Can surgeons differentiate between painful shoulders that grow Cutibacterium acnes and infection benefitting from treatment?

The purpose of our study is to augment the knowledge of patient dissatisfaction after a shoulder arthroplasty. A total of 353 shoulders were prospectively enrolled into the Shoulder Arthroplasty Failure Experience (SAFE) project. Of these, 282 patients had complete data for the final analysis, including demographic information, medical history, physical examination, standard radiographs, and the Simple Shoulder Test (SST) scores. These data were analyzed to determine the frequency of 17 possible characteristics of an unsatisfactory arthroplasty. Pain was the most common reason for patients to seek an evaluation (241 of 282 shoulders). Shoulder function was substantially reduced at presentation, with patients only able to perform an average of 2.6 of 12 SST functions. Overall, technical factors such as component malpositioning and glenohumeral malalignment were the most common characteristics identified among all the shoulders. Loosening of glenoid components was noted in 85 of the 136 total shoulder arthroplasties, and glenoid erosion was found in 51 of 80 hemiarthroplasties performed for degenerative conditions. Patients with an unsatisfactory outcome after shoulder arthroplasty present with poor shoulder function and pain. Component malposition, glenohumeral malalignment, and glenoid failure are all prevalent features among patients with an unsatisfactory outcome.

Cutibacterium acnes is a lipophilic, anaerobic, gram-positive bacillus that mainly colonizes the pilosebaceous glands of human skin. It has been implicated as the leading cause of prosthetic joint infection (PJI) after shoulder arthroplasty. However, PJI caused by C acnes rarely manifests as overt clinical, laboratory, or imaging features. In fact, more than 40% of shoulders undergoing revision arthroplasty are likely to be culture positive. However, rates of infection following a positive culture can be as low as 5%. The purpose of this review was to put forth alternative explanations for this discordance between positive cultures and infection. We describe C acnes roles as a commensal, bystander, and/or contaminant organism; the role of cultures in diagnosis and other methods that may be more accurate; its existence in a shoulder microbiome; and the variable virulence of C acnes. C acnes is an important cause of shoulder PJI in some patients. However, there is a large body of literature that suggests other functions that need to be considered. Further research is needed to define the role of C acnes that is logically explained by all of the literature and not only some.