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DCCJP > M4 Spinal Biomechanics > Flashcards

M4 Spinal Biomechanics Flashcards

1
Q

Failure of the Anterior Fontanel occurs mostly with:

A 
Hydrocephalus
trisomy 13
Cleidocranial dysplasia
Hypothyroidism
Hypophosphatasia
Down’s Syndrome
Osteogenesis Imperfecta
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2
Q

3 primary functions of the vertebral column

A
  1. Support the trunk and transmit the weight to the pelvis and lower extremities.
  2. Protect the spinal cord and membranes
  3. Provide a central axis for the thorax.
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3
Q

4 main curvatures of the spinal column.

A

 Cervical (Lordotic) Secondary Curve
 Thoracic (Kyphotic) Primary Curve
 Lumbar (Lordotic) Secondary Curve
 Sacral (Kyphotic) Primary Curve

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4
Q

The frequency of:

Cleft Posterior arch

A

3% to 4%

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5
Q

Frequency of Cleft Anterior arch

A

1%

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6
Q

Normal variants throughout the body occur about how often?

A

~5%

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7
Q

The standard deviation of bilateral asymmetry of the vertebral column.

A

2.5 mm

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8
Q

Elongated mastoid or something covering C1 TP

A

15%

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9
Q

Mechanics -

A

the study of forces and their effects.

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10
Q

Biomechanics

A

is the application of mechanical laws to living structures

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11
Q

Kinematics

A

branch of mechanics that deals
with the geometry of the motion of objects,
including displacement, velocity, and
acceleration, without taking into account the forces that produce the motion.

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12
Q

Kinetics

A

the study of the relationships
between the force system acting on a body
and the changes it produces in body motion

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13
Q

Displacement

A 
The change in position 
of a body. 
 Linear – in one direction
 Angular – multiple directions at once. 
       Spinning
       Arcing
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14
Q

Lever

A

a rigid bar that pivots about a
fixed point, or axis or fulcrum, when a
force is applied to it.

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15
Q

Force (or resistance)

A

applied by muscles at some point along the lever to move the body part.
A push or pull exerted on a body
producing acceleration.
 Newton’s second law, a force acting on a
the body causes an acceleration in the direction
of the force.

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16
Q

Velocity

A

The change in position over
time.
 Includes magnitude and direction.

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17
Q

Acceleration

A

The change in velocity
over time. (m/s2)
 Can be constant, increase or decrease.
 Negative acceleration = deceleration.

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18
Q

Mass

A

The quantity of matter within a

given object.

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19
Q

Intertia

A 
The property of a body to 
remain at rest, or in a uniform motion 
unless acted upon by another force. 
-Newton’s first law.
-The mass of a body determines the 
magnitude of this resistance.
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20
Q

Mass moment of Inertia

A 
Rotating 
bodies that move at a constant angular 
velocity.
 Bodies at rest have a fixed axis.
 These bodies tend to stay at rest or in 
motion unless acted upon by an external 
force. 
 Resistance to change is determined by the 
mass of the body.
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21
Q

Momentum

A 
Mass x velocity
 An amount of motion
 Increasing the mass of the body or the 
velocity will increase the momentum
“Moment of force” The 
product of force and distance through 
which the force acts. 
 Example is using a wrench. A twisting 
around an axis of rotation.
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22
Q

Center of Mass

A

the point at which the
entire mass of the body is equally
distributed.
 Often termed “center of gravity.”

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23
Q

Work

A

Force x displacement

 Force acting over a distance.

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24
Q

Impulse

A

The force which two colliding

bodies exert on each other.

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25
Q

First Class Lever

A

the axis (fulcrum) is located between the force and the resistance, like a teeter-totter.

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26
Q

Second Class Lever

A

the resistance is between the axis and the force. Wheelbarrow.

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27
Q

Third Class Lever

A

the force is between the axis and the resistance. snow shovel

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28
Q

X-axis

A

Coronal (flexion and extension)

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29
Q

Y-axis

A

Longitudinal (axial rotation)

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30
Q

Z-axis

A

sagittal (lateral flexion)

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31
Q

Cartesian coordinate system hand

A

right hand

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32
Q

Sagittal Plane

A

Y and Z axes

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33
Q

Horizontal Plane

A

X and Z axes

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34
Q

Frontal Plane

A

X and Y axes.

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35
Q

X-axis rotation

A

Flexion = +OX
Extension = -OX
Sagittal plane

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36
Q

Y-axis rotation

A

Right rotation = -OY
Left rotation = +OY
Horizontal plane

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37
Q

Z-axis rotation

A

Right lateral bend = +OZ
Left lateral bend = -OZ
Vertical plane

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38
Q

Coronal Axis

A

X-Axis

Flexion and Extension through the sagittal plane

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39
Q

Flexion is motion in the anterior direction for

A

joints of the head, neck, trunk, upper

extremity, and hips

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40
Q

Flexion is motion in the posterior direction for

A

joints of the of the knee, ankle, foot, and toes

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41
Q

Sagittal Axis

A

z-axis
Movements of abduction and adduction of the extremities, as well as lateral flexion of the spine, occur around this axis and through the coronal plane.

Lateral flexion is a rotational movement and is used to denote lateral movements of the head, neck, and trunk in the coronal plane.

Abduction and adduction are also motions in a coronal plane.

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42
Q

Sagittal definition

A

Latin for “like an arrow” as in the spine

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43
Q

Lateral flexion

A

a rotational movement and is used to denote lateral movements of the head, neck, and trunk in the coronal plane. usually combined with some element of rotation.

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44
Q

Longitudinal Axis

A

Y-axis

This axis is vertical, extending in a head-to-toe direction.
Movements of the medial (internal) and lateral (external)
rotation in the extremities, as well as axial rotation in the spine, occur around it and through the transverse plane.

Axial rotation is used to describe this type of movement
for all areas of the body except the scapula and clavicle.

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45
Q

Rotation

A

 Rotation occurs about an anatomic axis.
 In the human extremity, the anterior surface of the
extremity is used as a reference area.
 Rotation of the anterior surface toward the midsagittal
plane of the body is medial (internal) rotation, and
rotation away from the midsagittal plane is lateral
(external) rotation.
 Rotation of the head, spine, and pelvis is
described as rotation of the anterior surface
posteriorly toward the right or left.
 Rotation of the scapula is movement about a
sagittal axis, rather than about a longitudinal
axis.
 Because the head, neck, thorax, and pelvis
rotate about longitudinal axes in the
midsagittal area, rotation cannot be named in
reference to the midsagittal plane.
 The terms clockwise or counterclockwise are used.

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46
Q

Translational movements

A

 Lateral-to-Medial glide and Medial-to-Lateral glide
(laterolisthesis) translate along the x-axis.
 Distraction and Compression translate along the y-
axis.
 Curvilinear motion combines both rotational and
translational movements and is the most common
motion produced by the joints of the body.

47
Q

joint movement

A

 The potential exists for each joint to exhibit three
translational movements and three rotational
movements, constituting 6 degrees of freedom.
 The extent of each movement is based more or less
on the joint anatomy and, specifically, the plane of the
joint surface.

48
Q

synovial joints

A 
 The most common joints of the human 
appendicular skeleton.
 The components of a typical synovial joint 
include
 bony elements,
 subchondral bone, 
 articular cartilage, 
 synovial membrane, 
 fibroligamentous joint capsule, 
 articular joint receptors.
49
Q

Joint types of the spine

A 
 Synarthrotic
 Symphysis—fibrocartilage
 Intervertebral discs
 Diarthrotic
 Trochoid (pivot) 
 Atlantoaxial joint
 Plane (nonaxial)
 Posterior facet joints in the spine
50
Q

Boney elements of the joints function

A

The bony elements provide the
supporting structure that gives the joint
its capabilities and individual
characteristics by forming lever arms to
which intrinsic and extrinsic forces are
applied.

51
Q

Articular Cartilage

A

 Articular cartilage covers the articulating bones
in synovial joints and helps to transmit loads
and reduce friction.
 It is bonded tightly to the subchondral bone
through the zone of calcification,
 the end of bone visible on x-ray film.
 The joint space visible on x-ray film is
composed of the synovial cavity and non-
calcified articular cartilage.

52
Q

Articular cartilage composition

A

In its normal composition, articular cartilage has four
histologic areas or zones.
 Gliding zone
 Transitional zone
 Radial Zone
 Zone of calcified cartilage
 The outermost zone of cartilage is known as the
gliding zone, which itself contains a superficial layer
(outer) and a tangential layer (inner).
 The gliding zone also has a role in protecting the deeper elastic cartilage.

53
Q

Gliding Zone of cartilage

A

contains a superficial layer
(outer) and a tangential layer (inner).
 The gliding zone also has a role in protecting the deeper elastic cartilage.
 The outer segment is made up solely of collagen
randomly oriented into flat bundles.
 The tangential layer consists of densely packed layers
of collagen, which are oriented parallel to the surface
of the joint.
 This orientation is along the lines of the joint motion, which
implies that the outer layers of collagen are stronger when
forces are applied parallel to the joint motion rather than
perpendicular to it.
 Providing a great deal of strength to the joint in normal motion.

54
Q

Transitional zone of cartilage

A

lies beneath the gliding zone.
 It represents an area where the orientation of
the fibers begin to change from the parallel
orientation of the gliding zone to the more
perpendicular orientation of the Radial Zone.

55
Q

Zone of calcified cartilage

A

where the articular cartilage meets the Subchondral plate

56
Q

Articular cartilage nutrition

A

 Articular cartilage is considered mostly
avascular.
 Articular cartilage must rely on other sources
for nutrition, removal of waste products, and
the process of repair.
 Therefore intermittent compression (loading)
and distraction (unloading) are necessary for
adequate exchange of nutrients and waste
products.
 The highly vascularized synovium is
believed to be a critical source of
nutrition for the articular cartilage it
covers.
 The avascular nature of articular
cartilage limits the potential for cartilage
repair by limiting the availability of the
repair products on which healing
depends.

57
Q

Degeneration of the articular cartilage

depends on:

A 
 the size and depth of the lesion
 the integrity of the surrounding 
articular surface
 the age and weight of the patient
 associated meniscal and ligamentous 
lesions
 other biomechanical factors
58
Q

Continuous passive motion and articular cartilage injury

A 
Continuous passive motion has 
increased the ability of full-thickness 
defects in articular cartilage to heal, 
producing tissue that closely resembles 
hyaline cartilage.
59
Q

ligamentous elements of spinal synovial joints

A

 The primary ligamentous structure of a
synovial joint is the joint capsule.
 Throughout the vertebral column, the joint
capsules are thin and loose.
 The capsules are attached to the opposed
superior and inferior articular facets of
adjacent vertebrae.

60
Q

spinal joint capsules have how many layers

A 
 Outer layer - composed of dense 
fibroelastic connective tissue made up of 
parallel bundles of collagen fibers. 
 Middle layer - composed of loose 
connective tissue and areolar tissue 
containing vascular structures.
 Inner layer - consists of the synovial 
membrane.
61
Q

synovial fluid

A

 The exact role of synovial fluid is unknown,
 it is thought to serve as a joint lubricant or at least to interact
with the articular cartilage to decrease friction between joint
surfaces.
 This is of clinical relevance because immobilized joints
have been shown to undergo degeneration of the
articular cartilage.
 Synovial fluid is similar in composition to plasma, with
the addition of mucin (hyaluronic acid), which gives it a
high molecular weight and its characteristic viscosity.

62
Q

3 models of joint lubrication

A

 The Hydrodynamic Model
 The Elastohydrodynamic Model
 The Boundary Lubrication Model

63
Q

The Hydrodynamic Model of joint lubrication

A

 Synovial fluid fills in spaces left by the
incongruent joint surfaces.
 During joint movement, synovial fluid is
attracted to the area of contact between the
joint surfaces, resulting in the maintenance
of a fluid film between moving surfaces.
 This model was the first to be described and
works well with quick movement.

64
Q

The Elastohydrodynamic Model of joint lubrication

A

 Considers the viscoelastic properties of articular
cartilage where deformation of joint surfaces occurs
with loading, creating increased contact between
surfaces.
 This would effectively reduce the compression
stress to the lubrication fluid.
 Although this model allows for loading forces, it
does not explain lubrication at the initiation of
movement or the period of relative zero velocity
during reciprocating movements.

65
Q

The Boundary Lubrication Model of joint lubrication

A

 Here, lubricant is adsorbed on the joint surface,
which would reduce the roughness of the surface
by filling the irregularities and effectively coating the
joint surface.
 This model allows for initial movement and zero
velocity movements.
 The boundary lubrication model, combined with the
elastohydrodynamic model, create a mixed model,
which meets the demands of the human synovial
joint

66
Q

Elasticity –

A

The tendency of tissue, under
load, to return to its original size and
shape after removal of the load.
No energy is lost to deformation.

67
Q

Plasticity –

A

the property of a material that
instantly deforms when a load is applied to
it and does not return to its original shape
when removing the load.

68
Q

Viscosity –

A

The property of a material that
does not deform instantaneously when a
load is applied.
Stress will develop but the deformation is
delayed.
Deformation is, therefore, relative to time.

69
Q

Viscoelasticity –

A

A combination of viscosity
and elasticity.
The property of a material to deform slowly
and nonlinearly when a load is applied.
Also, the property of the material to return to
its original shape and size, slowly and
nonlinearly when the load is removed.
Examples include articular cartilage and
interverterbral disks.

70
Q

Creep

A

When a constant load is applied to a
ligament, it will first elongate to a given length.
Left at a constant load, it will continue to
elongate over time in an exponential fashion up
to a finite maximum.
Creep is this elongation over time.
Expressed as the percent elongation relative to its
length immediately after the load was applied.
An increase in strain that occurs during a constant
stress from loading.
A body undergoing creep may or may not
return to its original shape.
Returning to its original shape will depend on
the load, and whether the structure underload
is damaged.
A damaged disk can deform faster under load than
a normal intervertebral disk.

71
Q

tension–relaxation phenomena

A 
observed when ligaments are subjected to 
a stretch and hold overtime
The tension in the ligament increases 
immediately upon the elongation to a 
given value.
As time elapses, the tension decreases 
exponentially to a finite minimum while the 
length does not change.
72
Q

strain rate

A

Strain Rate - The tension developed in a ligament also
depends on the rate of elongation or Strain Rate.
Slow rates of elongation are associated with the
development of relatively low tension,
where as higher rates of elongation result in the development of
high tension.
The fast stretch of ligaments, such as in high-frequency
repetitive motion (sports activities) are known to result in
high incidents of ligamentous damage or rupture.
Fast rates of stretch, may exceed the physiological loads
that could be sustained by a ligament safely, while still
within the physiological length range.

73
Q

Hysteresis -

A

The inability to track the same length–
tension curve when subjected to a single stretch–release
or load–unload cycle, is termed Hysteresis.
Hysteresis is also associated with repetitive motion when
a series of stretch–release cycles are performed
overtime.
When the ligament is stimulated repetitively with
constant peak load, the hysteresis develops along the
length axis,
i.e., the ligament length limits increase with each cycle reflecting
the hysteresis associated with the development of creep
Conversely, when cycles of constant peak
stretch are applied, the peak tension decreases
in sequential cycles, reflecting the on going
development of tension–relaxation.
The impact of progressive hysteresis, is
manifested by:
gradually decreasing tension in the ligament,
development of joint laxity,
reduced joint stability
increased risk of injury.
Clinical:
Repetitive sports and occupational tasks should be
limited in duration and allow sufficient rest periods to
facilitate recovery of normal ligament function.

74
Q

Frequency of Cyclic Motion

A

Ligament behavior is also dependent on
the frequency of load application and
unloading.
Cyclic loading of a ligament with the same
peak load, but at a higher frequency,
results in larger creep development and
longer period of rest required for the full
recovery of the creep
Occupational and sports tasks requiring
repetitive motion at high frequency, and
induce larger creep in the ligaments.
This requires longer rest time to recover, and
may increase the risk for cumulative creep
from one session to the next, in the same day
and from day-to-day.
Larger creep results in increased laxity of
the joint as the activity goes on, and the
associated risks as discussed above.

75
Q

Ligaments as sensory organs

A

Anatomical studies demonstrate ligaments in the
extremity joints and the spine are endowed with
mechanoreceptors consisting of:
Pancinian,
Golgi,
Ruffini
bare nerve endings

76
Q

Flexion and extension at the atlantoaxial

articulation are limited by

A

the transverse ligament and tectorial membrane, respectively.

77
Q

Lateral bending at the atlantoaxial articulation is restricted by

A

the contralateral alar ligament and some very minimal anteroposterior translation may occur at this joint.

78
Q

AO flexion limitation

A

Flexion was limited by
impingement of the odontoid
process on the foramen magnum

79
Q

AO extension limitation

A

tectorial membrane

80
Q

AO lateral flexion limitation

A

Contralateral alar ligament.

81
Q

In vivo –

A

experimentation relating to the
study of the whole living subject in a
natural environment.

82
Q

In vitro (ex vivo) -

A

experimentation relating
to the study of the whole living subject
outside its natural environment.

83
Q

In silico –

A

experimental studies which

simulate the living system.

84
Q

Osteokinematic Movement-

A

The physiologic movement
which occurs at the joint when muscles contract or when
gravity acts on bone to cause motion.
describes how each bony joint partner moves relative to the
other.

85
Q

Arthrokinematic Movement-

A

The specific movements
that occur at the articulating joint surfaces.
considers the forces applied to the joint
include the accessory motion present in a particular articulation
(coupled motion)

86
Q

Instantaneous Axis of Rotation (IAR)-

A

Term denotes the location point of the axis around
which motion occurs
In addition, when an object moves, the axis around
which the movement occurs can vary in placement
from one instant to another.
Asymmetric forces applied to the joint can cause a
shift in the normal IAR.
This concept is designed to describe plane
movement, or movement in two dimensions.

87
Q

Helical Axis of Motion (HAM)-

A

The axis of motion when three-dimensional motion
occurs between objects
a screw axis of motion
“The nature and extent of individual joint motion
are determined by the joint structure and,
specifically, by the shape and direction of the
joint surfaces.”
Harmony Medical

88
Q

“Joint play”

A

is an accessory movement of the
joint that is essential for normal functioning of
the joint. Present in open-packed position.

89
Q

Resting Position of a joint (Neutral Position)-

A

occurs when the joint capsule is most relaxed and the
greatest amount of play is possible.
When injured, the joint will move to its maximum
loose-packed position to allow for swelling.

90
Q

Close-Packed Position-

A

when the joint capsule and ligaments are maximally
tightened.
In the Close-Packed Position, there is maximal
contact between the articular surfaces, making the
joint very stable and difficult to move or separate.

91
Q

Compression-

A

occurs when a joint moves
toward its close-packed position.
The spine is more
susceptible to compressive load injury.

92
Q

Distraction-

A 
occurs when a joint moves 
toward its open-packed position.
Distractive and Tensile Loading injuries 
are less common but do occur during 
whiplash type injuries.
93
Q

Flexion –

A

COMPRESSION of anterior
structures and TENSILE LOADING of
posterior structures.

94
Q

Extension -

A

COMPRESSION of posterior
structures and TENSILE LOADING of
anterior structures.

95
Q

Rotation (Torsional Loading) –

A

occurs
when the body of a moves in concentric
circles or an arc.
Rotation is potentially more damaging to the
vertebra because it involves shearing, tensile
and compressive forces combined with
rotation.

96
Q

Stress –

A

measured per unit area. Force
involves internal stress within the body
that arises as a result of external loads
applied to the body.

97
Q

Most common place for a compression fracture

A

T11-T12

98
Q

Hooke’s Law –

A

deformation of a body
increases in proportion to the load that is
applied.
Strain increases in proportion to the body’s
internal stress that is resisting the applies
load.

99
Q

Functional Spinal Unit –

A

Two adjacent
vertebrae and the joint that links them,
with the skeletal muscle that moves the
articulation.

100
Q

Joint motion consists of five qualities of
movement that must be present for normal
joint function.

A 
Joint Play
Active Range of Motion 
Passive Range of Motion
End Feel
Paraphysiologic Movement
101
Q

Paraphysiologic Movement

A

is the small amount of
movement past the elastic barrier
typically occurs after cavitations
Movement of the joint beyond the Paraphysiologic
Barrier takes the joint beyond its limit of anatomic
integrity and into a Pathologic Zone of Movement.
When the joint enters the pathologic zone, there is
damage to the joint structures, including osseous and
soft tissue

102
Q

The individual coupled motions are governed by

A

the architecture of the vertebrae (smooth,
rough, etc.),
their joint surface inclination,
the associated ligaments,
the interactive functioning of the paraspinal
muscles
and the physiologic anteroposterior curvature
of the spine in the sagittal plane.

103
Q

Bogduk and Mercer describe the function of

the cervical anatomy as follows:

A 
AnatomicalFunctional
Atlas, Cradle
The Axis, Axis
The C2-3 Junction, The Root
Typical Cervical Vertebrae,The Column
104
Q

The Cradle

A

The atlas vertebra serves to cradle the occiput.
The articulation consists of the occipital condyles
joining with the superior articular surface of the
atlas lateral masses.
The articulation of the atlanto-occipital joints is
strong, and allows mainly for the nodding
movements between the two structures.
In all other respects the head and atlas move
and function essentially as one unit.
The stability of the atlanto-occipital joint comes mainly
from the depth of the atlantal lateral mass superior articular surfaces.
The sidewalls of the lateral mass prevent the occiput from sliding sideways;
The front and back walls prevent anterior and posterior
gliding of the head
The only physiological movements possible at this
joint are Flexion and Extension

105
Q

Occ-C1 Axial Rotation

A

Axial rotation and lateral flexion are not physiological movements of the atlanto-occipital joints.
They cannot be produced in isolation by the action of
muscles. But they can be produced artificially by forcing the head into these directions while fixing the atlas.
Axial rotation is prohibited by impaction of the
contralateral condyle against the anterior wall of its
socket and simultaneously by impaction of the ipsilateral
condyle against the posterior wall of its socket.
For the head to rotate, the condyles must rise up their
respective walls.

106
Q

Paradoxical Tilt of Atlas

A 
Occiput and dorsal part of Atlas Arch 
approach each other rather than moving 
away from one another at the end of 
flexion
• Reverse is also true on extension
107
Q

AO flexion and extension degree of motion

A

Flexion CO/C1 (3.5 degrees)

Extension CO/C1 (21.0 degrees)

108
Q

Flexion of C0-C2 Stage 1

A

Forward movement of occiput in relation to atlas 8
degrees (nutation) (+OX)
All other segments are neutral

109
Q

Flexion of C0-C2 Stage 2

A

C1-C2 tilt forward (+OX)
C2-C3 to C6-C7 undergo flexion
Axis tilts forward 45 degrees with respect to C7
Occ-C1 moves into extension (-ox), preventing
an abnormal position of the spinal cord.

110
Q

AO rotation degrees

A

Dvorak reports occipitoatlantal rotation around

the x-axis between 13-50 degrees.

111
Q

AO lateral flexion

A

takes place around
the sagittal axis
Amounts to approximately 5 deg.
(Penjabi et al, 1988; White and Panjabi, 1990; Penning, 1976)
Greater when the head is slightly flexed
Resisted by the alar ligaments

Mean maximum lateral bending of the cervical
spine to one side was 1.6oto 5.7o at each
level.

112
Q

AO rotation

A

Axial rotation has been reported to be between 2.4°– 8°
that can take place at this joint, as well as minimal lateral
and axial rotation and anteroposterior translation. (N.
Bogduk, S. Mercer)
The lower levels were reported from live patients
The higher levels were reported from cadaver studies
Authors such as Panjabi, White Penning and Fielding
have reported axial rotation between the occiput and
atlas to be nonexistent.
Depreux and Mestdagh (1974) report approximately 5o
of motion.
Measurements are higher with atlantoaxial fussion.
Gutmann (1981) reports the occiput and atlas will rotate
together, with respect to the axis.
Dvorak and Hyek (1986), using cadaver spines recorded
axial rotation between 4.5oand 5.9oto the right and left
respectively.

113
Q

Atlanto-axial joint cartilage structure

A

The articular cartilages of both the atlas
and the axis joint are convex, thus, the
articulation is biconvex.
The spaces formed anteriorly and
posteriorly, where the articular surfaces
diverge, are filled by intra-articular
meniscoids.

114
Q

Explanation for Atlas paradoxical motion at end range flexion and extension

A

At full flexion of the neck, the atlas can extend.
This arises because the atlas, rests between the head and axis, and is balanced on the summits of the lateral atlantoaxial facets, and thus is subject to compression loads.
If the net compression passes anterior to the contact point in the lateral atlantoaxial joint, the lateral mass of the atlas will be squeezed into flexion.
Conversely, if the line of compression passes behind the contact point, the atlas will extend; even if the rest of the cervical spine flexes.
If during flexion, the chin is tucked backwards, the paradoxical extension of the atlas is virtually assured, because the retraction of the chin favors the line of weight-bearing of the skull to fall behind the center of the lateral atlantoaxial joints.

DCCJP (7 decks)

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