Parametric Design Optimisation of Proximal Humerus Plates Based on Finite Element Method

Abstract

Optimal treatment of proximal humerus fractures remains controversial. Locking plates offer theoretical advantages but are associated with complications in the clinic. This study aimed to perform parametric design optimisation of proximal humerus plates to enhance their mechanical performance. A finite element (FE) model was developed that simulated a two-part proximal humerus fracture that had been treated with a Spatial Subchondral Support (S3) plate and subjected to varus bending. The FE model was validated against in vitro biomechanical test results. The predicted load required to apply 5 mm cantilever varus bending was only 0.728% lower. The FE model was then used to conduct a parametric optimisation study to determine the orientations of inferomedial plate screws that would yield minimum fracture gap change (i.e. optimal stability). The feasible design space was automatically identified by imposing clinically relevant constraints, and the creation process of each FE model for the design optimisation was automated. Consequently, 538 FE models were generated, from which the obtained optimal model had 4.686% lower fracture gap change (0.156 mm) than that of the manufacturer’s standard plate. Whereas its screws were oriented towards the inferomedial region and within the range of neck-shaft angle of a healthy subject. The methodology presented in this study promises future applications in patient-specific design optimisation of implants for other regions of the human body.

Trends in the Characterization of the Proximal Humerus in Biomechanical Studies: A Review

“…Perren stated that bone anisotropy is not significant in ORIF, so it can be ignored when treating bone as a material [55]. The literature corroborates this, showing that using isotropic material properties for the bone is sufficient for analysis under simple loads [3,5,[23][24][25][26]28,30,54,56].…”

“…According to the recent literature, most proximal humerus fracture studies using FEA tend to investigate factors involving open reduction and internal fixation (ORIF) treatment with a locking plate [5,[28][29][30][31]33], due to the popularity of the treatment in the last few years, and also because of the high failure rate it has. Biomechanical studies turn around this treatment, investigating either the bone behavior or the effects of the locking plate configuration (Table 1); in any case, the interaction of both is relevant.…”

“…Jabran et al [28] Optimize the proximal humerus locking plate parametric design by determining the orientation of the inferomedial ORIF locking plate screws.…”

“…The 3-part fracture (AO/OTA 11B1.1) mostly involves the surgical neck and greater tuberosity. The 2-part fracture (AO/OTA 11A2.1) patterns involving the surgical neck are not as relevant as they once were, but can still be useful for some researchers, considering the simplicity of the fracture pattern; for example, the studies by Jabran et al [28], Zhang et al [5], Dahan et al [3], and Mendoza-Muñoz et al [49]. The 2-part fracture is considered a simple fracture because only one bone segment is displaced from the rest of the bone, and usually the fracture occurs in the surgical neck; on the other hand, even though 3-part fractures commonly involve the surgical neck as well, there are two displaced segments instead of one.…”

“…Nevertheless, discrepancies exist between studies due to the lack of standards for the characterization of the bone model, including in proximal humerus studies. Each researcher uses different bone material properties and natures; for instance, there are studies were the orthotropic nature is preferred for the bone [20,21], while others use the isotropic nature [3,5,[22][23][24][25][26][27][28], even when anisotropy is the actual nature of bone tissues. The research papers also differ in their modeling technique.…”