Bone resorption in autologous cryopreserved cranioplasty: quantitative evaluation, semiquantitative score and clinical significance

Background: Changes after reimplantation of the autologous bone have been largely described. However, the rate and the extent of resorption in cranial grafts have not been clearly defined. Aim of our study is to evaluate the bone flap resorption (BFR) after cryopreservation. Methods: We retrospectively reviewed 27 patients, aged 18 years or older, subjected to cranioplasty (CP) adopting autologous cryopreserved flap. The BFR was derived from the percentage of decrease in flap volume (BFR%), comparing the first post-operative computed tomography (CT) and the last one available (performed at least 1 year after surgery). We also proposed a semiquantitative scoring system, based on CT, to define a clinically workable BFR classification. Results: After a mean ± SE follow-up of 32.5 ± 2.4 months, the bone flap volume decreased significantly (p < 0.0001). The mean BFR% was 31.7 ± 3.8% and correlated with CT-score (p < 0.001). Three BFR classes were described: mild (14.8% of cases) consisting in minimal bone remodelling, CT-score ≤ 6, mean BFR% = 3.5 ± 0.7%; moderate (51.9% of cases) corresponding to satisfactory cerebral protection, CT-score < 13, mean BFR% = 25.6 ± 2.2%; severe (33.3% of cases) consisting in loss of cerebral protection, CT-score ≥ 13, mean BFR% = 54.2 ± 3.9%. Females had higher BFR% than males (p = 0.022). BFR classes and new reconstructive surgery were not related (p = 0.58). Conclusions: BFR was moderate or severe in 85.2% of re-implanted cryopreserved flaps. The proposed CT-score is an easy and reproducible tool to define resorption extent.