Mid-term outcomes after distally locked-to-standard primary stem exchange in 29 hip-prosthesis patients

AbstractBackgroundCementless locked femoral stems are used for revision surgery in patients with bone loss to induce spontaneous bone reconstruction, allowing subsequent replacement by a standard primary stem. The small number of patients and short follow-ups available to date preclude a valid assessment of this strategy.HypothesisAfter distally locked stem revision, replacement by a standard primary stem does not induce complications, and the quality of the bone reconstruction allows strong fixation of a regular primary stem.Materials and methodsWe retrospectively evaluated 29 patients in whom a distally locked femoral stem was replaced by a standard primary stem between 1998 and 2010 (cemented in 27, cementless in 2 cases). The reason for the procedure was stem breakage, stem migration, or thigh pain. Mean patient age was 63years (range, 39–78years). Outcomes were evaluated based on the Postel-Merle d’Aubigné [PMA] score and Harris Hip Score [HHS]. In addition, radiographs were obtained to assess prosthesis fixation and the Hofmann cortical index measured the bone reconstruction.ResultsThe distally locked stem was removed via a postero-lateral approach without femoral osteotomy in all the 29 cases. In one patient, an intra-operative fracture occurred during femoral preparation. Mean follow-up after the exchange procedure was 75months (range, 3–188months). Postoperative ccomplications occurred in 9 (32%) patients and consisted of chronic infection in 2 patients (after 3 and 76months), post-traumatic peri-prosthetic fractures treated with internal fixation in 3 patients (after 100, 138, and 182months), aseptic loosening in 3 patients (after 13, 39, and 122months), and recurrent instability in one patient (after 63months). All cause revision stem survival after 75months was 72% (95% confidence interval, 47%–87%). In the 19 patients who still had their revision stem at last follow-up, the mean PMA score was 16.7 (range, 13–18) and the mean HHS was 88.2 (range, 59–99). The Hofmann index remained unchanged [36.5% (range, 28%–58%) before the exchange and 32.9% (range, 20%–57%) after the exchange; P=0.129].DiscussionThis study confirms the feasibility of substituting a distally locked stem with a standard primary stem. No specific complications occurred and no technical difficulties arose when extracting the long stems. However, the 32% complication rate and, more specifically, the occurrence of loosening in 10% (3/29) of patients mandates caution in the use of this technique, which should not be proposed routinely, and suggests a need for considering cementless fixation of the standard primary stem.Level of evidenceLevel IV, retrospective study

Internal friction phenomena in composites based on PZT-type ferroelectric powder and ferrites

The aim of the work was to determine the phenomena of internal friction (mechanical losses) occurring in ferroelectric-ferromagnetic composites created based on PZT-type ferroelectric powder and ferrite. The composites were obtained using ceramic powders – multi-component PZT-type solid solutions with ferroelectric properties. Their magnetic component included zinc-nickel powder Ni0.64Zn0.36Fe2O4. 30 × 10 × 1 mm3 test specimens were obtained using free sintering. Temperature Q -1(T) and amplitude Q -1(ε) internal friction dependencies were determined. Wide high temperature maxima were observed with regard to the internal friction temperature dependencies obtained for the tested specimens. The conducted measurements of amplitude (isothermal) dependencies of internal friction Q -1(ε) for the tested composites have allowed for interpreting the previously observed maximum on the temperature dependencies of internal friction