Aim

Femoral or tibial massive bone defects (AORI F2B-F3 / T2B-T3) are common in septic total knee replacement. Different surgical techniques are described in literature. In our study we show clinical and radiological results associated with the use of tantalum metaphyseal cones in the management of cavitary bone defects in two-stage complex knee revision.

Diagnosis of chronic prosthetic joint infection (PJI) is often challenging. Painful prosthesis is frequently due to an infection but to diagnose it is somethimes difficult. All recent guidelines stress the central role of joint punction in diagnosis of PJI if the infection is not demonstrated. However which test on synovial fluid must be carried out is not so clearly defined. Total white blood cell count and differential leukocite count are usually considered useful in diagnosis but cut offs reported by different studies are quite different. Moreover this test needs a relatively large amount of fluid and blood contamination of it largely affects the result. What's more the synovial fluid WBC count may be unreliable in the setting of a metal-on-metal bearing or corrosion reaction.

Routine cultures should be maintained between 5 and 14 days, their sensitivity appears low in chronic infection even if witholding antimicrobial therapy before the collection of the fluid can increase the likelihood of recovery an organism.

Synovial leukocyte esterase can be performed as a rapid office or intraoperative point of care test using urinalysis strips. It is cheap and easy to perform, but the presence of blood in the sample can affect the result and it needs centrifugation.

Recently a new test has been proposed to detect alfa-defensine in synovial fluid. It shows a high sensitivity and an exellent specificity.

We performed 25 joint punctions on 25 patients with suspected PJI (enrollment is going on). Synovial fluid collected was tested for: leukocite esterase, WBC count and differential, colture in blood colture bottle for anerobe and aerobes (BacT/ALERT Biomerieux, inc) and detection of alfa-defensine level (Synovasure – Zimmer)

In patients who underwent surgery at least 5 samples of periprotesic tissue were collected for microbiologic analysis and the removed implant was sonicated according with the methodic. Furthermore samples for frozen section were sent and a histologic examination was made according to the Moriewitz – Kerr classification. The MSIS criteria was utilized to classify the case as infected or not.

Prosthetic joint infections (PJI) occur in 0.8–1.9 % of arthroplasties, but the absolute number is increasing because of the frequency of procedures. Two stage exchange is the most effective strategy, but failures are often described. Culture of perioperative tissues during removal of arthroplasty is a standard procedure but culture during second step is equally important to define a success or a failure.

We retrospectively reviewed PJI treated with two stage-exchange from January 2011 and December 2012 at “Ospedale S. Maria Misericordia”, Albenga-Italy. The procedure calls for bacterial culture not only during first step but also during reimplantation. Antibiotic treatment is prolonged after reimplantation until the cultures availability. A failure was defined by persistence of infection for positive culture or reocurrence of infection during a follow up of at least 2 years in patients with negative cultures. Three positive cultures yielding phenotypically identical organisms, or a single specimen of a virulent microorganism (e.g. Staphylococcus aureus) were required to rule out false positive for contaminants. Patients with persistence of infection were treated for 3 months with antibiotics.

86 patients underwent the two stage treatment: 45 hip and 41 knee prosthesis. The average ESR before arthroplasty removal was 59 mm/ 1st h (range 5–120), the average CRP was 3.9 mg/dl (range 0.3 – 34). Coagulase-negative staphylococci were isolated in 31 cases, Staphylococcus aureus in 19, Streptococcus spp in 8 and enterococci in 4. Gram-negatives were isolated in 4 patients and polymicrobial infection in 6 patients. In 14 patients (16%) no pathogen was identified.

A positive culture during reimplantation was documented in 11 (13%) cases: 8 coagulase-negative staphylococci, 2 Staphylococcus aureus, 1 Candida sp. All patients received 3 months of therapy after surgery and 6 of them were free of infection at 2 years of follow up after the end of treatment. Among the 75 patients with negative cultures, a relapse was documented in 2 (3%), after 5 and 24 months, respectively. These cases were treated with arthrodesis and 6 weeks antibiotic treatment, with resolution of infection but poor functional results. Overall the success rate of our strategy was 92% (79/86).

In patients treated with two-stage exchange, the combination of cultures at reimplantation and antibiotic suppressive treatment for 3 months in presence of positive cultures, are associated with a high rate of success. Only a prolonged follow up can rule out a relapse and agree with a true resolution of infection.

Of the 6075 patients enrolled in EU-CORE registry, 206 patients had orthopaedic device-related infections. Significant underlying diseases were reported in 71% patients, most frequently cardiovascular disease (38%). The common sites of infection were knee (40%) and hip (33%). Among the 170 patients with available culture results, 135 (79%) were positive. Coagulase-negative staphylococci (CoNS, 44%) and Staphylococcus aureus (43%, of those 47% were methicillin resistant) were the most commonly isolated pathogens. Daptomycin was used empirically in 48% patients and as second-line therapy in 67% patients. During daptomycin therapy, 67% patients had undergone surgery (debridement, 61%; removal of foreign device, 39%; incision and drainage, 9%). Over half of the inpatients (54%) received concomitant antibiotics. Daptomycin was most frequently prescribed at a dose of 6 mg/kg/day (48%), with a median duration of therapy of 16 (range, 1–176) days. The overall clinical success rate was 85%, and was similar whether daptomycin was administered as first- or second-line therapy. The success rates achieved for infections caused by S. aureus and CoNS were 86% and 83%, respectively. Among the 79 patients who entered the long-term follow-up, 85% had a sustained response. Adverse events (AEs) and serious AEs possibly related to daptomycin were reported in 4.4% and 1.9% patients, respectively.

Results from this real-world clinical experience showed that daptomycin is an effective and well-tolerated treatment option for orthopaedic device-related infections with a high success rate up to 2 years of follow-up.