Finite element analysis of the cervico-trochanteric stemless femoral prosthesis

doi:10.1016/S0268-0033(03)00085-8

Clinical Biomechanics

Volume 18, Issue 6, July 2003, Pages S53-S58

https://doi.org/10.1016/S0268-0033(03)00085-8 Get rights and content

Abstract

Objective. To investigate the biomechanical performance of a newly designed cervico-trochanteric stemless prosthesis by comparing the stress distribution with that of the traditional stem-type porous-coated anatomic prosthesis.

Design. Three-dimensional finite element models were created for the intact femur, cervico-trochanteric implanted femur and porous-coated anatomic implanted femur. The stress distributions on the femur and the implant were compared. The effects of using two or three screws fixation for the cervico-trochanteric implanted femur were also investigated.

Background. Local bone loss after implantation of traditional stem-type prostheses remains an unsolved problem during the long-term application of total hip replacement. The stress shielding effect and osteolysis were thought to be the two main factors that result in local bone loss after prosthesis implantation. In order to eliminate the mechanical and the biological causes of bone loss after total hip arthroplasty, a newly designed stemless femoral prosthesis was investigated.

Methods. Three-dimensional finite element models were created for the intact, cervico-trochanteric (with two or three fixation screws), and porous-coated anatomic implanted femora with the geometry of a standardized composite femur. Analysis was performed for a loading condition simulating the single-legged stance. The von Mises stress distributions of each model were analyzed and compared.

Results. The results can be summarized as follows: (1) Von Mises stress in the proximal, medial femur for the cervico-trochanteric implanted model was higher than that of the intact model and the porous-coated anatomic implanted model; (2) stress-shielding effect of the cervico-trochanteric models (with two or three fixation screws) were eliminated as compared with the porous-coated anatomic model; (3) no obvious difference in von Mises stress distribution for the cervico-trochanteric implanted model with two or three fixation screws.

Conclusions. The cervico-trochanteric femoral prosthesis may reduce the stress-shielding effect of the proximal femur and achieve a more physiological stress distribution on the proximal femur than that of the porous-coated anatomic prosthesis.
Relevance

The new concept of cervico-trochanteric stemless prosthesis has proven to possess several advantages based on the current results, and may be an alternative for traditional stem-type prostheses in future clinical applications.

Introduction

Since the introduction of Charnley hip prosthesis in the early 1960s, total hip arthroplasty (THA) has proven to be a successful surgical procedure due to the improvements of prosthetic design, biomaterials and surgical technique (Harris, 1984; Callaghan, 1992). However, there is still a great concern of bone loss associated with stress shielding and osteolysis (Kroger et al., 1997; McCarthy et al., 1991; Chao and Coventry, 1981). Stress shielding is a mechanical cause of bone loss and is characterized by adaptive remodeling changes in the proximal femoral cortical bone following stem implantation (Marchetti et al., 1996; Lewis et al., 1984; Engh and Bobyn, 1988). The proposed mechanism of stress shielding is based on Wolff’s law of remodeling. The redistribution of stress results in a decrease in the bone mineral density around the proximal femur, which may influence the longevity of the prosthesis. Osteolysis is another cause of bone loss following THA. This biological process of periprosthetic bone resorption is associated with the generation of particulate debris, especially the polyethylene wear particles (Shih et al., 1994; Murray and Rushton, 1992). To eliminate these two well-known complications of THA, the surface replacement arthroplasty was once widely used in the 1980s (Trentani and Vaccarino, 1981; Head, 1981; Bassett et al., 1982; Buechel et al., 1994; Herbeterts et al., 1983). However, it was proved a failure in design because of significant interface stress concentration (Huiskes et al., 1985). New types of stemless prostheses were designed in the 1990s to solve the clinical problems of stress shielding and osteolysis with reduced interface stress that ensures secure fixation (Munting and Verhelpen, 1995; Shih et al., 1997).

In the current study, we used the finite element method to investigate the biomechanical performance of a newly designed cervico-trochanteric (C-T) stemless prosthesis. Three-dimensional finite element models (FEMs) were created for the intact femur, C-T implanted femur, and the traditional stem-type porous-coated anatomic (PCA) implanted femur. The stress distributions on the femur were analyzed and compared among each models. The effects of using two or three fixation screws on the C-T prosthesis were also investigated.

Section snippets

Methods

The newly designed C-T femoral prosthesis and the fixation screws were made of Titanium and are shown in Fig. 1. The three holes are made with inner threads for initial locking after fastening of the screws. The traditional PCA femoral prosthesis (Howmedica, Rutherford, NJ, USA) used in this investigation is a stem-type design made of cobalt–chrome (Co–Cr) alloy. The femora used for the current study were commercially available synthetic products (Pacific Research Laboratory Inc., Vashon

Results

The von Mises equivalent stress distributions on the medial side for each of the femoral models: intact femur, C-T (with two screws) implanted femur, C-T (with three screws) implanted femur, and the PCA implanted femur were obtained from the analyses and shown in Fig. 4 with gray-scale fringes. As shown in Fig. 4, there was a local high stress on the region of the proximal femur adjacent to the distal edge of the C-T prosthesis. This was caused by the stress-concentration effect near the edge

Discussion

The finite element method has become a useful tool in analyzing the stresses in structures of complex shapes, loading and material behavior. Numerous applications in orthopedics have been presented and proven to be a successful tool in predicting the mechanical characteristics of skeletal parts in interesting circumstances (Cody et al., 1999; Testi et al., 1999). The convergence of FEM model plays an important role on the reliability of the final results, whereas the method used in this study

Conclusions

The present study demonstrates that the stress shielding of the C-T implanted femur was significantly eliminated as compared to that of the traditional PCA implanted femur. Moreover, the C-T prosthesis possesses the following features, and might be an alternative for traditional stem-type prostheses for clinical application after future clinical trials: (1) prevention of the stress-shielding effect (decrease bone atrophy); (2) prevention of endosteal osteolysis; (3) preservation of bone stock

Acknowledgments

This study was supported by the grant from the National Science Council of the Republic of China (grant no. NSC-89-2320-B-033-001-M08). The computing facilities provided by the National Center for High-Performance Computing are greatly appreciated.

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Finite element analysis of the cervico-trochanteric stemless femoral prosthesis

Abstract

Introduction

Section snippets

Methods

Results

Discussion

Conclusions

Acknowledgments

J. Biomech.

J. Biomech.

J. Biomech.

J. Biomech.

Clin. Biomech.

Comput. Meth. Prog. Bio.

Radiology of failed surface replacement total hip arthroplasty

Am. J. Roentgenol.

Osteolysis around uncemented acetabular components of cobalt–chrome surface replacement hip arthroplasty

Clin. Orthop. Relat. R

Total hip arthroplasty: clinical perspective

Clin. Orthop. Relat. R

Fracture of femoral component after total hip replacement. An analysis of 58 cases

J. Bone Joint Surg. Am.

The influence of stem size and extent of porous coating on femoral bone resorption after primary cementless hip arthroplasty

Clin. Orthop. Relat. R

Will stress shielding limit the longevity of cemented femoral components of total hip replacement

Clin. Orthop. Relat. R