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Ligaments and Tendons Part 3 David Flanigan, MD Assistant Professor of Clinical Orthopaedics Team Physician The OSU Sports Medicine Center
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Objectives Block Objectives Contrast the differences between tendons and ligaments Define the histology and composition of ligaments Identify the function of ligaments Explain the stress/strain curve and how it applies to ligaments Define crimp and anisotrophic and how they apply to ligaments Define the histology and composition of tendons Identify the function of tendons
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Difference Ligaments vs Tendons Resistance to tension Tendon Uniformly stiff Does not elongate Allows conservation of energy Ligament Built-in laxity Allows small forces across joint Protects joint
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What are ligaments? Fibrous soft tissue Connect bone to bone Allow normal joint motion Prevent abnormal motion, instability
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Role of ligaments Secondary restraint during normal activity under load Weight-bearing Guide unloaded motion E.g. knee “screw-home” Stop abnormal motion to avoid further damage
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Function and anatomy Ropes, not bars Resist tension only Redundancy across joint Example 1: 4 main knee ligaments Example 2: ankle ligaments Block all undesirable motions loads pass across articulating surfaces
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Anisotropic Properties Strong in tension Weak in compression Anisotropic Mechanical properties depend on the orientation of the force applied
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Muscles are 1 st line of defense Hiking over rocky terrain example Inversion resisted 1 st by peroneus muscles Ligaments come into play when muscle inactive or too weak
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http://www.merck.com/mmhe/print /sec05/ch072/ch072c.html http://www.eorthopod.com/eorthopodV2/index.php/fuseacti on/topics.detail/ID/1e69153b4390c6eff3095daeefe6031a/To picID/f3734010e47d0fce02d98570d66e2a38/area/19 Ankle Ligaments
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Ligaments guide motion Ankle Guides linear action of muscles into rotation PCL Femoral rollback ACL Screw-home
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Physiologic structure of ligaments Non-linear stiffness Laxity at low loads High stiffness at high loads Highly aligned collagen fascicles “Crimp” to provide non-linearity Straighten out first (low stiffness) Fibrils stretch (high stiffness) Boorman et al (2006) Journal of Orthopaedic Research 24(4):795.
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Load [N] Elongation [mm] Reproduced from Woo et al., 2000 Low Stiffness High Stiffness Load and Elongation
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Physiologic structure of ligaments Primarily collagen I Same as bone Enthesis = attachment Direct attachment 4 zones of increasing density, calcification Continuous collagen fibers Indirect attachment No fibrocartilage Merge into periosteal layer Not as strong Woo et al. (1987) Journal of Bone & Joint Surgery 69A:1208.
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Ligament maintenance 3 principal cell types Fusiform Ovoid, spheroid Vascular supply Inside—endoligament Outside—epiligament Diffusion of nutrients to cells
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Role in proprioception Where joint is in space Presence of nerve fibers in ligament Observed disruption of proprioception after injury Longer to heal than structural component— perception of instability Physical therapy, rehab help bring back
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Ligament injury Grade I—pain, no instability Grade II—some torn fibers, minimal instability Grade III—completely torn Always from excessive tension Dislocations always include ligament injury IIIIII
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Tendons Dense regular connective tissue highly specialized to transmit high tensile loads from muscle to bone Type I collagen comprises 86% of the dry weight; type III collagen- 5% Epitenon and then paratenon surround the fascicles http://www.clinicalsportsmedicine.com/articles/tendonstructure.gif http://arthritis-research.com/content/figures/ar416-1-l.jpg
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Tendon Insertion Specialized direct insertion Four zones Tendon Fibrocartilage Mineralized fibrocartilage Bone Sharpey’s fibers- Collagen bundles that extend from the tendon or periosteum into the bone. http://anatomy.iupui.edu/courses/histo_
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Two Types of Tendons Tendons that pull in a straight line are not enclosed by a sheath but by a paratenon (Achilles tendon), which is loose connective tissue continuous with the tendon Tendons which are required to bend (flexor tendons of the hand) are enclosed by a tendon sheath which directs the tendon path and acts like a pulley; motion is assisted by synovial fluid produced by epitenon
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Injury and Repair Three mechanisms of injury Direct trauma/ laceration Indirect trauma with intrasubstance injury or avulsion from bone Sudden tensile stress Repetitive submaximal overload or repetitive pressure against a bony surface http://www.mccainortho.com/Patella%20Fx%20406b.jpg
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Thank You David.Flanigan@osumc.eduQuestions?
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