Study on the Influence of Prosthetic Materials on Femoral Stress in Surface Hip Arthroplasty
Release time:
2026-01-23
0 Introduction
Pioneering designs for hip arthroplasty emerged as early as the 1940s, but the first prosthetic device featuring two identical implants for the femoral head and acetabulum appeared in the early 1970s [1]. However, early hip resurfacing procedures demonstrated shorter prosthesis longevity compared to total hip arthroplasty. In the early 1990s, McMinn et al. [2] in the UK and Wagner et al. [3] in Germany pioneered the use of cobalt-chromium acetabular components for hip resurfacing, followed shortly thereafter by Amstutz et al. [4] in the US. Short-term clinical reports, coupled with laboratory simulations validating ultrahigh molecular weight polyethylene (UHMWPE) as a replacement for metal acetabular cups, propelled the rapid global adoption of hip resurfacing in the early 21st century. Representative surface hip prostheses currently used in hip resurfacing surgery include the Comet-2000 and Birmingham prostheses from Corin (UK) and the ConservePlus hybrid prosthesis from Stryker (USA). Their common features include bearing surfaces made of high-carbon cobalt-chromium alloy, biologically fixed acetabular components, and cemented femoral components [5].
In recent years, rising living standards and an aging population have driven rapid growth in joint replacement procedures. Surface hip arthroplasty—involving removal of damaged hip surfaces and implantation of a surface prosthesis—maximizes preservation of hip bone structure and function. Consequently, it represents a favorable treatment option for middle-aged and young patients with femoral head necrosis or end-stage osteoarthritis [6].
With ongoing advancements in materials science and biomechanics, artificial hip development has matured significantly. Substantial progress has been made in prosthesis material selection, design manufacturing, and surgical implantation techniques. Research indicates [7] that different materials exhibit varying degrees of stress shielding effects, and hip prostheses made from low-modulus materials can effectively reduce stress shielding. Among these, zirconium-niobium alloys rank among the most favored materials in biomedical applications due to their excellent biocompatibility, corrosion resistance, high strength, and superior wear resistance after high-temperature oxidation [8]. They have been applied in manufacturing femoral condyle prostheses for knee arthroplasty and femoral head prostheses for total hip arthroplasty. Regarding fixation methods, cemented prostheses secure the femoral component to bone using specialized bone cement, significantly enhancing postoperative stability. Cementless prostheses primarily rely on osteoblast ingrowth into sintered pores or the rough surface of the prosthesis to achieve natural fixation and optimal therapeutic outcomes. Both cemented and cementless prostheses induce stress shielding at the proximal femur, leading to reduced bone mineral density and resorption around the implant [9].
Finite element analysis can determine internal femoral stresses and simulate various structures, enabling investigation of how different materials and fixation methods affect the femur. This study employed finite element analysis to compare a cementless zirconium-niobium alloy femoral prosthesis featuring a 3D-printed porous structure with a conventional cemented cobalt-chromium alloy femoral prosthesis of identical design. It analyzed stress transfer in the proximal femur before and after prosthesis implantation to evaluate the stress shielding mitigation capability of the porous zirconium-niobium alloy prosthesis. This novel surface hip prosthesis was fabricated by casting a zirconium-niobium alloy model. The designed model data was then input into a computer-controlled metal 3D printing device. Utilizing a high-energy beam, medical alloy powder within the forming equipment was scanned layer by layer and melted at high temperatures. Following the shape of the surface hip prosthesis model, the material was fused and deposited on the surface contacting the femur. The resulting prosthesis exhibits a trabecular porous structure on its inner surface [10].
1 Materials and Methods
1.1 Model Construction
Femur images were obtained from an adult male with no history of injury or disease. CT scan data were imported into Mimics software for reverse modeling. Appropriate gray values were selected to distinguish bone from surrounding tissues, constructing the initial three-dimensional femur model. The femur model was optimized in Geomagic Wrap software to obtain three-dimensional models of both cortical and cancellous bone. Using SolidWorks software, the models were solidified. Through Boolean operations, the cortical and cancellous bone structures were combined to reconstruct a complete femur model, as shown in Figure 1.
Based on the commonly used surface hip prosthesis model in current surgery, the femoral head prosthesis utilizes zirconium-niobium alloy material. Its outer surface undergoes oxidation treatment to form a metal-ceramic material, while the surface contacting the femur features a trabecular porous structure achieved through 3D printing. The prosthesis is implanted using a cementless press-fit technique. The constructed prosthesis model features a stem length of 50 mm and a diameter of 6 mm, as shown in Figure 2. This model analyzes the stress levels in the surrounding femur after implantation and loading of the zirconium-niobium alloy femoral prosthesis, comparing it with a standard cemented cobalt-chromium alloy prosthesis of identical design as a control. Given that cobalt-chromium alloy is harder than zirconium-niobium alloy, with elastic moduli of 230 and 97 GPa respectively [11], it can be hypothesized that the zirconium-niobium alloy prosthesis transfers more load to the femur. Consequently, femoral stress is higher than with the cobalt-chromium alloy prosthesis.
Using SolidWorks software, the prosthesis was implanted according to [12]. The STEP-format surface hip replacement prosthesis was assembled with the aforementioned complete femur model, yielding the simplified hip surface replacement model shown in Figure 3.
1.2 Material Properties
The assembled model was imported into ABAQUS software for simulation. Different elastic moduli and Poisson's ratios were assigned to cortical and cancellous bone [13], as detailed in Table 1.
The elastic modulus of the trabecular structure in the zirconium-niobium alloy prosthesis is 1380 MPa, with a Poisson's ratio of 0.33. These properties were obtained from experiments on porous titanium alloy specimens with 80% porosity prepared using an electron beam melting (EBM) machine [14]. The cobalt-chromium alloy prosthesis is fixed to the bone by coating the resected femoral surface with a 1.5 mm thick layer of bone cement. The bone cement material used is polymethyl methacrylate (PMMA) [15].
For the implant model, complete integration at the implant-bone, implant-cement, and cement-bone interfaces was assumed to simulate full osseointegration and cement fixation.
1.3 Boundary Conditions and Load Configuration
To better simulate the human standing posture, the model was sectioned along the femoral shaft cross-section at the lower edge of the small rotor, yielding a proximal femur segment. Its lower surface was fully fixed. Simulating a human mass of 70 kg, a 350 N load was applied to both the intact femur and the prosthesis, corresponding to half the gravitational force, as shown in Figure 4.
1.4 Validity Verification
The model was imported into ABAQUS software for simulation. The highest point of the femoral prosthesis was coupled to the underlying surface, with a 350N load applied at the coupling point. Full displacement constraints were applied to the lower surface of the proximal femur. Results showed that stress shielding occurred in various regions of the femur beneath the prosthesis, with stress distributions consistent with those reported in [16]. Additionally, this study identified stress concentration in the cortical bone near the prosthesis edge and stress shielding at the femoral head, consistent with the findings in [17], thereby validating the constructed model.
1.5 Observation Indicators
Through finite element simulation analysis, effective stress contour plots were obtained for two types of surface hip prostheses post-implantation, and the average stress values in the cancellous bone beneath the prosthesis were recorded. To more clearly observe stress distribution in the proximal femur, this region was divided into six zones [18], as shown in Figure 5.
Analysis of stress shielding effects post-implantation based on average femoral stress values calculated before and after surface hip prosthesis implantation. The magnitude of stress shielding is expressed as the stress shielding ratio, calculated using the following formula:
where η is the stress shielding ratio; σ_(pre) is the bone stress before implantation; σ_(post) is the bone stress after implantation [19].
2 Simulation Results
2.1 Average Femoral Stress
Stress contour plots of the femur and cancellous bone before and after prosthesis implantation are shown in Figures 6 and 7. Since the volume of cortical bone changes before and after prosthesis implantation, following the segmentation method described in Section 1.5, several trabecular bone nodes were selected from each region. The quantitative values of average equivalent stress in each zone of the proximal femoral trabecular bone were calculated (see Table 2) to determine which material's prosthesis imposes greater load on the femur post-implantation and in which zone of the proximal femur the stress shielding effect is most pronounced.
2.2 Stress Shielding Analysis
Using the results from Table 2, the stress shielding rates after implantation of cobalt-chromium alloy and zirconium-niobium alloy prostheses were calculated according to Equation (1). The results are shown in Figure 8.
The normal cortical bone of the femoral head bears higher stress than the cancellous bone. Following total hip arthroplasty, a significant portion of the stress within the femoral head is transferred to the implanted metal prosthesis. Finite element analysis revealed that the stress on the femoral neck cortical bone is greater than that on the cancellous bone beneath the femoral neck and prosthesis. The stress on the cancellous bone beneath the prosthesis is shielded by the prosthesis, resulting in lower stress levels compared to the cancellous bone of the femoral neck.
Compared to cobalt-chromium alloys, zirconium-niobium alloys transfer more load from the prosthesis to the femur. Results show stress shielding rates decreased by 9.0%, 7.7%, 9.7%, 11.5%, 9.2%, and 9.5% in zones 1–6, respectively, with more pronounced stress relief in the inner-lower region of the femoral head.
3 Discussion
The material properties of prosthetic components influence load transfer onto the femur. Under normal conditions, forces that should be transmitted through the bone are instead borne primarily by the implant rather than the post-implantation bone. Implanting prostheses harder than natural bone leads to stress shielding. The elastic modulus of prosthetic materials determines their resistance to external forces. Materials with high elastic modulus concentrate stress more intensely under load, while those with low elastic modulus distribute stress more effectively. However, excessively low elastic modulus in prosthetic materials compromises the integrity of the prosthesis-bone interface, promotes micro-motion at the interface, and increases wear debris generation.
The objective of this study was to compare changes in femoral stress induced by two hip prostheses sharing identical design but differing in material and fixation method. This aimed to validate that implants with lower elastic modulus, such as zirconium-niobium alloys, can generate higher stress in the peri-prosthetic femur compared to cobalt-chromium alloy implants, thereby reducing stress shielding. Simulation results confirmed that the novel cementless, porous zirconium-niobium alloy prosthesis achieves superior stress transfer, effectively mitigating stress shielding and reducing post-operative bone resorption, demonstrating clinical significance.
Ong et al.[20] identified non-physiological stress-strain distributions in the proximal femur following total hip arthroplasty via finite element analysis, particularly demonstrating pronounced stress shielding in the medial-inferior region of the femoral head—consistent with the present findings. Torres Pérez et al. [21] demonstrated that trabecular titanium alloy implants facilitate robust osseointegration and promote load transfer to the underlying bone. Su Zaiquan et al. [22] reported satisfactory outcomes with zirconium-niobium alloy femoral heads in total hip replacements for young and middle-aged patients, effectively reducing the risk of prosthesis loosening and peripheral bone resorption. Yang Deyu et al. [23] conducted a randomized survey of 26 total knee arthroplasty patients. Based on evaluation results, they concluded that zirconium-niobium alloy total knee prostheses are an ideal choice for knee replacement, significantly alleviating pain and reducing prosthesis loosening. The results of this study indicate that compared to cobalt-chromium alloys, zirconium-niobium alloys reduced stress shielding in the medial-inferior region of the femoral head by up to 11.5%. This validates that zirconium-niobium alloys effectively mitigate stress shielding and can decrease periprosthetic bone resorption.
Since stress shielding after prosthesis implantation affects bone growth, previous studies have found that porous joint prostheses exhibit favorable bone ingrowth properties. This study constructed a cementless zirconium-niobium alloy surface hip prosthesis model with a porous structure. Comparing it with a cemented cobalt-chromium alloy prosthesis demonstrated that the porous zirconium-niobium alloy prosthesis mitigates the stress shielding effect following joint replacement. Driven by modern additive manufacturing technologies, incorporating porous structures into orthopedic implants has been shown to significantly reduce implant stiffness. The porous and rough surfaces of implants promote biomechanical bonding, ensuring effective integration between the implant and bone tissue [24]. Research indicates that porous structures with pore sizes between 100–400 μm are optimal for bone implants, as these dimensions facilitate cell penetration, tissue ingrowth, vascularization, and nutrient transport to healing tissues [25].
This study established a proximal femur model for hip resurfacing, treating the femur as a linear elastic material for finite element analysis, yielding reasonably credible results. However, the study has the following limitations: (1) It did not consider how different fixation methods for zirconium-niobium alloy prostheses affect stress shielding mitigation; (2) This study employed static mechanical analysis without accounting for the influence of ligaments, muscles, and other structures in the hip region on the stress state of the femur [26]; (3) The study only simulated the mechanical state during human standing. Further research could simulate the stress state of the hip joint during walking to investigate stress distribution in the proximal femur.
References: Chinese Medical Equipment Journal·Vol.46·No.12·December·2025; Study on the Influence of Prosthetic Materials on Femoral Stress in Surface Hip Arthroplasty;
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