Winston J. Warme,Jason E. Hsu

Periprosthetic shoulder infections associated with Propionibacterium have become a diagnostic challenge for surgeons treating patients with refractory pain and stiffness. This organism can complicate not only shoulder arthroplasties but also nonarthroplasty procedures, such as shoulder arthroscopy and spine surgery. The predilection for the shoulder and the back is likely related to the topographic variation of the skin microbiome. The highest density of Propionibacterium is typically found in the pilosebaceous glands of the oily anterior part of the chest and back, and so bacteria can easily be introduced into the deep tissues at the time of surgery.

The shoulder arthroplasty community is far from a consensus on how to diagnose and manage revision arthroplasty associated with positive Propionibacterium cultures. Periprosthetic shoulder infections do not present with typical signs of erythema and drainage as with periprosthetic hip and knee infections. The presentation can be clandestine, with patients reporting vague stiffness and discomfort often years after an initially successful arthroplasty and often presenting with “aseptic” component loosening.

As we know, because Propionibacterium is a fastidious, slow-growing organism, its growth and identification are more difficult than that associated with organisms such as Staphylococcus and Streptococcus. Often, surgeons attempting to make the diagnosis of a periprosthetic shoulder infection will send multiple specimens from different areas of the shoulder for culture and then are obligated to wait two to three weeks to confirm the diagnosis. Many may wonder: what is the clinical relevance of something that takes three weeks to grow and only grows in one or two of many specimens sent to the microbiology laboratory?

The authors should be commended for a well-done study that tackles this difficult and important question. By reviewing preoperative, intraoperative, and microbiology data from forty-six revision shoulder arthroplasties associated with positive cultures of Propionibacterium, they conclude that faster time to positivity and a higher proportion of positive cultures could help clinicians distinguish a “true positive” from a “false positive” culture result.