76. PROPIONIBACTERIUM ACNES INFECTIONS IN REVISION SHOULDER SURGERY: AN ANALYSIS OF 20 CONSECUTIVE CASES WITH POSITIVE INTRA-OPERATIVE CULTURES

Abstract

Purpose: The objectives of this study were to correlate the clinical course of all patients with positive intra-operative P. acnes cultures in revision shoulder surgery with the cultures and intraoperative findings to determine the clinical significance of the positive cultures.

Method: From 2005 to 2007 all revision shoulder surgeries were managed with a standard protocol in which

1. antibiotics were withheld until cultures obtained,

2. at least four fluid and tissue cultures were submitted,

3. frozen sections were obtained of any tissue grossly suspicious for infection, and

4. the surgeons’ pre-, intra-, and post-operative suspicion for infection were recorded.

Samples were observed for growth for 28 days. All cases were reviewed at a mean follow-up of 4.2 months (range, 1–12). Comparisons were made between infection cases and “clinically Insignificant” cases, with respect to: (1) risk factors, (3) symptoms/signs of infection, (2) active range-of-motion, (2) Simple Shoulder Test (SST) scores, values of (3) WBC, (4) ESR and (5) CRP, number of positive cultures for (6) P acnes and (7) other organisms and (8) subjective pre-operative, intra-operative and postoperative suspicion for occult infection.

Results: P. acnes was cultivated from 20 cases in 19 patients. Five cases (25%) were considered significant infections, while fifteen cases were considered “clinically insignificant”. The mean number of cultures positive for P. acnes was 1.7 (range, 1–4) per case. The mean active forward flexion (p=0.03) and internal rotation (p=0.03) was less for infection cases than for clinically Insignificant cases. Pre-operative ESR (p=0.04) and CRP (p=0.02) values were higher for infection cases. Infection cases had a higher number of positive intra-operative cultures for other organisms (p=0.04).

Conclusion: No combination of clinical parameters would reliably predict clinical infection in patients with positive intra-operative P. acnes cultures in revision shoulder surgery. In particular, positive P. acnes intra-operative cultures do not always represent true clinical infections. Pre-operative loss of range-of-motion, elevated ESR and CRP and positive intra-operative cultures for other organisms appear to correlate with true infections. The determination of a clinically significant infection needs to be based on the entirety of the clinical and laboratory information for each shoulder case.