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 Adult Hip Reconstruction Test 6: Total Hip Arthroplasty Techniques
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The Journal of Bone and Joint Surgery (American) 86:813-820 (2004)
© 2004 The Journal of Bone and Joint Surgery, Inc.

Effects of Dorsal Flanges on Fixation of a Cemented Total Hip Replacement Femoral Stem

Sophia N. Sangiorgio, MS1, Edward Ebramzadeh, PhD1, Donald B. Longjohn, MD2 and Lawrence D. Dorr, MD3

1 Biomechanics Laboratory, Los Angeles Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, CA 90007-2697. E-mail address for E. Ebramzadeh: ebramzad{at}usc.edu. E-mail address for S.N. Sangiorgio: ssangiorgio{at}laoh.ucla.edu
2 Department of Orthopaedics, Keck School of Medicine, University of Southern California, University Park Campus, Los Angeles, CA 90089
3 Dorr Arthritis Institute of Centinela Hospital, 501 East Hardy Street, Suite 300, Inglewood, CA 90301

Investigation performed at the Biomechanics Laboratory of the J. Vernon Luck, Sr., MD, Orthopaedic Research Center, Los Angeles Orthopaedic Hospital, Los Angeles, and the Dorr Arthritis Institute of Centinela Hospital, Inglewood, California

In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from Centerpulse Orthopaedics, Austin, Texas. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: Although current designs of cemented femoral stems for total hip replacement include both those with and those without a flanged shape at the proximal end, the influence of anteroposterior dorsal flanges on the fixation of the stem is not completely understood. The purpose of this study was to assess the effects of flanges on femoral stem stability and load transfer to the femur with use of an in vitro model.

Methods: We measured femoral surface strains and three-dimensional micromotion in synthetic femora under cyclic loading with four types of stems: those with flanges and those without flanges in two sizes each. The four types of stems were otherwise identical; that is, all of them were straight, polished, and collarless. Stem-cement micromotion measurements and strain measurements were repeated with three stems of each type, whereas bone-cement micromotion measurements were made with one stem of each type.

Results: Flanges had a greater influence on femoral strains and micromotion than did the difference in the cement thickness resulting from the different stem sizes. Specifically, the flanged stems produced greater strains on the medial femoral surface but smaller strains on the anterior surface than did the non-flanged stems. Flanged stems achieved tighter mechanical interlock within the cement, but these stems increased bone-cement micromotion. Specifically, the motion per cycle of flanged stems within the cement mantle was smaller than that of non-flanged stems, whereas the motion per cycle of the cement mantle within the femoral canal was greater with the flanged stems than with the non-flanged stems.

Conclusions: Flanges on a total hip femoral stem increase the interlock between the stem and the cement and decrease the proximal-medial stress-shielding. However, these advantages occur with increased bone-cement interface motion, which may be detrimental to the survival of the implant.

Clinical Relevance: The findings help to predict the consequences of the use of dorsal flanges for femoral stems and should be considered in the design of new femoral stems.


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