title: Computer assisted planning and orbital surgery: patient-related prediction of osteotomy size in proptosis reduction.
abstract: BACKGROUND
  Proptosis is characterized by a protrusion of the eyeball due to an increase of the orbital tissue volume. To recover a normal eyeball positioning, the most frequent surgical technique consists in the osteotomy of orbital walls combined with the manual loading on the eyeball. Only a rough clinical rule is currently available for the surgeons but it is useless for this technique. The first biomechanical model dealing with proptosis reduction, validated in one patient, has been previously proposed by the authors.
  
  
  METHODS
  This paper proposes a rule improving the pre-operative planning of the osteotomy size in proptosis reduction. Patient-related poroelastic finite element models combined with sensitivity studies were used to propose two clinical rules to improve the pre-operative planning of proptosis reduction. This poroelastic model was run on 12 patients. Sensitivity studies permitted to establish relationships between the osteotomy size, the patient-related orbital volume, the decompressed tissue volume and the eyeball backward displacement.
  
  
  RESULTS
  The eyeball displacement and the osteotomy size were non-linearly related: an exponential rule has been proposed. The patient-related orbital volume showed a significant influence: a bi-quadratic analytical equation liking the osteotomy size, the orbital volume and the targeted eyeball protrusion has been established.
  
  
  CONCLUSIONS
  Two process rules derived from patient-related biomechanical FE models have been proposed for the proptosis reduction planning. The implementation of the process rules into a clinical setting is easy since only a sagittal radiography is required. The osteotomy size can be monitored using optical guided instruments.
authors.affiliation: TIMC Laboratory, UMR CNRS 5525, La Tronche, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Luboz
authors.forename: Dominique
authors.initials: D
authors.lastname: Ambard
authors.forename: Pascal
authors.initials: P
authors.lastname: Swider
authors.forename: Frank
authors.initials: F
authors.lastname: Boutault
authors.forename: Yohan
authors.initials: Y
authors.lastname: Payan
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D005094:Exophthalmos / Q000601:surgery*; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D008297:Male; D010027:Osteotomy / Q000379:methods*; D025321:Surgery, Computer-Assisted