Anterior cruciate ligament reconstruction complicated by Propionibacterium acnes infection: case series.

Anterior cruciate ligament (ACL) reconstruction is one of the most commonly performed orthopaedic procedures. While generally successful, failure resulting in revision surgery is reported to be between 1.9 - 4.9%. However, when not related to traumatic re-injury, failure mechanism is poorly understood. One potential but understudied mechanism of ACL reconstruction failure is infection. We describe three patients with previous ACL reconstructions who later developed infection with Propionibacterium acnes. Two cases presented with knee pain and swelling, and one presented with instability. While only two of the three cases received antibiotic treatment, all three cases were free of knee and infectious symptomatology at most recent follow-up. P. acnes infection may represent one potential mechanism for biologic failure of ACL reconstruction and anaerobic operative cultures may be used to identify its presence.