anatomy and mobility of the spine. figure 9.1 all joints are trade-off between mobility and...
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Anatomy and Mobility of the Spine
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Figure 9.1
All joints are trade-off between mobility and stability
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Factors that influence mobility and stability of a joint
• Articulating surface and surrounding bones– Determines types of movements possible– Bone-hitting-bone can limit movements
• Joint capsule and ligaments– Can restrict or permit movements
• Muscle that crosses joint or is near joint– Can stabilize joints– Can limit movement
• E.g., hip and knee flex more passively than actively
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Spine:
A series of 24 individual vertebrae + sacrum (5 fused vertebrae) + coccyx (~4 fused vertebrae).
Functionally:
• bears and transmits upper body weight onto the pelvis while permitting movement.
– Accomplished by being made of many individual bones stacked on one another
– Small movement between each vert considerable mobility with decent stability
• protects the spinal cord
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Regions• Cervical — secondary curve—created and
maintained by muscle use associated with upright posture
• Thoracic—primary curve—present at birth and maintained by associated bones
• Lumbar — secondary curve—created and maintained by muscle use associated with upright posture
• Sacrococcygeal—primary curve—present at birth and maintained by associated bones
• Presence of Curves places body weight in the correct place for upright posture.
• Primary curvatures are less mobile, but more stable and less prone to injury.
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Vertebral Anatomy
• Body is the weight bearing portion• Processes are sites of muscle and ligament attachment• the pedicle and lamina help create the vertebral foramen through
which passes the spinal cord (also protects the cord)• Articulating processes help define movements that are possible
between adjacent vertebrae
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Intervertebral Joints
There are two joints between individual vertebrae1. Joints between bodies: symphysis—intervertebral discs
– disc both absorbs shock and acts as a flexible spacer that allows intervertebral movement.
2. Joint between superior and inferior articulating processes (facets): synovial joint
– direction/orientation and shape of the articulating processes defines/determines what kind of movements are possible between vertebra—especially the degree of rotation possible
nucleus pulposus
annulus fibrosus
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intervertebral disk--symphisis
synovial joint –plane-- between articulating processes
Joints of the spine
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Spinal nerves pass through this opening
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• Refer to lecture notes for details on the structure and function of intervertebral discs
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Herniation of disc (rupturing and protrusion of nucleus pulposus) can pinch nerves between the expanded disc and nearby bone structures which creates pressure on the nerve and thus pain and dysfunction.
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Joint Mobility
Mobility (types and range of motion) at a joint can be influenced by:
1. shape of articulating bone surfaces and boney structures interfering with joint movement (bone-bone interference)
2. ligaments becoming tight and braking/stopping further movement in a particular direction
3. the compression of soft tissue (e.g., muscle, adipose) preventing further joint movement.
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Ligaments of the spine
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anterior ligaments
Posterior ligaments
lateral ligaments
Ligaments of the Spine:Simplified Scheme
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Bones are held in place and supported in much the same way that a pole is supported/held in place by guy-lines/ropes anchoring them into the ground.
Bone—which structurally bears/transmits compressive force is supported (i.e., held in place) by fibrous tissue and muscle—tensile structures (the tensegrity model)
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SPINAL EXTENSION
In extension/hyperextension:• spinous processes move toward one another and can limit
movement on the side being moved to • Anterior ligaments become tight and limit/brake movement• Note: nucleus pulposus is being pushed anteriorly
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SPINAL FLEXION
In Flexion:• There are no boney structures of the vertebrae to limit
flexion• Posterior ligaments become tight and act as a brake to
flexion• Note: the disc is stressed toward the posterior.
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LATERAL FLEXION (I.E., SIDE BENDING)
Lateral flexion• The transverse processes on the side being flexed
toward (ipsilateral) move toward one another and will limit movement
• the lateral ligament on the opposite side (contralateral) will become tight to limit movement
• Note: disc being stressed toward the side being bent away from (contralateral).
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ROTATION
Largely influenced by orientation of articulating processes and presence/absence of ribs