Explanted skull flaps after decompressive hemicraniectomy demonstrate relevant bone avitality. Is their reimplantation worth of the risk?

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Abstract Objective Reimplantations of autologous skull flaps after decompressive hemicraniectomies (DH) are associated with dramatic high rates of postoperative bone flap resorption (BFR). In the context of our clinical trial DRKS00023283, we assessed histologically the cell viability of explanted bone flaps in certain periods of time after DH, in order to conclude whether precursors of BRF may be developed during their storage.Methods Skull bone flaps explanted during a DH between 2019 and 2020 for a vascular disease or traumatic brain injury were sterile stored in a freezer at either − 23°C or -80°C. After their thawing process, the skulls have been collected for histological investigations. Parameters of bone metabolism, namely PTH1 and OPG have been analyzed via immunohistochemistry. H&E stain was used to assess the degree of avital bone tissue, whereas the repeated assays were performed after 6 months.Results A total of 17 stored skull flaps (8–23°C; 9–80°C) were analyzed. Median age of our cohort was 70 years; 9 patients (53%) were male. Duration of cryopreservation varied between 2 and 17 months. Relevant degree of bone avitality has been observed in all skull flaps, which has been significantly increased at the repeated evaluation after 6 months (p < 0.001). Preservation at -23°C (p = 0.006) as well as longer time of storage (p < 0.001) have been identified as prognostic factors for higher rates of bone avitality in a linear mixed regression model.Conclusions Our novel finding shows a clear benefit from a storage at -80° C, which should be carefully considered for the future management and storage of explanted skull flaps. Our analysis further revealed a significant degree of bone avitality, a potential precursor of BFR, also in skull flaps stored for several weeks. To this end, we should reconsider whether the reimplantation of autologous skull flaps instead of synthetic skull flaps is still justified.

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