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Assessment of the primary rotational stability of uncemented hip stems using an analytical model: comparison with finite element analyses.

Zeman ME, Sauwen N, Labey L, Mulier M, Van der Perre G, Jaecques SV - J Orthop Surg Res (2008)

Bottom Line: The analytical approach can be considered as a first attempt to theoretically evaluate the primary stability of hip stems without using FEM, which makes it fast and inexpensive compared to other methods.A reasonable agreement was found in the stability ranking of the stems obtained with both methods.Based on the results of this study, the analytical model might be useful as a comparative tool for the assessment of the primary stability of cementless hip stems.

View Article: PubMed Central - HTML - PubMed

Affiliation: Katholieke Universiteit Leuven (K,U,Leuven), Division of Biomechanics and Engineering Design (BMGO), Celestijnenlaan 300C, 3001 Heverlee, Belgium.

ABSTRACT

Background: Sufficient primary stability is a prerequisite for the clinical success of cementless implants. Therefore, it is important to have an estimation of the primary stability that can be achieved with new stem designs in a pre-clinical trial. Fast assessment of the primary stability is also useful in the preoperative planning of total hip replacements, and to an even larger extent in intraoperatively custom-made prosthesis systems, which result in a wide variety of stem geometries.

Methods: An analytical model is proposed to numerically predict the relative primary stability of cementless hip stems. This analytical approach is based upon the principle of virtual work and a straightforward mechanical model. For five custom-made implant designs, the resistance against axial rotation was assessed through the analytical model as well as through finite element modelling (FEM).

Results: The analytical approach can be considered as a first attempt to theoretically evaluate the primary stability of hip stems without using FEM, which makes it fast and inexpensive compared to other methods. A reasonable agreement was found in the stability ranking of the stems obtained with both methods. However, due to the simplifying assumptions underlying the analytical model it predicts very rigid stability behaviour: estimated stem rotation was two to three orders of magnitude smaller, compared with the FEM results.

Conclusion: Based on the results of this study, the analytical model might be useful as a comparative tool for the assessment of the primary stability of cementless hip stems.

No MeSH data available.


Related in: MedlinePlus

Loading on a hip prosthesis. (a) single force  on the head (b) equivalent combination of force  and moment  on the stem. If  is considered as a vector with three components (Rx, Ry, Rz),  would cause torque around the three axes and is represented by double-arrow-headed vector components (Mx, My, Mz). In this study, only Mz was considered.
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Figure 2: Loading on a hip prosthesis. (a) single force on the head (b) equivalent combination of force and moment on the stem. If is considered as a vector with three components (Rx, Ry, Rz), would cause torque around the three axes and is represented by double-arrow-headed vector components (Mx, My, Mz). In this study, only Mz was considered.

Mentions: Figure 2a shows a prosthesis with an external load on the head H. This situation is of course mechanically equivalent to the situation shown in figure 2b, where the moment in point O is due to the pure force on the head H of the prosthesis (in other words: can be deduced from as: ). We will continue with the representation in 2b.


Assessment of the primary rotational stability of uncemented hip stems using an analytical model: comparison with finite element analyses.

Zeman ME, Sauwen N, Labey L, Mulier M, Van der Perre G, Jaecques SV - J Orthop Surg Res (2008)

Loading on a hip prosthesis. (a) single force  on the head (b) equivalent combination of force  and moment  on the stem. If  is considered as a vector with three components (Rx, Ry, Rz),  would cause torque around the three axes and is represented by double-arrow-headed vector components (Mx, My, Mz). In this study, only Mz was considered.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2570665&req=5

Figure 2: Loading on a hip prosthesis. (a) single force on the head (b) equivalent combination of force and moment on the stem. If is considered as a vector with three components (Rx, Ry, Rz), would cause torque around the three axes and is represented by double-arrow-headed vector components (Mx, My, Mz). In this study, only Mz was considered.
Mentions: Figure 2a shows a prosthesis with an external load on the head H. This situation is of course mechanically equivalent to the situation shown in figure 2b, where the moment in point O is due to the pure force on the head H of the prosthesis (in other words: can be deduced from as: ). We will continue with the representation in 2b.

Bottom Line: The analytical approach can be considered as a first attempt to theoretically evaluate the primary stability of hip stems without using FEM, which makes it fast and inexpensive compared to other methods.A reasonable agreement was found in the stability ranking of the stems obtained with both methods.Based on the results of this study, the analytical model might be useful as a comparative tool for the assessment of the primary stability of cementless hip stems.

View Article: PubMed Central - HTML - PubMed

Affiliation: Katholieke Universiteit Leuven (K,U,Leuven), Division of Biomechanics and Engineering Design (BMGO), Celestijnenlaan 300C, 3001 Heverlee, Belgium.

ABSTRACT

Background: Sufficient primary stability is a prerequisite for the clinical success of cementless implants. Therefore, it is important to have an estimation of the primary stability that can be achieved with new stem designs in a pre-clinical trial. Fast assessment of the primary stability is also useful in the preoperative planning of total hip replacements, and to an even larger extent in intraoperatively custom-made prosthesis systems, which result in a wide variety of stem geometries.

Methods: An analytical model is proposed to numerically predict the relative primary stability of cementless hip stems. This analytical approach is based upon the principle of virtual work and a straightforward mechanical model. For five custom-made implant designs, the resistance against axial rotation was assessed through the analytical model as well as through finite element modelling (FEM).

Results: The analytical approach can be considered as a first attempt to theoretically evaluate the primary stability of hip stems without using FEM, which makes it fast and inexpensive compared to other methods. A reasonable agreement was found in the stability ranking of the stems obtained with both methods. However, due to the simplifying assumptions underlying the analytical model it predicts very rigid stability behaviour: estimated stem rotation was two to three orders of magnitude smaller, compared with the FEM results.

Conclusion: Based on the results of this study, the analytical model might be useful as a comparative tool for the assessment of the primary stability of cementless hip stems.

No MeSH data available.


Related in: MedlinePlus