Download What are ligaments?

Ligaments and Tendons Part 3
David Flanigan, MD
Assistant Professor of Clinical Orthopaedics
Team Physician
The OSU Sports Medicine Center
Objectives
 Block Objectives
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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?
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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.eorthopod.com/eorthopodV2/index.php/fuseacti
on/topics.detail/ID/1e69153b4390c6eff3095daeefe6031a/To
picID/f3734010e47d0fce02d98570d66e2a38/area/19
http://www.merck.com/mmhe/print
/sec05/ch072/ch072c.html
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.
Load and Elongation
400
300
Load
200
[N]
High Stiffness
100
Low Stiffness
0
0
2
4
6
Elongation [mm]
Reproduced from Woo et al., 2000
8
10
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
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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%
http://arthritis-research.com/content/figures/ar416-1-l.jpg
 Epitenon and then paratenon
surround the fascicles
http://www.clinicalsportsmedicine.com/articles/tendonstructure.gif
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
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Direct trauma/ laceration
Indirect trauma with
intrasubstance injury or avulsion
from bone
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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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