University of Oulu

Korhonen, T.K., Salokorpi, N., Ohtonen, P. et al. Acta Neurochir (2019) 161: 473.

Classification of bone flap resorption after cranioplasty : a proposal for a computed tomography-based scoring system

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Author: Korhonen, Tommi K.1,2; Salokorpi, Niina1,2; Ohtonen, Pasi3;
Organizations: 1Department of Neurosurgery, Oulu University Hospital, Oulu, Finland
2Research Unit of Clinical Neuroscience, Neurosurgery, University of Oulu, Oulu, Finland
3Division of Operative Care, Oulu University Hospital, Oulu, Finland
4Department of Anatomy and Cell Biology and Department of Surgery, MRC Oulu, University of Oulu, Oulu University Hospital, Oulu, Finland
5PEDEGO Research Unit, MRC Oulu, University of Oulu, and Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland
6Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.6 MB)
Persistent link:
Language: English
Published: Springer Nature, 2019
Publish Date: 2019-06-11


Background: Bone flap resorption (BFR) is the most prevalent complication resulting in autologous cranioplasty failure, but no consensus on the definition of BFR or between the radiological signs and relevance of BFR has been established. We set out to develop an easy-to-use scoring system intended to standardize the interpretation of radiological BFR findings.

Methods: All 45 autologous cranioplasty patients operated on at Oulu University Hospital from 2004 to 2014 were identified, and the bone flap status of all the available patients was evaluated using the new scoring system. Derived from previous literature, a three-variable score for the detection of BFR changes is proposed. The variables “Extent” (estimated remaining bone volume), “Severity” (possible perforations and their measured diameter), and “Focus” (the number of BFR foci within the flap) are scored from 0 to 3 individually. Using the sum of these scores, a score of 0–9 is assigned to describe the degree of BFR. Additionally, independent neurosurgeons assessed the presence and relevance of BFR from the same data set. These assessments were compared to the BFR scores in order to find a score limit for relevant BFR.

Results: BFR was considered relevant by the neurosurgeons in 11 (26.8%) cases. The agreement on the relevance of BFR demonstrated substantial strength (κ 0.64, 95%CI 0.36 to 0.91). The minimum resorption score in cases of relevant BFR was 5. Thus, BFR with a resorption score ≥ 5 was defined relevant (grades II and III). With this definition, grade II or III BFR was found in 15 (36.6%) of our patients. No risk factors were found to predict relevant BFR.

Conclusions: The score was proven to be easy to use and we recommend that only cases with grades II and III BFR undergo neurosurgical consultation. However, general applicability can only be claimed after validation in independent cohorts.

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Series: Acta neurochirurgica
ISSN: 0001-6268
ISSN-E: 0942-0940
ISSN-L: 0001-6268
Volume: 161
Issue: 3
Pages: 473 - 481
DOI: 10.1007/s00701-018-03791-3
Type of Publication: A1 Journal article – refereed
Field of Science: 3126 Surgery, anesthesiology, intensive care, radiology
Funding: Open access funding provided by University of Oulu including Oulu University Hospital. The Finnish Medical Society Duodecim provided financial support in the form of a grant. The sponsor had no role in the design or conduct of this research.
Copyright information: © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.