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Bone Structure and Fracture Healing Kate Markland, Nov 2003
Bone function <ul><li>Bone is one of the hardest structures of the animal body; it also possesses a certain degree of toug...
Compact/Cortical bone <ul><li>Does not have any spaces or hollows in the bone matrix that are visible to the eye. It is de...
Trabecular/Cancellous/Spongy bone <ul><li>Always in the interior, It consists of slender fibers and lamellæ, which join to...
Woven Bone (primary bone) <ul><li>forms embryonic skeleton, and is largely absent from normal bone after age 4 yrs  </li><...
<ul><li>Periosteum   </li></ul><ul><li>Encloses bone, except where it is coated with articular cartilage </li></ul><ul><li...
Bone remodelling <ul><li>Remodeling of bone occurs throughout life.  It is a balance between bone growth and breakdown </l...
Bone behaviour under various loading modes   <ul><li>Bone is  Anisotropic  (i.e it has different mechanical properties whe...
 
Fracture Healing
Haematoma Formation <ul><li>Vessels are torn and a haematoma forms between and around the fracture surfaces, within the pe...
Inflammation and Proliferation <ul><li>–  Time of injury to 24-72 hours  </li></ul><ul><li>Injured tissues and platelets r...
Callus Formation <ul><li>–  2 weeks </li></ul><ul><li>Bone is uniting in correct position </li></ul><ul><li>Thick cellular...
Consolidation   <ul><li>Continuing osteoclastic and osteoblastic activity. </li></ul><ul><li>Woven bone is transformed int...
Remodelling <ul><li>–  Middle of repair phase up to 7 years  </li></ul><ul><li>Remodelling of the woven bone is dependent ...
Primary Healing <ul><li>Cancelluous bone is of uniform spongy texture and has no intermedullary canal </li></ul><ul><li>Un...
Factors influencing bone healing <ul><li>Systemic  </li></ul><ul><li>Age  </li></ul><ul><li>Hormones  </li></ul><ul><li>Fu...
Fracture Fixation <ul><li>Numerous systems have been developed to assist a bone’s natural healing properties </li></ul><ul...
Rehabilitation <ul><li>Aim: to preserve function so far as possible while the fracture is uniting </li></ul><ul><li>Use in...
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Bone Structure and Fracture Healing

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Bone Structure and Fracture Healing

  1. 1. Bone Structure and Fracture Healing Kate Markland, Nov 2003
  2. 2. Bone function <ul><li>Bone is one of the hardest structures of the animal body; it also possesses a certain degree of toughness and elasticity. </li></ul><ul><li>Bone is viscoelastic (= time dependent property where the deformation of the material is related to the rate of loading, hysteresis, creep, stress relaxation) </li></ul><ul><li>Mechanical - gives the skeleton the necessary rigidity to function as attachment and lever for muscles and supports the body against gravity. </li></ul><ul><li>Chemical - Calcium homeostasis & metabolism </li></ul><ul><li>Hematological - Haemopoesis </li></ul>
  3. 3. Compact/Cortical bone <ul><li>Does not have any spaces or hollows in the bone matrix that are visible to the eye. It is dense in texture, like ivory. Always placed on the exterior of the bone </li></ul><ul><li>Consists almost entirely of extracellular substance - the matrix .  </li></ul><ul><li>Osteoblasts deposit the matrix in the form of thin sheets which are called lamellae . Lamellae are microscopic structures.  </li></ul><ul><li>In mature compact bone most of the individual lamellae form concentric rings ( Concentric lamellae) around larger longitudinal canals (approx. 50 µm in diameter) within the bone tissue. These canal are called Haversian canals .  </li></ul><ul><li>Haversian canals typically run parallel to the surface and along the long axis of the bone.  </li></ul>
  4. 4. Trabecular/Cancellous/Spongy bone <ul><li>Always in the interior, It consists of slender fibers and lamellæ, which join to form a reticular structure resemblaing to lattice-work. The ends of long bones (or epiphyses) consist mainly of spongy bone. </li></ul><ul><li>Lamellae in trabecular bone do not form Haversian systems </li></ul><ul><li>Lamellae of trabecular bone are deposited on depending on the mechanical forces on the bone </li></ul>
  5. 5. Woven Bone (primary bone) <ul><li>forms embryonic skeleton, and is largely absent from normal bone after age 4 yrs </li></ul><ul><li>is seen in fracture callus in both children and adults </li></ul><ul><li>does not contain lamellae, and rather has a relatively disorganized array of collagen and irregular mineralization pattern </li></ul>
  6. 6. <ul><li>Periosteum </li></ul><ul><li>Encloses bone, except where it is coated with articular cartilage </li></ul><ul><li>It provides a means for vessels reach the hard tissue. </li></ul><ul><li>Marrow </li></ul><ul><li>The interior of each of the long bones of the limbs presents a cylindrical cavity filled with marrow and lined by a highly vascular areolar structure, the medullary membrane </li></ul>
  7. 7. Bone remodelling <ul><li>Remodeling of bone occurs throughout life.  It is a balance between bone growth and breakdown </li></ul><ul><li>Osteoblast - bone forming cell </li></ul><ul><li>Osteoclast - bone resorbing cell </li></ul><ul><li>Osteoid - unmineralized organic matrix produced by osteoblasts </li></ul><ul><li>Wolff’s Law – Bone is laid down where needed and resorbed where not needed </li></ul><ul><li>Piezoelectricity – Mechanical stress creates electricity potential which increases bone density </li></ul><ul><li>Disuse leads to bone resorbtion, reducing its stiffness and strength. </li></ul>
  8. 8. Bone behaviour under various loading modes <ul><li>Bone is Anisotropic (i.e it has different mechanical properties when loaded along different axes). </li></ul><ul><li>Adult cortical bone is stronger in compression than tension and weakest in shear. </li></ul><ul><li>Most fractures occur as a result of several loading modes </li></ul>
  9. 10. Fracture Healing
  10. 11. Haematoma Formation <ul><li>Vessels are torn and a haematoma forms between and around the fracture surfaces, within the periosteum. </li></ul><ul><li>Bone at the fracture site surfaces is deprived of blood and phagocytosis occurs to remove 1-2mm of bone </li></ul><ul><li>Lots of swelling </li></ul>
  11. 12. Inflammation and Proliferation <ul><li>– Time of injury to 24-72 hours </li></ul><ul><li>Injured tissues and platelets release vasoactive mediators, growth factors and other cytokines. </li></ul><ul><li>These cytokines influence cell migration, proliferation, differentiation and matrix synthesis.   </li></ul>
  12. 13. Callus Formation <ul><li>– 2 weeks </li></ul><ul><li>Bone is uniting in correct position </li></ul><ul><li>Thick cellular mass with islands of immature/woven bone and cartilage form callus </li></ul><ul><li>Sufficient ossification to be visible on X-ray </li></ul><ul><li>Bone can now take more stress </li></ul>
  13. 14. Consolidation   <ul><li>Continuing osteoclastic and osteoblastic activity. </li></ul><ul><li>Woven bone is transformed into more mature lamellar bone. </li></ul><ul><li>On Xray the tissue looks whiter </li></ul><ul><li>The bone is now strong enough to carry normal loads </li></ul><ul><li>Children 4-6 weeks </li></ul><ul><li>Adults 3-5 months </li></ul>
  14. 15. Remodelling <ul><li>– Middle of repair phase up to 7 years </li></ul><ul><li>Remodelling of the woven bone is dependent on the mechanical forces applied to it (Wolff’s Law - 'form follows function') </li></ul><ul><li>Fracture healing is complete when there is repopulation of the medullary canal </li></ul>
  15. 16. Primary Healing <ul><li>Cancelluous bone is of uniform spongy texture and has no intermedullary canal </li></ul><ul><li>Union can occur directly between the bone surfaces </li></ul><ul><li>New blood vessels and proliferating osteogenic cells from the fracture surfaces penetrate the haematoma until they meet and fuse </li></ul><ul><li>Osteoblasts then lay down the intercellular matrix which becomes ossified to form woven bone. </li></ul>
  16. 17. Factors influencing bone healing <ul><li>Systemic </li></ul><ul><li>Age </li></ul><ul><li>Hormones </li></ul><ul><li>Functional activity </li></ul><ul><li>Nerve function </li></ul><ul><li>Nutrition </li></ul><ul><li>Drugs (NSAID) </li></ul><ul><li>Local </li></ul><ul><li>Degree of local trauma </li></ul><ul><li>Degree of bone loss </li></ul><ul><li>Vascular injury </li></ul><ul><li>Type of bone fractured </li></ul><ul><li>Degree of immobilisation </li></ul><ul><li>Infection </li></ul><ul><li>Local pathological condition </li></ul>
  17. 18. Fracture Fixation <ul><li>Numerous systems have been developed to assist a bone’s natural healing properties </li></ul><ul><ul><li>Plates Screws </li></ul></ul><ul><ul><li>Pins External fixators </li></ul></ul><ul><ul><li>Intramedullary nails </li></ul></ul><ul><li>Fixation systems are typically compared in terms of stabilization (stiffness) </li></ul><ul><li>Performance of a fracture fixation system will depend on: </li></ul><ul><ul><li>Natural stability of fracture </li></ul></ul><ul><ul><li>State of contact between fragments </li></ul></ul>
  18. 19. Rehabilitation <ul><li>Aim: to preserve function so far as possible while the fracture is uniting </li></ul><ul><li>Use injured part as naturally as possible within the limitations imposed by treatment </li></ul><ul><li>Active exercise, to preserve muscle function </li></ul><ul><li>early: static contractions </li></ul><ul><li>mid: mobilising the joints and building muscle power </li></ul><ul><li>late: increase intensity to regain full power </li></ul><ul><li>Weight bearing </li></ul><ul><ul><ul><li>Prolongs inflammatory response aiding formation of new bone </li></ul></ul></ul>

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