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Custom-designed orthopedic implants evaluated using finite element analysis of patient-specific computed tomography data: femoral-component case study.

Harrysson OL, Hosni YA, Nayfeh JF - BMC Musculoskelet Disord (2007)

Bottom Line: The proposed design will customize both the articulating surface and the bone-implant interface to address the most common problems found with conventional knee-implant components.The proposed design shows a more even stress distribution on the bone-implant interface surface, which will reduce the uneven bone remodeling that can lead to premature loosening.The proposed custom femoral component design has the following advantages compared with a conventional femoral component. (i) Since the articulating surface closely mimics the shape of the distal femur, there is no need for resurfacing of the patella or gait change. (ii) Owing to the resulting stress distribution, bone remodeling is even and the risk of premature loosening might be reduced. (iii) Because the bone-implant interface can accommodate anatomical abnormalities at the distal femur, the need for surgical interventions and fitting of filler components is reduced. (iv) Given that the bone-implant interface is customized, about 40% less bone must be removed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Industrial and Systems Engineering, North Carolina State University, Campus Box 7906, Raleigh, USA. harrysson@ncsu.edu

ABSTRACT

Background: Conventional knee and hip implant systems have been in use for many years with good success. However, the custom design of implant components based on patient-specific anatomy has been attempted to overcome existing shortcomings of current designs. The longevity of cementless implant components is highly dependent on the initial fit between the bone surface and the implant. The bone-implant interface design has historically been limited by the surgical tools and cutting guides available; and the cost of fabricating custom-designed implant components has been prohibitive.

Methods: This paper describes an approach where the custom design is based on a Computed Tomography scan of the patient's joint. The proposed design will customize both the articulating surface and the bone-implant interface to address the most common problems found with conventional knee-implant components. Finite Element Analysis is used to evaluate and compare the proposed design of a custom femoral component with a conventional design.

Results: The proposed design shows a more even stress distribution on the bone-implant interface surface, which will reduce the uneven bone remodeling that can lead to premature loosening.

Conclusion: The proposed custom femoral component design has the following advantages compared with a conventional femoral component. (i) Since the articulating surface closely mimics the shape of the distal femur, there is no need for resurfacing of the patella or gait change. (ii) Owing to the resulting stress distribution, bone remodeling is even and the risk of premature loosening might be reduced. (iii) Because the bone-implant interface can accommodate anatomical abnormalities at the distal femur, the need for surgical interventions and fitting of filler components is reduced. (iv) Given that the bone-implant interface is customized, about 40% less bone must be removed. The primary disadvantages are the time and cost required for the design and the possible need for a surgical robot to perform the bone resection. Some of these disadvantages may be eliminated by the use of rapid prototyping technologies, especially the use of Electron Beam Melting technology for quick and economical fabrication of custom implant components.

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Comparison of stress distribution on bone surface for conventional and custom implant with loading and reaction force in center location. Maximum stresses are shown in red color at a level above 5 MPa. Green contour stress levels are 2.5 MPa.
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Figure 8: Comparison of stress distribution on bone surface for conventional and custom implant with loading and reaction force in center location. Maximum stresses are shown in red color at a level above 5 MPa. Green contour stress levels are 2.5 MPa.

Mentions: All FEA plots were done at the same stress scale level. All stresses plotted were Von Mises. Figure 8 shows the result of the first load case for both the conventional and custom implant design (center position). Both bones were loaded identically according to the specification in the subsection describing the finite element analysis. The conventional bone interface showed stress concentrations along the sharp edges, while the custom implant showed a more uniform stress distribution. The level of the contact surface stresses and the stress distributions for the conventional bone interface were in the same range as previous studies [17,18]. For the conventional implant, the center position stresses were on average 2.17 MPa at the sharp edges; and for the custom implant, the center position stresses were on average 2.53 MPa in the contact regions. The average stresses at the contact edges for the conventional implant were 1.59 MPa and 1.3 MPa for the back and middle positions, respectively.


Custom-designed orthopedic implants evaluated using finite element analysis of patient-specific computed tomography data: femoral-component case study.

Harrysson OL, Hosni YA, Nayfeh JF - BMC Musculoskelet Disord (2007)

Comparison of stress distribution on bone surface for conventional and custom implant with loading and reaction force in center location. Maximum stresses are shown in red color at a level above 5 MPa. Green contour stress levels are 2.5 MPa.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2100040&req=5

Figure 8: Comparison of stress distribution on bone surface for conventional and custom implant with loading and reaction force in center location. Maximum stresses are shown in red color at a level above 5 MPa. Green contour stress levels are 2.5 MPa.
Mentions: All FEA plots were done at the same stress scale level. All stresses plotted were Von Mises. Figure 8 shows the result of the first load case for both the conventional and custom implant design (center position). Both bones were loaded identically according to the specification in the subsection describing the finite element analysis. The conventional bone interface showed stress concentrations along the sharp edges, while the custom implant showed a more uniform stress distribution. The level of the contact surface stresses and the stress distributions for the conventional bone interface were in the same range as previous studies [17,18]. For the conventional implant, the center position stresses were on average 2.17 MPa at the sharp edges; and for the custom implant, the center position stresses were on average 2.53 MPa in the contact regions. The average stresses at the contact edges for the conventional implant were 1.59 MPa and 1.3 MPa for the back and middle positions, respectively.

Bottom Line: The proposed design will customize both the articulating surface and the bone-implant interface to address the most common problems found with conventional knee-implant components.The proposed design shows a more even stress distribution on the bone-implant interface surface, which will reduce the uneven bone remodeling that can lead to premature loosening.The proposed custom femoral component design has the following advantages compared with a conventional femoral component. (i) Since the articulating surface closely mimics the shape of the distal femur, there is no need for resurfacing of the patella or gait change. (ii) Owing to the resulting stress distribution, bone remodeling is even and the risk of premature loosening might be reduced. (iii) Because the bone-implant interface can accommodate anatomical abnormalities at the distal femur, the need for surgical interventions and fitting of filler components is reduced. (iv) Given that the bone-implant interface is customized, about 40% less bone must be removed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Industrial and Systems Engineering, North Carolina State University, Campus Box 7906, Raleigh, USA. harrysson@ncsu.edu

ABSTRACT

Background: Conventional knee and hip implant systems have been in use for many years with good success. However, the custom design of implant components based on patient-specific anatomy has been attempted to overcome existing shortcomings of current designs. The longevity of cementless implant components is highly dependent on the initial fit between the bone surface and the implant. The bone-implant interface design has historically been limited by the surgical tools and cutting guides available; and the cost of fabricating custom-designed implant components has been prohibitive.

Methods: This paper describes an approach where the custom design is based on a Computed Tomography scan of the patient's joint. The proposed design will customize both the articulating surface and the bone-implant interface to address the most common problems found with conventional knee-implant components. Finite Element Analysis is used to evaluate and compare the proposed design of a custom femoral component with a conventional design.

Results: The proposed design shows a more even stress distribution on the bone-implant interface surface, which will reduce the uneven bone remodeling that can lead to premature loosening.

Conclusion: The proposed custom femoral component design has the following advantages compared with a conventional femoral component. (i) Since the articulating surface closely mimics the shape of the distal femur, there is no need for resurfacing of the patella or gait change. (ii) Owing to the resulting stress distribution, bone remodeling is even and the risk of premature loosening might be reduced. (iii) Because the bone-implant interface can accommodate anatomical abnormalities at the distal femur, the need for surgical interventions and fitting of filler components is reduced. (iv) Given that the bone-implant interface is customized, about 40% less bone must be removed. The primary disadvantages are the time and cost required for the design and the possible need for a surgical robot to perform the bone resection. Some of these disadvantages may be eliminated by the use of rapid prototyping technologies, especially the use of Electron Beam Melting technology for quick and economical fabrication of custom implant components.

Show MeSH
Related in: MedlinePlus