title: Mechanism of sternotomy dehiscence.
abstract: OBJECTIVE
  Biomechanical modelling of the forces acting on a median sternotomy can explain the mechanism of sternotomy dehiscence, leading to improved closure techniques.
  
  
  METHODS
  Chest wall forces on 40 kPa coughing were measured using a novel finite element analysis (FEA) ellipsoid chest model, based on average measurements of eight adult male thoracic computerized tomography (CT) scans, with Pearson's correlation coefficient used to assess the anatomical accuracy. Another FEA model was constructed representing the barrel chest of chronic obstructive pulmonary disease (COPD) patients. Six, seven and eight trans-sternal and figure-of-eight closures were tested against both FEA models.
  
  
  RESULTS
  Comparison between chest wall measurements from CT data and the normal ellipsoid FEA model showed an accurate fit (P < 0.001, correlation coefficients: coronal r = 0.998, sagittal r = 0.991). Coughing caused rotational moments of 92 Nm, pivoting at the suprasternal notch for the normal FEA model, rising to 118 Nm in the COPD model (t-test, P < 0.001). The threshold for dehiscence was 84 Nm with a six-sternal-wire closure, 107 Nm with seven wires, 127 Nm with eight wires and 71 Nm for three figure-of-eights.
  
  
  CONCLUSIONS
  The normal rib cage closely fits the ellipsoid FEA model. Lateral chest wall forces were significantly higher in the barrel-shaped chest. Rotational moments generated by forces acting on a six-sternal-wire closure at the suprasternal notch were sufficient to cause lateral distraction pivoting at the top of the manubrium. The six-sternal-wire closure may be successfully enhanced by the addition of one or two extra wires at the lower end of the sternotomy, depending on chest wall shape.
authors: Department of Cardiothoracic Surgery, Mater Dei Hospital, Msida, Malta Department of Anatomy, University of Malta, Msida, Malta aaron.casha@um.edu.mt.
authors: Aaron R
authors: AR
authors: Casha
authors: Department of Cardiothoracic Surgery, Mater Dei Hospital, Msida, Malta.
authors: Alexander
authors: A
authors: Manché
authors: Metamaterials Unit, Faculty of Science, University of Malta, Msida, Malta.
authors: Ruben
authors: R
authors: Gatt
authors: Metamaterials Unit, Faculty of Science, University of Malta, Msida, Malta.
authors: Edward
authors: E
authors: Duca
authors: Department of Anaesthesia, Mater Dei Hospital, Msida, Malta.
authors: Marilyn
authors: M
authors: Gauci
authors: Department of Anatomy, University of Malta, Msida, Malta.
authors: Pierre
authors: P
authors: Schembri-Wismayer
authors: Department of Anatomy, University of Malta, Msida, Malta.
authors: Marie-Therese
authors: MT
authors: Camilleri-Podesta
authors: Metamaterials Unit, Faculty of Science, University of Malta, Msida, Malta.
authors: Joseph N
authors: JN
authors: Grima
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001864:Bone Wires; D003198:Computer Simulation; D003371:Cough / Q000150:complications* / Q000503:physiopathology; D020342:Finite Element Analysis; D006801:Humans; D008297:Male; D008953:Models, Anatomic; D008954:Models, Biological; D011312:Pressure; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications* / Q000503:physiopathology; D015203:Reproducibility of Results; D012307:Risk Factors; D056346:Sternotomy / Q000009:adverse effects*; D013249:Sternum / Q000000981:diagnostic imaging / Q000601:surgery*; D013314:Stress, Mechanical; D013529:Surgical Wound Dehiscence / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control; D014057:Tomography, X-Ray Computed; D058106:Wound Closure Techniques / Q000009:adverse effects* / Q000295:instrumentation
keywords: Biomechanics; Dehiscence; Median sternotomy