Fatigue crack growth rate does not depend on mantle thickness: an idealized cemented stem construct under torsional loading

Abstract

Retrieval studies indicate that cemented stem loosening in femoral components of total hip replacement can initiate at the stemcement interface. The etiology of the crack propagation process from the stem-cement interface is not well understood, but cracks are typically associated with thin cement mantles. In this study, a combination of experimental and computational methods was used to investigate the fatigue crack propagation process fi-om the stern-PMMA cement interface using a novel torsional loading model. Constructs with thin ( I mm). medium (3 mm) or thick (7 mm) cement mantles were evaluated. Crack growth was stable for all cases and the rate of crack growth diminished with increasing crack length. Crack growth rate did not depend on mantle thickness ( p > 0.05) over the first 1 mm of crack length, but cracks in thin mantles reached the full thickness of the mantle in the fewest number of loading cycles. The fracture mechanics-based finite element models indicated decreased stress intensity factors with increasing crack length and were consistent with the experimental findings. When combined with a fatigue crack growth Paris-law for PMMA cement. the finite element models provided reasonable predictions of the crack growth process.

Morphologic analysis of the distal humerus with special interest in elbow implant sizing and alignment

“…8 This may result in fracture caused by stem perforation during insertion or premature implant loosening. 17 Crack propagation resulting from cyclic loading occurs at the same rate for any cement thickness, 10 which would result in premature failure of the cement mantle at the thinnest areas.…”

The design features of cemented femoral hip implants

“…117 Mechanical and finiteelement studies of the propagation of fatigue cracks in the cement showed that the rate of growth of the crack was independent of the thickness of the cement mantle. 114,118 However, cracks in thin cement reached full-thickness in fewer loading cycles. 118 After loading of cemented stems, regions of thin cement (< 2 mm) presented fewer cement cracks but more full-thickness cracks than the other regions.…”

The behavior of the micro-mechanical cement–bone interface affects the cement failure in total hip replacement

“…This has widely been implemented in FEA-models in which the stem-cement interface was invoked as a frictional contact layer (Perez et al, 2009; Hertzler et al, 2002; Verdonschot and Huiskes, 1997). Recently, however, experiments have demonstrated that the movements at the cement-bone interface are also substantial (Mann et al, 2010; Race et al, 2010).…”