Septic arthritis is a rare form of infection in the healthy adult population, especially adults who have never been submitted to any articular procedure. Our objective is to describe a rare case of an infectious arthritis of a hip caused by bone abscess in a previously healthy patient with few risk factors.

This is the case of a 40 year-old female, who had a history of heavy smoking and low socioeconomic status. She was examined complaining with pain in the left hip and the x-ray showed a lytic image in the intracapsular femoral neck, but it was overlooked and the diagnosis of bone abscess was missed. She was to the hospital 3 weeks later with intense pain and a suppurative and swollen right thigh. Blood analyses were compatible with infection (elevated white-blood cells and C-reactive protein). Pelvic CT scan showed a lytic image in the intracapsular femoral neck with pus inside the hip. It also showed a huge abscess and infiltration of the tissues surrounding. She was then submitted to multiple surgeries in order to drain the abscess and articular cleaning. A S. aureus MSSA was isolated and an adequate antibiotic was instituted. Although this measures, there was only partial clinical and analytical success.

We eventually ended-up by resecting the femoral head, which had no viability, as shown in an MRI, and was behaving as a sequestrum, justifying the impossibility in controlling the infection. The femoral head was replaced by a temporary cement-spacer impregnated with vancomycin, and the patient maintained adequate antibiotic therapy until normalization of the infection parameters. She now has no signs of infection, and is waiting to be submitted to a total hip replacement.

This is a rare case of a septic arthritis with an uncommon onset in a healthy woman who had never been submitted to a hip procedure and had no local risk factors for the development of such pathology. In the research we did, we found no other case similar to this, in which the arthritis started as an intracapsular bone abscess with hematogenous origin. Reporting this case, we would also like to emphasize that, although its rarity, it is extremely important to always exclude septic arthritis in cases of joint pain, in order to prevent catastrophic consequences.

Infection after total knee replacement, which is a serious and expensive complication, often represent a diagnostic and therapeutic problem. The current incidence of infection after the primary procedure is 1 to 3%, depending on the published series. A correct and timely diagnosis, classification between early and delayed infection, and which microorganisms are involved, are crucial steps in defining prevention and treatment strategies.

Determination of the annual and three years incidence of infection after primary total knee replacement; evaluation of the microorganisms involved and its resistance patterns; assessment of treatment – surgical approach and selection of antibiotics.

Collection of clinical and laboratorial data of all patients who underwent primary total knee arthroplasty between 2011 and 2013 in our hospital; definition of periprosthesic infection cases following the Musculoskeletal Infection Society (MSIS) criteria.

During the study period, 526 primary knee replacements were performed in 521 patients; with 41 patients having bilateral replacements. The mean follow-up period was 30 months; 5 patients had no follow up and 1 died in the post operatory.

We reported 9 prosthetic infections, of which 2 did not reached the MSIS criteria, but were also considered based on high clinical suspicion. The majority of the cases (6) were delayed infections. The calculated 3 year incidence of infection after primary knee replacement was 1,6%, with annual rates of 3,0% (2011), 1,7% (2012) and 0,9% (2013). The microorganisms isolated were as follows: Staphylococcus aureus and coagulase-negative staphylococci, resistant to penicillin; Streptococcus agalactiae and one isolate of Serratia marcescens, both showing multiple antibiotic resistances.

Only one case was treated with surgical debridement and conservation of prosthesis, in the other 8 cases a two-stage implant revision procedure was performed. The antibiotics selected were vancomycin, fluoroquinolones and association of gentamicin and clindamycin.

Our local infection rates are in line with the published series from reference surgical centers. The annual incidence is decreasing, probably because the majority of our infection cases are delayed (recent years, shorter follow up period) and our preventive measures are improving. The microorganisms identified are also in agreement with published data, and our antibiotic resistance pattern is a valuable information to consider in a first empirical approach.

Treatment options suitable to each case, and antibiotic protocols need to be improved in our local practice. Preventive measures in delayed infections are still under debate, and represent another future challenge.