We prospectively studied bacterial colonization and infectious complications in 39 patients with arm and leg amputations previously treated with 45 transcutaneous osseointegrated titanium implants. All patients attending the osseointegration outpatient clinic at Sahlgrenska University Hospital, Göteborg, Sweden, for scheduled or emergency visits between January and June 2005 were included. No patients refused to participate. At least 3 months had elapsed since the second surgical procedure (abutment insertion). This cohort was followed longitudinally for an average of 3 years to identify implant infections and cross sectionally surveyed twice (at inclusion and after approximately 3 years) for bacterial presence, local infection, and antibiotic use. All skin-penetrating loci were subjected to separate clinical, bacteriologic, and radiographic assessment. There were 18 women and 21 men with a mean age of 49.3 years (range, 28–74 years). Amputations were the result of either trauma or neoplasia. Thirty-three of the implants were femoral (bilateral in one), four each were ulnar and radial (bilateral in one), three were humeral, and one was tibial. The patients had been living with the implant(s) a mean of 54 months (range, 3–132 months). Indications for these implants were severe discomfort when using conventional socket prostheses or poor stump conditions [13
The treatment involves two separate surgical procedures. A titanium screw (fixture) is inserted into the residual bone and allowed to integrate for 6 months before the skin-penetrating extension (abutment) is inserted [28
]. Based on the experience of successful skin-penetrating implants in the head and neck regions [29
], the skin is attached directly to the distal end of the residual bone to reduce soft tissue mobility and risk of infection. We consider the implant osseointegrated when it is stable on clinical examination, pain free when loaded [28
], and there are no signs of loosening seen on radiographs, ie, no radiolucent zone around the implant. Postoperative followup includes clinical examination (pain evaluation, implant stability, skin and soft tissue condition), a rehabilitation protocol [14
], and radiographs at 6 months and 1, 2, 3, 5, 7, 10, and 15 years after surgery.
We used the following five definitions for implant infection and required all stated criteria for the given diagnosis:
(1) definite implant infection: (a) clinical symptoms of implant-related infection, (b) radiographic signs consistent with periimplant bone infection, and (c) at least three of five intraoperatively obtained cultures yielding identical pathogens; (2) probable implant infection: (a) clinical symptoms of implant-related infection, (b) radiographic signs consistent with periimplant bone infection, and (c) positive relevant culture not as defined previously; (3) possible implant infection: (a) clinical symptoms of implant-related infection, (b) radiographic signs consistent with periimplant bone infection, and (c) no relevant cultures; (4) local infection in the skin penetration area: (a) local signs/symptoms of infection (inflammation with or without secretion) in the skin penetration area but no symptoms of deep infection, (b) no radiographic signs consistent with periimplant bone infection, and (c) with or without relevant cultures; (5) bacterial colonization around the skin-implant interface: (a) neither local inflammatory signs nor other clinical symptoms of infection, with or without secretion, at the skin-implant interface, (b) no radiographic signs consistent with periimplant bone infection, and (c) positive bacterial culture from the skin-implant interface. We considered radiographic evidence of osteolysis with or without periosteal sclerosis around a previously integrated implant to be consistent with implant infection. The definitions also were based on previously proposed culture diagnostics in infected hip and knee arthroplasties [19
At inclusion patients were examined clinically and asked to answer a questionnaire (Appendix 1) regarding infectious complications and antibiotic use during the 6 months preceding the visit. Without any preparation of the surrounding skin, samples were taken from the skin-implant interface with a sterile cotton swab, transported in a coal-based medium, and cultured on routine agar plates for at least 2 days. A second set of bacterial cultures was performed 3 years later and an identical questionnaire was answered. Patients who were not scheduled for a visit at this time collected bacterial samples (cotton swabs) themselves according to careful written instructions and, if necessary, with the assistance of their attending clinic. These patients were experienced in handling the skin-implant area and we anticipated no methodologic problems with the patients performing their own cultures. Cultures and questionnaires were sent to Sahlgrenska University Hospital by mail. Sampled cultures transported in a coal-based medium are expected to survive a 2-day transport by mail. Culturing the samples then was performed at our certified laboratory.
All cultures were examined by one (SK) experienced bacteriologic analyst. The number of colony forming units (CFU) was defined as +++ (> 100 CFU), ++ (10–100 CFU), or + (< 10 CFU). A routine disk method was used to determine antibiotic resistance.
The latest scheduled or symptom-prompted radiographs at inclusion and followup were checked for signs of bone infection. All patients had radiographs performed within 6 months of inclusion. Followup radiographs were obtained for 31 patients. Of the remaining eight patients, two already had osteomyelitic changes at the beginning of the study, four were excluded, and two were without infectious symptoms.
Four patients were lost to followup. In one, the implant was extracted owing to mechanical loosening in a previously radiated femur (October 2006). In another patient, chronic skin infection led to abutment removal (February 2007). Complete skin healing over the retained implant followed. Two patients (one Swedish) did not complete the followup protocol for nonmedical reasons. Their admitting medical centers were contacted and no implant infections were reported. The study was approved by the ethical committee at the University of Gothenburg.