Modern metal-on-metal bearings produce less wear debris and osteolysis, but have the potential adverse effect of release of ions. Improved ceramic-on-ceramic bearings have the lowest wear of all, but the corrosion process has not been analysed.

Our aim was to measure the serum ion release (ng/ml) in 23 patients having stable hip prostheses with a ceramic-on-ceramic coupling (group A) and to compare it with the release in 42 patients with a metal-on-metal bearing (group B) in the medium term. Reference values were obtained from a population of 47 healthy subjects (group C). The concentrations of chromium, cobalt, aluminium and titanium were measured.

There was a significant increase of cobalt, chromium and aluminium levels (p < 0.05) in group B compared with groups A and C. Group A did not differ significantly from the control group. Despite the apparent advantage of a metal-on-metal coupling, especially in younger patients with a long life expectancy, a major concern arises regarding the extent and duration of ion exposure. For this reason, the low corrosion level in a ceramic-on-ceramic coupling could be advantageous.

There is no diagnostic, non-invasive method for the early detection of loosening after total hip arthroplasty. In a pilot study, we have analysed two serum markers of bone remodelling, procollagen I C-terminal extension peptide (PICP) and cross-linked N-terminal telopeptide (NTx), as well as the diagnostic performance of NTx for the assessment of osteolysis. We recruited 21 patients with loosening (group I), 18 with a well-fixed prosthesis (group II) and 17 at the time of primary arthroplasty for osteoarthritis (OA) (group III). Internal normal reference ranges were obtained from 30 healthy subjects (group IV).

The serum PICP level was found to be significantly lower in patients with OA and those with loosening, when compared with those with stable implants, while the NTx level was significantly increased only in the group with loosening, suggesting that collagen degradation depended on the altered bone turnover induced by the implant. This hypothesis was reinforced by the finding that the values in the pre-surgery patients and stable subjects were comparable with the reference range of younger healthy subjects.

A high specificity and positive predictive value for NTx provided good diagnostic evidence of agreement between the test and the clinical and radiological evaluations. The NTx level could be used to indicate stability of the implant. However, further prospective, larger studies are necessary.

Aims: Different polyurethane foam matrices (PUF) loaded with hydroxyapatite (HA) or α-tricalcium phosphate were proposed as scaffold for bone regeneration [1,2]. In this work new PUFs were developed and loaded with HA or α-TCP.

Methods: PUFs were synthesized by a one-step polymerisation from a hydrophilic polyol mixture (LF 2946, Elastogran, Italy) and polymeric MDI (B141, BASF), using Fe acetyl-acetonate as catalyst and 2% water as expanding agent. The composites were prepared in the same way, by adding HA or α-TCP to the reacting mixture.

In vitro cell interactions were evaluated with human osteoblasts (HOB, 2nd passage) isolated from the trabecular bone of the femoral head of patients undergoing total hip replacement and cultured following the usual procedure. HOB cells (1x105 cells/sample) were kept in contact with the scaffolds for 7 and 14 days. At each time endpoint HOB metabolic activity, intracellular and released ALP were evaluated.

Results: By water adsorption test, newly synthesized PUFs showed a higher hydrophilicity compared to that of the previous matrices (600% vs 110% water uptake after 100h). Due to the presence of inorganic salts, composite scaffolds showed density values higher (0.131B80.200g/cm3) than those of unloaded PUFs (0.071B80.093g/cm3). Yet, open cell percentage (57–75%) and average pore size (350B8520mm) resulted similar to those of the PUFs.

HOB cells grown on scaffold samples showed an increase of metabolic activity from 7 to 14 days. The amount of intracellular ALP increased too, whereas the amount of ALP in the medium was quite low. HOB cells, after 14 days, appeared closely adherent to the scaffolds, with an elongated and flattened shape.

Conclusions: These preliminary results showed that, even if slow, the growth of HOB onto PUF scaffolds was quite good. After 14 days, PUF composites showed higher cells growth than PUF-matrices, confirming the role of the bone-like inorganic particles in improving osteoblasts functions. Long-term in vitro tests are now in progress.

Total joint arthroplasty is the most significant advance in the treatment of end-stage arthritic disease of major joints. Despite the clinical success of this surgical procedure, however, some total joint prostheses fail, and although a failed prosthesis can be replaced, the results of revision arthroplasty are not as good as the first time. Studying the failed prosthesis and the associated bone and soft tissues provides insight into the causes of failure.

Most prosthetic failures are the result of structural limitations of the implant components. Although material failure may be sudden, a much more common cause is gradual aseptic loosening of the prostheses. Aseptic loosening is caused by both mechanical (gradual loss of material by wear) and biological (osteoclastic resorption of adjacent bone) factors. Wear particles induce a foreign body reaction characterized by a pseudomembrane composed of granulomatous tissues including macrophages, fibroblasts, giant cells, and osteoclasts in addition to debris particles. The extent of this response is driven by the number, size, composition, surface area, and types of particles present. Although there are differences in the relative local toxicity of each of these particles, the end result is the same. These mechanical and biological factors are unavoidable, and the success of a total joint prosthesis depends on the rate with which they occur. Polyethylene wear particles (1–200 ?) are the primary cause of loosening. They are strongly birefringent under polarized light microscopy. Smaller particles are phagocytized by histiocytes, whereas larger particles are surrounded by foreign body giant cells. Fragmentation of PMMA may also cause particulate debris. The presence of these particles (30–100 ?) may be deduced by empty spaces into the soft tissues, often bordered by foreign body giant cells, since PMMA is dissolved by xylene during routine histological techniques. Metal oxides form on the surface of chrome-cobalt or titanium alloys due to an electrolytic process, and stresses on the surface of the metal shear the oxides into the surrounding tissues, causing a black pigmentation of the tissues. Histologically, the black deposits of oxidized metals are seen extracellularly as well as in the cytoplasm of histiocytes. In addition to oxidation, metal undergoes corrosion and, as a result, metal ions enter the soft tissues and the bloodstream. A ceramic-on-ceramic coupling generates a significantly lower amount of debris as compared to the conventional metal-on polyethylene solution. When present, ceramic debris cause a mild histiocytic reaction without giant cells and virtually no osteoclastic bone resorption. There are various secretory proteins at the interfacial membrane that can affect bone turnover, including the cytokines IL-1, IL-6, Il-10, and TNF-a. Other factors involved with bone resorption include the enzymes responsible for catabolism of the organic component of bone, such as MMPs. Prostaglandins, in particular PGE2, are also known to be important intercellular messengers in the osteolytic cascade. More recently, several mediators known to be involved in stimulation or inhibition of osteoclast differentiation and maturation, such as RANKL and osteoprotegerin, have been suggested as key factors in the development and progression of osteolysis.

Infection around a prosthesis also causes loosening in approximately 1–5% of cases. Total joint prostheses become infected by two mechanisms, wound contamination at the time of surgery by Staph. aureus or Staph.epidermidis, and late hematogenous spread of organisms (Staphylo- and Streptococci, E. Coli, Pseudomonas, and anaerobes). The following factors facilitate bacterial growth. First, reaming and sawing, as well as PMMA polymerization, cause necrosis of necrotize bone adjacent to the implant, and such nonvascularized area permits bacteria to grow, safe from circulating host defenses. Second, a highly hydrated matrix of extracellular polymeric substances (biofilm) is formed that defends bacteria from antibiotics and phagocytosis. Third, some metals, such as nickel or cobalt, may depress macrophage function. The distinguishing histologic features of an infected prosthesis is an acute inflammatory reaction: a finding of > 5 PMN or of > 50 lymphocytes/hp field are presumptive for infection. Because some low-grade infections fail to stimulate an acute inflammatory reaction, they go undiagnosed until postoperative period when microbacterial culture results are available. To date, no single routinely used clinical or laboratory test has been shown to achieve ideal sensitivity and specificity for the diagnosis of prosthetic joint infection, and in most cases the diagnosis depends on a combination of clinical features, radiographic findings, and laboratory results. Intra-operative tissue cultures may be falsely negative because of prior antimicrobial exposure, a low number of organisms, inappropriate culture media, or atypical organisms. Conversely, cultures may be falsely positive because of contamination in the operating room, during transport, or in the laboratory. If the implant is removed, the entire prosthesis can be cultured. Moreover, because prosthetic joint infection is a biofilm-mediated infection, techniques that sample bacteria in biofilm, such as sonication or enzymatic treatment, may improve the diagnosis of prosthetic joint infection. More recently, molecular techniques are being used to detect nucleic acid in samples from infected patients even when conventional techniques are negative because of unusual microbial growth requirements or failure to grow after antimicrobial exposure or due to unfavourable environmental conditions. A disadvantage of such approach is its extreme sensitivity, leading to the possibility of false positive results.

The clinical presentation of prosthetic joint infection may be indistinguishable from that of aseptic implant failure. In many cases, culture of granulomatous tissue around failed prostheses, preoperatively diagnosed as aseptically loosened, reveals the presence of bacteria that may per se significantly contribute to the recruitment, maturation and activation of osteoclasts and that superimpose to the foreign body reaction to wear debris. The presence of a smouldering infection in case of “aseptic” failure observed in revision arthroplasties. A systematic investigation on all retrieved implants is mandatory to define the precise role of each potential factor contributing to the pathogenesis of failure, in order to further improve the quality of care of patients having total joint arthroplasty.

We aimed to assess whether the immunological abnormalities which have been observed in patients with loose total hip replacements (THRs) are present in patients with a well-fixed prosthesis.

We examined blood samples from 39 healthy donors, 22 patients before THR and 41 with well-fixed THRs of different types (15 metal-on-metal, 13 metal-on-polyethylene, 13 ceramic-on-ceramic). Before THR, the patients showed a decrease in leukocytes and myeloid cells in comparison with healthy donors, and a prevalence of type-1 T lymphocytes, which was confirmed by the increase in ratio of interferon-γ to interleukin 4. Moreover, patients with metal-on-metal or metal-on-polyethylene implants showed a significant decrease in the number of T lymphocytes and a significant increase in the serum level of chromium and cobalt, although no significant correlation was observed with the immunological changes. In the ceramic-on-ceramic group, leukocytes and lymphocyte subsets were not significantly changed, but a significant increase in type-2 cytokines restored the ratio of interferon-γ to interleukin 4 to normal values.

We conclude that abnormalities of the cell-mediated immune response may be present in patients with a well-fixed THR, and that the immunological changes are more evident in those who have at least one metal component in the articular coupling.