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Research Papers

Primary Stability of Cementless Stem in THA Improved With Reduced Interfacial Gaps

[+] Author and Article Information
Youngbae Park, DonOk Choi

Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Republic of Korea

HoChul Shin

Intelligent Robot Research Division, Electronics and Telecommunications Research Institute, Daejeon, 305-700, Republic of Korea

Carolyne Albert

Department of Materials Engineering, and Department of Orthopaedics, University of British Columbia, 2329 West Mall, Vancouver, BC, V6T 1Z4, Canada

Yong-San Yoon1

Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Republic of Koreaysyoon@kaist.ac.kr

1

Corresponding author.

J Biomech Eng 130(2), 021008 (Mar 28, 2008) (7 pages) doi:10.1115/1.2898761 History: Received August 16, 2006; Revised June 25, 2007; Published March 28, 2008

Large interfacial gaps between the stem and the bone in cementless total hip arthroplasty may prevent successful bone ingrowth at the sites, and can also be a passage for wear particles. Furthermore, interfacial gaps between the stem and the bone are believed to compromise the primary stability of the implant. Thus, a broaching method that serves to reduce gaps is expected to give clinically preferable results. A modified broach system with a canal guide is introduced to enhance the accuracy of femoral canal shaping in comparison with the conventional broach system for a Versys fibermetal taper stem. The primary stability of the hip systems and the ratios of the stem surface in contact with the femur were measured in a composite femur model. With the conventional method, an average of 67% of the stem surface was shown to be in contact with the bone, and an average stem micromotion/migration of 35μm290μm was observed under 1000cycles of stair climbing loads. With the modified method, the stem-bone contact ratio significantly increased to 82% (p<0.05), and the average micromotion/migration reduced to 29μm49μm, respectively (p<0.05 for migration). Our finite element models of the hip systems supported that the difference in micromotion could be attributed to the difference in interfacial contact. Interfacial gaps occurring with the conventional broach system were effectively reduced by the proposed method, resulting in improved primary stability.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Modified broaching technique. (Left) The guide inserted into the femoral canal allows only axial movement of the broach. (Right) CAD model of the modified broach system. The canal guide is intended to be initially installed deep enough such that the proximal broach will rest on the canal guide when the broaching is completed.

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Figure 2

Loading setup diagram for the stability test

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Figure 3

(Right) Composite femur with the stem under loading with the motion measurement device in place. (Left) Diagram of the motion measurement device (some of the LVDTs are omitted for simplicity of the diagram). The measurement reference point is 40mm below the shoulder of the implant.

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Figure 4

Magnitude of the distal migration during cyclic loads (thick solid line: conventional method, thin dotted line: modified method)

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Figure 5

Stem-bone contact ratio for each broaching method as a function of the gap threshold. Lines of p<0.05 and p<0.1 show the gap threshold below which the contact ratio differed between the two groups.

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Figure 6

Gap frequency with each broaching method. A black area means that a gap was observed at that location in all six specimens.

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