Monday, September 1, 2014

Propionibacterium acnes in primary shoulder surgery - a surprising result

Propionibacterium acnes in shoulder surgery: true infection, contamination, or commensal of the deep tissue?

These authors assessed Propionibacterium in intraoperative samples of different tissue layers in 118 consecutive patients (mean age, 59.2 years; 75 men, 43 women) undergoing first-time shoulder surgery.
Patients in this study had either an anterolateral approach for open rotator cuff reconstruction/open subacromial decompression or a deltopectoral approach for shoulder arthroplasty or open anterior shoulder stabilization. Patients were excluded if they had tumors or systemic inflammatory diseases or if they had received systemic or topical antibiotics or anti-inflammatory medications within 6 months before surgery. Patients with subacromial injection before the surgery were identified.

Preoperative antibiotics were withheld until the final intraoperative sample was collected. Intraoperative samples were correlated to preoperative subacromial injection, the type of surgical approach, and gender. One skin, one superficial, one deep tissue, and one test sample were cultured for each patient.

Samples were cultured on Columbia agar, chocolate agar,Schaedler agar, and Schaedler kanamycin-vancomycin agar plates and inoculated in thioglycollate broth. Cultures were observed for 14 days.

The cultures were positive for P. acnes in 36.4% of cases. 35 of the 75 men were Propionibacterium–positive , while  8 of the 43 female patients were Propionibacterium–positive.

Subacromial injection was not associated with bacterial growth of Propionibacterium other bacteria. 

Skin samples were positive for Propionibacterium in 8.5%, superficial samples were positive in 7.6%, deep samples were positive in 13.6%, and both samples (superficial and deep) were positive in 15.3% of cases (P < .0001). 

Propionibacterium was detected in the anterolateral approach in 27.1% of cases and in the deltopectoral approach in 9.3% of cases.

Two patients in this study had a postoperative infection requiring revision surgery. During the revision, intraoperative samples confirmed the presence of Propionibacterium in both cases. The patients were both male and were positive for P. acnes in all tissue layers (skin, superficial, and deep) at the index operation.

One segment of the Discussion was of particular interest: " Our data demonstrate that P. acnes colonization of intraoperative samples is predominantly a male problem, confirming reports from shoulder revision surgery and topical skin testing. Men have more sebaceofollicular glands with a greater volume, resulting in a greater P. acnes load. A strong positive correlation has been reported between male sex, pore size, and sebum excretion.White men reportedly have a sebum average of 3 mg/cm2 of skin surface (with large interindividual variability), whereas white women have only 0.7 mg/cm." 

Comment: This is a very well done and important study. The authors were very careful with their methodology, even using test samples to check for contamination (none of the 118 were positive for Propionibacterium). 

Their results strongly suggest that primary surgical wounds are routinely contaminated with Propionibacterium,  most likely from the patient's own skin and that this contamination is not prevented by careful surgical preparation and draping. In view of the fact that Propionibacterium is adept at forming biofilms on implants and is known to be associated with delayed implant failure, three actions seem in order: (1) patients having shoulder surgery, especially males, need to be informed of the risk of Propionibacterium colonization,  (2) thorough irrigation and careful handling of implants should be exercised to reduce the effects of the contamination, and (3) infection with Propionibacterium should be suspected when  shoulder procedures are followed by unexpected pain, stiffness or component loosening, even if the onset of symptoms is delayed substantially beyond the index procedure.