Sunday, November 30, 2014

Propionibacteriium and Staph infection in shoulder arthroplasty - not that easy to treat.

Management of deep postoperative shoulder infections: is there a role for open biopsy during staged treatment?

The authors'  current treatment algorithm for infected shoulder arthroplasty includes explant of the infected prostheses, followed by antibiotic cement spacer placement and at least a 6-week course of antibiotic therapy before reimplantation of a new prosthesis. Even with this vigorous treatment they note that reinfection rates of between 0% and 37% have been reported after a 2-stage revision.

They reviewed 18 patients having periprosthetic shoulder infections and osteomyelitis after previous surgery who were treated with a standardized protocol of irrigation and debridement, removal of implants, antibiotic cement spacer placement (1 gram vancomycin and 1.2 grams tobramycin for every bag of polymethyl methacrylate), and pathogen-directed antibiotic therapy for 6 weeks. Open biopsies were performed in the operating room after a 4-week antibiotic holiday period. Revision arthroplasty was performed at a later date if final cultures were without evidence of infection. If evidence of infection persisted, then another course of I&D and antibiotic treatment was performed.

Four patients (22%) had evidence of persistent infection on specimens from open biopsy and required another course of formal I&D, spacer exchange, and a 6-week course of antibiotic therapy. After a second course of therapy, specimens from repeat biopsies were sterile for 3 of these 4 patients, and their prosthesis was able to be replanted. One patient had positive cultures again at his third biopsy and required a third round of surgical and antibiotic therapy according to the protocol. Results from specimens from this patient’s third open biopsy were negative, and he was replanted with a RTSA.

At the first revision, the most common pathogens isolated were Propionibacterium acnes (44%), Staphylococcus epidermidis (39%), and S aureus (22%). The infecting pathogen in 75% of patients with persistent infection was P acnes, and 38% of patients with P acnes infection had recurrence. 

Mean follow-up of 24 months showed no signs of recurrent infection in any patient and an average American Shoulder and Elbow Surgeon score of 71.

These authors recognize that simple needle aspirates are insufficient for excluding infection: often the organisms reside in biofilms such that tissue biopsies are necessary to recover them.

Note that the patients in this case series had obvious periprosthetic infections with deep draining sinus, purulent drainage from the wound, erythema, abnormal white blood cell, C-reactive protein, erythrocyte sedimentation rate, computed tomography, magnetic resonance imaging, and

joint aspiration.

It is indeed impressive to note the persistence of positive cultures after such a vigorous initial course of surgical and medical treatment. 

While this is a labor intensive and expensive protocol, it is rewarding to see that all 18 of these patients were free of clinical signs of infection two years after their last revision procedure.

Finally, it is important to distinguish these cases of clinically apparent periprosthetic infection with the revision arthroplasty with positive cultures but without clinical signs of infection.


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