The Journal of Bone and Joint Surgery, Vol 65, Issue 4 495-499, Copyright © 1983 by Journal of Bone and Joint Surgery, Inc
A stress analysis of acetabular reconstruction in protrusio acetabuli
RD Crowninshield, RA Brand and DR Pedersen
We are reporting the results of a finite-element analysis of acetabular
reconstruction for total hip replacement in the presence of protrusio
acetabuli. In a protruded acetabulum, cortical bone stresses on the medial
part of the pelvic wall increase with medial placement of the acetabular
component, while normal placement of the component (more lateral placement)
reduces these stresses. Metal backing of a polyethylene acetabular
component causes a reduction in the peak cement and trabecular-bone
stresses. A metal protrusio ring about only the periphery of the acetabular
component increases stress levels within the lateral part of the pelvic
cortex and has little effect on stresses in the medial part of the pelvic
wall. A complete metal protrusio cup increases stresses in the lateral part
of the pelvic cortex while decreasing substantially the stresses in the
medial part of the cortex and the trabecular bone. Prosthetic reinforcement
of the medial part of the acetabular wall has little effect on stress
patterns in the acetabular region. Clinical Relevance: The major long-term
problem with cemented total hip prostheses is loosening. Loosening is
probably related in part to the stress state in the cement and surrounding
bone. The protruded acetabulum is particularly difficult to reconstruct in
a manner that ensures longevity of the total hip replacement. In patients
with protrusio acetabuli, the prosthetic acetabulum should be placed in a
normal and not in a protruded position. A metal-backed acetabular component
or a complete metal cup incorporated within the cement reduces stress
levels within the medial aspect of the pelvic bone and thus may reduce the
incidence of loosening.
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