These authors searched the PubMed and Embase databases for articles on shoulder arthroplasty infection. They found that Propionibacterium was the most commonly reported organism, representing 38.9% of infections, followed by Staphylococcus species.
Risk factors for shoulder shoulder arthroplasty infection include previous surgery, increased age, male sex, increased body mass index, diabetes mellitus, radiation therapy, lymphedema, malignant disease, oral steroid use, and prior osteomyelitis.
The average white blood cell count in 13 studies was 7472 cells/µL. Ten studies reported a mean erythrocyte sedimentation rate of 27.6 mm/h, whereas 14 studies reported a mean C-reactive protein level of 2.6 mg/dL.
P. acnes in intraoperative culture specimens was an independent risk factor for failed treatment for shoulder PJI.
The average white blood cell count in 13 studies was 7472 cells/µL. Ten studies reported a mean erythrocyte sedimentation rate of 27.6 mm/h, whereas 14 studies reported a mean C-reactive protein level of 2.6 mg/dL.
P. acnes in intraoperative culture specimens was an independent risk factor for failed treatment for shoulder PJI.
Single-stage revision produced the highest mean Constant score; implant retention resulted in the best range of motion.
Comment: This is an interesting summary of the available literature and points to how little we actually know about the evaluation and management of failed arthroplasties with positive cultures.
It is generally recognized that there is no useful definition of a 'periprosthetic shoulder infection'.
'Obvious' infections can be identified by applying the Musculoskeletal Infection Society criteria (presence of a sinus track to the prosthesis, 2 positive tissue or fluid culture samples, or 4 of 6 minor criteria (elevated ESR and CRP, elevated leukocyte count, elevated neutrophil percentage, purulence in the joint, isolated microorganism at culture, or > 5 neutrophils per high-power field on histology).
However, a large percentage of failed arthroplasties with positive cultures present in the 'stealth' mode months or years after the index surgery, presenting only as pain, stiffness, and / or implant loosening. These cases cannot be dismissed as 'false positives' because of the absence of the MSIS criteria.
In this study it is telling that over half of the cases were diagnosed over a year after the index surgery - in these instances, the infection could not have been 'obvious'.
The 'stealth' presentation problem confounds not only the criteria for 'infection' but also the definition of 'success' in treatment of failed arthroplasties with positive cultures. If these cases can present subtly years later, how can we know if and when they are 'cured'?
It is important to recall that whether or not a shoulder is culture positive depends on how many and what type of samples are submitted for culture and how and how long the samples are cultured.
This study does provide support for our current approach to failed arthroplasties that includes implant removal, primary reimplantation and postoperative antibiotic therapy because (1) we don't know at the time of surgery what the cultures will show, (2) if the cultures are positive, it is likely that the implants have a bacteria-containing biofilm that cannot be treated without implant exchange, and (3) function is better with a single stage exchange.
Long term followup of carefully characterized cases will be essential for resolving the many questions that currently face us regarding failed arthroplasties with positive cultures.
As we've learned recently, it's not over until it's over:
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