Skip to main content Accessibility help
×
Home
  • Print publication year: 2011
  • Online publication date: June 2012

6 - Elasticity

from Part II - Mechanics

Summary

Inquiry

What modifications could you make to a hip stem to minimize stress shielding of the surrounding bone while still using metals common to orthopedic implants?

An interesting property of human bones is the manner in which they efficiently build up bone density where the bones are under higher loading, and remove bone density where strength is not needed. This property can be seen in the increased bone strength of the dominant arm of tennis players as compared to the non-racquet-holding arm (Ashizawa et al., 1999). Because the dominant arm is constantly subjected to loading as a result of the impact between the ball and racquet, the bone in that arm has greater bone density than the non-dominant arm, which presumably sees only everyday loading.

This property of bones is of importance to designers of hip stems as it has been shown that patients who have hip implants with a high stiffness stem were experiencing noticeable bone loss. This phenomenon, known as stress shielding, was thought to be occurring because the hip implants themselves were taking up so much of the loading that the body removed from the now extraneous surrounding bone. This in turn led to implant problems, as the remaining bone was not strong enough to stabilize the hip stems, as shown in Figure 6.1. Because of this, researchers turned their attention to developing materials and implants that might provide the same strength and durability with decreased stiffness, forcing the bone to take up more of the load. By the end of this chapter, a method for determining the stresses in various configurations of materials and stem cross-sections, in order to reduce stress shielding, will be developed.

Related content

Powered by UNSILO
References
Ashizawa, N.Nonaka, K.Michikami, S.Mizuki, T.Amagai, H.Tokuyama, K.Suzuki, M. 1999 Tomographical description of tennis-loaded radius: reciprocal relation between bone size and volumetric BMDJournal of Applied Physiology 86 1347
Nazarian, A.Hermannsson, B.J.Muller, J.Zurakowski, D.Snyder, B.D. 2009 Effects of tissue preservation on murine bone mechanical propertiesJournal of Biomechanics 42 82
Venkatsubramanian, R.T.Wolkers, W.F.Shenoi, M.M.Barocas, V.H.Lafontaine, D.Soule, C.L.Iaizzo, P.A.Bischof, J.C. 2010 Freeze-thaw induced biomechanical changes in arteries: role of collagen matrix and smooth muscle cellsAnnals of Biomedical Engineering 38 694
Wren, T.A.L.Yerby, S.A.Beaupre, G.S.Carter, D.R. 2001 Mechanical properties of the human Achilles tendonClinical Biomechanics 16 245
Yoon, H.S.Katz, J.L. 1976 Ultrasonic wave propagation in human cortical bone, II: Measurements of elastic properties and microhardnessJournal of Biomechanics 9 459
Bibliography
Courtney, T.H. 2000 Mechanical Behavior of MaterialsBoston, MAMcGraw-Hill
Dowling, N.E. 2007 Mechanical Behavior of Materials, Engineering Methods for Deformation, Fracture and FatigueUpper Saddle River, NJPearson Education
Gibson, L.J.Ashby, M.F. 1997 Cellular Solids, Structure and PropertiesCambridge, UKCambridge University Press
Popov, E.P. 1990 Engineering Mechanics of SolidsEnglewood Cliffs, NJPrentice-Hall
Sadd, M.H. 2005 Elasticity, Theory, Applications and NumericsBurlington, MAElsevier