Wear measurements of 100 explanted hips have been carried out on a Taylor Hobson 365 Roundness Machine using the LIRC Wear Protocol. It was found that 50% of explanted cups were wearing less than 5 μm/year and 60% of components were wearing less than 10 μm/year. Wear tests on hip joint simulators predict wear rates between 2 and 8 μm/year. However, 6% of cups are wearing faster than 100 μm/year, with 16% of cups have wear patches deeper than 100 μm and that 4% have a wear patch deeper than 300 μm.
Cup position is an important factor, all of the high wearing components are outside the Lewinick’s Box, however it is shown that mal position is does not always lead to extreme wear. Further analysis is taking place to calculate the size of the contact patch between head and cup (based on patient data and biomechanics) and the proximity of the contact patch to the edge of the cup.
P. aeruginosa produce N-3-oxododecanoyl homoserine lactone (3OC12-HSL), a so-called “quorum-sensing molecule” that provides signals for the production of virulence factors and for bacterial biofilm formation in a paracrine manner. We now found that 3OC12-HSL, but not its 3-deoxo-isomer or acyl homoserine lactones with shorter fatty acids, is also able to activate human polymorphonuclear neutrophils (PMN) in vitro: 3OC12-HSL enhanced the phagocytosis of opsonised bacteria in vitro; up-regulated the surface expression of phagocytosis-related receptors, and was chemotactic for PMN. Because induction of chemotaxis implies the polarisation of the cell by receptors expressed on the surface, we performed uptake studies with radiolabelled 3OC12-HSL. At 4° C we found saturable binding of the radiolabelled 3OC12-HSL, which could be inhibited by an excess of unlabelled 3OC12-HSL, indicating specificity of binding, and hence expression of a distinct surface receptor. By use of selective inhibitors, a signalling pathway, comprising phosphotyrosine kinases, phospholipase C, protein kinase C, mitogen activated protein kinase C was delineated, but in contrast to the well-studied chemokines C5a and interleukin 8, the chemotaxis in response to 3OC12-HSL did not depend on pertussis toxin-sensitive G proteins. Selective surface receptors for 3OC12-HSL have been identified in various bacteria species, but scrutinising a human gene bank did not reveal homologous structures. While the characterisation of the surface receptor awaits further studies, the functional consequence of the cross-kingdom signalling is obvious: by recognising and responding to 3OC12-HSL PMN are attracted to the site of a developing biofilm, and thus may prevent its progression and by that persistent infection.
Implant-associated osteomyelitis is caused by persistent bacterial infections, predominantly by staphylococci species forming biofilms on implants or osteosynthesis – materials. In the majority of patients the systemic immune response appears to be inconspicous with only minor upregulation of activation-associated receptors on the polymorphonuclear neutrophils (PMN). We found, however, evidence the activation of T cells, apparent as the expansion of CD4+ and CD8+ T cells bearing the activation-associated receptor CD11b. These cells also lacked the co-stimulatory molecule CD28, which is a further indicator for T cell activation. Moreover, small populations of T cells expressing Toll-like receptors (TLR)1, TLR2 or TLR4 were detected in the patients, while in healthy donors less than 1 % of T cells express TLR. A preferential association of TLR1- and TLR2-expression with CD28-CD11b+ cells was seen, compatible with the fact these cells represent an activated phenotype. In addition to the peripheral blood we also analysed leukocytes recovered from the infected site during surgery for removal of the implant. Predominantly PMN were found, highly activated as judged from their surace recpetor pattern, but also CD4+ and CD8+ T cells. As expected, these T cells represented an activated phenotype, and particularly the CD8+ cells expressed CD57, a receptor identifying end-differentiated T cells. The T cells recovered from the infected site, but not the peripheral blood T cells, produced interferon gamma, a cytokine known to support the function of phagocytic cells. In conclusion our data provide evidence that in response to local, persistent bacterial infections T cells are activated to acquire – among others – receptors selective for bacterial products, which in turn might modulate the T cell function and hence the host defence.
The formation of bacterial biofilms is increasingly recognised as the leading cause of chronic infections. It limits the application of implant materials including catheters, heart valves, or orthopaedic prostheses. It is generally assumed that the infection persists because bacteria organised as biofilms escape the host defence mechanisms. Nevertheless, when studying patients with infected implants, we found a massive infiltration of leukocytes particularly polymorphonuclear neutrophils, PMN, into the site of infection, which led to the question, whether the PMN interact with the bacterial biofilm or not. The interaction of human PMN with Staphylococcus aureus biofilms was studied in vitro. S.aureus was cultivated on glass cover slips for various times under conditions allowing formation of biofilms. Adherence of PMN to biofilms and phagocytosis of the bacteria were observed by confocal laser scan microscopy and time lapse video microscopy. Migration of PMN on and into the biofilm was identified as being phagocytosis, apparent as uptake of bacteria into the cell. Concominantly, in the wake of migrating PMN bacteria depleted zones appeared, which increased in size with time. In addition to phagocytosis, release from PMN of DNA and also of elastase was seen, suggesting the formation of neutrophil extracellular traps (NETs). So far, the signal for DNA release and NET formation has not been identified; of note is, however, that they occurred preferentially on established “old” biofilms and in the absence of the opsonising human serum, while phagocytosis was most efficient with developing “young” biofilms. Taken together, our data provide evidence that bacteria in biofilms are not entirely protected against host defence but that phagocytosis is still possible, especially when the biofilm is opsonised with human serum. Whether NET formation also contributes to bacteria killing in biofilms cannot be decided as yet but remains an attractive alternative.
P.aeruginosa causes acute and chronic-destructive infections, particularly wound infections, or device-associated infections by colonising respiratory tubes, catheters, or implants. The pathogenicity of P.aeruginosa is largely attributed to the relative resistance towards host defence. Especially when organised as biofilms, the bacteria evade phagocytosis and killing by polymorphonuclear neutrophils (PMN). To elucidate the evasion mechanisms, the migration of PMN towards and through P.aeruginosa biofilms was studied. Migration of PMN towards P.aeruginosa biofilms was tested using various in vitro techniques. We found that PMN migrated towards developing P.aeruginosa biofilms, attracted by the quorum-sensing molecule N-3-oxododecanoyl homoserine lactone (3OC12-HSL). Mature biofilms which no longer produced 3OC12-HSL did not attract PMN. Addition of interleukin 8, a potent chemokine, restored the migratory capacity. Once arrived at the biofilms, PMN readily attached with no important difference between developing and mature biofilms. Migration into and penetration of the films, however, was only seen with developing films. By mass spectroscopy it became obvious that a major difference between developing and mature biofilms was the composition of the extracellular polymer substance, of which alginate is a prominent component. A series of experiments with isolated alginate showed that PMN did not migrate on or into alginate-containing matrices, but remained affixed at the contact site just as they did on mature biofilms. The mechanism of this firm attachment is still under investigation; prominent up-regulation of various adhesion molecules was seen, which could provide possible explanation. Mature biofilms, most probably due to the composition of the extracellular polymer substance, do not allow the penetration of PMN. Consequently, bacteria embedded in deeper layers of the biofilm are protected against the host response. Due to the restricted movement of PMN, the bactericidal activity of PMN is only efficient against bacteria in the immediate vicinity, explaining the inefficient host defence.
In selected patients, knee arthrodesis is a well-recognised salvage procedure after infected total knee arthroplasty (TKA). Several procedures of arthrodesis have been introduced and should be adapted to the individual situation of the patient. In our center we regularly treat elderly patients after multiple revision operations; in 36% defects of the bone, soft tissue or the extensor mechanisms are present. In these cases we prefer arthrodesis to reimplantation. Because of the high rate of non-unions when using an external fixator, we perform arthrodesis by use of an intramedullary rod system. The objective of this study was to compare the results of different rod systems for knee arthrodesis after TKA infection. We reviewed the results of 3 rod systems in 34 patients: cementless system (Brehm; n=9), cement rod usually used in tumor patients (Mutars; n=7) and a regular cement rod system (Link; n=18). In the group of cementless rods we had to explantate 3 rods because of a relapse of the infection. This is most propably due to the technical design of the system: in poor soft tissue situation the tissue is compressed by the voluminary docking part which causes continuous necrosis. This problem can be avoided by an early tissue flap. Of the Mutars rod system we had to explantate 2 systems; one because of an infection, the other one due to telescoping, which can be avoided by use of a longer stem with the option to interlock. In the group of the Links system no revision was necessary. In our opinion, arthrodesis of the knee using a rod system is a satisfactory salvage procedure following an infected TKA, especially in elderly patients, and can provide reliable, painless extremity and satisfactory quality of life.
