Utility of Pre-Implantation Gram Stains and Cultures for Allografts Used in Orthopaedic Surgical Procedures: A Pilot Study

Background: At present, accredited tissue banks in the United States disinfect or sterilize most of their musculoskeletal allografts before distribution to surgeons for transplantation. Consequently, allograft-associated bacterial infections are relatively uncommon among graft recipients. Notwithstanding, orthopaedic surgeons continue to culture allografts before implantation into patients. Although these cultures generally remain negative, physicians invariably initiate antimicrobial therapy among recipients of culture-positive grafts, despite absence of symptoms in the recipient.

Objective: To evaluate the utility of pre-implantation gram stains and cultures of tissues about to be implanted in patients.

Methods: Pre-implantation gram stains and cultures were obtained for (i) allografts before and after pre-operative manipulation; and (ii) metal hardware that were to be implanted into patients undergoing orthopaedic surgery at the University of Florida.  We obtained additional cultures of the incision site after skin disinfection and at the time of skin closure.  The same designated person obtained all cultures; the surgeons carrying out the procedures and the operating room were the same. All gram stains and cultures were worked up in the microbiology department, Shands Hospital at the University of Florida.  Collected data were analyzed using Epi Info (CDC, Atlanta, GA).

Results: We obtained gram stains and cultures for 21 allografts destined for anterior cruciate ligament repair and for 7 metal prosthesis used in various orthopaedic procedures.  All allografts used in the 21 procedures had undergone a sterilization process (chemical, irradiation, or both); metal hardware had been sterilized (irradiation and autoclave) to sterility assurance levels of 10^-6.  Allografts and hardware were designated sterile in their final packaging.  All gram stains were negative.  Only three cultures were positive: two from allografts immediately after opening but before manipulation (Staphylococcus aureus and Micrococcus sp.) and one from a hardware procedure incision site (Enterococcus sp.)

Conclusions: These preliminary data show low frequency of bacterial growth when pre-implantation cultures of sterilized allograft and metal hardware are obtained.  Moreover, the nature of the organisms indicate that they did not originate from the grafts or hardware but were likely caused by extrinsic contamination when the cultures were obtained, or in the case of hardware, originated in the patient.  Our pilot data suggest orthopaedic surgeons should not obtain pre-implantation gram stains or cultures.  Positive cultures lead to unnecessary antimicrobial therapy. Further research, including prospective studies, are needed to determine the true incidence of surgical site infections following orthopaedic procedures that utilize musculoskeletal allografts.