Rate of Craniotomy Fusion After Free Bone Flap

Background: Craniotomy has been performed in neurologic surgery for over a century. Replacement of free bone flaps in routine craniotomies is widely practiced, however, the rate of fusion after free flap replacement is unknown. Objective: To assess timing and rate of fusion after routine craniotomies. Methods: A retrospective cohort study of 2200 patients who underwent craniotomies from 2002 to 2005. Fusion rates and time to fusion were evaluated. When time to fusion was taken into consideration, univariate and multivariate analyses of the impact of clinical factors on fusion rate were also examined. Results: Of 171 patients with postoperative computed tomography of over 2200 patients undergoing craniotomy, 103 (60%) demonstrated solid fusion, 26 (15%) had probable fusion, and 42 (25%) had not achieved fusion. There were no significant differences when fusion was compared with demographics such as age, sex, body mass index, and history of tobacco use. Radiation therapy had a significant impact on fusion: those receiving radiation were less likely to achieve fusion (P = 0.0082). The fusion rates at 12, 24, and 36 months after surgery were 15%, 41%, and 54%, respectively. Conclusion: As expected, craniotomy fusion rates after free flap replacement increased steadily over time. We were not able to demonstrate that clinical factors such as age, sex, body mass index, diagnosis, fixation material, and radiation had an impact on fusion rate when time to fusion was accounted for. Patients receiving radiation, however, experienced fusion less frequently. Because of the scarcity of previous studies in this area, this current study serves as a platform for future studies on fusion rates after free flap replacement.