Evaluation of Aerosol Electrospray Analysis of Metal-on-Metal Wear Particles from Simulated Total Joint Replacement.

Wear is a common cause for aseptic loosening in artificial joints. The purpose of this study was to develop an automated diagnostical method for identification of the number and size distribution of wear debris. For this purpose, metal debris samples were extracted from a hip simulator and then analyzed by the electrospray method combined with a differential mobility analyzer, allowing particle detection ranging from several nanometers up to 1 µm. Wear particles were identified with a characteristic peak at 15 nm. The electrospray setup was successfully used and validated for the first time to characterize wear debris from simulated total joint replacement. The advantages of this diagnostic method are its time- and financial efficiency and its suitability for testing of different materials.

A cementless hip system with a new surface for osseous integration.

PURPOSE: The failure of total hip systems caused by wear-particle-induced loosening has focused interest on factors potentially affecting wear rate. Remnants of the blasting material were reported on grit-blasted surfaces for cementless fixation. These particles are believed to cause third-body wear and implant loosening. The purpose of this study was to evaluate the early clinical and radiological outcomes of a cementless hip system with a new, contamination-free, roughened surface with regard to prosthesis-related failures. METHODS: Between May 2004 and March 2009, 202 consecutive primary total hip arthroplasties (THAs) (192 patients with a mean age of 62.6 years) were performed using a cementless stem (Hipstar®) and a hemispherical acetabular cup (Trident®). RESULTS: At a minimum follow-up of two years, five revisions (2.5%) due to aseptic loosening of the stem and three (1.5%) of the cup were necessary. The cumulative rate of prostheses survival, counting revision of both components and with aseptic failure as end point, was 92.9% at 8.8 years. Radiolucent lines up to three millimetres were evaluated in the proximal part of the femur in 61% of cases. CONCLUSIONS: Although the incidence of radiolucent lines was decreased, the revision rate was considerably increased compared to other uncemented hip implants with grit-blasted surfaces in the short- to mid-term follow-up of our study. Subsequent studies are needed to confirm whether these changes in implant material and surface affect the radiological and clinical outcome in the long term.

Contamination of surfaces for osseointegration of cementless total hip implants by small aluminium oxide particles: analysis of established implants by use of a new technique.

BACKGROUND: The failure of total hip replacements because of wear, particle-induced osteolysis, and aseptic loosening has focussed interest on factors potentially affecting the rate of wear. In this context the effect of particle release from the bone-implant interface of cementless implants is poorly understood. The surface structure for bony ongrowth of many cementless implants is created by grit-blasting. Remnants from this process (Al2O3 particles) on these surfaces have been reported; these remnants have the potential to cause third-body wear. METHODS: We report a novel technique for isolation and quantification of alumina particle contamination. Stems from different manufacturers were electrochemically activated and etched to isolate the alumina residues. After filtration the particles were characterised by scanning electron microscopy and energy-dispersive X-ray analysis. RESULTS: Many Al2O3 particles were found on all the implants tested. A mean of 426,814 particles per mm(2) was measured. Particle size distribution ranged from 0.125 to 66.304 µm with a peak in the range 0.25-1 µm. CONCLUSIONS: Our main finding was a large amount of small Al2O3 particles on all blasted surfaces. On the basis of our results these alumina particle remnants cannot be excluded as a factor causing increased third-body wear.

Postmortem study of femoral osteolysis associated with metal-on-metal articulation in total hip replacement: an analysis of nine cases.

BACKGROUND: Improved metal-on-metal articulations were reintroduced in total hip replacement to avoid the osteolysis sometimes seen with conventional ultra-high molecular weight polyethylene bearings. Osteolysis and local lymphocytic infiltration have been reported at revision of some metal-on-metal devices. We report similar and additional results in a study of second-generation metal-on-metal hip implants retrieved post mortem. METHODS: Components and surrounding tissues were collected post mortem from seven patients with nine total hip replacements (Zweymüller SL stem with an Alloclassic cup) with Metasul metal-on-metal articulations. All available patient information was recorded. Radiographs of the hips were evaluated for osteolysis. Sections of joint capsule as well as of the femoral implant with surrounding bone were reviewed, and energy-dispersive x-ray analysis was used to evaluate the composition of wear products. The amount of wear was measured for each component (nine femoral heads and eight cup inserts), when possible, by a coordinate measurement machine with use of the dimensional method. RESULTS: The patients died between three and ten years after arthroplasty, and six of the seven were asymptomatic at the time of death. One patient, with the highest rate of total wear (i.e., wear of femoral head and acetabular cup; 7.6 microm/yr), had increasing hip pain for one year, and histological analysis confirmed the radiographic findings of osteolysis. For two other patients, histological analysis confirmed the radiographic findings of asymptomatic osteolysis. For three patients, histological analysis revealed osteolysis that had escaped conventional radiographic analysis. Joint capsule tissue showed evidence of metallosis in all hips and local lymphocytic infiltration in eight hips. Energy-dispersive x-ray analysis revealed elements attributable to CoCrMo alloy in all hips and traces of corrosion products in three hips. CONCLUSIONS: The postmortem findings of osteolysis and/or lymphocytic infiltration associated with eight clinically well-functioning, low wear devices (a total wear rate of <4 microm/yr) suggest there may be frequent, unappreciated femoral bone loss and local immunological response in patients with second-generation metal-on-metal hip implants. Compared with previous postmortem studies, our findings showed the extent of osteolysis was similar to that with metal-on-polyethylene articulations.

Presence of corrosion products and hypersensitivity-associated reactions in periprosthetic tissue after aseptic loosening of total hip replacements with metal bearing surfaces.

Aseptic loosening of articular implants is frequently associated with tissue reactions to wear particles. Some patients, who had received metal-on-metal articulations, present early symptoms including persistent pain and implant failure. These symptoms raise the suspicion about the development of an immunological response. Furthermore, the generation of rare corrosion products in association with metallic implants has been observed. Corrosion products are known to enhance third-body wear and contribute to the loss of the implant. The purpose of this study was to investigate periprosthetic tissue containing solid corrosion products after aseptic loosening of second-generation metal-on-metal total hip replacements made of low-carbon cobalt-chromium-molybdenum alloy for the presence of immunologically determined tissue changes. Periprosthetic tissue of 11 cases containing uncommon solid deposits was investigated by light microscopy. In order to confirm the presence of corrosion products, additional methods including scanning electron microscopy (SEM) investigation, energy dispersive X-ray (EDX) and Fourier transform infrared microspectroscopy (FTIR) analysis were used. All investigated cases revealed solid chromium orthophosphate corrosion products as well as metallic wear particles to a various extent. Moreover, various intense tissue reactions characteristic of immune response were observed in all cases. The simultaneous presence of corrosion products and hypersensitivity-associated tissue reaction indicates that a relationship between corrosion development and implant-related hypersensitivity may exist.

Characterization, quantification, and isolation of aluminum oxide particles on grit blasted titanium aluminum alloy hip implants.

BACKGROUND: This study was undertaken to verify whether or not the microstructure of aluminum alloy implants interferes with the characterization and quantification of aluminum inclusions on their surfaces, resulting from grit blasting. METHODS: Four factory-fresh prostheses were investigated by scanning electron microscopy and X-ray microanalysis. Specimens were cut out of the stems and the cross-sections analyzed. The specimens were etched in hot 25% hydrochloric acid. The hydrochloric acid was subsequently filtered with a 0.2-microm-pore filter. The filters were scanned using electron microscopy and X-ray microanalysis. RESULTS: Aluminum oxide particles were found on all investigated stems; the diameter of the particles ranged from 4 to 100 microm. One hundred fifty-four particles were counted per mm(2). No particles were seen on the cross-sections of the implants. Scanning electron microscopy of the Millipore filters revealed aluminum oxide particles. CONCLUSION: Remnants of grit blasting were found only on the surfaces; none were observed on cross-sections. We conclude that the microstructure of titanium aluminum alloy does not interfere with the identification and quantification of particles. Particles were identified on the filters by electron microscopy and X-ray microanalysis. Aluminum oxide on the surface of grit-blasted titanium aluminum alloy implants is, in fact, a residue of grit blasting.

Retrieval study of uncemented metal-metal hip prostheses revised for early loosening.

A tribologic assessment was performed on 22 metal-metal hip prostheses from a single manufacturer, following removal for early aseptic loosening after a mean service life of 32 months (range, 12-59 months). The mean linear wear rate was 7.6 microm/year (range, 2.9-12.8 microm/year). This was below the rates previously observed in other modern metal-metal combinations. A novel contour analysis technique using a coordinate measuring machine showed the mean volumetric wear rate to be 2.02 mm(3)/year (range, 0.55-3.74 mm(3)/year), which corresponds to a mean gravimetric wear rate of 16.9 mg/year (range, 4.6-31.4 mg/year). The mean clearance of 39.8 microm (range, 30-50 microm) was within the optimal range for hard-hard bearing combinations. Evidence of abrasive, adhesive, and third-body wear was found on all bearing surfaces. The tribologic assessment did not indicate manufacturing defects as a cause of early loosening. Equally, third-body wear was too low to be considered a causative factor for early loosening.