DELAYED INFECTIONS FOLLOWING POSTERIOR TSRH SPINAL INSTRUMENTATION FOR IDIOPATHIC SCOLIOSIS – REVISITED

B.S. Richards, MD;
K. Emara, MD
Texas Scottish Rite Hospital for Children, Dallas, TX, USA

In an index report to the SRS in 1994, 10 patients (7% incidence) were found to have delayed infections due to low virulent skin flora. The organisms, thought to be introduced at the time of spinal instrumentation, required prolonged incubation of the cultures in order to be identified.

PURPOSE:
Determine 1) the incidence of delayed infection in a larger idiopathic scoliosis population treated with TSRH instrumentation, 2) the proper wound management following hardware removal, and 3) whether the previously identified bacterial trend remains consistent.

METHODS:
All idiopathic scoliosis patients who were >2 years following surgery with posterior TSRH instrumentation were included. Those with delayed infections were retrospectively reviewed. The time of presentation (infection) from the index operation, the clinical picture at presentation, sedimentation rate, presence of pseudarthrosis, organisms grown on culture, type of wound closure, and duration of antibiotics were examined.

RESULTS:
483 patients (8 staff surgeons) who were > 2 years postop were identified. Twenty–three of them (20 F, 3 M) had delayed infections for an incidence of 4.8%. Time of presentation averaged 27 months following initial surgery (range 11–79 months). Upon presentation, spontaneous drainage had occurred in 15 patients, fluctuance in 6, and neither in the remaining 2 (pain and fever). The sedimentation rate averaged 48 (range 17–100). All patients had their instrumentation removed. Pseudarthroses were noted in three patients. Primary closure (1 stage) was performed in 14 patients and delayed primary closure (> 2 stages) in 9 patients. All of the wounds healed uneventfully. Two of the three pseudarthroses were reinstrumented (one acute, one delayed). Deep wound cultures at the time of hardware removal grew Propionibacterium acnes in twelve patients, staph epidermidis (or staph coagulase negative) in four patients, micrococcus varians in one patient, and staph aureus in one patient. Five patients had negative cultures despite prolonged incubation periods. Following hardware removal, all patients received parenteral antibiotics (2–14 days duration) followed by oral antibiotics (7–60 days) in 21 patients.

CONCLUSIONS:
Low virulent skin organisms (P. acnes and staph epidermidis) continue to be primarily responsible for delayed infections following posterior spinal instrumentation. Intraoperative seeding followed by subclinical quiescent periods appears to be the method by which the infection occurs. Primary wound closure following hardware removal results in successful wound healing. Delayed primary wound closure after 48 hours is unnecessary. Short term postoperative parenteral antibiotics (2–5 days) followed by short term oral antibiotics (7–14 days) is recommended.