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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

Upper and anteroposterior view of the five stem geometries. From left to right: RotaMIN, RotaLOW, RotaMED, RotaHIGH and RotaMAX.
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Figure 3: Upper and anteroposterior view of the five stem geometries. From left to right: RotaMIN, RotaLOW, RotaMED, RotaHIGH and RotaMAX.

Mentions: For five stem designs, a FE model of the bone-implant complex was built, that aimed at replicating the simplified assumptions of the analytical model as good as possible. The stems were chosen in such a way that they span a wide range of antirotation values, based on the analytical model. STL-files of the stem geometries were provided by the university hospital orthopaedics department, which allowed calculation of the resistance against axial rotation with the proposed analytical model. Export of stem geometries in STL format was available as a utility within the system software of the IMP system used in the Leuven university hospital. The antirotation values for all five stems are shown in table 1. The names of the stems refer to their mutual ranking, based on the antirotation values; the resistance against rotation increases from left (RotaMIN) to right (RotaMAX) in table 1. The stem geometries are shown in figure 3.


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)

Upper and anteroposterior view of the five stem geometries. From left to right: RotaMIN, RotaLOW, RotaMED, RotaHIGH and RotaMAX.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Upper and anteroposterior view of the five stem geometries. From left to right: RotaMIN, RotaLOW, RotaMED, RotaHIGH and RotaMAX.
Mentions: For five stem designs, a FE model of the bone-implant complex was built, that aimed at replicating the simplified assumptions of the analytical model as good as possible. The stems were chosen in such a way that they span a wide range of antirotation values, based on the analytical model. STL-files of the stem geometries were provided by the university hospital orthopaedics department, which allowed calculation of the resistance against axial rotation with the proposed analytical model. Export of stem geometries in STL format was available as a utility within the system software of the IMP system used in the Leuven university hospital. The antirotation values for all five stems are shown in table 1. The names of the stems refer to their mutual ranking, based on the antirotation values; the resistance against rotation increases from left (RotaMIN) to right (RotaMAX) in table 1. The stem geometries are shown in figure 3.

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