Biomechanics & Surgery: Tissue Mechanics IV PDF

Biomechanics & Surgery: Tissue Mechanics IV Ligament / Tendon n Structure and metabolism of tendons – construction of tendons – collagen fibers and other substances – cells of tendon n Biomechanics, function and development – function of tendon – mechanical properties of tendon Readings: OPTIONAL –...

Biomechanics & Surgery: Tissue Mechanics IV Ligament / Tendon n Structure and metabolism of tendons – construction of tendons – collagen fibers and other substances – cells of tendon n Biomechanics, function and development – function of tendon – mechanical properties of tendon Readings: OPTIONAL – n Lim et al. Functional Outcome of Acute Achilles Tendon Rupture With and Without Operative Treatment Using Identical Functional Bracing Protocol. Foot & Ankle International, 2017, Vol. 38(12) 1331– 1336 Available on D2L Vassilios G. Vardaxis, Ph.D. Tendon - Ligament: Objectives At the completion of this topic the students should be able to: – Describe the components and organization of dense regular connective tissues (Specifically tendons and ligaments) – Describe the mechanical behavior of tendons and ligaments in response to tensile loads – Describe physical factors affecting the mechanical behavior of tendons and ligaments – Describe biological factors affecting the mechanical behavior of tendons and ligaments – Discuss the response of tendons and ligaments to stress deprivation and remobilization – Describe the mechanical properties of tendons and ligaments during healing Vassilios G. Vardaxis, Ph.D. Musculotendinous Unit: Basic Structure n transmits tensile forces created in the muscle to the bone n composed of collagen and elastin embedded in a matrix of proteoglycan and water n synthesized by tenocytes and tenoblasts Proximal attachment n each muscle has proximal and distal tendon Distal attachment – MTJ: myotendinous junction: tendon-muscle – OTJ: osteotendinous junction: tendon-bone Vassilios G. Vardaxis, Ph.D. Tendon vs. Ligament: Composition n Tendon: muscle to bone – transmit tensile forces n Ligament: bone to bone – limits joint motion n Compositional differences tendons vs. ligament Vassilios G. Vardaxis, Ph.D. Tendon: Micro-architecture Vassilios G. Vardaxis, Ph.D. General Biomechanical Behavior Tendons: withstand unidirectional tensile loads Ligaments: resist high tensile loads in one direction and smaller tensile loads in other directions. Vassilios G. Vardaxis, Ph.D. Tendon & Surrounding Structures n Tendon synovial sheaths – closed duct around tendons gliding on bone surfaces – frequently observed in tendons of hand and feet – the sheath is formed of two membranes: inner (visceral) and outer (parietal) sheets Vassilios G. Vardaxis, Ph.D. Tendon & Surrounding Structures n synovial sheaths (cont.): – parietal sheet has synovial cells – space between parietal and visceral membrane is filled with synovial (peritendinous) fluid n facilitates smooth gliding of the tendons n aiding the nutrition of tendons – Under the annular pulleys that act as a fulcrum, adding a mechanical advantage to flexion Vassilios G. Vardaxis, Ph.D. Tendon & Surrounding Structures n paratenon (a.k.a peritendinous sheet): – those tendons which do not have synovial sheath may have paratenon to reduce friction – composed of loose fibrillar tissue (type I and III collagen) – functions as an elastic sleeve that permits free movement of tendon against surrounding tissue – inner surface has synovial cells Vassilios G. Vardaxis, Ph.D. Tendon & Surrounding Structures n epitenon: – – – located under the paratenon and surrounds the tendon fibrillar network of collagen with strands of 10 nm thickness strands run oblique, longitudinal or transverse to the long axis of the tendon Vassilios G. Vardaxis, Ph.D. Tendon & Surrounding Structures Epitenon fibers at 60° to the tendon axis. Reorient to 30° after stretching (angle decreases) Vassilios G. Vardaxis, Ph.D. Tendon & Surrounding Structures n endotenon: – – – – – thin network of crisscross collagen fibrils envelopes the primary, secondary and tertiary fiber bundles together proteoglycans are present between endotenon and tendon fibers à hydration allows fiber bundles to glide with respect to each other carry blood vessels, nerves and lymph to tendon Thorpe et al, 2010 Vassilios G. Vardaxis, Ph.D. Tendon: Internal architecture n crimping of tendons: – – – – – a wavy formation within fascicles varies and irregular along fibers believed to result from cross linking of fibers disappears when stretched and reappears when unloaded removal of crimp dominates low strain range (