PPT 1.6: Biomechanics and Physiology of Tendons and Ligaments

What does a tendon do?

Attach muscle to bone

What does a tendon transmit?

Tensile of the muscle load to bone

How does a tendon use proprioception?

GTOs

What does a ligament do?

Connect bone to bone

What does a ligament augment?

Joint stability

What does a ligament prevent?

Excessive mobility

What does a ligament guide?

Joint motion

How does a ligament use proprioception?

Mechanoreceptors

What are tendons comprised of?

1. Cells (20%)

2. Extracellular matrix (80%)

What cells are tendons comprised of?

1. Tenocytes

2. Specialized fibroblast cell

What is the function of cells in tendons?

To produce and degrade extracellular matrix in response to mechanical load

What percent of the extracellular matrix in tendons is water?

55-70%

What is the dry weight of tendons composed of?

1. Collagen (60-80%)

2. Elastin (2%)

3. Proteoglycans (<0.2%)

4. Proteins (4-5%)

What type of collagen is in the extracellular matrix of tendons?

Type I (since they can sustain large tensile loads with some compliance)

What are ligaments comprised of?

1. Cells (20%)

2. Extracellular matrix (80%)

What kind of cells are in ligaments?

Fibroblast

What is the function of cells in ligaments?

To produce and degrade extracellular matrix in response to mechanical load

What percent of the extracellular matrix in ligaments is water?

70%

What is the dry weight comprised of in the extracellular matrix of ligaments?

1. Collagen (75%)

2. Elastin (5%)

3. Proteoglycans (5%)

4. Proteins (10%)

What type of collagen is found in ligaments?

Mostly Type I (85%)

Compare ligaments to tendons.

1. Ligaments have a lower percentage of collagen

2. Ligaments have a higher percentage of proteoglycans and water

3. Ligaments have less organized collagen fibers

How does a tissue get its strength?

Due to the cross-links between collagen fibrils

How are tendons and ligaments different in structure and composition?

Tendons have parallel bundles of collagen fibers while ligaments have nearly parallel bundles of collagen fibers

What loose connective tissue surrounds tendons?

1. Paratenon

2. Epitenon

What is a paratenon?

Tendon sheath with two layers to assist in gliding that surrounds tendons

What is an epitenon?

Synovial like membrane, prominent in areas of high friction that surrounds tendons

What percentage of the extracellular matrix in tendons is blood supply?

1-2%

What is blood supply in tendons derrived from?

Vessels in the perimysium, periosteal insertion, or other surrounding tissue

What is loose connective tissue surrounds ligaments?

Epiligament

What is an epiligament?

Connects directly to periosteum of bone

How is blood supply in ligaments?

Sparse as well

What is the epiligament continuous with in terms of blood supply?

The periosteum where blood is obtained

What occurs to blood supply when intra-articular?

The synovium replaces contributes to vascularity

What are the four zones of tendon insertion into bone?

Zone 1: Collagen fibers

Zone 2: Fibrocartilage

Zone 3: Mineralized fibrocartilage

Zone 4: Cortical bone

What are biomechanical properties of tendons and ligaments?

1. Viscoelastic

2. Resists tensile forces

3. Flexible

What is hysteresis?

Loss of energy during cyclic loading and unloading of a viscoelastic substance (ex. jumping)

What does the elastic component of tendons allow?

Return to original shape

What are repetitive strain injuries?

Despite low loads, cumulative damage from repeated elongation and shortening

Why does pain occur during repetive strain injuries?

Inflammation (neurovascular ingrowth?)

What are other factors of repetitive strain injuries?

Age, force, ergonomic factors

What is viscoelasticity?

All biological material having fluid and solid like properties

What is material behavior dependent on?

Time or rate

What is load(stress)-relaxation? (2)

1. Specimen is stretched to constant length

2. Initial rapid decrease in stress and then more slowly

What is creep-deformation? (2)

1. Specimen placed under constant load (stress is constant)

2. Length (deformation) initially increases rapidly and then more slowly

What are the four areas of ligament failure? (4)

1. Loads for clinical knee test

2. Physiologic activity

3. Microfailure

4. Complete rupture

What are the factors affecting biomechanical behavior?

1. Maturation/aging

2. Pregnancy/postpartum

3. Mobilization/immobilization

4. Comorbidities

5. Pharmacalogical agents

How does maturing/aging affect biomechanical behavior?

Insertion point has the optimal strength at skeletal maturity

When does optimal crosslinking occur?

Strength is reached at age ~20

What occurs as you are greater than 20 years old?

Diameter of tendon/ligament and density of fibrils decreases

How does pregnancy/postpartum affect biomechanical behavior?

Relaxin affects the production of collagen from fibroblasts by decreasing tensile strength and stiffness

How does mobilization/immobilization affect biomechanical behavior?

More activity = stronger

Less activity = weaker

How do comorbidities affect biomechanical behavior?

1. DMI (Metabolic influence/shift)

2. Inherited conditions that alter the structure or density of collagen

How do injuries occur in tendons and ligaments?

High stress, high strain, or both

What are tendon injuries related to?

Cross sectional area of tendon and amount of force due to contraction

What is tendinopathy?

Inflammation of a tendon (multifactorial)

How do injuries in ligaments occur?

Due to viscoelasticity (fast rate -> ligament failure; slow rate -> bone failure)

What are the three types of common ligament injuries?

1. First degree sprain

2. Second degree sprain

3. Third degree sprain

What occurs during a first degree sprain?

Pain, but no join instability

What occurs during a second degree sprain?

Pain and joint instability

What occurs to collagen fibers in a second degree sprain?

Partial rupture (failure of some collagen fibers)

What is a third degree sprain?

Pain, complete instability

What occurs to collagen fibers in a third degree sprain?

Total rupture

What are the phases of tendon and ligament repair?

1. Inflammatory

2. Proliferative

3. Remodeling/maturation

What occurs during the inflamatory phase of tissue repair?

Hematoma forms

What occurs during the proliferative phase of tissue repair?

Fibroplast proliferation

What occurs during the remodeling/maturation phase of tissue repair?

Collagen matrix maturation