Joint Biomechanics - Trunk Flashcards
Skeleton of the Trunk
Vertebral column is a complex structure that demands mobility and stability of the trunk and the extremities, as well and providing protection for the spinal cord.
Vertebrae of the Trunk
33 in total. Cervical spine: 7 Thoracic spine: 12 Lumbar spine: 5 - Mobile part Sacrum: 5 Coccyx: 3-4 - Immobile part \+ Sternum and ribs
What is the normal curvature of the trunk?
- Cervical lordosis
- Thoracic kyphosis
- Lumbar lordosis
- Sacral kyphosis
What is the function of the spine?
- Skeleton of the trunk
- Supports the body and participated in the thoracic and pelvic cavity
- Provides attachments for the ribs and strong muscles
- Protects thoracic and pelvic viscera
- Protects the spinal cord
- Provides stable mobility
- Protects organs
What is the function of the cervical spine?
- Most mobile region of the spine
- Supports the weight of the head (around 4kg)
- High compressive loading due to strong muscles
- Protects the spinal cord and part of medulla oblongata
- Positions the head in space and adapts the visual fields according to external stimuli.
Cervical Spine - Vertebrae and Joints
Atlas: C1
Axis: C2
Atlanto-occipital joint
Atlanto-axis joint
Intervertebral joint C2-C7 with IVD
Zygapophyseal joint
Joints between two adjacent laminae
Joints between two adjacent transverse processes
Joints between two adjacent spinous processes
Which equilibration process helps stabilize the head?
Must balance the weight of the head on top of a relatively thin and long lever, making it vulnerable to traumatic forces.
The increased development of the spinous process of C7(longer than others) that will serve as a lever for the muscular system. Important muscle attachment site for extensor muscles than help keep the head upright.
Cervical Gravity Line
Corresponds to a line from the center of the tip of the odontoid process that should touch the anterior body of C7.
If the line falls forwards of C7: forward head posture.
Upper Cervical Spine
Atlas C1 has no spinous process or body.
There is a specific movement between the occiput and atlas.
Dens axis of C2 is instead of the vertebral body and permits rotation.
Rotation starts between C1 and C2, no IVD between.
Atlanto-occipital Joint
Paired joints.
Between superior concave articular facets of atlas and convex condyles of the occiput.
No IVD.
Atlanto-occipital Joint - Flexion
Flexion: 10°
During flexion, occipital condyles glide postero-superiorly on the lateral masses of the atlas.
Limited by tension developed in:
- Posterior part of the joint capsules
- Posterior neck muscles (sub-occipitals)
- Posterior A-O membrane
- Ligamentum nuchae
Atlanto-occipital Joint - Extension
Extension: 20°
During extension, the occipital condyles slide anteriorly on the lateral masses of the atlas.
Limited by:
- The approximation of the occiput with the suboccipital muscles (mass of the muscle is in the way).
- The posterior arch of the atlas and axis.
- Tension in anterior A-O membrane and joint capsules.
Which articulation permits the nodding of the head?
Atlanto-occipital joint
Atlanto-occipital Joint - Lateral Flexion
8° on each side: movement of the skull against the atlas (5°) and the axis against C3 (3°).
Slipping of the occipital condyles:
- Ipsilateral side: moves towards the midline
- Contralateral side: moves away form the midline
Limited by:
- Tension in the joint capsule
- Contralateral alar ligament
Atlanto-occipital Joint - Rotation
Secondary to the rotation of the atlas around the dens of the axis. With regards to the lateral masses of the atlas: one occipital condyle moves forward and the other backwards.
We don’t analyze rotation in the joint because there is almost none (2°).
Atlanto-axial Joint
Lateral: Paired joints, between the inferior concave articular facets of the atlas and the superior facets of the axis.
Medial: Unpaired, between the dent of the atlas and the cartilage-covered anterior surface of the transversal atlantis ligament.
Atlanto-axial Joint - Rotation
45°
Rotation starts between C1 and C2, the head and C1 move as a single unit.
The lateral masses of the atlas glide over the articular surface of the axis (one forward, one backwards).
Limited by ligamentous structures: alar ligament.
Atlanto-axial Joint - Flexion/Extension
Flexion: 6-12°, the transverse ligament bends downwards.
Extension: 5-10°, the transverse ligament bends upwards.
Lateral mass of the atlas rolls and slides on the superior articular facet of the axis. - Permitted by the transverse ligament increasing the flexibility of the atlanto-axial joint.
What are the two principal functions of the Intervertebral Disc?
- Separate two vertebral bodies (between C2 and S1), increasing the available motion.
- Transmit load from one vertebral body to the next.
Intervertebral Disc Thickness
Increases from cervical (3mm) to lumbar (9mm).
It is related to both the amount of motion and magnitude of the loads that must be transmitted.
Low weight bearing in cervical compared to high weight bearing in lumbar.
Three main components of IVD
- Nucleus pulposus
- Annulus Fibrosus
- Cartilaginous endplate
Nucleus Pulposus
Gelatinous structure 40-50%.
High water content: deformed under hydrostatic pressure, increasing in response to compressive loading and generates pressure in the annulus fibrosus.
Water content decreases with age (90% to 70%).
Annulus Fibrosus
Allows for the deformation.
15-25 concentric layers (lamellae).
Outer zone: fibrous sheath that possess high tensile strength made of type I collagen fibers. It connect the marginal ridges of two successive vertebrae.
Inner zone: fibrocartilaginous made of type II collagen fibers.
Cartilaginous Endplate (CEP)
Thin layers of hyaline cartilage that bind the disc superiorly and inferiorly separating it from the cancellous bone of the vertebral bodies above and below.
Under compression, the nucleus pulposus presses against the CEP and bony endplates, and it deforms.
Intravertebral Disc - Cervical
2/5 the height of the vertebrae (5mm).
Position of the nucleus polposus within the disc is central.
Oval shaped.
Intervertebral articulations in the cervical spine prevent the IVD from completely filling the vertebral body.
Intravertebral Disc - Thoracic
Disc is 1/4 the height of the vertebrae (7mm).
Position of the nucleus polposus is central.
Heart shaped.
Intravertebral Disc - Lumbar
Disc is 1/3 the height of the vertebrae (10mm)
Position of the nucleus polposus is posterior, because the posterior longitudinal ligament is weaker in lumbar region.
Kidney shaped.
Herniated Disc
Flexion of the spine is most responsible.
Annulus fibrosus is broken, nucleus polposus pops out, compressing the nerves.