title: Orbital stress analysis: part III: biomechanics of orbital blowout fracture repair using bioresorbable poly-L/DL-lactide (P[L/DL]LA 70:30) implant.
abstract: OBJECTIVE
  The purpose was to study the biomechanics of bone fracture repair, of the orbital floor, using osteosynthetic bioresorbable implant and how to improve the implant design.
  
  
  METHODS
  A finite element model of the orbit and the globe of 1 patient who experienced orbital blowout fracture and treated with bioresorbable poly-L/DL-lactide (P[L/DL]LA 70:30) implant (PolyMax; Synthes, Oberdorf, Switzerland) was generated based on computed tomographic scans. Simulations were performed with a computer using a commercially available finite element software. The effects of changing the geometry, bony support, and method of fixation of the implant on the finite element model predictions were investigated.
  
  
  RESULTS
  The factor that had the biggest impact on the predicted principal strain magnitudes was absence of bony support of the implant (up to 65%). Applying elastic fixation reduced stresses (up to 40%) posteriorly. The principal stresses inside the bone and the implant were evenly distributed when elastic fixation was applied to the implant. Applying rigid fixation increased stresses (up to 50% and 80% anteriorly and posteriorly, respectively). The resulting stress values indicated a likely rapid failure of the osteosynthetic implant when rigid fixation was applied.
  
  
  CONCLUSIONS
  Applying rigid fixation induced a significant increase in stress patterns. Principal stresses were reduced remarkably when elastic fixation was applied to the implant. The role of fixation becomes more prominent when there is no bony support posteriorly and/or medially. It is recommended to avoid rigid fixation and to apply elastic fixation when using bioresorbable P(L/DL)LA 70:30 implants to reconstruct inferior orbital wall bony defects.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Euro-Oral Hammaslääkärikeskus Fredrikinkatu, Helsinki, Finland. Jalsukhun@hotmail.com
authors.forename: Jehad
authors.initials: J
authors.lastname: Al-Sukhun
authors.forename: Heikki
authors.initials: H
authors.lastname: Penttilä
authors.forename: Nureddin
authors.initials: N
authors.lastname: Ashammakhi
mesh_terms: D020341:Absorbable Implants; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D001863:Bone Screws; D003198:Computer Simulation; D055119:Elastic Modulus; D020342:Finite Element Analysis; D005544:Forecasting; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D017102:Fracture Healing / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D009915:Orbit / Q000503:physiopathology*; D009917:Orbital Fractures / Q000601:surgery*; D011091:Polyesters; D011474:Prosthesis Design; D011475:Prosthesis Failure; D019651:Plastic Surgery Procedures / Q000295:instrumentation / Q000379:methods; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; C033616:poly(lactide)