Abstract
Introduction: Bone loss, lack of ingrowth, and use of extended trochanteric osteotomies (ETO) all contribute to loss of proximal support in revision hip arthroplasty, leading to increased stem stresses. Clinical observations of fractured, distally fixed, proximally unsupported stems necessitates methods to mitigate proximal femoral bone loss. This study evaluated various cabling and strut techniques to reduce stem stresses seen with bone loss and ETO.
Methods: Finite element analysis (FEA) was performed on a clinical case of a fractured revision stem after an ETO. Stem stresses were determined and multiple treatment options were evaluated.
An instrumented extensively porous coated stem was implanted in composite femur models (n=3) and mechanically tested. The stem stresses resulting from proximal overbroaching, ETO, cable grips, and various cable and strut constructs were determined.
Results: Stem stresses increased 62 percent with a strut cabled above the distal portion of the ETO using FEA methods. This increase was reduced to as little as 10 percent when a third cable was added distal to the ETO.
Stem stresses increased 98 when a proximally loose stem was combined with an ETO using laboratory tests. This stress was decreased by up to 37 percent when a long trochanteric plate was utilized.
Discussion and conclusion: This study demonstrates the importance of proximal femoral support to the stresses imparted upon a cementless revision hip prosthesis. In the presence of proximal bone loss, an ETO dramatically increases these stresses, which can be reduced by cabling and strut techniques.
Editoral Secretary Mr Peter Howard. Correspondence should be addressed to BHS at the Royal College of Surgeons, 35 - 43 Lincoln’s Inn Fields, London WC2A 3PN.
