Our aim was to investigate the prevalence ofPropionibacterium (P.) acnesin the subcutaneous fat and capsule of patients undergoing shoulder surgery for frozen shoulder or instability.Patients and Methods
A total of 46 patients undergoing either an arthroscopic capsular release or stabilisation had biopsies taken from the subcutaneous fat and capsule of the shoulder at the time of surgery. These samples were sent for culture in enrichment, and also for Nucleic Acid Amplification testing. The prevalence ofP. acnesand other microbes was recorded. Fisher's exact test of binary variables was used to calculate the association with significance set at p < 0.05. Assessment of influence of independent variables including a pre-operative glenohumeral injection, fat colonisation and gender, was undertaken using binary linear regression.Results
A total of 25 patients (53%) hadP. acnesin one or more tissue samples and 35 (74%) had other bacterial species. The same microbe was found in the subcutaneous fat and the capsule in 13 patients (28%). There was no statistically significant association between the surgical pathology and capsular colonisation withP. acnes(p = 0.18) or mixed identified bacterial species (p = 0.77). Male gender was significantly associated with an increased capsular colonisation ofP. acnes(odds ratio (OR) 12.38, 95% confidence interval (CI) 1.43 to 106.77, p = 0.02). A pre-operative glenohumeral injection was significantly associated with capsularP. acnescolonisation (OR 5.63, 95% CI 1.07 to 29.61, p = 0.04. Positive fat colonisation withP. acneswas significantly associated with capsularP. acnes(OR 363, 95% CI 20.90 to 6304.19, p < 0.01). Regression models pseudo R2 found fat colonisation withP. acnesto explain 70% of the variance of the model. Patients who had a pre-operative glenohumeral injection who were found intra-operatively to have fat colonisation withP. acneshad a statistically significant association with colonisation of their capsule withP. acnes(OR 165, 95% CI 13.51 to 2015.24, p < 0.01).Conclusion
These results show a statistically significant association between subcutaneous skinP. acnesculture andP. acnescapsular culture, especially when the patient has undergone a previous injection. The results refute the hypothesis thatP. acnescauses frozen shoulder.