Ligaments and Tendons Part 3

David Flanigan, MD

Assistant Professor of Clinical Orthopaedics

Team Physician

The OSU Sports Medicine Center

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

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

What are ligaments?

Fibrous soft tissue Connect bone to bone Allow normal joint motion Prevent abnormal motion,

instability

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

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

Anisotropic Properties

Strong in tension Weak in compression Anisotropic

Mechanical properties depend on the orientation of the force applied

Muscles are 1st line of defense

Hiking over rocky terrain example

Inversion resisted 1st by peroneus muscles

Ligaments come into play when muscle inactive or too weak

http://www.merck.com/mmhe/print/sec05/ch072/ch072c.html

http://www.eorthopod.com/eorthopodV2/index.php/fuseaction/topics.detail/ID/1e69153b4390c6eff3095daeefe6031a/TopicID/f3734010e47d0fce02d98570d66e2a38/area/19

Ankle Ligaments

Ligaments guide motion

Ankle Guides linear action of

muscles into rotation PCL

Femoral rollback ACL

Screw-home

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.

0

100

200

300

400

0 2 4 6 8 10

Load[N]

Elongation [mm]Reproduced from Woo et al., 2000

Low Stiffness

High Stiffness

Load and Elongation

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.

Ligament maintenance

3 principal cell types Fusiform Ovoid, spheroid

Vascular supply Inside—endoligament Outside—epiligament Diffusion of nutrients to

cells

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

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

I II III

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

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_

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

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

Thank You

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