gms | German Medical Science

Objective: Since the release of recent large prospective trials establishing decompressive hemicraniectomy in acute malignant middle cerebral artery (MCA) infarction as a standard procedure, the number of surgical interventions has dramatically increased. Consequently this puts an emphasis on cranioplasty and it's associated complications. The two major ones are surgical site infection and aseptic bone resorption of the autologous transplant. So far risk factors for aseptic bone necrosis such as age, number of fragments and hydrocephalus. Have been identified but a thorough understanding of the underlying pathophysiology is missing. Thus we performed a clinical and osteopathological investigation, so far including 7 patients.

Method: Patients who had to undergo surgical revision for aseptic bone resorption after autologous replantation were entered into a prospective registry. All implants had been cryogenically preserved. Parameters recorded were serum parameters of bone metabolism, time to revision, significant co-morbidities and overall clinical presentation. Removed specimens underwent rigorous osteopathologic evaluation. The findings were correlated with the radiological findings from preoperative ct-scans.

Results: In osteopathological investigations we found the coexistence of osteolytic and osteblastic activity within the necrosis. New lamelliform bone structures with vital osteocytes are rebuilt parallel to ongoing resorption. Osteogenesis is guided by the residual bone matrix following the preexisting structures. Osteogenic activity was reduced in regions adjacent to fatty marrow residues. Evaluation of the bone metabolism markers revealed no underlying systemic causes for necrotic transformation.

<img alt="" height="206" src="http://www.porstmann-kongresse.de/dgnc/1_VitalBone.jpg" width="275" />

<img alt="" height="206" src="http://www.porstmann-kongresse.de/dgnc/2_Necrosis.jpg" width="275" />

<img alt="" height="206" src="http://www.porstmann-kongresse.de/dgnc/3_Borders.jpg" width="275" />

Conclusions: A cryoconserved implant is reintegrated into the existing skull structure as is shown by the migration of osteocytes and newly formed lamelliform bone. Insufficiency of this process to lead to fully integrated bone flap reintegration may be due to the residual fatty bone marrow contained in the bone flap which seems to act as a barrier for osteogenesis. This may obstruct the reorganization of the bone structure, inducing aseptic bone necrosis. In regard of these findings surgical techniques have to be adapted and verified in future trials.