Biomechanics of spine

Cervical & Thoracic

1

12 Thoracic

5 Lumbar

5 Sacral

7 Cervical

4 Coccygeal2

The Curves

• Primary and

• Secondary curves.

3

Typical vetebrae

A. The anterior portion

of a vertebra is called

the vertebral body.

B. The posterior portion

of a vertebra is called

the vertebral or neural

arch.

The neural arch is

further divided into the

pedicles and the

posterior elements.

4

Typical vetebrae

• The posterior

elements are the

laminae, the

articular

processes, the

spinous process,

and the

transverse

processes.

5

Vertical Trabeculae

• The various

trabeculae are

arranged along

the lines of force

transmission.

6

The Inter vertebral Disk

7

The Inter vertebral Disk

A. Under compressive

loading, the NP attempts

to expand. Tension in the

AF rises.

B. A force equal in

magnitude but opposite in

direction is exerted by the

AF on the NP, which

restrains radial expansion

of the NP and establishes

equilibrium.

The nuclear pressure is

transmitted by the AF to

the end plates.

A B

8

IVD Problems

9

Ligaments

10

Joints

• Interbody Joints

• Zygapophyseal

Articulations

11

Kinematics

• Flexion

• Extension

• Lateral flexion

• Rotation.

12

Kinematics

A. The addition of an

intervertebral disk

allows the vertebra

to tilt, which

dramatically

increases ROM at

the interbody joint.

B. Without an

intervertebral disk,

only translatory

motions could

occur.

13

Kinematics

Coupled Motion

• Lateral flexion is

coupled with

axial rotation

14

Kinetics

• Axial Compression

• Bending

• Torsion

• Shear

15

Kinetics A. Side-to-side translation (gliding)

occurs in the frontal plane.

B. Superior and inferior

translation (axial distraction

and compression) occur

vertically.

C. Anteroposterior translation

occurs in the sagittal plane.

D. Side-to-side rotation (tilting) in

a frontal plane occurs around

an anteroposterior axis.

E. Rotation occurs in the

transverse plane around a

vertical axis.

F. Anteroposterior rotation

(tilting) occurs in the sagittal

plane around a frontal axis.

16

Biomechanics of spine

Cervical Region

17

Structure

Two distinct regions:

• The upper cervical ,

or craniovertebral

region and

• The lower cervical

region

18

Craniovertebral RegionATLAS

19

The atlas is a markedly atypical vertebra.

It lacks a body and a spinous process.

Craniovertebral Region

AXIS

• The dens

(odontoid process)

arises from the

anterior portion of

the body of the

axis.

• The superior

zygapophyseal

facets are located

on either side of

the dens.

20

Craniovertebral Articulations

• The median atlantoaxial

articulation is seen, with

the posterior portion

(transverse ligament)

removed to show the dens

and the anterior arch of

the atlas.

• The two lateral

atlantoaxial joints between

the superior

zygapophyseal facets of

the axis and the inferior

facets of the atlas can be

seen on either side of the

median atlantoaxial joint.

21

Craniovertebral Ligaments

• Atlantal cruciform

ligament

• Alar ligaments

22

Craniovertebral Ligaments

A. Posterior

atlanto-occipital

and atlantoaxial

membranes.

B. Anterior atlanto-

occipital and

atlantoaxial

membranes.

23

Craniovertebral Ligaments

• The tectorial

membrane is a

continuation of

the posterior

longitudinal

ligament.

24

The Lower Cervical Region

The body of a

typical cervical

vertebra is small

and supports

uncinate processes

on the

Postero lateral

superior and

inferior surfaces.

25

Intervertebral Disk

A. Superior view

shows crescent-

shaped anulus

fibrosus.

B. B. Lateral view

shows

uncovertebral

cleft.

26

Interbody Joints

• The cervical vertebra

exhibit raised

superolateral lips

known as uncinate

processes.

• These articulate with

the margins of the

vertebral body

above, forming the

uncovertebral joint

or "joint of

Luschka."

27

A. Lateral view of an inter body

saddle joint of the lower cervical

spine.

B. Anterior view showing how the

convex inferior surface of the

superior vertebra fits into the

concave superior surface of the

inferior vertebra.

Zygapophyseal Joints

28

Kinematics

Nodding motions of

the atlanto-occipital

joints.

A. Flexion.

B. B. Extension.

29

Kinematics

• Superior view of rotation

at the atlantoaxial joints:

The occiput and atlas

pivot as one unit around

the dens of axis.

30

Kinematics

A. Flexion of the lower

cervical spine combines

anterior translation and

sagittal plane rotation

of the superior

vertebra.

B. Extension combines

posterior translation

with sagittal plane

rotation.

• The range for flexion

and extension increases

from the C2/C3 segment

to the C5/C6 segment,

and decreases again at

the C6/C7 segment

31

Kinetics

• cervical region bears less weight and is

generally more mobile.

• No disks are present at either the atlanto-

occipital or atlantoaxial articulations;

• The trabeculae show that the laminae of

both the axis and C7 are heavily loaded

32

Biomechanics of spine

Thoracic Region

33

Structure

• The 1st and 12th

are transitional

vertebrae

• 1st, 9th, 10th, 11th,

12th are atypical

vertebrae

34

Typical Thoracic Vertebrae

A. Lateral view of the thoracic

vertebra shows the superior

and inferior facets of the

zygapophyseal joints and the

demifacets for articulation with

the ribs.

B. Overlapping of spinous

processes in thoracic region.

C. Superior view of a thoracic

vertebra, showing the small,

circular vertebral foramen, the

costotubercular facets for

articulation with the tubercles

of the ribs, and the superior

costocapitular facets for

articulation with the heads of

the ribs.

35

Intervertebral Disks

36

Articulations

• Interbody Joints

• Zygapophyseal

Joints

37

Kinematics

• the range of flexion and

extension is extremely

limited

• Rotation of a thoracic

vertebral body to the left

produces a distortion of

the associated rib pair

that is convex posteriorly

on the left and convex

anteriorly on the right.

38

Kinetics

• The thoracic region is subjected to

increased compression forces in

comparison with the cervical

region, because of the greater

amount of body weight that needs

to be supported and the region’s

kyphotic shape.

39

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