What is a shoulder infection?

While the diagnosis of obvious shoulder infection is easy: the patient has local and systemic signs of inflammation, abnormal joint fluid and serum lab tests, and positive cultures for indisputable pathogens. 

On the other hand, the diagnosis of a stealth shoulder infection is complicated: the most frequently implicated bacteria (Cutibacterium) is a commensal organism commonly isolated from normal skin, normal deep tissues and healthy shoulder joints. In a stealth infection the usual clinical evidence of infection is absent.

A pragmatic definition of bacterial infection is "bacteria doing harm". That is, the presence of bacteria in and of itself is not sufficient to prove infection. Bacteria in the large intestine; bacteria in sebaceous glands; bacteria recovered from normal joints would not meet the definition whereas E. coli colitis, acne, and joint sepsis would. 

A recent paper,The incidence of subclinical infection in patients undergoing revision shoulder stabilization surgery: a retrospective chart review, exemplifies the challenge. The authors sought to identify the incidence of subclinical infection in 107 patients undergoing revision shoulder stabilization surgery by an experienced shoulder surgeon. Notably the average time from the instability repair to revision was 8 years. The reasons for revision were not provided. Surgical findings (synovitis, purulence, gram stain results) were not given. 

Twenty-nine patients (27.1%) had positive cultures. Patients had multiple specimens sent for culture; the average and range for the number of cultures submitted is not provided. Thirteen patients had only1 positive culture (11 for Cutibacterium). 9 patients had two positive cultures Eight had 3 or more positive cultures (all for Cutibacterium). 

 The paper does not state whether the patients were given antibiotic coverage for the several weeks while the culture results were pending rather than waiting until the results were finalized. The treatment for those patients with positive cultures is not provided.

Twenty-six of these patients (90%) had positive Cutibacterium cultures. The average time to culture positivity was 11 days.

The paper does not state whether any patients developed clinical manifestations of infection.

Comment: It is difficult to know whether these positive cultures obtained on average 8 years after surgery in the absence of other supporting evidence actually represent an infection, i.e. did the bacteria cause harm?

If the surgeon is suspicious of an infection, a reasonable strategy would be to perform a thorough debridement and irrigation at the time of revision, take cultures for Cutibacterium, consider topical antibiotics, and postoperative antibiotics to be continued until the culture results are finalized.     Bases covered.

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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).