M.Sc Thesis

M.Sc StudentBernstein Benjamin
SubjectForces and Moments Acting on the Sternum: Pre and Post
DepartmentDepartment of Mechanical Engineering
Supervisors PROFESSOR EMERITUS Assa Rotem (Deceased)


Midline sternotomy is a surgical procedure frequently used in thoracic surgery in which the sternum (breastbone) is bisected and later sutured, typically using stainless steel wires or plastic bands.  No consensus exists among surgeons as to how tightly sutures should be adjusted.  A potentially dangerous complication of midline sternotomy is sternal dehiscence, a condition in which the two sternal halves separate, or the sutures penetrate into the sternal bone.  Presumably these types of complications occur when sutures are adjusted too loosely or too tightly, respectively.  Clinical evidence suggests that sternal dehiscence often occurs as a result of strong coughing.

Biomechanical comparisons of midline sternotomy closures have relied on the simple theoretical model developed by Casha, et. al. which predicts the overall force applied across a sternotomy during coughing.  The geometric distribution of that force has not been explored.

A new model based on anatomic geometry and incorporating muscular forces was developed in MATLAB in order to simulate the geometric distribution of sternal midline forces during cough.  Rather than a uniform inferior-superior distribution of force, the new model predicts relatively high lateral separation forces concentrated mainly in the region of the fourth and fifth rib interspaces.

Appropriate sternotomy wire closure tensions were calculated based on the developed forces, and these tensions were validated by finite element analysis and comparison to experimental results.