1. Ligaments and Tendons Part 3 David Flanigan, MD Assistant Professor of Clinical Orthopaedics Team Physician The OSU Sports Medicine Center

2. 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

3. 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

4. What are ligaments?  Fibrous soft tissue  Connect bone to bone  Allow normal joint motion  Prevent abnormal motion, instability

5. 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

6. 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

7. Anisotropic Properties  Strong in tension  Weak in compression  Anisotropic  Mechanical properties depend on the orientation of the force applied

8. 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

9. 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

10. Ligaments guide motion  Ankle  Guides linear action of muscles into rotation  PCL  Femoral rollback  ACL  Screw-home

11. 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.

12. Load [N] Elongation [mm] Reproduced from Woo et al., 2000 Low Stiffness High Stiffness Load and Elongation

13. 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.

14. Ligament maintenance  3 principal cell types  Fusiform  Ovoid, spheroid  Vascular supply  Inside—endoligament  Outside—epiligament  Diffusion of nutrients to cells

15. 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

16. 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

17. 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

18. 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_

19. 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

20. 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

22. Thank You David.Flanigan@osumc.eduQuestions?

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