Three questions arise with respect to periprosthetic infections:
I. How do we know if the shoulder is infected?
II. How do we treat the possibly infected shoulder?
III. How do we know if our infection treatment was successful?
When we have a shoulder that is not doing well after arthroplasty and is in need of revision we can consider three scenarios:
A. Obvious mechanical failure (bone failure (fracture), soft tissue failure (rotator cuff, subscapularis, deltoid), implant failure (breakage or loosening). If the decision is made for surgery, we obtain deep tissue and/or implant cultures knowing that the risk of mechanical failure is increased in the presence of infection. Commonly we keep the patient on oral antibiotics until the results of the cultures are finalized.
B. Obvious infection (findings such as swelling, tenderness, erythema, wound drainage, elevated serum inflammatory markers, purulent joint fluid, obvious synovitis). The causative organism - often virulent, such as MRSA or gram negative bacteria - can commonly be recovered by preoperative culture of fluid aspirated from the swollen joint. In such situations a two-stage revision (first a spacer and then a revision arthroplasty) combined with culture-specific antibiotics is often considered because the causative organism is frequently virulent.
C. Everything else. In this situation the shoulder is often painful and stiff without obvious cause. Or there may be a degree of component loosening or glenoid wear. In this situation, preoperative tests (serum lab tests and cultures or lab tests of joint fluid aspirates) and intraoperative frozen sections are relatively insensitive to the presence of a stealth infection from organisms such as Cutibacterium - the most common bacterial cause of periprosthetic shoulder infection. Serum blood tests (WBC, C-reactive protein, sedimentation rate) are often normal. Joint fluid may not be available on aspiration; if available, cultures of joint fluid may show no growth in spite of a periprosthetic infection. Frozen section results may be equivocal (e.g. > 5 white cells in several high powered fields). The final results of deep tissue and explant cultures are not available until weeks after the revision is completed, so that these results cannot inform the surgical procedure.
So it is this group "C" that can create confusion. In most cases, the diagnosis of periprosthetic infection cannot be ruled out with any reasonable degree of certainty by preoperative or intraoperative tests. Thus for most of these cases we consider the "guilty until proven innocent" approach: harvest at least five deep tissue and/or explant samples for Cutibacterium-specific culture (broth, aerobic and anaerobic media observed for three weeks), perform a single-stage revision with thorough debridement and lavage, and cover the patient with antibiotics (often oral Doxycycline) until the culture results are final - at which time antibiotics are stopped, continued or modified based on the outcome of the cultures.
The next question is: if a periprosthetic infection is diagnosed by multiple positive intraoperative cultures, how do we know if our treatment of the infection was successful? The answer is: in most cases we do not know. A number of authors state that an infection "cure" can only be documented if a patient has a second revision at which time cultures are negative. Most patients do not have a "perfect" shoulder after revision surgery. If the patient has persistent symptoms but doesn't want yet another surgery, we don't know if bugs remain in the shoulder. The tipping point for yet another revision needs to be based multiple factors, most importantly whether there is evidence that repeat revision is likely to improve the quality of life of the patient.
While this is a highly simplified approach, it can serve as a starting point for individualizing the care of each patient.
Factors affecting risk of recurrence with periprosthetic infection in shoulder arthroplasty is an interesting paper to review in light of the above. These authors reviewed 790 revision arthroplasties for a minimum of two years. 114 had least 1 positive culture. A recurrence was defined as a revision surgery that grew the same organism - by this definition patients having a single stage revision had a 5% rate of recurrence (i.e. a second revision with a positive culture). Cases caused by the highly virulent methicillin-resistant Staphylococcus aureus (MRSA) - obvious infections - had a recurrence rate of 30.8% compared to 4.0% and 5.9% in Cutibacterium and Coagulase-negative staphylococci, respectively.
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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).
