Lecture 2 Flashcards

Forces and loads

1
Q

What comprises a typical Functional Spinal Unit (FSU) or spinal joint?

A

A typical FSU is made up of the vertebra above and below, ranging from C2/C3 to L4/L5, where the superior vertebra moves on the inferior vertebra.

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2
Q

Which spinal joints are considered atypical?

A

Atypical spinal joints include
C0/C1,
C1/C2,
L5/S1,
sacroiliac joint, and symphysis pubis. (not technically - part of spine)

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3
Q

What structures make up a Functional Spinal Unit (FSU)? (9)

A

two vertebral bodies,
an intervertebral disc between the vertebrae, two facet joints (IAP and SAP),
two facet capsules,
the Posterior Longitudinal Ligament (PLL),
the Anterior Longitudinal Ligament (ALL), t
he Ligamentum Flava,
Interspinous and Supraspinous ligaments
two Intertransverse ligaments.

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4
Q

How are patterns of motion defined in spinal anatomy?

A

Patterns of motion are defined as the configuration of a path that the geometric center of the body describes as it moves through its range of motion.

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5
Q

What factors determine patterns of motion in the spine?

A

Patterns of motion in the spine are determined by the orientation of the facet joints and the intervertebral discs.

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6
Q

What is coupled motion in the context of spinal anatomy?

A

Coupled motion refers to motion in which rotation or translation of a body about or along one axis is consistently associated with simultaneous rotation or translation about or along another axis, representing the normal pattern of motion of all joints of the spine.

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7
Q

What is paradoxical motion in the context of spinal anatomy?

A

Paradoxical motion occurs when the typical pattern of motion does not occur, potentially indicating instability and deformation of the tissues that make up the spinal column. For example, if a functional spinal unit is supposed to move in flexion or +θX, paradoxical motion would involve movement in extension or -θX.

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8
Q

What is an example of paradoxical motion in the spine?

A

Paradoxical motion in the spine occurs when there is excessive motion within the Functional Spinal Unit (FSU) or an atypical pattern of motion, such as abnormal coupling or changes in the Instantaneous Axis of Rotation (IAR).

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9
Q

Describe a scenario where paradoxical motion occurs in the spine.

A

Paradoxical motion can be observed when the overall pattern of motion of one spinal region is in one direction, while the local FSU moves in the opposite direction.

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10
Q

What are some potential causes of paradoxical motion in the spine?

A

Potential causes of paradoxical motion in the spine include excessive motion within the FSU, abnormal coupling, changes in the Instantaneous Axis of Rotation (IAR), and pathological conditions leading to instability or deformation of spinal tissues.

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11
Q

What are the long-term consequences of paradoxical motion in the spine?

A

Over time, paradoxical motion can lead to deformation of the associated joints, altering the ability of the structures to manage forces and loads adequately.

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12
Q

What is kinematics?

A

Kinematics is the study of motion of rigid bodies, without consideration of the forces involved in causing the motion. For example, it examines the range and pattern of motion of spinal joints.

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13
Q

What is kinetics?

A

Kinetics is the study of the relationship between the forces acting on a body and the changes it produces in the body’s motion. It analyzes external forces (e.g., gravity) and internal forces (e.g., muscle forces) involved in body movement. For instance, it examines how muscles apply forces to bones during activities like running.

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14
Q

What does kinematics focus on in the study of motion?

A

Kinematics focuses on describing the motion of rigid bodies, including parameters such as displacement, velocity, and acceleration, without considering the forces that cause the motion.

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15
Q

What aspect of motion does kinetics analyze?

A

Kinetics analyzes the forces acting on a body and their effects on the body’s motion. It considers both external forces (such as gravity) and internal forces (such as muscle forces) involved in movement.

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16
Q

What are potential causes of paradoxical motion in the spine in younger individuals?

A

Potential causes of paradoxical motion in younger individuals may include ligament laxity, muscle weakness or imbalance, poor posture, congenital abnormalities, or traumatic injuries.

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17
Q

What are potential causes of paradoxical motion in the spine in older individuals?

A

may include degenerative changes in the spine (such as disc degeneration, facet joint arthritis), spinal stenosis, osteoporosis, muscle weakness or atrophy, and age-related changes in spinal alignment or curvature.

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18
Q

What are external forces in the context of spinal mechanics?

A

External forces are forces that act on the spine from the outside, including gravitational forces, applied loads (e.g., lifting objects), and external resistance encountered during activities such as pushing or pulling.

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19
Q

Can you provide an example of an external force acting on the spine?

A

When you lift a heavy object, the weight of the object and the force of gravity are examples of external forces acting on the spine.

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20
Q

What are internal forces in the context of spinal mechanics?

A

Internal forces are forces generated within the body to counteract or respond to external forces. In the spine, these forces are produced by muscles, tendons, and ligaments to maintain stability, control movement, and resist deformation.

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21
Q

Can you give an example of an internal force acting on the spine?

A

When you lift a heavy object, your spinal muscles contract to generate internal forces that stabilize the spine, distribute the load, and control movement. These internal forces act as the body’s internal support system.

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22
Q

How are external and internal forces connected in spinal biomechanics?

A

: External forces and internal forces are interconnected in spinal biomechanics, as the mechanics of deformable bodies involve the relationships between externally applied loads and their internal effects.

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23
Q

What generates forces that load the joints in spinal biomechanics?

A

Forces that load the joints are generated by muscles and transmitted by tendons in spinal biomechanics.

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24
Q

What is the consequence when a bone is unable to withstand a force in spinal biomechanics?

A

When a bone is unable to withstand a force in spinal biomechanics, it may result in injuries such as fractures, microfractures, or stress injuries. Additionally, it can lead to degenerative changes in the bone, including bone remodeling or osteoporosis over time.

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25
Q

How is a force defined in the context of biomechanics?

A

a mechanical disturbance or action that tends to change the state of rest or motion of a rigid body when applied to that body. It is measured in newtons (N).

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26
Q

What two components are necessary to describe any force?

A

To describe any force, there must be a stated direction (vector) of that force and an indication of how much force is applied, as described by Newton’s second law, F = ma (force equals mass times acceleration).

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27
Q

What does the term “load” refer to in biomechanics?

A

In biomechanics, “load” is a general term describing the application of a force and/or torque to a structure.

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28
Q

Provide an example of a load in biomechanics?

A

When a person lifts a weight, the spine experiences a load. For instance, the L5 vertebra is subjected to forces from the upper body and the lifted weight, as well as a bending moment or torque caused by the forces being away from the center of the L5 vertebra.

29
Q

What is a static load in biomechanics?

A

type of load where the force remains constant with respect to time when applied to the object.

30
Q

What characterizes a dynamic load in biomechanics?

A

A dynamic load in biomechanics is a type of load where the force varies with time when applied to the object.

31
Q

What is an ultimate load in biomechanics?

A

refers to the largest load a structure can sustain without failure.

32
Q

Types of Forces

A

*Tensile / Tension / Distractive * Compression
* Shear
* Torque
* Gravity (weight)

33
Q

What is tension or distraction force in biomechanics?

A

Tension or distraction force is a force that elongates fibers of a material, pulling or stretching it.

34
Q

provide an example of tension force in biomechanics

A

When a rubber band is stretched, tension is applied, causing the rubber fibers to elongate.

35
Q

What happens to spinal structures when the spine is flexed in terms of tension force?

A

When the spine is flexed, tension force is applied, pulling or stretching the spinal structures axially through the body.

36
Q

What is compression force in biomechanics?

A

Compression force is a force that pushes together fibers of a material, attempting to shorten it.

37
Q

Can you provide an example of compression force in biomechanics?

A

The weight of a building applies compression to its foundation, pushing the fibers of the material together.

38
Q

How does compression force affect the intervertebral disc (IVD) in the spine?

A

In the spine, the intervertebral disc (IVD) is the main compression-carrying component. It is subjected to compression even when a person is standing still.

39
Q

What is shear force in biomechanics?

A

Shear force is the intensity of force parallel to the surface on which it acts, tending to cause one portion of an object to slide, displace, or shear with respect to another portion of the object.

40
Q

Can you provide an example of shear force in everyday life?

A

when using scissors, also known as “shears,” where the blades slide against each other to cut material.

41
Q

Why is shear force especially important at the L5/S1 joint in the spine?

A

Shear force is particularly important at the L5/S1 joint due to the lumbar lordosis. A compressive load on the spine can result in shear load at this joint, potentially affecting spinal stability and integrity.

42
Q

What is torsion in biomechanics?

A

Torsion is the rotation forces acting around the long axis of a structure, causing twisting or torsional deformation.

43
Q

Can you provide an example of torsion in everyday life?

A

An example of torsion is torsional fractures of the tibia, where the bone experiences twisting forces around its long axis.

44
Q

What happens to objects loaded in torsion in terms of internal stress distribution?

A

Objects loaded in torsion develop internal shear stress, with maximal stress at the periphery and no stress at the neutral axis.

45
Q

: What is bending in biomechanics?

A

occurs when an eccentric (non-axial) force is applied to a structure, causing it to bend.

46
Q

What happens to a structure when it undergoes bending?

A

Bending creates compressive stress on one side of the structure and tensile stress on the opposite side.

47
Q

Forces acting on the spine (Internal & External)

A

-Body weight
-Tension in the spinal ligaments -Tension in surrounding muscles -Intra-abdominal pressure
-Any applied external load

48
Q

What is the function of the ligamentum flavum in the spine?

A

The ligamentum flavum connects the laminae of adjacent vertebrae and contributes to spinal stability.

49
Q

How does the composition of the ligamentum flavum differ from other spinal ligaments?

A

Unlike most spinal ligaments that are mainly collagen with minimal elasticity, the ligamentum flavum contains a high percentage of elastin fibers, providing it with greater elasticity.

50
Q

Why is the ligamentum flavum under tension even when the spine is in its normal anatomical position?

A

Due to its high elasticity, the ligamentum flavum is under tension even in the normal anatomical position of the spine, contributing to spinal stability.

51
Q

What role does the tension in the ligamentum flavum play in spinal biomechanics?

A

The tension in the ligamentum flavum creates a slight constant compressive force on the intervertebral discs, known as “prestress,” which provides intrinsic support to the spine.

52
Q

What forces act on the spine when a person is in an upright standing position?

A

When upright, the total body center of gravity is anterior to the spine, placing the spine under a constant forward bending moment.

53
Q

How does the body counteract the forward bending moment on the spine during upright standing?

A

To maintain body position, the forward bending moment on the spine must be counteracted by tension in the back extensor muscles.

54
Q

What happens to the torque and tension in the extensor muscles as the trunk is flexed?

A

As the trunk is flexed, the moment arm increases, resulting in an increasing flexor torque. This leads to increasing compensatory tension in the extensor muscles to maintain body position.

55
Q

What challenge do spinal muscles face in counteracting flexion torques?

A

Spinal muscles have extremely small moment arms with respect to the vertebrae, requiring them to generate large forces to counteract flexion torques.

56
Q

What is the major force acting on the spine, typically derived from

A

The major force acting on the spine is usually derived from muscle activity.

57
Q

How does compression on the lumbar spine change with different postures?

A

Compression on the lumbar spine increases with sitting compared to upright standing, increases further with spinal flexion, and increases even more with a slouched sitting position.

58
Q

What postural changes lead to increased compression on the lumbar spine?

A

Increased compression on the lumbar spine occurs with sitting, particularly with spinal flexion and a slouched sitting position.

59
Q

How does body weight load the spine in terms of compression and shear forces?

A

Body weight loads the spine in compression as well as shear, especially in the lumbar spine, where shear creates a tendency for vertebrae to displace anteriorly.

60
Q

What happens to compression and shear forces on the facet joints as tension in the spinal extensors increases?

A

As tension in the spinal extensors increases, compression and shear on the facet joints also increase.

61
Q

How do lateral flexion and rotation affect spinal loads compared to flexion/extension?

A

Lateral flexion and rotation create much larger spinal loads than those created by flexion/extension.

62
Q

What spinal loads result from 50 Nm of extension torque at L4/L5?

A

50 Nm of extension torque at L4/L5 results in 800 N of compression on the spine.

63
Q

What spinal loads result from 50 Nm of lateral flexion and rotation torques at L4/L5?

A

50 Nm of lateral flexion and rotation torques at L4/L5 result in 1400 N and 2500 N of compression on the spine, respectively.

64
Q

Breakdown of the forces and loads acting on the spine when

Student studying at desk for several hours:

A

Compression: Spinal discs experience compression due to prolonged sitting.

Tension: Ligaments and muscles experience tension to maintain posture.

Shear: Minimal shear force may occur due to leaning forward or slouching.

65
Q

Breakdown of the forces and loads acting on the spine when

Warehouse worker lifting heavy boxes

A

Compression: Spinal discs experience compression due to the weight of the boxes.

Tension: Ligaments and muscles experience tension to stabilize the spine during lifting.

Shear: Shear forces may occur if the worker twists while lifting or carries the load asymmetrically.

66
Q

Breakdown of the forces and loads acting on the spine when
Athlete performing deadlifts at the gym:

A

Compression: Spinal discs experience compression due to the weight lifted.

Tension: Ligaments and muscles experience tension to support the spine during lifting.

Shear: Shear forces may occur if the athlete twists or bends incorrectly during the lift.

67
Q

Breakdown of the forces and loads acting on the spine when
Young mum carrying baby in a front carrier:

A

Compression: Spinal discs experience compression due to the weight of the baby.

Tension: Ligaments and muscles experience tension to support the spine and stabilize the body.

Shear: Minimal shear force may occur if the mum leans forward or twists while carrying the baby.

68
Q

Breakdown of the forces and loads acting on the spine when
Construction worker digging a trench:

A

Compression: Spinal discs experience compression due to the physical exertion of digging.

Tension: Ligaments and muscles experience tension to stabilize the spine and support the body during digging.

Shear: Shear forces may occur if the worker twists the torso while digging or lifts heavy loads improperly.