Ward's triangle being in the center [21]. These three areas form the triangle, and Xu et al hypothesized that this area, when under physiologic load, reduces shear forces and the bending moment of the femur and balances the distribution throughout [21].…”

“…Studies on the proximal femur have found that the thickest cortex is found at the upper wall of the femoral neck, as well as the medial and lateral walls of the trochanteric area, with Ward's triangle being in the center [21]. These three areas form the triangle, and Xu et al hypothesized that this area, when under physiologic load, reduces shear forces and the bending moment of the femur and balances the distribution throughout [21]. The triangular theory is in line with Koch's theory, with his descriptive analysis of the thick inferior-medial femoral neck cortex, and its critical role in withstanding the balance of the forces placed on the proximal femur.…”