Review Question - QID 213910

The patient has developed a prosthetic joint infection (PJI) after his rTSA. Risk factors for PJI after TSA include coagulopathy, smoking, male, CSI within 3 months of surgery, TSA due to a fracture, revision TSA, ESRD, Lupus and rheumatoid arthritis (RA).

Periprosthetic shoulder infections are a major cause of revision after TSA with rates of 3-4%. They are more common to occur in the first 2 years and the most likely pathogen is P. Acnes (which is concentrated primarily in the axilla). P. Acnes requires incubation between 7-21 days prior to growth and as such, cultures are usually negative in the first 3-5 days. Methods to prevent shoulder PJI include antibiotic prophylaxis (clindamycin for P. acnes), hydrogen peroxide prep, using derma bond, and using silver-impregnated dressings. Treatment of shoulder PJI is similar to treatment of hip/knee PJI with the gold standard being a 2 stage revision and implant exchange.

Frangiamore et al. performed a prospective study on 33 patients with painful shoulder arthroplasty that required revision surgery, 11 of which were diagnosed as infected. The pre-operative intra-articular fluid was obtained and sent for α-defensin, which was compared to baseline data on normal α-defensin levels in the shoulder. Synovial α-defensin had sensitivity and specificity of 63% and 95% for PJI. The authors concluded that articular α-defensin was more effective than current diagnostic testing in predicting positive cultures and may be an effective adjunct in the workup of shoulder PJI.

Richards et al. performed a retrospective cohort study on 3906 patients who underwent primary TSA to determine the patient-specific risk factors for deep infection. The authors noted that male patients had a 2.5 increased likelihood of infection compared to females. Patients having a TSA after a fracture had a 3 fold higher risk of infection compared to elective TSAs. They noted that BMI, race, ASA score, and diabetes status were not associated with infection risk. They also found that P. Acnes was the most commonly cultured organism, accounting for 31% of isolates.

Werner et al. performed a retrospective database query of Medicare patients who underwent arthroplasty after ipsilateral shoulder injection to assess the risk of the timing of pre-operative intra-articular corticosteroid injections on the risk of post-operative infection. The authors created 3 arthroplasty cohorts: arthroplasty within 3 months of injection (n = 636), arthroplasty between 3 and 12 months after injection (n = 1573), and matched control arthroplasty (n = 6211). Infection rates within 3 and 6 months postoperatively were assessed. The incidence of infection after arthroplasty at 3 months (3.0%; OR, 2.0; P = .007) and 6 months (4.6%; OR, 2.0; P = .001) was significantly higher in patients who underwent injection within 3 months before arthroplasty compared with controls. The authors concluded that there was a significant increase in postoperative infection in Medicare patients who underwent injection within 3 months before shoulder arthroplasty. This association was not noted when shoulder arthroplasty occurred >3 months after injection.

Figure A: AP of the shoulder revealing a well-placed rTSA prosthesis.

Incorrect Answers:
Answer 1: There are several medical comorbidities that place a patient at increased risk for a shoulder PJI: coagulation, ESRD, Lupus, and RA.
Answer 2: A TSA placed for a fracture has a 3-fold increase in the rate of shoulder PJI compared to an elective TSA.
Answer 3: Males have a 2.5-fold increase rate of shoulder PJI compared to females.
Answer 4: Smokers have a significantly increased risk of shoulder PJI as compared to non-smokers.