ABSTRACT
BACKGROUND: Greatly higher elastic modulus of traditional metal prosthesis than bone elastic modulus is mechanical factor for aseptic loosening of artificial joint, resulting in stress shielding, bone resorption and bone atrophy.OBJECTIVE: To measure femoral stress after prosthetic replacement made of carbon fiber reinforced poly-ether-ether-ketone (CF/PEEK), and compare with domestic AML prosthesis, so as to explore the application prospect of compound material in total hip femoral head prosthesis. DESIGN, TIME AND SETTING: Comparative analysis was performed at Orthopedics Laboratory, First Hospital of Soochow University and Institute of Biomechanical Engineering of Shanghai University from September 2002 to March 2004.MATERIALS: CF/PEEK prosthesis was designed by the authors, composed of long CF/PEEK compound material as inner layer, 100 Gpa and short CF/PEEK compound material as outer layer, 20 Gpa; the layer intensity at stress center was strengthened, and the appearance and size of the CF/PEEK prosthesis simulated domestic AML cobalt alloy prosthesis (Beijing Huajiehao Company). Five pairs (10 femurs) of femurs were from fresh adult cadavers. METHODS: Five pairs of human cadaveric femora were divided equally into left and right groups: one group received a cobalt-chrome molybdenum alloy (CoCrMo) implant and the other received CF/PEEK implant. Strain-gauge rosettes were attached to external surface of each implant and proximal femora. The loading condition simulated single-limb stance. MAIN OUTCOME MEASURES: strains distribution on the normal femur and femoral surface after replacement with two kinds of prostheses; shearing strain at femur-prosthesis interface of two groups.RESULTS: Following prosthesis implantation, the strains exhibited a progressive proximal-to-distal increase, which was similar to that in the intact femur, and the strain was maximum near the distal prosthesis. The strains on the medial and lateral surface of the femur were reduced after implantation of both types of implants. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of CF/PEEK prosthesis than in the CoCrMo one. CONCLUSION: Mechanical performance of CF/PEEK compound prosthesis is similar to bone tissue, and can provide similar strain under loading condition. Therefore, it can provide immediate postoperative stability and proximal loading transfer.
ABSTRACT
[Objective]To develop a new femoral prosthesis that can integrate with femur compactly and increase proximal femoral stress transfer,and further improves the long-term curative effect of total hip arthroplasty.[Method]Five pairs of human cadaver femora were divided equally into two groups one of which received a cobalt-chrome molybdemum alloy(CoCrMo) implant and the other a carbon fiber reinforced polyetheretherketone composite(CF/PEEK) implant.Six strain-gauge rosettes were attached to the external surface of each implant and proximal femora.The loading conditions simulated single-limb stance and the strains were recorded first with the femora intact and then with the femoral components of two different designs implant inserted.[Result]After the insertion of a femoral component,the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis.On the medial and lateral aspects of the proximal femur,thc strains were reduced after implantation of both types of implant.The pattern and magnitude of the strains,however,were closer to those in the intact femur after insertion of the CF/PEEK stem than that of CoCrMo stem.[Conclusion]Our findings suggest that the CF/PEEK stem can provide immediate postoperative stability,better proximal loading transfer in the metaphysis and further reduce stress shielding,bone resorption and osteanabrosis,thus prevent the implant from failuri.
ABSTRACT
Objective To explore the initial stability of a carbon fiber reinforced polyetheretherketone composite (CF/PEEK) stem in human femurs after total hip replacement. Methods 8 pairs of human cadaveric femurs were used to test the CF/PEEK prosthesis versus a conventional cementless stem of cobalt-chrome molybdemum alloy(CoCrMo). The bone-femoral prosthesis interface motion was measured in vitro using displacement transducers. Combined axial and torsional loads and simulated single-leg stance loading were applied. Subsidence, rotation and interface motion were measured with load cycles up to 1 000 N. Results The extent of the micro-motion in the proximal femoral region was larger than that in the distal femoral region. The CF/PEEK composite prosthesis showed less dynamic micro-motion in the proximal region compared with the CoCrMo alloy prosthesis stem, with the average difference being 42%. The extent of the distal micro-motion in the 2 groups was small but the difference was significant (P