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Biomechanics of Soft Tissue Injury Student Version


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The Biomechanics of Soft Tissue Injury.

Composition of Connective Tissue
Composition – basic elements
Structure-how the elements are arranged
Function –the relative contribution of each element

Analyse the ability of the major connective tissue elements to resist mechanical force

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Biomechanics of Soft Tissue Injury Student Version

  1. 1. Soft Tissue Injury Kate Markland Senior Physiotherapist
  2. 2. Contents <ul><li>Composition of Connective Tissue </li></ul><ul><li>Composition – basic elements </li></ul><ul><li>Structure-how the elements are arranged </li></ul><ul><li>Function –the relative contribution of each element </li></ul><ul><li>Analyse the ability of the major connective tissue elements to resist mechanical force </li></ul><ul><li>Structure and Function of Skeletal Muscle </li></ul>
  3. 3. Tendons and Ligaments <ul><li>Tendon: join skeletal muscle to bone, long and straight, transmit force in one direction act as shock absorbers. </li></ul><ul><li>Ligaments: link two bones to strengthen joints and limit movements. </li></ul>
  4. 4. Principal components of connective tissues . (Culav, Clark, & Merrilees, 1999)
  5. 5. The Collagen Fibre <ul><li>triple polypeptide helix region within the molecule </li></ul><ul><ul><li>primary function of resisting tensile loads </li></ul></ul><ul><li>There are many different types of collagen found in CT – up to 11 different forms. </li></ul><ul><li>The fibril-forming collagens account for 70% of the total body collagen and are found in tendons and ligaments </li></ul>(Culav, Clark, & Merrilees, 1999)
  6. 6. Elastin fibres <ul><li>Less frequently found in connective tissue. </li></ul><ul><li>Allow tissues such as the skin to withstand repeated stretching and deformation. </li></ul><ul><li>May increase in length by 150% and still return to the original configuration. </li></ul>Elastin fibres consist of an elastin core and microfibres located mostly around the periphery (Culav, Clark, & Merrilees, 1999)
  7. 7. Fibre orientation influences the biomechanical properties of a structure <ul><li>Tendon </li></ul><ul><ul><li>Collagen fibres are grouped in bundles that are relatively parallel. </li></ul></ul><ul><ul><li>Resist unidirectional forces </li></ul></ul><ul><ul><li>Efficiently transmit forces generated by muscles to bones </li></ul></ul><ul><li>Ligament </li></ul><ul><ul><li>Collagen fibers less parallel way </li></ul></ul><ul><ul><li>Need to resist  multi-directional forces.  </li></ul></ul>  (Threlkeld, 1992)
  8. 8. &quot;undulations or crimping&quot; Scanning electron micrographs of collagen from human knee ligaments at a magnification of x10,000. When the fibres are not under load, they may be wavy or crimped. When the fibres are under tensile load, the crimping tends to straighten out.   (Threlkeld, 1992)
  9. 9. Proteoglycans <ul><li>PG molecules have negative charges which bind water </li></ul><ul><ul><li>stabilises collagen structures increasing structure’s strength </li></ul></ul><ul><ul><li>making the matrix gel-like and tissues spongy & resilient </li></ul></ul><ul><ul><li>ability to resist compressive forces </li></ul></ul><ul><li>PG’s are characterised by a core protein </li></ul><ul><li>Tissues subjected to high compressive forces e.g. articular cartilage have a large PG content </li></ul>(Culav, Clark, & Merrilees, 1999)
  10. 10. Glycoprotiens <ul><li>Small but important proportion of the total matrix. </li></ul><ul><li>Integral to stabilizing the matrix </li></ul><ul><li>Providing linkage between matrix components and between cells and matrix components. </li></ul>(Culav, Clark, & Merrilees, 1999)
  11. 11. Mechanical forces that stress CT are either stretching or compression (Threlkeld A, 1992). Compression mainly loads cartilage, nucleus pulposus and bone Stretching mainly loads ligaments, capsules, tendons and muscles
  12. 12. Components and Mechanical Properties of the Common Connective Tissues (Culav, E., Clark, C., Merrilees, M. 1999) Resists tension and moderate compression and accommodates stretching 1% Collagen Elastin Fibroblasts Dermis Resists tension, compression, and torsion Very small percentage of dry weight Collagen Osteoblasts Osteocytes Bone Resists compressive forces 8%–10% Collagen Chondrocytes Articular cartilage Resists tensional forces 0.2% Collagen Tenocytes Tendon Content Mechanical Properties PG % of dry weight Dominant Fibre Principal Cell Type Tissue
  13. 13. Stress = Load (Newtons) Area (m 2)
  14. 14. Strain = change in length original length <ul><li>Deformation of the shape compared to the original shape. </li></ul><ul><li>Strain has no unit of measurement as it is a ratio </li></ul><ul><li>Stress divided by strain is defined as the modulus of elasticity </li></ul><ul><ul><li>an indicator of an object’s likelihood to deform when a force is applied </li></ul></ul>
  15. 15. Anisotropy <ul><li>Direction of force application essential factor in failure characteristics. </li></ul><ul><li>As biological tissues are not homogenous the loading response is dependent on the direction of the load. </li></ul><ul><li>Anisotropic: direction-dependent response </li></ul>
  16. 16.   (Threlkeld, 1992)
  17. 17. The resistance of CT to deformation Toe region “taking uo the slack” elastic area deformation changes are reversible.  Microfailure permanent deformation of CT Complete tissue failure Area under curve represents energy uptake Injury (Strain) (Stress)   (Threlkeld, 1992)
  18. 18. Creep and Hysteresis <ul><li>Creep = slow response to maintained stretch with gradual elongation </li></ul><ul><li>Hystereis = if load within elastc limits when the force is removed, tissues return to their intial state </li></ul><ul><li>Lengthening of the elongation related to the velocity of the stretch </li></ul><ul><ul><li>Load quickly tissue behaves more stiffly </li></ul></ul><ul><ul><li>the slower the stretch the greater the lengthening </li></ul></ul>Hysteresis Creep   (Threlkeld, 1992)
  19. 19. Mean Ultimate Strengths of Selected Collagenous Tissues <ul><li>All tissues were tested at a strain rate of approximately 8.3 to 8.5 rnm/s. </li></ul>  (Threlkeld, 1992) 848 N (86 kg) Noyes et aI Gracilis tendon 1,297 N (121 kg) Noyes et aI Semitendinosus tendon 3,028 N (306 kg) Noyes et aI Patellar bone-tendon-bone unit 667 N (68 kg) Kennedy et a1 Tibial collateral ligamen 870 N (89 kg) Kennedy et al Posterior cruciate ligament 627 N (64 kg) 1,730 N (1 75 kg) Kennedy et al Noyes et aI Anterior cruciate ligament Mean Ultlmate Strength Author Structure
  20. 20. Summary of biomechanical forces influencing soft tissue <ul><li>Connective tissue composition </li></ul><ul><ul><li>PG content </li></ul></ul><ul><ul><li>Fibre type </li></ul></ul><ul><ul><li>Fibre orientation </li></ul></ul><ul><li>Mechanical forces </li></ul><ul><ul><li>Load (Stress) </li></ul></ul><ul><ul><li>Direction (Anisotropy) </li></ul></ul><ul><ul><li>Time (Viscoelastic properties) </li></ul></ul><ul><li>Stress strain curve </li></ul>
  21. 21. References <ul><li>Culav, E., Clark, H., & Merrilees, M. (1999). Connective tissues: matrix compostion and its relevance to physical therapy. Physical Therapy, 79 (3), 308-319. </li></ul><ul><li>Threlkeld, A (1992). The effects of manual therapy on connective tissue. Physical Therapy, 72(12), 893-902. </li></ul><ul><li>Zeuner, J. (2004). The effects of mechanical therapy on tissue repair and remodelling. The McKenzie Institute USA Journal, 12(3), 19-25. </li></ul>