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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

Contour plots and peak values of the maximum principle stress for the nonstemmed systems. (A) Isometric view. (B) Sectioned view. (C) Maximum principle stress along the central bar, central screw, and locking screw.
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Fig5: Contour plots and peak values of the maximum principle stress for the nonstemmed systems. (A) Isometric view. (B) Sectioned view. (C) Maximum principle stress along the central bar, central screw, and locking screw.

Mentions: The maximum principle stress distribution patterns of the nonstemmed systems are shown in Figure 5. For the fitting system, the concave design of the cup slot makes it the stress raiser (45.1 MPa) compared with the other region (Figure 5A). For the resurfacing system, the central bar serves as the stabilizer for the superimposed cup and bears most of the physiological loads, resulting in high stress concentration at the cup-bar junction (29.2 MPa) (Figure 5B). Both hip compression and muscular contraction were transferred to the fitting cup through the central screw and taper, thus leading to stress concentration at the cup-taper junction (40.0 MPa). For the fitting cup, one of the stabilizing mechanisms is the locking screw. Consequently, stress is mostly concentrated at the cup/locking screw junctions (47.2 MPa). The intersecting hole of the central screw also makes it the stress-concentrated site (33.2 MPa). The stress distribution along the central bar was the bell-shaped pattern with the peak value at the middle region (Figure 5C).Figure 5


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)

Contour plots and peak values of the maximum principle stress for the nonstemmed systems. (A) Isometric view. (B) Sectioned view. (C) Maximum principle stress along the central bar, central screw, and locking screw.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig5: Contour plots and peak values of the maximum principle stress for the nonstemmed systems. (A) Isometric view. (B) Sectioned view. (C) Maximum principle stress along the central bar, central screw, and locking screw.
Mentions: The maximum principle stress distribution patterns of the nonstemmed systems are shown in Figure 5. For the fitting system, the concave design of the cup slot makes it the stress raiser (45.1 MPa) compared with the other region (Figure 5A). For the resurfacing system, the central bar serves as the stabilizer for the superimposed cup and bears most of the physiological loads, resulting in high stress concentration at the cup-bar junction (29.2 MPa) (Figure 5B). Both hip compression and muscular contraction were transferred to the fitting cup through the central screw and taper, thus leading to stress concentration at the cup-taper junction (40.0 MPa). For the fitting cup, one of the stabilizing mechanisms is the locking screw. Consequently, stress is mostly concentrated at the cup/locking screw junctions (47.2 MPa). The intersecting hole of the central screw also makes it the stress-concentrated site (33.2 MPa). The stress distribution along the central bar was the bell-shaped pattern with the peak value at the middle region (Figure 5C).Figure 5

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