Review Question - QID 220055

The patient has an obviously loose and dislocated glenoid base plate (Illustration A). A periprosthetic joint infection workup of the shoulder with aspiration results yielding a positive culture for Staphylococcus aureus does, in fact, have a high specificity and positive predictive value for infection (Answer 2).

The value of joint aspiration in the evaluation of shoulder prosthetic joint infections (PJI) is less clear than in the lower extremity counterparts, namely total hip and knee PJI. Shoulder aspiration, even under imaging guidance, rarely yields enough synovial fluid for analysis and culture, making dry taps frequent. The presence of a dry tap alone, however, does not rule out infection. Fluoroscopic and ultrasonography-guided aspiration, furthermore, may ensure intra-articular placement of the tools for aspiration, but both techniques are operator-dependent, add additional costs, and have not been shown to increase aspirate or culture yields. In the event that enough fluid is obtained, positive culture results do have a high specificity and positive predictive value for infection, but still exhibit an overall low sensitivity and negative predictive value in the absence of an adequate fluid sample.

Dilisio et al. reviewed the use of arthroscopic tissue culture for the evaluation of periprosthetic shoulder infection compared to fluoroscopically guided glenohumeral aspiration. The authors retrospectively reviewed 19 patients who had undergone culture of arthroscopic biopsy tissue during the evaluation of a possible chronic periprosthetic shoulder infection and found that 41% of those with culture results at that time had a positive result, which included Propionibacterium acnes in each case. All arthroscopic biopsy culture results were consistent with the culture results obtained during the revision surgery, yielding 100% sensitivity, specificity, positive predictive value, and negative predictive value. In contrast, fluoroscopically guided glenohumeral aspiration yielded a sensitivity of 16.7%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 58.3%. They concluded that arthroscopic tissue biopsy is a reliable method for diagnosing periprosthetic shoulder infection and identifying the causative organism.

Paxton et al. reviewed the diagnosis and management of periprosthetic joint infections of the shoulder. The authors note that the most common organisms responsible for the infection are Cutibacterium acnes (formerly Propionibacterium acnes) (∼39%) and coagulase-negative Staphylococcus (∼29%). They also highlight the fact that while periprosthetic joint infections of the shoulder due to Staphylococcus aureus and other highly virulent organisms are often easy to diagnose and are usually treated with two-stage revisions, infections with C. acnes and coagulase-negative Staphylococcus pose a challenge to the surgeon because traditional diagnostic tests (erythrocyte sedimentation rate, C-reactive protein, and joint aspiration) have a low sensitivity due to the lack of an inflammatory response. They conclude that unexpected positive cultures for C. acnes during revision surgery are not uncommon and that the proper management is still under investigation and remains a challenge.

Figure A is an AP radiograph of the shoulder showing a clearly loose and dislocated glenoid baseplate and glenosphere, which is also demarcated with a red arrow in Illustration A showing the articulating surface of the glenosphere that should be positioned 180 degrees in the opposite direction..

Incorrect Answers:
Answer 1: Shoulder aspiration has been shown to have both a low sensitivity and a low negative predictive value for ruling out a periprosthetic joint infection.
Answer 3: Patients should be off antibiotics for 2 weeks before aspiration for optimal culture results.
Answer 4: A dry tap alone is not sufficient to rule out a periprosthetic joint infection of the shoulder.
Answer 5: Though fluoroscopic guidance increases the likelihood of accurate intra-articular aspiration, it has not been shown to increase the positive or negative predictive values of shoulder aspirations for the diagnosis of shoulder PJI.