Comparison of Internal and External Distraction in Frontofacial Monobloc Advancement: A Three-Dimensional Quantification

Abstract

Crouzon syndrome is characterized by multiple craniofacial suture fusions leading to skull deformation and midfacial hypoplasia. Although there is a degree of phenotypic variance, Background: Crouzon syndrome is characterized by complex craniosynostosis and midfacial hypoplasia. Where frontofacial monobloc advancement (FFMBA) is indicated, the method of distraction used to achieve advancement holds an element of equipoise. This two-center retrospective cohort study quantifies the movements produced by internal or external distraction methods used for FFMBA. Using shape analysis, this study evaluates whether the different distraction forces cause plastic deformity of the frontofacial segment, producing distinct morphologic outcomes. Methods: Patients with Crouzon syndrome who underwent FFMBA with internal distraction [Hôpital Necker-Enfants Malades (Paris, France)] or external distraction [Great Ormond Street Hospital for Children (London, United Kingdom)] were compared. Digital Imaging and Communications in Medicine files of preoperative and postoperative computed tomographic scans were converted to three-dimensional bone meshes and skeletal movements were assessed using nonrigid iterative closest point registration. Displacements were visualized using color maps and statistical analysis of the vectors was undertaken.Results: Fifty-one patients met the strict inclusion criteria. Twenty-five underwent FFMBA with external distraction and 26 with internal distraction. External distraction provides a preferential midfacial advancement, whereas internal distractors produce a more positive movement at the lateral orbital rim. This confers good orbital protection but does not advance the central midface to the same extent. Vector analysis confirmed this to be statistically significant (P < 0.01). Conclusions: Morphologic changes resulting from monobloc surgery differ depending on the distraction technique used. Although the relative merits of internal and external distraction still stand, it may be that external distraction is more suited to addressing the midfacial biconcavity seen in syndromic craniosynostosis.

Discussion: Comparison of Internal and External Distraction in Frontofacial Monobloc Advancement: A Three-Dimensional Quantification

“…6 To further study the specific differences in the effects between internal and external distractors, which is currently lacking in the pertinent literature, Rickart et al combined the unique experience of two European groups, Great Ormond Street for Children (GOSH) (London, United Kingdom) and Hôpital Necker-Enfants Malades (Necker) (Paris, France) on 51 Crouzon syndrome patients who underwent frontofacial monobloc advancement between 2004 and 2019. 11 The second objective of the authors was to understand "patterns of relapse" following midface advancement. Highresolution reformatted computed tomography was used for morphometric analysis at three surgical intervals: preoperatively, early postoperatively, and during midterm follow-up (imaging taken from 170 to 479 days for the GOSH group, and 120 to 437 days for the Necker group).…”

“…It is logical to assume, as stated by the authors, 11 that the degree of sagittal advancement is directly related to the region in the craniofacial skeleton where distraction forces are placed. To expand this analysis, it is necessary to understand the unique characteristics of the patients who underwent homogeneous monobloc advancement across the frontofacial segment using internal distractors.…”

“…The authors stated that the outcomes achieved by midface advancement “persist into the late postoperative stage.” 11 Considering that the GOSH and Necker groups have different philosophies regarding appropriate patient age at the time of surgery, with the majority of patients operated on by the GOSH group being at least 8 years old, and almost the total number of patients operated on by the Necker group being younger than 8 years, it is likely that the older GOSH patients will show a reduced rate for requiring secondary midface advancement. To identify “patterns of relapse” for both groups based on postoperative computed tomographic scans taken at varying intervals, it would be interesting to know how many patients from each group during long-term follow-up required secondary midface advancement.…”

“…The remarkable multicenter European study published by Rickart and collaborators 11 demonstrates the crucial importance of appropriate distractor selection before midface advancement. In light of the authors’ statement that external halo devices are “more suited to addressing the midfacial biconcavity,” Apert syndrome patients may be better candidates for midface advancement by means of external distractors, whereas Crouzon and Pfeiffer syndrome patients with severe exorbitism, especially patients presenting corneal ulcers, may be better candidates for midface advancement using internal distractors.…”