The selection criteria for the study participants are shown in . The baseline demographic characteristics of the 131 patients undergoing 134 cranioplasties are displayed in . There was a higher proportion of men compared to women (62.5% vs. 37.5%) and many patients had a history of medical problems (41.2%). The mean ages at craniectomy and cranioplasty were 49.7 and 50.1 years, respectively. The causes of decompressive craniectomy, in order of frequency, included vascular lesions (47.3%), head trauma (46.5%) and brain tumor (6.1%). The location of craniectomy was either right (56.5%), left (41.2%) or bilateral (2.3%). A total of 83 patients received autogenous graft materials (63.3%), which were all cryopreserved bone grafts. Artificial bone materials were used in 48 patients (36.6%); of these, 27 patients were repaired with polymethylmethacrylate (PMMA), 12 patients reconstructed with porous polyethylene (Medpor; Porex Surgical, Newnan, GA, USA) and 9 patients with bone cement. The mean duration of cranioplasty surgery was 2.9 hours. Neurologic outcomes at cranioplasty indicated good recovery in 76 patients (58%), moderate disability in 24 (18.3%), severe disability in 15 (11.5%) and a vegetative state in 16 (12.2%). The duration of prescription for prophylactic antibiotics was more than 1 week in 113 patients (86.3%) and less than 1 week in 18 (13.7%). The order of type of administered prophylactic antibiotics was third generation, first generation and second generation cephalosporin. The time interval between craniectomy and cranioplasty was less than 3 months in 84 patients (64.1%) and over 3 months in 47 (35.9%).
Demographic details of 131 patients undergoing craniectomy and subsequent cranioplasty
Mean event-free survival durations for patients receiving cryopreserved and artificial bone grafts for cranioplasty infection were 3211 and 3539 days, respectively. There was no significant difference in long-term outcome for cranioplasty infection between cryopreserved and artificial bone grafts in the Kaplan-Meier event-free survival curve (p=0.074) (). The mean event-free survival times based on early or late repair for site infection were 3200 and 3529 days, respectively; there were no significant differences between the two groups (p=0.083) (). In an analysis of cranioplasty infection rate in the subgroup of the cryopreserved graft group that received sterilization with or without EO gas, no statistical significance was found (p=0.146) (). Cox-regression analysis showed that only the patient's neurologic outcome at the time of cranioplasty was significantly related to cranioplasty infection (p=0.04) (). The patients with poor outcome versus good outcome at cranioplasty showed a HR of 5.203 with a 95% CI of 1.075 to 25.193 for cranioplasty infection (). The HR for site infection between late cranioplasty versus early cranioplasty was 0.502 (95% CI, 0.096-2.624, p=0.414). The HR for cranioplasty infection of an artificial graft versus cryopreserved bone was 0.303 (95% CI, 0.061-1.516, p=0.146). Although other variables, including age, sex, cause of craniectomy, medical problems, and mechanical complications failed to show statistical significance in this model, we observed a trend between a shorter duration of cranioplasty and site infection (p=0.088) (). The profiles of 14 patients with cranioplasty infection are summarized in . The overall incidence of cranioplasty infection was 10.6% and the mean duration to infection was 71.5 days (range, 4-629 days). The incidence rates for site infection in cryopreserved and artificial bone grafts were 14.4% and 4.2%, respectively. The incidence rates for site infection for early and late repair were also 14.4% and 4.2%. Within 2 weeks, 8 of 14 patients (57.1%) showed infection after cranial repair. Cultured microorganisms at the infection site were methicillin-resistant Staphylococcus aureus in 6 patients, methicillin-resistant coagulase-negative staphylococci in 3, Staphylococcus aureus in 1, Pseudomonas aeruginosa in 1, Enterobacter aerogenes in 1, Staphylococcus chromogenes in 1, and Candida guilliermondii in 1. Acute cranioplasty infection within 2 weeks occurred in 8 patients and chronic infection over 2 weeks occurred in 6. Seven of the patients with cranioplasty infection were treated via removal of the infected bone graft. One patient underwent wound revision and abscess removal. The other 7 patients with site infections were successfully treated with antibiotics only ().
Fig. 2 Kaplan-Meier event-free survival curves at 10 years for cranioplasty infection according to graft material (p=0.074) (A), and cranioplasty timing (p=0.083) (B) in 131 cranioplasty patients, and according to sterilization methods (p=0.146) (C) in 83 patients (more ...)
Factors potentially associated with cranioplasty infection
Summary of 14 patients with cranioplasty infection after decompressive craniectomy
Postoperative complications within 2 weeks after cranioplasty are shown in . Epidural hematoma, subdural hematoma and brain contusion occurred postoperatively within 2 weeks, but none of these events required surgical intervention. There were 77 patients who underwent postoperative brain CT among 83 patients repaired with cryopreserved bone graft. Mean follow-up duration of brain CT scanning of 77 patients was 480 days (range, 1-3361). Resorption of the cryopreserved bone graft occurred in 15 patients (19.4%). The median time from cranioplasty to bone resorption was 834 days (range, 207-3152). Sterilization methods did not affect the resorption rate of the cryopreserved bone graft ().
Postoperative complications within 2 weeks after cranioplasty. EDH, SDH, NA and NC stand for epidural hematoma, subdural hematoma, not applicable and not checked, respectively. Numbers in parentheses indicate the number of patients.
Resorption rate and time of cryopreserved bone grafts according to sterilization methods*