Cranioplasty with autogenous bone flaps cryopreserved in povidone iodine: a long-term follow-up study

OBJECTIVE The aim of this study was to investigate the long-term therapeutic efficacy of cranioplasty with autogenous bone flaps cryopreserved in povidone iodine and explore the risk factors for bone resorption. METHODS Clinical data and follow-up results of 188 patients (with 211 bone flaps) who underwent cranioplasty with autogenous bone flaps cryopreserved in povidone-iodine were retrospectively analyzed. Bone flap resorption was classified into 3 types according to CT features, including bone flap thinning (Type I), reduced bone density (Type II), and osteolysis within the flaps (Type III). The extent of bone flap resorption was graded as mild, moderate, or severe. RESULTS Short-term postoperative complications included subcutaneous or extradural seroma collection in 19 flaps (9.0%), epidural hematoma in 16 flaps (7.6%), and infection in 8 flaps (3.8%). Eight patients whose flaps became infected and had to be removed and 2 patients who died within 2 years were excluded from the follow-up analysis. For the remaining 178 patients and 201 flaps, the follow-up duration was 24-122 months (mean 63.1 months). In 93 (46.3%) of these 201 flaps, CT demonstrated bone resorption, which was classified as Type I in 55 flaps (59.1%), Type II in 11 (11.8%), and Type III in 27 (29.0%). The severity of bone resorption was graded as follows: no bone resorption in 108 (53.7%) of 201 flaps, mild resorption in 66 (32.8%), moderate resorption in 15 (7.5%), and severe resorption in 12 (6.0%). The incidence of moderate or severe resorption was higher in Type III than in Type I (p = 0.0008). The grading of bone flap resorption was associated with the locations of bone flaps (p = 0.0210) and fragmentation (flaps broken into 2 or 3 fragments) (p = 0.0009). The incidence of bone flap collapse due to bone resorption was higher in patients who underwent ventriculoperitoneal (VP) shunt implantation than in those who did not (p = 0.0091). CONCLUSIONS Because of the low incidence rates of infection and severe bone resorption, the authors conclude that cranioplasty with autogenous bone flaps cryopreserved in povidone-iodine solution is safe and effective. The changes characteristic of bone flap resorption became visible on CT scans about 2 months after cranioplasty and tended to stabilize at about 18 months postoperatively. The bone resorption of autogenous bone flap may be classified into 3 types. The rates of moderate and severe resorption were much higher in Type III than in Type I. The grade of bone flap resorption was associated with bone flap locations. Fragmented bone flaps or those implanted in patients treated with VP shunts may have a higher incidence of bone flap collapse due to bone resorption.