Metal wear particle characterization from metal on metal total hip replacements: transmission electron microscopy study of periprosthetic tissues and isolated particles.

The less intense tissue reaction around metal on metal total hip replacements (THRs) compared to metal on polyethylene (PE) THRs may be explained by the differences in the characteristics of metal wear particles. In this study, transmission electron microscopy was used to study metal wear particles that were either in situ in cells or had been extracted from the cells by a new technique based on enzymatic tissue digestion. The tissues were obtained from 13 patients undergoing revision of metal on metal THRs with cobalt-chromium-molybdenum (CoCrMo) bearing couples. Most of the CoCrMo wear particles were smaller than 50 nm (range 6-834 nm) and round to oval in shape with irregular boundaries. This size range is considerably smaller than that reported for PE particles. While even a small volume of metal wear will produce high numbers of particles, the apparently less severe local tissue reaction to metal particles may be due to the possibility that corrosion, dissolution, and dissemination of metal particles may result in fewer local biological effects than the long-term retention of PE particles in the periprosthetic tissues.

Tissue reaction to metal on metal total hip prostheses.

The periprosthetic tissue reaction to polyethylene wear debris in metal on polyethylene total hip replacements is strongly implicated as the cause of osteolysis. This has led to a renewed interest in metal on metal total hip replacements. However, little is known about the role of wear debris in failures of these prostheses. Capsular and interface tissues from 9 long and short term metal on metal total hip replacement retrievals were studied to assess the tissue reaction around these prostheses. As compared with metal on polyethylene cases, the extent of the granulomatous inflammatory reaction and the presence of foreign body type giant cells was much less intense in metal on metal cases, likely because of the lower numbers and overall smaller size of metal wear debris particles. This may lead to a better transport of the particles from the joint tissues and a lower incidence of periprosthetic osteolysis around metal on metal hip replacement.

Metal versus polyethylene wear particles in total hip replacements. A review.

Research has recently been focused on the development of hip replacements with alternative bearing surfaces with cobalt chrome alloy, to avoid the production of polyethylene wear particles in hip replacements and polyethylene wear debris mediated bone lysis. Cobalt chrome on cobalt chrome bearing surfaces are being reevaluated. Characterization of wear particles and studies on the reaction of the body to these particles, have played an important role in the determination of the factors that cause aseptic loosening and will therefore play an important role in the comparison of metal on polyethylene and metal on metal hip prostheses. In this paper, a comparison between the different aspects of metal and polyethylene wear particles is made using data from the literature and the authors' experience. The authors conclude that techniques need to be optimized to isolate and characterize individual metal wear particles from periprosthetic tissues and they advocate the performance of in vitro studies with these in vivo generated wear particles or comparable particles.

Cobalt and chromium concentrations in patients with metal on metal total hip replacements.

There has been a resurgence of interest in the use of metal on metal bearings in total hip arthroplasty. Although the use of metal on metal bearing couples would eliminate or substantially reduce particulate polyethylene generation (depending on the presence or absence of polyethylene in the implant system), there is concern about the potential for increased particulate and ionic metal generation in comparison with polyethylene on metal bearings. These metallic degradation products may be transported away from the implant site and distributed systemically. Chromium concentrations in the serum and urine and cobalt concentrations in the serum were measured in subjects with cobalt chromium alloy metal on metal total hip replacements and in controls without implants. Eight subjects with long term (> 20 years) McKee-Farrar total hip replacements had 9-fold elevations in serum chromium, 35-fold elevations in urine chromium, and at least 3-fold elevations in serum cobalt concentrations in comparison with controls. Six subjects with short term (< 2 years) metal on metal surface replacement arthroplasties had 3-fold elevations in serum chromium, 4-fold elevations in urine chromium, and 4-fold elevations in serum cobalt concentrations in comparison with subjects with McKee-Farrar implants. Although the toxicologic importance of these trace metal elevations has not been established, serum and urine metal concentrations may be useful markers for the tribologic performance of metal on metal bearings.

Malignant peripheral nerve sheath tumors in patients with and without neurofibromatosis.

Malignant peripheral nerve sheath tumors (MPNST) are rare. They account for 10% of all soft tissue sarcomas. The incidence of MPNST in patients with neurofibromatosis type 1 (NF-1) is 4%. A retrospective study was undertaken to evaluate the prognosis of patients with MPNST and NF-1 vs patients with MPNST alone. Twenty-two patients with MPNST were diagnosed. The MPNST was diagnosed with NF-1 in 11 patients (50%). Treatment was defined as curative in 20 patients (90%), non-curative in one patient (5%), and one patient received no treatment. The median disease-free survival (DFS) was 14 months (range 0-153 months). The median overall survival 24 months (range 1-153 months). There were three patients with isolated local failures (14%), four patients with local and distant failures (18%), and seven patients with isolated distant failures (32%). There was no statistical difference between patients with and without NF-1. Five patients with NF-1 developed a second MPNST (45%), none of the patients without NF-1 did (P = 0.018). A statistically worse survival was found when the duration of the first symptoms had been longer than six months. Patients with MPNST have a poor prognosis with a high risk for local and distant failures (> 50%). There is no statistical difference in the final outcome for MPNST with or without NF-1, but patients with NF-1 have a high risk for developing a second MPNST.