Ten patients who had been managed with posterior spinal arthrodesis and Texas Scottish Rite Hospital instrumentation because of idiopathic scoliosis had a delayed deep wound infection at an average of twenty-five months after the operation. The signs of infection included spontaneous drainage in eight patients and fluctuance in two patients, Ln addition, six patients - including five of the eight who had drainage - had mild pain in the back. The average erythrocyte sedimentation rate was thirty-nine millimeters per hour (range, nineteen to eighty-one millimeters per hour). The instrumentation was removed from all of the patients. In two patients, a pseudarthrosis that had not been noted on preoperative radiographs was noted intraoperatively; in both patients, the pseudarthrosis occurred at a level at which two hooks had been placed in one intervertebral space. Primary closure was performed in seven patients, and delayed primary closure was performed on the third postoperative day in three patients. All wounds healed uneventfully. Cultures of specimens taken from deep within the wound were positive for Propionibacterium acnes (five patients), Staphylococcus epidermidis (two patients), a rare coagulase-negative Staphylococcus species (one patient), or Micrococcus varians (one patient). No organisms grew on culture of the specimen obtained from the remaining patient. Propionibacterium acnes required an extended period of incubation before identification. Antibiotics were administered parenterally to all of the patients after the removal of the hardware, and this treatment was followed by oral administration of antibiotics for nine of the patients. We suspect but cannot prove - that several of the delayed infections resulted from intraoperative seeding and remained subclinical for an extended period of time. Low-virulence skin flora, particularly Propionibacterium acnes, may be responsible for delayed clinical infections after posterior spinal instrumentation and should not be dismissed as contaminants.
