The utility and cost of atypical cultures in revision shoulder arthroplasty

At the time of revision shoulder arthroplasty, it is common practice to take cultures to evaluate for prosthetic joint infection even when an alternative cause of failure has been identified. Although isolation of fungal or acid-fast organisms is rare, it remains common practice to send all specimens for aerobic, anaerobic, and atypical (fungal and acid-fast) cultures. We hypothesize that the rate of positive atypical cultures at the time of revision shoulder arthroplasty is very low and routine use imposes a considerable financial burden on the health care system.

A retrospective review of all revision shoulder arthroplasties performed between January 1, 2010, and December 31, 2019, at our institution was performed. Patients with a hemiarthroplasty, total shoulder arthroplasty, reverse shoulder arthroplasty, or pre-existing antibiotic spacer who underwent revision to hemiarthroplasty, total shoulder arthroplasty, reverse shoulder arthroplasty, antibiotic spacer, or resection arthroplasty were included. Electronic patient charts were reviewed to gather patient, surgical, and culture data. An analysis of the hospital billing charges associated with each culture was performed using our hospital billing database and the current procedural terminology (CPT) codes for aerobic, anaerobic, fungal, and acid-fast cultures. A secondary outcome analysis was performed to identify factors associated with positive cultures.

A total of 237 revision shoulder arthroplasties performed on 189 patients were analyzed. Cultures were sent on 158 of 237 (66.7%) surgeries with an average of 2.2 specimens per surgery. A total of 341 aerobic, 331 anaerobic, 187 fungal, and 174 acid-fast cultures were collected. Positive cultures were found in 52 of 341 (15.2%) aerobic cultures and 36 of 331 (10.9%) anaerobic cultures. The most commonly isolated organism was Cutibacterium acnes (42.2%), followed by methicillin-resistant Staphylococcus aureus (15.6%), coagulase-negative Staphylococcus species (13.3%), and methicillin-sensitive S. aureus (12.2%). There were zero positive fungal or acid-fast cultures in our series. The total billing charges for aerobic, anaerobic, fungal, and acid-fast cultures over the study period were $77,748, $23,832, $8,789, and $106,662, respectively, with atypical cultures accounting for 53.2% of the total charges for all cultures. For a single sample sent for all 4 culture types, atypical cultures account for 69% of the total amount charged.

Isolation of fungal or acid-fast organisms at the time of revision shoulder arthroplasty is rare and imposes a considerable financial burden when these atypical cultures are sent on a routine basis. The collection of fungal and acid-fast cultures should be reserved for patients in whom risk factors for these atypical organisms have been identified.