Minimum five-year wear rate of metal-on-highly cross-linked polyethylene in primary total hip arthroplasty.

PURPOSE: Highly cross-linked polyethylenes (PE) have been developed with encouraging results in terms of wear. Another body of the literature has indicated potential catastrophic failures related to reduced fatigue properties and oxidation. Each PE available on the market has its own processing characteristics. The aim of this retrospective study was to evaluate the minimum five-year wear properties of an original highly cross-linked PE in a consecutive series of primary THAs. METHODS: Between August 2005 and December 2007, 80 patients with a mean age of 62.7 years were included. All patients had a 28-mm CoCr femoral head articulating with a highly cross-linked insert (Highcross®, Medacta SA) that was 100 Mrads gamma radiated, remelted at 150 °C, and ethylene oxide sterilized. The primary criterion for evaluation was the femoral head penetration, as measured by Hip Analysis Suite software. The steady state wear was also calculated. Functional results were evaluated according to the WOMAC score. RESULTS: Complete data were available for analysis in 67 patients at a mean follow-up of 5.5 years. The mean femoral head penetration was 0.128 ± 0.62 mm and the steady state wear was-0.025 ± 0.22 mm/year. The WOMAC score significantly decreased from 16.5 ± 5.93 pre-operatively to 4.12 ± 5.5 at the latest follow-up (p <0.001). CONCLUSIONS: The minimal five-year results of this retrospective study indicate that this particular highly cross-linked and remelted polyethylene had a low wear rate. Longer-term results are needed to warrant that these mid-term data will generate less osteolysis and resultant aseptic loosening.

Trochanteric osteotomy in primary and revision total hip arthroplasty: risk factors for non-union.

BACKGROUND: Trochanteric osteotomies (TO) facilitate exposure and "true hip reconstruction" in complex primary and revision total hip arthroplasty (THA). However, non-union represents a clinically relevant complication. The purpose of the present study was to identify risk factors for trochanteric non-union. METHODS: All cases of THA approached by TO during the past 10 years were analyzed with respect to potential risk factors for non-union. RESULTS: In 298 cases complete data were available for analysis. Trochanteric union occurred in 80.5%, fibrous union in 5.4% and non-union 14.1%. Risk factor analysis revealed a four times higher risk for non-union in anterior trochanteric slide osteotomies compared to extended trochanteric osteotomies and a three times higher risk in cemented versus non-cemented stems. Multiple logistic regression analysis revealed patient's age and use of cement to be independent risk factors for non-union. CONCLUSIONS: Femoral cementation and increasing age negatively influence the union of trochanteric osteotomies.

Comparison of amorphous TCP nanoparticles to micron-sized alpha-TCP as starting materials for calcium phosphate cements.

The development of degradable bone cements with a mineral composition similar to natural bone was investigated using highly reactive calcium phosphate phases as starting materials. Mixtures of XRD-amorphous, glassy tricalcium phosphate (amorphous-TCP) nanoparticles of 25-60 nm size and micron sized, milled alpha-TCP were set by hydration with sodium phosphate buffer and investigated for possible application as single component calcium phosphate cements (CPCs). Isothermal calorimetry allowed a precise tracking of the setting process. Amorphous-TCP nanoparticles converted into calcium deficient hydroxyapatite with cement setting times below 12 min. The total energy release by the material during hardening corroborated the importance of high specific surface area and phase composition, that is, amorphous state of the nanometric starting material as repeatedly suggested earlier. The phase composition of the resulting CPCs was characterized by X-ray diffraction before and after setting. The morphology was investigated by nitrogen adsorption, scanning, and transmission electron microscopy and revealed the formation of highly porous calcium deficient hydroxyapatite with specific surface areas of up to 160 m(2) g(-1) after setting. In contrast to the very fast reaction time and highest specific surface area, the mechanical stability of the resulting CPC is still insufficient and requires further improvement.

Late onset imminent femoral fatigue fracture associated with intraoperative cement extrusion as a rare cause of thigh pain after total hip replacement.

INTRODUCTION: Cement extrusions on the femoral side after total hip replacement can occur in approximately 0.3% of cemented primary total hip replacements. Not recognised until a postoperative x-ray is performed, the willingness to dismiss and treat these extrusions conservatively is high. METHODS: We report on 3 patients presenting with sudden onset of thigh pain associated with an inability to weight-bear after a 2 to 15 month period of uneventful healthy recovery from cemented total hip replacement. On immediate postoperative x-rays occult cement extrusion in the posterolateral circumference of the femoral component tip were present. X-rays and CT scans showed no fracture signs. Scintigraphy revealed late increased uptake at the extrusion height. With the hypothesis of imminent femoral fatigue fracture, all patients underwent revision surgery. The defect sites were surgically exposed, thoroughly cleaned of cement, filled with iliac crest bone graft and stabilised with tension band plating. RESULTS: This procedure resulted in fully recovered asymptomatic patients at 6 weeks and after a mean follow-up period of 48 months, as demonstrated by their pain level and tolerance of full weight bearing. CONCLUSIONS: These cases lead us to adopt a low threshold for immediate revision when occult cement extrusion is recognised near the tip of a cemented stem on postoperative films, and to adopt a low threshold for surgical revision when, in the presence of cement extrusion, thigh pain is a complaint. We favour tension band plating and bone grafting over more complex implant revisions since a fast recovery was achieved in these patients.

Nanocomposites of high-density polyethylene with amorphous calcium phosphate: in vitro biomineralization and cytocompatibility of human mesenchymal stem cells.

Polyethylene is widely used as a component of implants in medicine. Composites made of high-density polyethylene (HDPE) containing different amounts of amorphous calcium phosphate nanoparticles were investigated concerning their in vitro biomedical performance. The nanoparticles were produced by flame spray synthesis and extruded with HDPE, the latter complying with Food and Drug Administration regulations. Mechanical properties such as Young's modulus and contact angle as well as in vitro biomineralization of the nanocomposites hot-pressed into thin films were evaluated. The deposition of a hydroxyapatite layer occurred upon immersion in simulated body fluid. Additionally, a cell culture study with human mesenchymal stem cells for six weeks allowed a primary assessment of the cytocompatibility. Viability assays (alamarBlue and lactate dehydrogenase detection) proved the absence of cytotoxic effects of the scaffolds. Microscopic images after hematoxylin and eosin staining confirmed typical growth and morphology. A preliminary experiment analyzed the alkaline phosphatase activity after two weeks. These findings motivate further investigations on bioactive HDPE in bone tissue engineering.

A computerized analysis-by-synthesis algorithm improves precision of linear wear measurements in total hip replacements.

Precision is important if small polyethylene wear rates are to be detected early and in small sample sizes. Using an automatic, computerized algorithm relying on a synthetic X-ray generated from a computer-assisted design (CAD) model of the implant may significantly improve precision of linear wear measurements. We compared this method to provide improved in vivo precision compared to the widely used Hip Analysis Suite software (version 8.0.1.7). Two anterior-posterior pelvic X-rays were taken on the same day of 18 total hip implants, and wear was measured by three observers using the two methods. Expected real wear was zero and defined as a reference value. Two sources of variability were estimated: one due to the instrument, and one due to different operators. A Wilcoxon Signed Rank Test was used for statistical comparisons. The overall precision (instrument variability and multioperator variability) given a 95% precision limit was significantly higher (p < 0.001) using the proposed method (+/-0.15 mm) when compared to the Hip Analysis Suite (+/-0.84 mm). Due to the availability of the full CAD data of the implant and to further automation of the measuring process, the newly proposed method provided improved precision in measuring polyethylene wear.