Migration and strains induced by different designs of force-closed stems for THA

Abstract

ObjectivesSubtle differences in stem design can result in different mechanical responses of the total hip arthroplasty. Tests measuring migration of the stem relative to the femur, as well as the strains in the cement mantle and on the femur can detect different mechanical behavior between stems.MethodsIn this article, conical, double and triple tapered stems were implanted in composite femurs and subjected to static and cyclic loads. Stems differed mainly on taper angle, calcar radius and proximal stiffness. Stem migration and strains on the femur and in the cement mantle were achieved.ResultsSignificant differences (p < 0.05) were noted in the permanent rotation between double and triple tapers, in the strains on the proximal medial femur between triple and both conical and double tapers, and in the strains on the lateral proximal femur between double tapers and both conical and triple tapers.ConclusionThe proposed mechanical tests were able to detect significant differences in the behavior of these resembling stems. Stem proximal stiffness and the calcar radius of the stem influence its rotational stability and the strain transmission to the femur.

Less early subsidence of cemented Exeter short stems compared with cemented Exeter standard stems in Dorr type A femurs

“…In general, changes in the stem shape affects the load transmission to the cement mantle, stem migration and potential stem survival. 34 We believe that the funnel-like shape of the short stem resists subsidence and complies with the anatomy of the proximal femur seen in Dorr type A femora and is the likely reason that Exeter short stems subsides less than the Exeter standard stems. The subsidence of the short stem was similar to that of the triple tapered short C-stem reported by Sundberg et al, 24 though not specifically in Dorr type A femora.…”

Temporal subsidence patterns of cemented polished taper-slip stems: a systematic review

“…Taper-slip, or force-closed, cemented polished femoral implants are designed to subside within the cement mantle in order to distribute load in a more physiological fashion. 6 This differs to the composite beam, or shape-closed designs, where fixation is required at all interfaces and subsidence signifies loosening. 7 The modern taper-slip stems now dominate the cemented hip market in the United Kingdom, with both double and triple-tapered designs available, but despite their popularity and increasingly widespread use, the magnitude and duration of subsidence have not yet been fully established.…”