LIGAMENT BIOMECHANICS

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LIGAMENT BIOMECHANICS

• Richard E. Hughes, Ph.D.
• Orthopaedic Surgery
• University of Michigan

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GOALS

• Biomechanics
• structural vs. material properties
• viscoelastic tissue
• Clinical implications
• OITE questions
• Summary

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LIGAMENT TESTING
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LOAD-ELONGATION CURVE
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LOAD-ELONGATION CURVE
TOE REGION
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NONLINEAR ELASTICITY
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STRUCTURAL vs. MATERIAL PROPERTIES
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STRESS AND STRAIN
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STRESS-STRAIN
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STRESS-STRAIN
E
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LIGAMENT IS VISCOELASTIC
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LOADING ORIENTATION
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FACTORS AFFECTING LIGAMENT BIOMECHANICS

• Skeletal maturity
• Age
• Immobilization / Remobilization / Exercise

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GOALS

• Biomechanics
• structural vs. material properties
• viscoelastic tissue
• Clinical implications
• OITE questions
• Summary

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LIGAMENT INJURY

• Grade I. Mild sprain.
• Tender to palpation and pain induced by ligament
  stress
• Grade II. Moderate sprain
• Acute pain and swelling
• Joint laxity
• Grade III. Severe sprain
• Pain, swelling, tenderness
• Ligament fibers completely disrupted
• Joint laxity/instability

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LIGAMENT HEALING

• Phase I. Inflammation
• Phase II. Matrix and cell proliferation
• Phase III. Remodeling and maturation

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GRAFT LOCATION
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JOINT GEOMETRY
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ACL RECONSTRUCTION
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GOALS

• Biomechanics
• structural vs. material properties
• viscoelastic tissue
• Clinical implications
• OITE questions
• Summary

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LIGAMENT ADAPTATION
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FIGURE 33 (Ortho. Basic Sci.)
Woo, S. L-Y et al. (1982) Biorheology 19 397-408
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The breaking strength of the medial collateral
ligament in rabbits is reduced by what percentage
following 9 weeks of cast immobilization?
OITE QUESTION

• 10
• 30
• 40
• 66
• 86

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The breaking strength of the medial collateral
ligament in rabbits is reduced by what percentage
following 9 weeks of cast immobilization?
OITE QUESTION

• 10
• 30
• 40
• 66
• 86

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SHOULDER STABILITY

• What is the effect of capsular and coracohumeral
  ligaments on glenohumeral stability?

Malicky, D.M. et al. (1996) JOR 14 282-288
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U of M SHOULDER FIXTURE
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U of M SHOULDER FIXTURE
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MATERIALS AND METHODS

• Cadaver shoulder (n8)
• Cuff forces applied
• Ligaments sectioned
• Measure force required for anterior subluxation

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RESULTS
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The main stabilizer in the shoulder to prevent
anterior glenohumeral instability with the arm
abducted and externally rotated is the
1. subscapularis muscle. 2. anterior glenoid
rim. 3. superior glenohumeral ligament. 4.
middle glenohumeral ligament. 5. inferior
glenohumeral ligament.
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The main stabilizer in the shoulder to prevent
anterior glenohumeral instability with the arm
abducted and externally rotated is the
1. subscapularis muscle. 2. anterior glenoid
rim. 3. superior glenohumeral ligament. 4.
middle glenohumeral ligament. 5. inferior
glenohumeral ligament.
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GOALS

• Biomechanics
• structural vs. material properties
• viscoelastic tissue
• Clinical implications
• OITE questions
• Summary

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STRUCTURAL vs. MATERIAL PROPERTIES
STRUCTURAL
MATERIAL
NORMALIZATION
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LIGAMENT IS VISCOELASTIC
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THANK YOU
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LOAD-ELONGATION CURVE
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ACL REPAIR

• Autograft
• Allograft
• Placement
• Fixation
• Tension