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.

Introduction: Posttraumatic osteitis is a localised inflammatory process leading to tissue destruction and eventually osteolysis. The molecular mechanisms underlying the disease progress are not yet fully understood. In a previous study we demonstrated infiltration of polymorphonuclear neutrophils (PMN) into the site of infection; the PMN were highly activated as seen by upregulation of the activation-associated surface receptors CD14 and CD64. In this study we analysed the superoxide generation by the infiltrated PMN as possible pathomechanism of the local tissue destruction.

Material and Methods: Ten patients with device-associated osteomyelitis requiring surgery were recruited into the study. When removing the infected implant the site was rinsed intraoperatively. The leukocytes were recovered, then activation-associated surface receptors were determined by cytofluorometry as was superoxide generation by reduction of cytochrome C.

Results: 1–2 x 10⁷ leukocytes were recovered from the «lavage» fluid; 80 to 90% were identified as PMN. The PMN were highly activated as seen by an upregulation of CD14 and CD64, and a concomitant downregulation of the selectin CD62L. In response to phorbol ester (PMA) the superoxide production of the infiltrated PMN was enhanced when compared to peripheral PMN of the same patient. The infiltrated PMN, but not the PMN of the peripheral blood, responded to the bacterial peptide f-Met-Leu-Phe (f-MLP) with superoxide production, indicating an enhanced responsiveness of the cells. The underlying molecular mechanisms were analysed in vitro using PMN of healthy donors: only the induction of superoxide production by f-MLP, but not by PMA, required a «priming» of the cells, for example by low doses of lipoploysaccharide (LPS) or cytokines (e.g. TNFa, IL-8).

Conclusions: In posttraumatic osteomyelitis PMN infiltrate the infected site; they are locally activated as seen by an upregulation of the appropriate receptors and by “priming” for superoxide generation. Priming of local PMN could on one hand potentiate the bactericidal activity, on the other hand contribute to tissue destruction. The occurrence of viable bacteria and activated «armed» PMN at the same site points to an esacpe mechanism, possibly due to biofilm formation. Due to their cytotoxic and proteolytic potential PMN might participate in local tissue destruction and osteolysis.

Introduction: The osteitis of the tibia still is a common problem in orthopaedic surgery. Long lasting treatment time and possible recurrent infections bring a lot of medical and social problems to the patient. We compared in this study a group being treated in the conventional way by bone grafting the defect with another group, which had an Ilizarov procedure to find out, which method brings better results for the patient.

Material and Methods: Each group consisted of 65 patients about the same age. The follow up time was averaged 7.5 years. The size of the defect was in the conventional group 2.5 cm in the Ilizarov group 6.4 cm. Patients were classified to the Cierny Mader Classifications in both groups. Each patient was examined at the time of follow up clinically and radiologically. Special topics were: Pain, job, social activity etc. Scores were evaluated using SF 36. More than this, a questionnaire was handed out to each patient which was filled out after the investigation and was mailed back from home, not to influence the patient during the investigation. These dates were scored by Nottingham Health Profile.

Results: Healing time with the Ilisarov group was longer on the total way, but related to 1 cm defect shorter. Time of hospitalization, number of operations were very similar in both groups. There were more leg length discrepancies and axis deviations in the Ilizarov group. Refering to the job 67% of the Ilizarov group, but only 48% of the conventional group returned to their original profession. Life quality (SF 36 and Nottingham Health Profile) testing was better in the Ilizarov group too. Recurrent infection was seen in the conventional group in 13.8%, in the Ilizarov group only in 9% including the pin track Osteitis. A recurrent infection in the callus distraction group was seen only in 1 case.

Conclusions: Ilizarov treated patients show better long tenn results, even if they are classified B-type hosts, according to the Cierny Mader Classification. They return earlier to work and demonstrate better life quality results. In future these results might even be better, if axis deviations and leg length discrepancies could be minimized. With host B patients the conventional treatment should not be favoured, Ilizarov procedure brings better results too.

After experimental and preclinical evaluation (HAP Paul Award 2001) of a CT-free image guided surgical navigation system for acetabular cup placement, the system was introduced into clinical routine. The computation of the angular orientation of the cup is based on reference coordinates from the anterior pelvic plane concept. A hybrid strategy for pelvic landmark acquisition has been introduced involving percutaneous pointer-based digitisation with the non-invasive bi-planar landmark reconstruction using multiple registered fluoroscopy images.

From January 2001 to May 2002 a total of 118 consecutive patients (mean age 68 years, 82 male, 36 female, 62 left and 56 right hip joints) were operated on with the hybrid CT-free navigation system. During each operation the angular orientation of the inserted implant was recorded.

To determine the placement accuracy of the acetabular components the first 50 consecutive patients underwent a CT scan seven to ten days postoperatively to analyse the cup position related to the anterior pelvic plane. This was done blinded with commercial planning software. There was no significant learning curve observed for the use of the system.

Mean values for postoperative inclination read 43° (SD 3.0, range 37 to 49) and anteversion 19° (SD 3.9, range 10 to 28). The resulting system accuracy, i.e., the difference between intraoperatively calculated cup orientation and postoperatively measured implant position shows a maximum error of 5° for the inclination (mean 1.5°, SD 1.1) and 6° for the anteversion (mean 2.4°, SD 1.3).

An accuracy of better than 5° inclination and 6° ante-version was achieved under clinical conditions, which implies that there is no significant difference in performance from the established CT-based navigation methods. Image guided CT-free cup navigation provides a reliable solution for future THA.