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Effects of stemmed and nonstemmed hip replacement on stress distribution of proximal femur and implant.

Chen CM, Tsai WC, Lin SC, Tseng CS - BMC Musculoskelet Disord (2014)

Bottom Line: The results showed that stress distributions of the two nonstemmed femora are consistently more similar to the intact femur than the stemmed one.The fitting system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress.The reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck, to the diaphysial bone, thus depressing the stress-shielding effect below the neck region.

View Article: PubMed Central - PubMed

Affiliation: Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, No, 43, Sec, 4, Keelung Rd, Taipei 106, Taiwan. orthodent.cax@gmail.com.

ABSTRACT

Background: Despite improvements in shape, material, and coating for hip stem, both stress shielding and aseptic loosening have been the major drawbacks of stemmed hip arthroplasty. Some nonstemmed systems were developed to avoid rasping off the intramedullary canal and evacuating the bone marrow due to stem insertion.

Methods: In this study, the finite-element models of one intact, one stemmed, and two nonstemmed femora with minimal removal of the healthy neck were investigated to evaluate their biomechanical effects. The resurfacing (ball-shaped) and fitting (neck-shaped) systems were respectively selected as the representative of the ready- and custom-made nonstemmed implants. The stress distribution and interface micromotion were selected as the comparison indices.

Results: The results showed that stress distributions of the two nonstemmed femora are consistently more similar to the intact femur than the stemmed one. Around the proximal femur, the stem definitely induces the stress-shielding phenomenon of its counterparts. The fitting system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress. Comparatively, the reamed femoral head provides weaker support to the resurfacing cup causing higher interfacial micromotion.

Conclusions: The reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck, to the diaphysial bone, thus depressing the stress-shielding effect below the neck region. If the hip-cup construct can be definitely stabilized, the nonstemmed design could be an alternative of hip arthroplasty for the younger or the specific patients with the disease limited only to the femoral head.

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Related in: MedlinePlus

Three implant and two interface lines were used to evaluate the differences in the distribution of screw stress and bone-cup micromotion. (A) and (B) Implant lines. (C) and (D) Interface lines.
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Fig2: Three implant and two interface lines were used to evaluate the differences in the distribution of screw stress and bone-cup micromotion. (A) and (B) Implant lines. (C) and (D) Interface lines.

Mentions: The pelvis and femur of a 24-year-old male participant without any hip disease were scanned in vivo using computed tomography (CT). The participant gave his consent to the collection and utilization of CT-scanning images used in the study. The CT-scanning images with 1-mm slice separation were three-dimensionally reconstructed as a proximal femur with triangular surface meshes using the software PhysiGuide, version 2.3.1 (Pou Yuen Technology Co., Ltd, Changhua, Taiwan) [24]. In this study, the pelvis was excluded and only the femur was used (Figure 1A). The femur consists of the cortical shell and cancellous core whose boundaries were defined from the grayscale difference of the CT image outlines (Figure 1B). The femoral model was further transformed into a solid model with smooth and seamless surfaces using the software SolidWorks, version 2011 (SolidWorks Corporation, Concord, MA, USA). The numerical modeling using CT-scanning images is conformed to the article of “free from ethical approval for scientific research” in the firth term of the article 5 on Research Involving Human Subjects Law by Ministry of Health and Welfare in Taiwan. Therefore, this study is exempt from ethical approval.The intact femur was used as the comparison baseline of the stemmed and nonstemmed systems. The stemmed system was the representative of the conventional hip system (Capital™, 3 M Health Care Ltd., Leicestershire, UK) (Figure 1B). The Durom™ resurfacing cup was the first nonstemmed system comprising a ball head and a central bar (Figures 1B and 2A). For the second nonstemmed system, the current author used the participant’s CT images to design the fitting cup having highly intimate contact with the participant’s neck (Figures 1B and 2B). For such a custom-made cup, a central screw was inserted through the anatomical axis of the femoral neck to further stabilize the fitting cup. If necessary, the use of a locking screw can turn the linkage of two screws into a stability-enhancing mechanism for the bone-cup construct. The cup slot was designed to avoid direct compression on the periarticular blood vessels and nerve roots. For the stemmed model, the bone stock above the neck was obliquely removed and the stem was instrumented into the intramedullary canal, same as in traditional stemmed THR. For the resurfacing and fitting systems, the inner cup makes intimate contact with the underlaid bones. For the fitting system, the threads of the central and locking screws were neglected to simplify the numerical analysis.Figure 1


Effects of stemmed and nonstemmed hip replacement on stress distribution of proximal femur and implant.

Chen CM, Tsai WC, Lin SC, Tseng CS - BMC Musculoskelet Disord (2014)

Three implant and two interface lines were used to evaluate the differences in the distribution of screw stress and bone-cup micromotion. (A) and (B) Implant lines. (C) and (D) Interface lines.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4197382&req=5

Fig2: Three implant and two interface lines were used to evaluate the differences in the distribution of screw stress and bone-cup micromotion. (A) and (B) Implant lines. (C) and (D) Interface lines.
Mentions: The pelvis and femur of a 24-year-old male participant without any hip disease were scanned in vivo using computed tomography (CT). The participant gave his consent to the collection and utilization of CT-scanning images used in the study. The CT-scanning images with 1-mm slice separation were three-dimensionally reconstructed as a proximal femur with triangular surface meshes using the software PhysiGuide, version 2.3.1 (Pou Yuen Technology Co., Ltd, Changhua, Taiwan) [24]. In this study, the pelvis was excluded and only the femur was used (Figure 1A). The femur consists of the cortical shell and cancellous core whose boundaries were defined from the grayscale difference of the CT image outlines (Figure 1B). The femoral model was further transformed into a solid model with smooth and seamless surfaces using the software SolidWorks, version 2011 (SolidWorks Corporation, Concord, MA, USA). The numerical modeling using CT-scanning images is conformed to the article of “free from ethical approval for scientific research” in the firth term of the article 5 on Research Involving Human Subjects Law by Ministry of Health and Welfare in Taiwan. Therefore, this study is exempt from ethical approval.The intact femur was used as the comparison baseline of the stemmed and nonstemmed systems. The stemmed system was the representative of the conventional hip system (Capital™, 3 M Health Care Ltd., Leicestershire, UK) (Figure 1B). The Durom™ resurfacing cup was the first nonstemmed system comprising a ball head and a central bar (Figures 1B and 2A). For the second nonstemmed system, the current author used the participant’s CT images to design the fitting cup having highly intimate contact with the participant’s neck (Figures 1B and 2B). For such a custom-made cup, a central screw was inserted through the anatomical axis of the femoral neck to further stabilize the fitting cup. If necessary, the use of a locking screw can turn the linkage of two screws into a stability-enhancing mechanism for the bone-cup construct. The cup slot was designed to avoid direct compression on the periarticular blood vessels and nerve roots. For the stemmed model, the bone stock above the neck was obliquely removed and the stem was instrumented into the intramedullary canal, same as in traditional stemmed THR. For the resurfacing and fitting systems, the inner cup makes intimate contact with the underlaid bones. For the fitting system, the threads of the central and locking screws were neglected to simplify the numerical analysis.Figure 1

Bottom Line: The results showed that stress distributions of the two nonstemmed femora are consistently more similar to the intact femur than the stemmed one.The fitting system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress.The reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck, to the diaphysial bone, thus depressing the stress-shielding effect below the neck region.

View Article: PubMed Central - PubMed

Affiliation: Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, No, 43, Sec, 4, Keelung Rd, Taipei 106, Taiwan. orthodent.cax@gmail.com.

ABSTRACT

Background: Despite improvements in shape, material, and coating for hip stem, both stress shielding and aseptic loosening have been the major drawbacks of stemmed hip arthroplasty. Some nonstemmed systems were developed to avoid rasping off the intramedullary canal and evacuating the bone marrow due to stem insertion.

Methods: In this study, the finite-element models of one intact, one stemmed, and two nonstemmed femora with minimal removal of the healthy neck were investigated to evaluate their biomechanical effects. The resurfacing (ball-shaped) and fitting (neck-shaped) systems were respectively selected as the representative of the ready- and custom-made nonstemmed implants. The stress distribution and interface micromotion were selected as the comparison indices.

Results: The results showed that stress distributions of the two nonstemmed femora are consistently more similar to the intact femur than the stemmed one. Around the proximal femur, the stem definitely induces the stress-shielding phenomenon of its counterparts. The fitting system with the anatomy-shaped cup can make intimate contact with the neck cortex and reduce the bone-cup micromotion and the implant stress. Comparatively, the reamed femoral head provides weaker support to the resurfacing cup causing higher interfacial micromotion.

Conclusions: The reserved femoral neck could act as the load-transferring medium from the acetabular cup, femoral neck, to the diaphysial bone, thus depressing the stress-shielding effect below the neck region. If the hip-cup construct can be definitely stabilized, the nonstemmed design could be an alternative of hip arthroplasty for the younger or the specific patients with the disease limited only to the femoral head.

Show MeSH
Related in: MedlinePlus