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Design process of cementless femoral stem using a nonlinear three dimensional finite element analysis.

Baharuddin MY, Salleh ShH, Zulkifly AH, Lee MH, Noor AM, A Harris AR, Majid NA, Abd Kader AS - BMC Musculoskelet Disord (2014)

Bottom Line: This present study proposed a new design process of the cementless femoral stem using a three dimensional model which provided more information and accurate analysis compared to conventional methods.The results showed better total fit (53.7%) and fill (76.7%) canal, with more load distributed proximally to prevent stress shielding at calcar region.The stem demonstrated lower displacement and micromotion (less than 40 μm) promoting osseointegration between the stem-bone and providing primary fixation stability.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Biomedical Engineering Transportation Research Alliance, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia. hussain@fke.utm.my.

ABSTRACT

Background: Minimal available information concerning hip morphology is the motivation for several researchers to study the difference between Asian and Western populations. Current use of a universal hip stem of variable size is not the best option for all femur types. This present study proposed a new design process of the cementless femoral stem using a three dimensional model which provided more information and accurate analysis compared to conventional methods.

Methods: This complete design cycle began with morphological analysis, followed by femoral stem design, fit and fill analysis, and nonlinear finite element analysis (FEA). Various femur parameters for periosteal and endosteal canal diameters are measured from the osteotomy level to 150 mm below to determine the isthmus position.

Results: The results showed better total fit (53.7%) and fill (76.7%) canal, with more load distributed proximally to prevent stress shielding at calcar region. The stem demonstrated lower displacement and micromotion (less than 40 μm) promoting osseointegration between the stem-bone and providing primary fixation stability.

Conclusion: This new design process could be used as a preclinical assessment tool and will shorten the design cycle by identifying the major steps which must be taken while designing the femoral stem.

Show MeSH
Contour plots of equivalent von Mises stress using stair climbing loading from (a) frontal view, (b) medial view and (c) lateral view.
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Figure 8: Contour plots of equivalent von Mises stress using stair climbing loading from (a) frontal view, (b) medial view and (c) lateral view.

Mentions: The von Mises stress distribution for intact femur using the stair climbing load demonstrated in Figure 8 showed the maximum stress of 108.4 MPa at medial calcar. This study used both types of physiological loading; normal walking and stair climbing. However, the result did not illustrate significant differences. The maximum stress observed was 65.38 MPa at the proximal region and minimum stress was 1.28 x 10-12 MPa at distal region as shown in Figure 9. When the limit was scaled to 600 000 Pa, we found that the stress was normally distributed at metaphyseal region which is essential for stability fixation, and to prevent stress shielding at the proximal level. The safety factor for this newly design stem was computed as 2.45. The comparison between other cementless stems at different cortical bone positions [13,20] showed that our newly designed stem was not inferior to other femoral stems. Our study showed highest stress at medial calcar with 60 MPa which indicated stress shielding did not occur at this region as shown in Figure 9 (c). The micromotion and displacement contour plots were shown in Figures 10 and 11. As these parameters are closely related to the promotion of bone osseointegration, we found that the maximum value for micromotion was 4.76 μm, and a displacement of 1.34 μm. Our study demonstrated the lowest micromotion compared to other femoral stems in physiological loading ranging from 1.5 – 5.0 μm as shown in Figure 10(c). This ensured that osseointegration occurred between the bone – stem interface, and fibrous tissue formation was prevented which reflected the implant’s fixation stability. We also noted the maximum total strain energy density of 1.31 kJ/m3, and contact normal stress of 28.95 MPa.


Design process of cementless femoral stem using a nonlinear three dimensional finite element analysis.

Baharuddin MY, Salleh ShH, Zulkifly AH, Lee MH, Noor AM, A Harris AR, Majid NA, Abd Kader AS - BMC Musculoskelet Disord (2014)

Contour plots of equivalent von Mises stress using stair climbing loading from (a) frontal view, (b) medial view and (c) lateral view.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3924227&req=5

Figure 8: Contour plots of equivalent von Mises stress using stair climbing loading from (a) frontal view, (b) medial view and (c) lateral view.
Mentions: The von Mises stress distribution for intact femur using the stair climbing load demonstrated in Figure 8 showed the maximum stress of 108.4 MPa at medial calcar. This study used both types of physiological loading; normal walking and stair climbing. However, the result did not illustrate significant differences. The maximum stress observed was 65.38 MPa at the proximal region and minimum stress was 1.28 x 10-12 MPa at distal region as shown in Figure 9. When the limit was scaled to 600 000 Pa, we found that the stress was normally distributed at metaphyseal region which is essential for stability fixation, and to prevent stress shielding at the proximal level. The safety factor for this newly design stem was computed as 2.45. The comparison between other cementless stems at different cortical bone positions [13,20] showed that our newly designed stem was not inferior to other femoral stems. Our study showed highest stress at medial calcar with 60 MPa which indicated stress shielding did not occur at this region as shown in Figure 9 (c). The micromotion and displacement contour plots were shown in Figures 10 and 11. As these parameters are closely related to the promotion of bone osseointegration, we found that the maximum value for micromotion was 4.76 μm, and a displacement of 1.34 μm. Our study demonstrated the lowest micromotion compared to other femoral stems in physiological loading ranging from 1.5 – 5.0 μm as shown in Figure 10(c). This ensured that osseointegration occurred between the bone – stem interface, and fibrous tissue formation was prevented which reflected the implant’s fixation stability. We also noted the maximum total strain energy density of 1.31 kJ/m3, and contact normal stress of 28.95 MPa.

Bottom Line: This present study proposed a new design process of the cementless femoral stem using a three dimensional model which provided more information and accurate analysis compared to conventional methods.The results showed better total fit (53.7%) and fill (76.7%) canal, with more load distributed proximally to prevent stress shielding at calcar region.The stem demonstrated lower displacement and micromotion (less than 40 μm) promoting osseointegration between the stem-bone and providing primary fixation stability.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Biomedical Engineering Transportation Research Alliance, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia. hussain@fke.utm.my.

ABSTRACT

Background: Minimal available information concerning hip morphology is the motivation for several researchers to study the difference between Asian and Western populations. Current use of a universal hip stem of variable size is not the best option for all femur types. This present study proposed a new design process of the cementless femoral stem using a three dimensional model which provided more information and accurate analysis compared to conventional methods.

Methods: This complete design cycle began with morphological analysis, followed by femoral stem design, fit and fill analysis, and nonlinear finite element analysis (FEA). Various femur parameters for periosteal and endosteal canal diameters are measured from the osteotomy level to 150 mm below to determine the isthmus position.

Results: The results showed better total fit (53.7%) and fill (76.7%) canal, with more load distributed proximally to prevent stress shielding at calcar region. The stem demonstrated lower displacement and micromotion (less than 40 μm) promoting osseointegration between the stem-bone and providing primary fixation stability.

Conclusion: This new design process could be used as a preclinical assessment tool and will shorten the design cycle by identifying the major steps which must be taken while designing the femoral stem.

Show MeSH