Bone Flap Resorption Following Cranioplasty with Autologous Bone: Quantitative Measurement of Bone Flap Resorption and Predictive Factors

OBJECTIVE: To quantitatively measure the degree of bone flap resorption (BFR) following autologous bone cranioplasty and to investigate factors associated with BFR. METHODS: We retrospectively reviewed 29 patients who underwent decompressive craniectomy and subsequent autologous bone cranioplasty between April 2005 and October 2014. BFR was defined as: 1) decrement ratio ([the ratio of initial BF size/craniectomy size]–[the ratio of last BF/craniectomy size]) >0.1; and 2) bone flap thinning or geometrical irregularity of bone flap shape on computed tomographic scan or skull plain X-ray. The minimal interval between craniectomy and cranioplasty was one month and the minimal follow-up period was one year. Clinical factors were compared between the BFR and no-BFR groups. RESULTS: The time interval between craniectomy and cranioplasty was 175.7±258.2 days and the mean period of follow up was 1364±886.8 days. Among the 29 patients (mean age 48.1 years, male: female ratio 20: 9), BFR occurred in 8 patients (27.6%). In one patient, removal of the bone flap was carried out due to severe BFR. The overall rate of BFR was 0.10±0.11 over 3.7 years. Following univariate analysis, younger age (30.5±23.2 vs. 54.9±13.4) and longer follow-up period (2204.5±897.3 vs. 1044.1±655.1) were significantly associated with BFR (p=0.008 and 0.003, respectively). CONCLUSION: The degree of BFR following autologous bone cranioplasty was 2.7%/year and was associated with younger age and longer follow-up period.