Will stress shielding limit the longevity of cemented femoral components of total hip replacement?
One must acknowledge the speculative nature of evaluating whether stress shielding will limit the longevity of cemented femoral components. One can, however, evaluate the data available from patients studied up to 20 years. Stress shielding does lead to disuse osteoporosis, particularly in the proximal medial cortex, and also more slowly and to a lesser extent elsewhere. Concern also exists that progressive endosteal enlargement will lead to failure of many or all cemented femoral stems. No evidence exists that disuse osteoporosis has limited the longevity of cemented femoral stems up to 20 years. Moreover, new data show that what has been described as the normal process of endosteal enlargement after inserting a cemented femoral component is a misinterpretation. What actually happens is that (1) neocortex develops around the cement mantle, (2) the original cortex thins, (3) the trabeculae in the zone of decreased density that develops between them maintain the structural integrity between those two bony masses, and (4) the implant remains rigidly fixed.
Harris
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Orthopaedic Biomechanics Laboratory, Massachusetts General Hospital, Boston 02114.
D016723:Bone Remodeling; D005269:Femur / Q000503:physiopathology*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D010024:Osteoporosis / Q000209:etiology; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013997:Time Factors