Applied Human Anatomy and Biomechanics
Course Content I. Introduction to the Course II. Biomechanical Concepts Related to Human Movement III. Anatomical Concepts & Principles Related to the Analysis of Human Movement IV. Applications in Human Movement V. Properties of Biological Materials VI. Functional Anatomy of Selected Joint Complexes
Why study? Design structures that are safe against the combined effects of applied forces and moments 1. Selection of proper material 2. Determine safe & efficient loading conditions
Application Injury occurs when an imposed load exceeds the tolerance (loadcarrying ability) of a tissue Training effects Drug effects Equipment Design effects
Properties of Biological Materials A. Basic Concepts B. Properties of Selected Biological Materials A. Bone B. Articular Cartilage C. Ligaments & Muscle-Tendon Units
Structural vs. Material Properties Structural Properties Load-deformation relationships of like tissues Material Properties Stress-strain relationships of different tissues
Terminology load the sum of all the external forces and moments acting on the body or system deformation local changes of shape within a body
Load-deformation relationship Changes in shape (deformation) experienced by a tissue or structure when it is subjected to various loads
Extent of deformation dependent on: Size and shape (geometry) Material Structure Environmental factors (temperature, humidity) Nutrition Load application Magnitude, direction, and duration of applied force Point of application (location) Rate of force application Frequency of load application Variability of magnitude of force
Types of Loads Uniaxial Loads Multiaxial Loads Axial Compression Tension Shear Biaxial loading responses Triaxial loading responses Bending Torsion
Types of Loads
Axial Loads Whiting & Zernicke (1998)
Shear Loads Whiting & Zernicke (1998)
Axial Loads Create shear load as well Whiting & Zernicke (1998)
Biaxial & Triaxial Loads Whiting & Zernicke (1998)
Structural vs. Material Properties Structural Properties Load-deformation relationships of like tissues Material Properties Stress-strain relationships of different tissues
Terminology Stress (σ) σ = F/A (N/m 2 or Pa) normalized load force applied per unit area, where area is measured in the plane that is perpendicular to force vector (CSA)
Terminology Strain (ε) ε = dimension/original dimension normalized deformation change in shape of a tissue relative to its initial shape
How are Stress (σ) and Strain (ε) related? Stress is what is done to an object, strain is how the object responds. Stress and Strain are proportional to each other. Modulus of elasticity = stress/strain
Typical Stress-Strain Curve F e =kx
Elastic region & Plastic region
Stiffness Fig. 3.26a, Whiting & Zernicke, 1998
Stiffness (Elastic Modulus)
A B C 1 2 3 4 5 6 7 Deformation (cm) Load (N) 1 5 10 15 20 25
Strength stiffness strength Yield Ultimate Strength Failure
Apparent vs. Actual Strain 1. Ultimate Strength 2. Yield Strength 3. Rupture 4. Strain hardening region 5. Necking region A: Apparent stress B: Actual stress
Tissue Properties Load (N) 1 5 10 15 20 25 Deformation (cm) A B C
Extensibility & Elasticity
Extensibility A ligament tendon B C Load (N) 1 5 10 15 20 25 1 2 3 4 5 6 7 Deformation (cm)
Rate of Loading Bone is stiffer, sustains a higher load to failure, and stores more energy when it is loaded with a high strain rate.
Bulk mechanical properties Stiffness Strength Elasticity Ductility Brittleness Malleability Toughness Resilience Hardness
Ductility Characteristic of a material that undergoes considerable plastic deformation under tensile load before rupture Can you draw???
Brittleness Absence of any plastic deformation prior to failure Can you draw???
Malleability Characteristic of a material that undergoes considerable plastic deformation under compressive load before rupture Can you draw???
Resilience
Toughness
Hardness Resistance of a material to scratching, wear, or penetration
Uniqueness of Biological Materials Anisotropic Viscoelastic Time-dependent behavior Organic Self-repair Adaptation to changes in mechanical demands
blast produce matrix clast resorb matrix cyte mature cell General Structure of Connective Tissue Distinguishes CT from other tissues Cellular Component Extracellular Matrix Resident Cells fibroblasts, osteocytes, chondroblasts, etc. Circulating Cells lymphocytes, macrophages, etc. Protein Fibers collagen, elastin Ground Substance (Fluid) synthesis & maintenance defense & clean up determines the functional characteristics of the connective tissue
Collagen vs. Elastin Collagen Great tensile strength 1 mm 2 cross-section withstand 980 N tension Cross-linked structure stiffness Tensile strain ~ 8-10% Weak in torsion and bending Elastin Great extensibility Strain ~ 200% Lack of creep
Bind cells Mechanical links Resist tensile loads Types of Connective Tissue Ordinary Special Irregular Ordinary Regular Ordinary Cartilage Bone Loose Adipose Regular Collagenous Regular Elastic Irregular Collagenous Irregular Elastic Number & type of cells Proportion of collagen, elastin, & ground substance Arrangement of protein fibers
Why study? Design structures that are safe against the combined effects of applied forces and moments 1. Selection of proper material 2. Determine safe & efficient loading conditions
Application Injury occurs when an imposed load exceeds the tolerance (loadcarrying ability) of a tissue Training effects Drug effects Equipment Design effects
Properties of Biological Materials A. Basic Concepts B. Properties of Selected Biological Materials A. Bone B. Articular Cartilage C. Ligaments & Muscle-Tendon Units
Mechanical Properties of Bone General Nonhomogenous Anisotropic Strongest Stiffest Tough Little elasticity
Material Properties: Bone Tissue Cortical: Stiffer, stronger, less elastic (~2% vs. 50%), low energy storage
Mechanical Properties of Bone Ductile vs. Brittle Depends on age and rate at which it is loaded Younger bone is more ductile Bone is more brittle at high speeds
Metal σ Glass Stiffest? Strongest? Brittle? Ductile? old young Bone ε
Tensile Properties: Bone Stiffness Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Collagen 50 1.2 - Osteons 38.8-116.6 - - Axial Femur (slow) 78.8-144 6.0-17.6 1.4-4.0 (fast) Tibia (slow) 140-174 18.4 1.5 Fibula (slow) 146-165.6 - - Transverse Femur (fast) 52 11.5 -
Compressive Properties: Bone Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Osteons 48-93 - - Axial Mixed 100-280 - 1-2.4 Femur 78.8-144170-209 6.0-17.6 8.7-18.6 1.4-4.0 1.85 Tibia 140-174 213 18.4 15.2-35.3 - Fibula 146-165.6 115 16.6 - Transverse Mixed 106-133 4.2 -
Other: Bone Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Shear 50-100 3.58 - Bending 132-181 10.6-15.8 - Torsion 54.1 3.2-4.5 0.4-1.2 Tension 78.8-174 6.0-18.4 1.4-4.0 Compression 100-280 8.7-35.3 1-2.4 From LeVeau (1992). Biomechanics of human motion (3 rd ed.). Philadelphia: W.B. Saunders.
Mechanical Properties of Selected Biomaterials Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Polymers (bone cement) 20 2.0 2-4 Ceramic (Alumina) 300 350 <2 Titanium 900 110 15 Metals (Co-Cr alloy) Cast Forged Stainless steel 600 950 850 220 220 210 8 15 10 Cortical bone 100-150 10-15 1-3 Trabecular bone 8-50 - 2-4 Bones (mixed) 100-280 8.7-35.3 1-2.4
Viscoelastic Properties : Rate Dependency of Cortical Bone With loading rate: Fig 2-34, Nordin & Frankel, (2001) brittleness Energy storage 2X ( toughness) Rupture strength 3X Rupture strain 100% Stiffness 2X
Viscoelastic Properties : Rate Dependency of Cortical Bone With loading rate: More energy to be absorbed, so fx pattern changes & amt of soft tissue damage Fig 2-34, Nordin & Frankel, (2001)
Effect of Structure Larger CSA distributes force over larger area, stress Tubular structure (vs. solid) More evenly distributes bending & torsional stresses because the structural material is distributed away from the central axis bending stiffness without adding large amounts of bone mass Narrower middle section (long bones) bending stresses & minimizes chance of fracture
Effects of Acute Physical Activity Fig 2-32a, Nordin & Frankel (2001)
Acute Physical Activity Tensile strength: 140-174 MPa Comp strength: 213 MPa Shear strength: 50-100 MPa Fig 2-32b, Nordin & Frankel (2001)
Acute Physical Activity Fig 2-32b, Nordin & Frankel (2001) As speed, ε and σ 5X in ε with speed ε walk = 0.001/s ε slow jog = 0.03/s
Acute Physical Activity In vivo, muscle contraction can exaggerate or mitigate the effect of external forces Fig 2-33, Nordin & Frankel (2001)
Chronic Physical Activity bone density, compressive strength stiffness (to a certain threshold)
Chronic Disuse bone density (1%/wk for bed rest) strength stiffness Fig 2-47, Nordin & Frankel (2001)
Repetitive Physical Activity Muscle Fatigue Injury cycle Ability to Neutralize Stresses on Bone Load on Bone Tolerance for Repetitions
Repetitive Physical Activity Fig 2-38, Nordin & Frankel (2001)
Applications for Bone Injury Crack propagation occurs more easily in the transverse than in the longitudinal direction Bending For adults, failure begins on tension side, since tension strength < compression strength For youth, failure begins on compression side, since immature bone more ductile Torsion Failure begins in shear, then tension direction
Effects of Age brittleness strength ( cancellous bone & thickness of cortical bone) ultimate strain energy storage
Effects of Age on Yield & Ultimate Stresses (Tension) 180 170 160 Stress (MPa) 150 140 130 120 110 100 20-29 30-39 40-49 50-59 60-69 70-79 80-89 Age (yrs) Femur - Yield Tibia - Yield Femur - Ultimate Tibia - Ultimate
Effects of Age on E elastic (Tension) 35.0 30.0 Elas tic Modulus (GPa) 25.0 20.0 15.0 10.0 20-29 30-39 40-49 50-59 60-69 70-79 80-89 Age (yrs) Femur Tibia
Effects of Age on Ultimate Strain (Tension) 0.045 0.040 0.035 Ultim ate Strain 0.030 0.025 0.020 0.015 0.010 0.005 0.000 20-29 30-39 40-49 50-59 60-69 70-79 80-89 Age (yrs) Femur Tibia
Effects of Age on Energy (Tension) 6 5.5 5 Ene r gy (MPa) 4.5 4 3.5 3 2.5 2 20-29 30-39 40-49 50-59 60-69 70-79 80-89 Age (yrs) Femur Tibia
Properties of Biological Materials A. Basic Concepts B. Properties of Selected Biological Materials A. Bone B. Articular Cartilage C. Ligaments & Muscle-Tendon Units
Deforms more than bone since is 20X less stiff than bone congruency High water content causes even distribution of stress High elasticity in the direction of joint motion and where joint pressure is greatest Compressibility is 50-60%
Tensile Properties: Cartilage Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Tension 4.41-10-100 Superficial 10-40 0.15-0.5 - Deep 0-30 0-0.2 - Costal 44-25.9 Disc 2.7 - - Annulus 15.68 - -
Compressive Properties: Cartilage Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Compression 7-23 0.012-0.047 3-17 Patella - 0.00228 - Femoral head - 0.0084-0.0153 - Costal - - 15.0 Disc 11 - -
Other Loading Properties: Cartilage Ultimate stress(mpa) Modulus of elasticity (GPa) Strain to Fracture (%) Shear Normal - 0.00557-0.01022 - Degenerated - 0.00137-0.00933 - Torsion Femoral - 0.01163 - Disc 4.5-5.1 - - Tension From LeVeau (1992). Biomechanics of human motion (3 rd ed.). Philadelphia: W.B. Saunders.
Properties of Biological Materials A. Basic Concepts B. Properties of Selected Biological Materials A. Bone B. Articular Cartilage C. Ligaments & Muscle-Tendon Units D. Skeletal Muscle
Structure and Function: Architecture The arrangement of collagen fibers differs between ligaments and tendons. What is the functional significance?
Biomechanical Properties and Behavior Tendons: withstand unidirectional loads Ligaments: resist tensile stress in one direction and smaller stresses in other directions.
Viscoelastic Properties : Rate Dependent Behavior Moderate strain-rate sensitivity With loading rate: Energy storage ( toughness) Rupture strength Rupture strain Stiffness
Viscoelastic Properties: Repetitive Loading Effects stiffness Enoka (2002), Figure 5.3, p. 219, From Butler et al. (1978)
Very small plastic region Idealized Stress-Strain for Collagenous Tissue Enoka (2002), Figure 5.3, p. 219, From Butler et al. (1978)
Ligamentum flavum Nordin & Frankel (2001), Figure 4-10, p. 110, From Nachemson & Evans (1968)
Tensile Properties: Ligaments Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Nonelastic 60-100 0.111 5-14 ACL 37.8-23-35.8 Anterior Longitudinal.0123 Collagen 50 1.2 -
Viscoelastic Behavior of Bone- Ligament-Bone Complex Fast loading rate: Ligament weakest Slow loading rate: Bony insertion of ligament weakest Load to failure 20% Energy storage 30% Stiffness similar As loading rate, bone strength more than ligament strength.
Ligament-capsule injuries Sprains 1 st degree 25% tissue failure; no clinical instability 2 nd degree 50% tissue failure; 50% in strength & stiffness 3 rd degree 75% tissue failure; easily detectable instabilty Bony avulsion failure (young people more likely if tensile load applied slowly)
Tensile Properties: Muscles & Tendons Ultimate stress (MPa) Modulus of elasticity (GPa) Strain to Fracture (%) Muscle 0.147-3.50-58-65 Fascia 15 - - Tendon Various 45-125 0.8-2.0 8-10 Various 50-150 - 9.4-9.9 Various 19.1-88.5 - - Mammalian 0.8-2 Achilles 34-55 - -
Enoka (2002), Figure 5.12, p. 227, From Noyes (1977); Noyes et al. (1984)
Enoka (2002), Figure 3.9, p. 134, From Schechtman & Bader (1997) EDL Tendon
ECRB Achilles Max muscle force (N) 58.00 5000.0 Tendon length (mm) 204.00 350.0 Tendon thickness (mm 2 ) 14.60 65.0 Elastic modulus (MPa) 726.00 1500.0 Stress (MPa) 4.06 76.9 Strain (%) 2.70 5.0 Stiffness (N/cm) 105.00 2875.0
Muscle-Tendon Interaction Stiffer tendon more brisk, accurate movements Less stiff, muscle contraction velocity, efficiency tendon compliance, small muscle length (as compared to M-T unit length High resilience Limited viscoelastic behavior, therefore, tendon in major site of storage of elastic energy in M-T unit Tensile strength of tendon 2X that of its muscle
Role of Elasticity in Human Movement Elasticity of tendon responsible for force transfer from muscle to bone enables storage and release of energy, reducing metabolic cost Material & structural properties of tendon determine the amount of resistance to stretch and, thus, amount of elastic force transferred to bone
Muscle Mechanical Stiffness Instantaneous rate of change of force with length Unstimulated muscles are very compliant Stiffness increases with tension High rates of change of force have high muscle stiffness, particularly during eccentric actions Stiffness controlled by stretch and tendon reflexes
Effects of Disuse Nordin & Frankel (2001), Figure 4-15a, p. 110, From Noyes (1977)
Effects of Disuse Nordin & Frankel (2001), Figure 4-15b, p. 110, From Noyes (1977)
Effects of corticosteroids stiffness rupture strength energy absorption Time & dosage dependent
Effect of Structure Whiting & Zernicke (1998), Figure 4.8a,b, p. 104, From Butler et al. (1978).
Miscellaneous Effects Age effects More compliant / less strong before maturity Insertion site becomes weak link in middle age stiffness & strength in pregnancy in rabbits Hormonal?
Summary Mechanical properties of biological materials vary across tissues and structures due to material and geometry differences. Understanding how age, physical activity, nutrition, and disease alter mechanical properties enables us to design appropriate interventions and rehabilitations. Understanding these mechanical properties allows us to design appropriate prosthetic devices to for joint replacement and repair.