Different therapeutic options for prosthetic joint infections exist, but surgery remains the key. With a two-stage exchange procedure, a success rate above 90% can be expected. Currently, there is no consensus regarding the optimal duration between explantation and the reimplantation in a two-stage procedure. The aim of this study was to retrospectively compare treatment outcomes between short-interval and long-interval two-stage exchanges.

Patients having a two-stage exchange of a hip or knee prosthetic joint infection at Lausanne University Hospital (Switzerland) between 1999 and 2013 were included. The satisfaction of the patient, the function of the articulation and the eradication of infection, were compared between patients having a short (2 to 4 weeks) versus a long (4 weeks and more) interval during a two-stage procedure. Patient satisfaction was defined as good if the patient did not have pain and bad if the patient had pain. Functional outcome was defined good if the patient had a prosthesis in place and could walk, medium if the prosthesis was in place but the patient could not walk, and bad if the prosthesis was no longer in place. Infection outcome was considered good if there had been no re-infection and bad if there had been a re-infection of the prosthesis

145 patients (100 hips, 45 knees) were identified with a median age of 68 years (range 19–103). The median hospital stay was 58 days (range 10–402). The median follow-up was 12.9 months (range 0.5–152). 28 % and 72 % of the patients had a short-interval and long-interval exchange of the prosthesis, respectively. Patient satisfaction, functional outcome and infection outcome for patients having a short versus a long interval are reported in the Table.

The patient satisfaction was higher when a long interval was performed whereas the functional and infection outcomes were higher when a short interval was performed. According to this study a short-interval exchange appears preferable to a long interval, especially in the view of treatment effectiveness and functional outcome.

Background: Antibiotic-loaded spacers and cement nails are commonly used in patients undergoing a two-stage implant exchange procedure for treatment of prosthetic joint infection (PJI). During re-implantation 2–6 weeks after implant removal, tissue specimens are collected to document successful eradication of infection. However, these specimens have limited sensitivity, especially in patients receiving antimicrobial treatment. We investigated the value of sonication of removed spacers and cement nails.

Methods: We prospectively included patients in whom a spacer or cement nail was removed from January 2007 through April 2009 during a two-stage exchange procedure. The removed temporary device was sonicated in a container with Ringer’s solution in an ultrasound bath for 5 min at 40 kHz (as described in NEJM2007;357:654). The resulting sonication fluid was cultured aerobically and anaerobically for 10 days. In parallel, > 2 tissue samples were collected for conventional cultures on blood agar plates and enrichment broth. PJI was defined as visible purulence, acute inflammation on histopathology, sinus tract or significant microbial growth in tissue or implant sonication cultures.

Results: In this ongoing study, 28 spacers and 10 cement nails from patients with confirmed PJI were included (median age 75 y; range 49–86 y). All devices were impregnated with antibiotics (gentamicin and/or vancomycin) and were placed in the hip (n=21), knee (n=9) or shoulder joint region (n=7). At the time of explantation, the following pathogens were isolated: coagulase-negative staphylococci (n=19), Staphylococcus aureus (n=7), Streptococcus agalactiae (n=3), Propionibacterium acnes (n=5) and mixed infection (n=4). All patients received systemic antibiotics for a median of 19 days (range 11–42 days) before removal of the spacer/nail. At the time of re-implantation, tissue cultures were negative in all 38 patients, whereas sonication cultures showed growth of Propionibacterium acnes in 2 of 38 patients (5%) with a hip and shoulder spacer, both in significant numbers (150 and 550 colonies/ml sonication fluid, respectively). These organisms were probably present as mixed infection already at the time of explantation, but were missed due to overgrowth due to another organism (S. aureus in one patient and coagulase-negative staphylococci in another). Both patients were not initially treated for the Propionibacterium acnes infection, but the treatment was given after re-implantation.

Conclusion: Sonication of removed spacers is a suitable approach to identify persistent infection in patients with a two-stage exchange. Sonication may replace the current standard approach consisting of multiple tissue specimens in order to document successful eradication of infection.

Background: Negative pressure wound treatment is increasingly used through a Vacuum-Assisted Closure (VAC) device in complex wound situations. For this purpose, sterile polyurethane (PU) and polyvinyl alcohol (PVA) foam dressings are fitted to the wound size and covered with an adhesive drape to create an airtight seal. Little information exists about the type and quantity of microorganisms within the foams. Therefore, we investigated VAC foams after removal from the wound using a validated method (sonication) to detect the bacterial bioburden in the foam consisting as microbial biofilms.

Methods: We prospectively included VAC foams (PU and PVA, KCI, Rümlamg, Switzerland) without antibacterial additions (e.g. silver), which were removed from wounds in patients with chronic ulcers from January 2007 through December 2008. Excluded were patients with acute wound infection, necrotizing fasciitis, underlying osteomyelitis or implant. Removed foams from regular changes of dressing were aseptically placed in a container with 100 ml sterile Ringer’s solution. Within 4 hours after removal, foams were sonicated for 5 min at 40 kHz (as described in NEJM2007;357:654). The resulting sonication fluid was cultured at 37°C on aerobic blood agar plates for 5 days. Microbes were quantified as No. of colony-forming units (CFU)/ml sonication fluid and identified to the species level.

Results: A total of 68 foams (38 PU and 30 PVA) from 55 patients were included in the study (median age 71 years; range 33–88 years, 57% were man). Foams were removed from the following anatomic sites: sacrum (n=29), ischium (n=18), heel (n=13), calves (n=6) and ankle (n=2). The median duration of being in place was 3 days (range, 1–8 days). In all 68 foams, bacteria were found in large quantities (median 105 CFU/ml, range 102–7 CFU/ml sonication fluid. No differences were found between PU and PVA foams. One type of organisms was found in 11 (16%), two in 17 (24%) and 3 or more in 40 (60%) foams. Gram-negative rods (Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa) were isolated in 70%, followed by Staphylococcus aureus (20%), koagulase-negative staphylococci, streptococci (8%), and enterococci (2%).

Conclusion: With sonication, a high density of bacteria present in VAC foams was demonstrated after a median of 3 days. Future studies are needed to investigate whether antimicrobial-impregnated foams can reduce the bacterial load in foams and potentially improve wound healing.