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Fracture Mechanisms (Long Bones)

Fracture Mechanisms (Long Bones). Direct and Indirect Direct Magnitude and area distribution of the force Rate at which force acts on the bone. Indirect. Transverse/Spiral . Spiral fracture/ Torsion load. Transverse fracture/ Bending load. max load of failure 3 1

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Fracture Mechanisms (Long Bones)

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  1. Fracture Mechanisms (Long Bones) • Direct and Indirect • Direct • Magnitude and area distribution of the force • Rate at which force acts on the bone

  2. Indirect

  3. Transverse/Spiral Spiral fracture/ Torsion load Transverse fracture/ Bending load max load of failure 3 1 Energy 1 1 Stiffness 8º of angulation 23 º of twist VERY STIFF LOW STIFFNESS Healing slow fast Area smaller larger

  4. Microcracks

  5. Factors Influencing Fracture Healing

  6. Fracture • 3 phases • Inflammation • Reparation • Remodeling • Endosteal and Periosteal callus formation which is replaced by haversian (secondary osteon) remodeling • Suppressed by rigid fixation • Excessive motion is also harmful

  7. Fracture Fixation Devices • In vitro studies to determine structural rigidity • Cadaver • Synthetic bone • Apply axial, bending, torsion to determine load-formation or torque deformation curves • Axial stiffness • Bending stiffness • Torsional stiffness

  8. External Fixation • Low axial stiffness • Success is dependent on type of fracture • Mode of reduction • Whether or not you have bones in contact • Maximum of about 1mm between them for successful remodeling

  9. External Fixation • Pin geometry and thread design • Bone thread preparation • Pin insertion technique • Pin-bone stress • Increased pin diameter • Increased pin number • Decreased side-bar separation • Decreased pin separation • Increased pin group separation • Think about as an engineering how you would change the external fixation to make it more stiff, but not too stiff and ugly to wear or open too much to infection, (pin wear, stress concentrations)

  10. Rigid Compression Plating • Definition: • Bringing entire fracture surfaces into contact • Compressing the fracture surfaces • Developed to prevent micromotion (too much micromotion causes fracture end resorption) • Implementation • Pre-load between 2 joined bones • Friction between bone and plate • Disadvantage?

  11. Rigid Compression Plating • Disadvantage: • “stress shielding”-no loading of bone so when remove the plate, bone refractures- also called postunion osteopenia. • How can we overcome this disadvantage? • Optimize plate removal • Biologically degradable material internally • Reduce rigidity

  12. Intramedullary Nails • Define intramedullary • Ream canal and place rod in canal- • Most chosen method by surgeons

  13. Experimental Studies • Canine tibial shaft osteotomy • Plate vs. Intramedullary • Rod-fixed osteotomies healed by periosteal callus • Plate-fixed healed by endosteal callus • No differences in final bone porosity • Differences in torsional stiffness disappeared after 4 months • Time to normal stiffness and strength was same

  14. Experimental Comparisons • Plate versus Ext. Fixation • Plate more rigid and bone had increased stiffness and max. torque • Increased porosity with ext. fixation (increased resorption) • Same biological union after 4 months

  15. Experimental Comparison • External Fixation • 4 versus 6 pins increased periosteal callus, but also increased porosity • Static compression increased rigidity of fixation, but did not change bone union at 4 months • Bilateral stiffer and results in bone with less porosity and stiffer union

  16. What you have gained • Be able to list advantages and disadvantages of various fixation methods, and how to overcome the disadvantages with engineering • Be aware and understand why 1 type of fixation doesn’t work for all types of fractures

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