Tendons attach muscle to bone and transmit tensile loads to allow movement. Ligaments stabilize joints by restricting excessive motion. Both tendons and ligaments are viscoelastic tissues that can withstand high tensile loads. Injury occurs when these tissues are loaded beyond their physiological range, potentially causing microfailures or gross tearing. Ligament injuries are clinically graded based on pain and joint stability. While immobilization can decrease mechanical properties, controlled mobilization after injury may allow properties to be recovered over time.

1. Tendon and Ligament

2. Roles of Ligaments and
Joint Capsules
• Assist in Stabilization of Joint
• Restrict Movement
• Prevent Excessive Motion

3. Roles of Tendons
• Attach muscle to bone
• Transmit tensile loads
• Position of muscle relative to joint

4. Mechanical Behavior of Tendons and
Ligaments
• Both are viscoelastic tissues
• Visco - a small amount of load results in quite
a bit of deformation (relative)
• Elastic - refers to Elastic Region
• Importance of viscoelastic qualities?

5. Properties of Tendon
• can sustain high tensile loads
• flexible to allow changes in direction of muscle
pull

6. Properties of Ligament
• guides movement
• resists applied force

7. Mechanical Properties
of Tendon and Ligament
• Strength
• Stiffness

8. Damage to Tendon and Ligament
• When load is great enough to cause injury,
damage is dependent on:
– rate and
– amount of load

9. Load-Deformation Curve
for Tendon and Ligament
• (0,0) - A: Toe Region
• A - B: Elastic Region
• B: Yield Point
• B - C: Plastic Region
• C: Ultimate Failure Point

10. Comparison of Bone to
Tendon and Ligament
• Identify similarities and differences between
these tissue types.

11. Mechanical Properties of
Tendon and Ligament
• Strength
• Stiffness

12. Injury Mechanisms
• Injury occurs when tissue is loaded beyond its
physiological range.
• Microfailure occurs before the yield point is
reached.

13. Injury Mechanisms cont.
• When yield point is exceeded, the ligament
begins to undergo gross failure.
• Results in abnormal joint displacement
• Displacement results in...

14. 3 Clinical Categories of
Ligament Injury
• Negligible Clinical Symptoms (Grade 1)
– no joint instability can be detected clinically
• Severe Pain (Grade 2)
– joint instability can be detected clinically
– strength and stiffness decreases by 50%
– instability can be masked by muscle involvement

15. 3 Clinical Categories of
Ligament Injury cont.
• Severe Pain (Grade 3)
– severe pain experienced during the injury with
less pain after the injury
– joint is completely unstable
– most collagen fibers have ruptured

16. Noyes Study (1977)
• Rhesus monkeys
• 8 wks immobilization
• returned to mobilization
• at 12 mo. mechanical properties were
comparable to non-immobilized ligaments.
• Drumroll?

17. Additional Factors Important
in Tendon Injury
• Amount of force produced by muscle
• Stress comparison between tendon and
muscle
• Loading Rates

18. Factors Affecting Biomechanical Properties of
Tendon and Ligament
• Aging
• Pregnancy
• Mobilization vs. Immobilization
• NSAIDs

19. Osteoarthritis
• Researchers suggest that a deficiency in
mechanisms that minimize peak forces may
cause osteoarthritis.