Biomechanical Comparison of Titanium and CFR-PEEK Intramedullary Nails Using Finite Element Analysis

Abstract

This study analyzes the biomechanical performance of intramedullary nails made of titanium alloy (Ti-6Al-4V) and carbon fiber-reinforced polyetheretherketone (CFR-PEEK) for the treatment of proximal femoral fractures, with a focus on their effects under different bone density conditions representing young and osteoporotic bone. Using finite element models and analyses simulating mid-stance gait loading and incorporating muscle forces adjusted for age-related reduction, the load transfer and stress distribution were evaluated, along with the osteogenic index (OI) as a measure of biological stimulus for bone healing. Results showed that titanium nails produced lower bone stresses but caused significant proximal stress shielding, particularly in osteoporotic bone, which could impair healing. In contrast, CFR-PEEK nails exhibited higher and more uniformly distributed stresses along the femoral diaphysis and shifted the osteogenic stimulus into a range promoting more mature bone formation in both young and elderly femora. The composite material’s elastic modulus closer to bone and its orthotropic fiber arrangement contributed to these effects. The study concludes that CFR-PEEK nails offer a promising alternative to titanium by reducing stress shielding and enhancing the biomechanical environment favorable for fracture healing, especially in osteoporotic patients. Future work will include dynamic loading conditions and experimental validation to optimize implant design.

1. Introduction

Hip fracture is the most severe type of bone pathology in elderly people, due to its high rates of morbidity and mortality, and the considerable economic burden it places on patients and healthcare systems [1,2,3]. Current projections suggest that hip fractures could affect up to 6.3 million individuals worldwide by 2050, with 3.25 million cases expected to occur in Asia [4]. Intertrochanteric fractures (ITFs) are among the most common types of hip fracture and are associated with poorer clinical outcomes in terms of mortality and disability. From a surgical standpoint, ITFs are typically treated using intramedullary implants, either on their own or alongside osteosynthesis devices, such as plates [5].

The concept of intramedullary nailing was introduced in the 1930s by Gerhard Küntscher, who developed a V-shaped nail to treat femoral fractures [6,7,8]. This innovation exploited the medullary canal to provide internal stabilization, reducing the need for prolonged immobilization in a cast and allowing for earlier mobilization. Over the following decades, improvements in design and materials were introduced, from initial stainless-steel nails to nails with more complex cross-sections (e.g., hourglass and cloverleaf shapes) to provide rotational stability in the 1950s. Subsequently, proximal and distal locking was introduced in the 1970s and 1980s, extending the range of applications to unstable fractures [9,10]. Meanwhile, titanium became established due to its biocompatibility and corrosion resistance [11,12,13].

Despite their widespread use, metallic nails present limitations related to their high axial stiffness. Metallic implants absorb an excessive portion of the load, thereby reducing the stress transferred to the surrounding bone (stress shielding), which may lead to osteopenia, decreased bone density, and an increased risk of delayed union or loss of fixation [14,15]. For effective healing, the load transmitted to the bone must be sufficient to activate the biological repair responses.

Recent studies emphasize the importance of a favorable mechanical environment in the consolidation process [16,17,18,19]. Controlled axial micromovements have been shown to stimulate callus formation and shorten healing times, confirming the role of moderate compressive stresses in tissue regeneration [20,21,22].

To overcome the limitations of traditional metallic implants, research has explored composite materials and novel implant design strategies [23,24,25]. Examples include porous magnesium-based scaffolds coated with polymers/bioglasses, and devices incorporating hydroxyapatite with shape-memory polymers that allow morphological adaptation and targeted compression [26]. CAD/CAM technologies and 3D printing now enable customized implants that optimize load transfer and bone integration [27,28,29].

In this context, carbon fiber-reinforced polyetheretherketone (CFR-PEEK) has emerged as an alternative to titanium for intramedullary nails. This composite material has an elastic modulus (≈3.5 GPa) closer to that of cortical bone (1–20 GPa) compared to titanium alloys (≈106 GPa), thereby promoting a more physiological load transfer and potentially reducing stress shielding [30,31]. Moreover, its radiolucency and minimal CT/MRI artifacts facilitate postoperative monitoring [32,33,34,35].

Over the past decades, the biomechanical study of fractures and fixation devices has increasingly relied on non-invasive numerical tools [36,37,38,39]. Among these, finite element analysis (FEA) has proven to be effective for assessing stresses and strains at the bone–implant interface [39,40,41]. FEA enables the analysis of realistic 3D models of the fractured segment and the simulation of physiological or critical conditions, which are often difficult to reproduce experimentally. Recent evidence indicates that nails made of PEEK or functionally graded materials can reduce stress shielding and improve stress distribution compared to traditional metals [42,43].

Despite the growing interest in alternatives to titanium, the literature still includes few systematic FEA studies on the behavior of CFR-PEEK intramedullary nails in femoral fractures. Moreover, analyses that link nail material selection to the patient’s bone density remain lacking.

An intertrochanteric fracture (ITF) is closely related to osteoporosis. As people age, reductions in bone mineral density (BMD) and cortical thickness are observed. For example, studies report a decrease of around 14% per decade after the age of 50, which leads to reduced mechanical strength [44]. ITFs may not respond as well to treatment with cortical support if these changes occur. Nevertheless, many numerical simulations use bone parameters derived from younger individuals, which underestimates the deterioration typical of elderly patients. Furthermore, clinical protocols often fail to adequately tailor strategies according to age and bone fragility.

Considering these issues, the present study uses Finite Element Analysis (FEA) to compare two types of intramedullary nail for treating proximal femoral fractures: one made of titanium and the other made of carbon fiber reinforced PEEK (CFR-PEEK). This comparison will be conducted under two different bone density conditions to simulate the effect of osteoporosis on treatment outcomes. The objective is to quantify the influence of the materials’ mechanical properties on stress transferred to the surrounding bone, paying particular attention to the fracture site and the risk of stress shielding.

The results may provide practical insights into implant material selection based on bone density, contributing to strategies that ensure adequate mechanical stability and a more physiological biomechanical environment. This could reduce the risk of delayed healing and long-term complications. Furthermore, FEA-based evidence may guide the development of new-generation devices capable of effectively balancing structural strength with the biological stimulation of bone healing.

2. Materials and Methods

2.1. Modeling

Three-dimensional geometric modeling was initially performed using Autodesk Inventor 2024 (Autodesk Inc., San Francisco, CA, USA) and then exported for processing in the finite element analysis environment. The femur geometry was obtained from the Sawbones database (https://sawbones.com/), while the intramedullary nail was modeled according to technical data available in the literature. The 3D model was processed in Mimics 19.0 software, where an intertrochanteric fracture of type 31-A2, according to the AO/OTA classification, was reproduced (Figure 1). To simulate the displacement of the head–neck segment, a 4 mm gap was introduced [45].

Subsequently, the nail was designed using the CAD software Autodesk Inventor and positioned within the intramedullary canal in accordance with surgical protocols [45,46] (Figure 2).

The intramedullary nail used in this study measured 410 mm in length and 17 mm in diameter. It was equipped with four locking screws: two proximal screws, each measuring 7 mm in diameter and 77 mm in length to ensure rotational stability, and two distal screws, each measuring 7 mm in diameter and 30 mm in length to ensure longitudinal stability.

Two materials were analyzed for the nail: a titanium alloy (Ti-6Al-4V) and CFR-PEEK (see Figure 3). For the CFR-PEEK nail, the fiber arrangement was defined according to the recommendations of Samiezadeh et al. [47]. Laminates composed of 10–20 plies with angular orientations of 0°, ±45° and 90° were considered to achieve an orthotropic and balanced configuration. This arrangement was found to be advantageous as it enables the intramedullary implant to achieve adequate axial flexibility whilst maintaining sufficient stiffness in bending and torsion. This ensures greater fracture stability and promotes the bone healing process. For sizing, adult femoral nails commonly use nominal outer diameters in the 9–12 mm range (cannulated designs), and structural CFR-PEEK laminates typically employ a fiber volume fraction $V_f$ of approximately 55–65%. Where needed for FEA, the longitudinal direction was aligned with the nail axis, and transverse/isotropic resin properties were assigned to the matrix-dominated directions.

2.2. Materials Properties

Bone was modeled as an orthotropic continuum with principal material axes aligned to the femoral anatomy [47,48,49,50]. The longitudinal modulus E33 and Poisson’s ratio ν were assigned as empirical functions of ash density ${\rho }_{ash}$(g/cm³) taken from Cen et al. [48]. Consistently with that work, E33 follows a power-law form:

$$E_{33}=a{{\rho }_{ash}}^b$$

(1)

where $a$ (scale) and $b$ (exponent) are empirical coefficients calibrated against experimental and virtual testing data of proximal femoral bone. Specifically, (a) defines the overall stiffness level at a reference density, while (b) controls the sensitivity of stiffness to variations in mineralization. In addition, following quantitative computed tomography (QCT) data reported in the literature for both young and elderly patients [51,52,53], the elastic constants of cortical and trabecular bone (E11, E22, E33, G12, G13, G23) were expressed as functions of ash density (g/cm³) according to Cen et al. [48] (

Table 1. Mechanical properties of cortical and trabecular bone of the femur.

Materials	Young Modulus [GPa]			Shear Modulus [GPa]			Poisson’s Ratio
	${\mathit{E}}_{11}$	${\mathit{E}}_{22}$	${\mathit{E}}_{33}$	${\mathit{G}}_{12}$	${\mathit{G}}_{13}$	${\mathit{G}}_{23}$	${\mathit{\nu }}_{12}$	${\mathit{\nu }}_{13}$	${\mathit{\nu }}_{23}$
Cortical bone	$0.57\ast E_{33}$	$0.57\ast E_{33}$	$10500{{\rho }_{ash}}^{2.29}$	$0.29\ast E_{33}$	$0.2\ast E_{33}$	$0.2\ast E_{33}$	0.37	0.3	0.3
Trabecular bone	$E_{33}\times {0.47 {\rho }_{ash}}^{0.12}$	$E_{33}\times {0.76 {\rho }_{ash}}^{0.09}$	$10500{{\rho }_{ash}}^{2.29}$	$E_{33}\times {0.26 {\rho }_{ash}}^{0.24}$	$E_{33}\times {0.45 {\rho }_{ash}}^{0.18}$	$E_{33}\times {0.29{\rho }_{ash}}^{0.17}$	$0.27{{\rho }_{ash}}^{-0.09}$	$0.14{\rho }_{ash}$	$0.14{{\rho }_{ash}}^{-0.07}$

).

Within this framework, reductions in ${\rho }_{ash}$ result in lower E33 (softer longitudinal response), higher strains for a given load, and modified implant–bone stress sharing, which directly impact stress shielding and osteogenic stimulus predictions.

To simulate the effects of aging on bone density, two values of ${\rho }_{ash}$ were considered: 0.956 g/cm³ for a healthy patient and 0.82 g/cm³ for an elderly patient [54]. Ti-6Al-4V was modeled as an isotropic material, while CFR-PEEK, being a composite, was modeled as an orthotropic material (

Table 2. Mechanical properties of nail materials.

Materials	Young Modulus [GPa]			Shear Modulus [GPa]			Poisson’s Ratio
	${\mathit{E}}_{11}$	${\mathit{E}}_{22}$	${\mathit{E}}_{33}$	${\mathit{G}}_{12}$	${\mathit{G}}_{13}$	${\mathit{G}}_{23}$	${\mathit{\nu }}_{12}$	${\mathit{\nu }}_{13}$	${\mathit{\nu }}_{23}$
CFR-PEEK	18	18	3.6	4.8	4.8	3.0	0.30	0.30	0.30
Ti-6Al-4V	110	110	110	41.2	41.2	41.2	0.34	0.34	0.34

) [55,56,57,58]. The intramedullary nails in CFR-PEEK were designed according to the fiber configuration (0°, ±45°, 90°) reported in [56]. However, the explicit modeling of individual fiber orientations within the finite element framework is not computationally feasible. Therefore, a homogenization strategy was adopted, representing the composite as an equivalent orthotropic material whose elastic properties reproduce the macroscopic behavior of the CFR-PEEK laminate. This simplification preserves the anisotropy and stiffness characteristics of the composite while avoiding the high computational cost of ply-by-ply or fiber-level modeling, in line with common practices in biomechanical simulations.

2.3. FEA Modeling

The assembled CAD model was imported into ANSYS Workbench R2023 to generate a finite element (FE) model. For geometric discretization, tetrahedral SOLID 187 elements were employed, as they are particularly suitable for modeling complex geometries and simulating three-dimensional structural behavior [59].

To optimize the balance between computational accuracy and processing time, a mesh size of 1 mm was assigned to the intramedullary nail and locking screws, while a coarser size of 2 mm was applied to the femur. This was in accordance with the findings of Toksoy et al. [60], who demonstrated that finer discretization of the implants and coarser discretization of the bone ensures reliable results while reducing computational cost. Additionally, a mesh convergence analysis was performed using the ‘relevance’ option in ANSYS. This confirmed that a 2 mm element size provided sufficient convergence, with deformation variations below 1% when the mesh was refined further (Figure 4).

The loading conditions applied to the finite element (FE) models of the femoral neck were carefully defined to simulate the mid-stance phase of gait under single-limb support [61]. Muscle forces were considered, including the three main groups of muscles: the abductors, the vastus lateralis and the iliopsoas, as well as the hip joint contact force. These muscle forces were modulated according to age, with a 40% reduction assumed for elderly subjects compared to younger ones. This is consistent with the loss of muscle mass and strength associated with aging [61,62,63].

The model accounted for the main joint and muscle forces, namely the joint reaction force (JRF), the abductor force (F_abd), the iliopsoas force (F_lp), and the vastus lateralis force (F_vl) [64]. The numerical values of forces used for young and elderly subjects are summarized in

Table 3. Forces acting on Hip Joint.

Force	Young (N)	Elderly (N)
JRF (Joint Reaction Force)	1170	1100
Fabd (Abductors)	300	180
Flp (Iliopsoas)	188	112.8
Fvl (Vastus lateralis)	292	175.2

.

Boundary conditions included nonlinear frictionless contact between the intramedullary nail and the endosteal canal; bonded contact at screw–bone interfaces; and a fully constrained distal femur (Figure 5). All contacts were implemented as surface-to-surface using the Augmented Lagrange formulation with program-controlled normal stiffness; separation was permitted at frictionless interfaces. Simulations were performed under quasi-static conditions with geometric/contact nonlinearity and automatic substepping.

The intramedullary nail–endosteal canal interface was modeled as nonlinear frictionless contact to represent the early postoperative, reamed canal condition with limited tangential load transfer, where construct stability is primarily provided by the locking screws.

2.4. Evaluation of the Osteogenic Response of Callus Based on Stress

To evaluate the osteogenic response of the bone callus, the principal stresses (r₁, r₂, r₃) obtained at each callus node from the finite element analysis were considered. In accordance with the study conducted by Carter et al. [65], once the principal stresses are known, the octahedral shear stress (S) can be calculated as:

$$S={\displaystyle \frac{1}{3}}\sqrt{{\left(r_1-r_2\right)}^2+{\left(r_2-r_3\right)}^2+{\left(r_3-r_1\right)}^2}$$

(2)

Subsequently, the dilatational stress (D) can be evaluated as:

$$D={\displaystyle \frac{1}{3}}\left(r_1+r_2+r_3\right)$$

(3)

These parameters are used to calculate the osteogenic stimulus index (I):

$$I=R_n\left(S+kD\right)$$

(4)

where k is an empirical parameter modulating the influence of dilatational stress and R_n represents the number of loading cycles. Both parameters were set to 1 since excessively high k values (e.g., 2.0) may overestimate the inhibitory effect of dilatational pressure, as observed in the study conducted by Gardner et al. [66]. R_n = 1 corresponds to the quasi-static load case.

The osteogenic stimulus index (I) condenses the local mechanical environment into a single metric by combining deviatoric and dilatational (hydrostatic) stress components. Higher I values generally reflect a more osteogenic and mechanically stable environment conducive to bone formation, whereas lower values indicate insufficient stimulus.

According to the osteogenic stimulus index (I), the following tissue differentiations in the bone callus can be identified [65]:

I ≈ 5 MPa: strong osteogenic stimulus and robust ossification;

I ≈ 2–5 MPa: formation of maturing bone tissue;

I ≈ 0.5–2 MPa: fibrous and cartilaginous tissues with initial ossification;

I < 0.5 MPa: early stage of soft tissue or regions with impeded ossification.

For the comparative analysis of the biomechanical behavior of the two models (titanium nail vs. CFR-PEEK nail) regarding stress transfer, von Mises equivalent stress was adopted as the main parameter. This criterion is widely used in biomechanical and engineering studies and allows the three-dimensional stress state within a material to be represented by a single scalar value. Furthermore, to facilitate interpretation of the results, the von Mises equivalent stress values were displayed as color maps generated by the FEM analysis. These maps provide an intuitive visualization of stress distribution across the different components of the model, highlighting the most loaded areas through a progressive color scale (from minimum to maximum values).

3. Results

To evaluate the distribution of von Mises stresses within the femur, the intramedullary nail, and along the bone–nail interface, stress data were extracted from the finite elements located immediately adjacent to the contact surfaces on both the bone and nail sides. The finite element analyses were conducted considering different combinations of nail material (titanium and CFR-PEEK) and bone condition (young and elderly femur).

3.1. Distribution of Von Mises Stresses in the Femur

In a young femur stabilized with a Ti-6Al-4V nail (Figure 6a), von Mises stresses are primarily distributed along the diaphyseal cortex, reaching a maximum value of 46 MPa. In the elderly femur with a titanium nail (Figure 6b), stress increases to a peak of 57 MPa with a marked concentration in the distal region of the femur.

Higher stress values are observed with CFR-PEEK compared to titanium, but they are more evenly distributed between the proximal and distal portions. In the young femur (Figure 6c), maximum stress reaches 75 MPa with a more homogeneous distribution along the diaphysis. In the elderly femur (Figure 6d), stresses increase to 84 MPa with peak values concentrated mainly at the proximal screw holes.

The sectional views illustrate the differences in load transfer. Marked stress shielding is evident with the titanium nail. In the proximal area of the young femur (Figure 6a), for example, bone stress is approximately 5.5 MPa, which is lower than the 22 MPa measured in the nail. In the distal area, the bone stress increases to 37.85 MPa, compared to 43 MPa in the nail. This illustrates the uneven distribution of stress between the proximal and distal areas. This phenomenon is even more pronounced with reduced bone density, such as in an elderly femur (Figure 6b).

With CFR-PEEK, bone stress levels are higher and more widespread, which is compatible with a more physiological mechanical environment and a clear reduction in stress shielding. In both the proximal and distal regions, bone stress tends to exceed nail stress (see Figure 6c,d). However, in the elderly femur (Figure 6d), these levels may exceed the capacity of osteoporotic tissue. Therefore, it is appropriate to modulate or customize the stiffness of the composite according to the quality of the host bone to maintain stress distribution within a safe range for tissue health.

3.2. Distribution of Von Mises Stresses in the Intramedullary Nail

Figure 7a–d illustrates the von Mises stress distribution in the nails across the four analyzed configurations.

In the titanium nail model with a young femur (Figure 7a), peak stress reached approximately 77 MPa, concentrated around the transverse holes for the locking screws. In the elderly femur (Figure 7b), maximum stress increased to 84 MPa, with a wider distribution along the nail due to the reduced mechanical support of the bone.

In the case of CFR-PEEK, stress levels were higher than for titanium but more evenly distributed along the nail’s length. The highest values remained localized around the proximal holes, reaching 115 MPa in the young femur and 131 MPa in the elderly one. This behavior results from the closer elastic modulus of CFR-PEEK to that of bone, which promotes a more balanced load transfer at the bone–implant interface, mitigates stress shielding, and ensures effective mechanical stimulation of the surrounding bone tissue without compromising implant integrity.

3.3. Evaluation of the Osteogenic Stimulus Index

Figure 8 presents a top (axial) sectional view of the proximal femur–nail assembly, centered on the proximal locking holes and screws and oriented along the femoral axis to depict load transfer and stress distribution in the most critical region for construct stability and fracture healing. Within this fracture section, the osteogenic index (OI) shows clear differences between materials and age groups, consistent with Carter’s thresholds [65].

For model A (Ti-6Al-4V nail), the average OI value is 1.8 MPa for young femur and 1.6 MPa for elderly femur. Both values fall within the 0.5–2 MPa range, which is indicative of initial ossification (i.e., prevalence of fibrous or cartilaginous tissue).

For the CFR-PEEK nail, an average OI of 2.7 MPa is recorded at the fracture site for a young femur and 3.7 MPa for an elderly femur. These values fall within the 2–5 MPa range, which indicates maturing bone formation.

Therefore, based on these results, CFR-PEEK provides a higher OI than titanium at the same age, shifting the stimulus from the “initial” range (0.5–2 MPa) to the maturation window (2–5 MPa). With titanium, age reduces OI (A→B), while with CFR-PEEK, OI increases (C→D). This suggests that the composite material has a greater ability to maintain or increase the stimulus, even in osteoporotic bone.

4. Discussion

Femoral fractures are commonly treated with intramedullary nails or adjunct osteosynthesis devices [67,68,69]. The implant’s material and geometry are critical design variables, as they govern load transfer, construct stability, and the mechanobiological stimulus required for timely healing [70]. Recently, alternatives to conventional metals (e.g., Ti-6Al-4V) such as carbon fiber-reinforced PEEK (CFR-PEEK) and functionally graded materials with tailored stiffness have garnered increasing interest [71]. These options aim to reduce the bone–implant stiffness mismatch, limit stress shielding, and where radiolucent improve radiographic assessment [72]. In a prospective study, Takashima et al. [73] evaluated a CFR-PEEK intramedullary nail for proximal femoral fractures: among 20 patients, 95% achieved union at a mean of 3.7 months, with no significant complications and no reoperations.

Consistently, Sacchetti et al. [74] showed that the radiolucency of CFR-PEEK allows for a more objective evaluation of the callus, with higher inter-observer reliability and without an increase in complications.

The present finite element analyses (FEA) study compared Ti-6Al-4V and carbon-fiber-reinforced PEEK (CFR-PEEK) intramedullary nails implanted in femoral models representing young and elderly/osteoporotic bone. Two principal findings emerged: (1) with the titanium nail, the femur experienced lower overall stresses but exhibited marked proximal stress shielding; and (2) with the CFR-PEEK nail, femoral stresses were higher and more uniformly distributed along the diaphysis. Regarding healing potential, the osteogenic index (OI) showed that titanium concentrated the mechanical stimulus within the 0.5–2 MPa range (early ossification), whereas CFR-PEEK shifted the stimulus toward 2–5 MPa (maturing bone) in both bone phenotypes. Overall, a nail with lower stiffness than titanium and mechanical properties closer to bone promotes greater load transfer to the surrounding bone, in agreement with prior literature.

Similarly, Samiezadeh et al. [75] showed that a hybrid composite nail produced controlled increases in stresses at the fracture site and reduced stress shielding at equivalent fragment stability. In terms of durability, Samiezadeh et al. [76] documented for a carbon/epoxy composite nail a high-cycle fatigue strength of approximately 70% of UTS (HCFS ≈ 70% UTS) with no modulus degradation (≈42 GPa), supporting the composite’s performance under repeated loading. Likewise, Steinberg et al. [77] found that CF-PEEK nails/plates offer stiffness and fatigue resistance comparable to metallic devices, with lower debris generation at metal–polymer interfaces.

Along the same line of time-modulated stress shielding, the absorbable-sheath nail concept tested via FE by Dong et al. [78] proposes a programmed transition of construct stiffness, with potential benefits across different healing phases.

A seemingly discrepant point relative to some FEM studies that model (C)PEEK as isotropic regards stresses within the nail: in those works [31,79], PEEK nail stresses are sometimes lower than in metals, whereas in our study—where CFR-PEEK was modeled as orthotropic peak stresses in the nail were higher (115–131 MPa). This difference can be explained by material assumptions (isotropic PEEK vs. laminated orthotropic CFR-PEEK), local geometric factors (proximal holes, screw layout), and boundary conditions. Even so, our peak values remain well below the fatigue limits reported for composite nails [80].

Limitations

This study has several limitations. Analyses were conducted under a quasi-static mid-stance load case with simplified, age-adjusted boundary conditions; dynamic effects, subject-specific muscle and ligament forces, and fatigue life were not considered. Bone–implant interfaces were idealized as fully bonded, precluding micromotion and contact-mediated stress redistribution. Bone properties were assigned via ash-density relations at two representative density classes (young vs. elderly) without extended sensitivity analysis or QCT-based continuous mapping. No experimental validation was performed, and only a single CFR-PEEK configuration was examined. Future work will incorporate subject-specific gait cycles, variable-amplitude cyclic/fatigue simulations with S–N-based cumulative damage, experimental validation, sensitivity analysis on OI model parameters, and optimization of CFR-PEEK lay-ups and graded stiffness to reduce peak nail stresses while maintaining an osteogenic index within the 2–5 MPa window.

5. Conclusions

This biomechanical study demonstrated that the material choice for intramedullary nails significantly affects stress distribution and the biological stimulus for bone healing in proximal femoral fractures. Finite element analysis results showed that CFR-PEEK nails, with an elastic modulus closer to that of cortical bone compared to titanium, promote more uniform load transfer and higher osteogenic stimulus in both young and osteoporotic bone. Conversely, titanium nails, while offering greater stiffness, lead to pronounced stress shielding especially in the proximal femur, which may impair the biological response necessary for healing. Moreover, the radiolucency of CFR-PEEK facilitates postoperative imaging by minimizing artifacts, improving fracture monitoring. These findings support the use of composite materials such as CFR-PEEK in the design of innovative intramedullary implants that outperform traditional metallic devices, particularly in elderly patients with decreased bone density. In conclusion, using CFR-PEEK nails presents a promising strategy to enhance clinical outcomes in hip fractures, combining adequate mechanical stability with optimized biological stimulation to accelerate and improve the healing process.