trunk Flashcards
√ A synovial condylar joint between the head of the mandible (condyle of the mandible) and the mandibular fossa and articular tubercle of the temporal bone. The articular surfaces are covered by firbrocartilage.
√ The capsule surrounds the joint and is attached above to the articular tubercle and the margins of the mandibular fossa,and below to the neck of the mandible.
√ Articular disc is an oval fibrous plate that divides the joint cavity into two separate synovial compartments. The
gliding movements of protrusion and retraction occur in the superior compartment. The hinge movements of
depression and elevation occur in the inferior compartment.
√ Ligaments strengthen the TMJ laterally and medially [temporomandibular ligament (lateral ligament),
sphenomandibular ligament, and stylomandibular ligament].
Temporomandibular joint ( TMJ)
The vertebral column, the axis of the body must meet two contradictory mechanical requirements:
RIGIDITY and PLASTICITY.
This column rests on the pelvis, extends to the head and at the level of shoulders supports the scapular girdle. At all levels there
are ligaments and muscular tighteners arranged as stays.
When the weight of the body is transferred on one limb, the pelvis tilts to the opposite side and the vertical column is forced to bend.
In the lumbar region ,it becomes convex towards the resting limb, then concave in the thoracic region and convex once more.
the para-vertebral muscles adapt automatically to restore the equilibrium.
The plasticity of the vertebral column lies in its make-up, i.e. ,multiple components superimposed on one another and interlinked by ligaments and muscles.
Its structure can therefore be altered by the muscular tighteners while it maintains its
rigidity
The position of the spinal column varies through its length.
In cervical region it lies in the post. 1/3 of the neck here it supports the weight of the head so it should lie close to the center of the gravity of the head.
In the thoracic region it is forced posteriorly to by the internal organs, specially the heart. So a thoracic vertebra is found in the post. ¼ of the rib cage.
In the lumbar region,where it must support the whole weight of the upper trunk, it lies centrally once more and just on the line of the gravity.
typical vertebrae
Analyzing the structure of a typical vertebra, one
can easily find that it is made up of two major
parts, i.e. , the vertebral body anteriorly and the
vertebral arch posteriorly.
When the vertebra is dismantled these parts may be recognized:
1) body, 2) vertebral arch, 3) & 4) articular
processes, 5) & 6) transverse processes, 7) spinous
process, 8) & 9) pedicles, 10) & 11) laminae.
However, it is important to note that in the
vertical plane these various constituents lie in
anatomical correspondence.
As a result, the entire vertebral column is made up of three PILLARS:
A major pillar, anteriorly located and made up by
the stacking of vertebral bodies;
two minor pillars, posterior to the vertebral body and made up by stacking of the articular processes.
The vertebral column as a whole is straight when viewed from the front or the back. on the other hand in the sagittal plane the vertebral column shows the following four curvatures:
1) The sacral curvature, which is fixed as a result of total fusion of the sacral vertebrae. It is convex posteriorly;
2) The lumbar curvature, concave posteriorly (45 degrees);
3) The thoracic curvature, convex posteriorly (40 degrees);
4) The cervical curvature, concave posteriorly (30-40 degrees);
the transition from the quadruped to the biped state has led first to the straightening and then to the
inversion of the lumbar curvature which was initially concave anteriorly.
During phylogeny
the same changes can be observed in the
lumbar region. On the first day of life the lumbar column
is concave anteriorly. At five months it is still slightly
concave anteriorly but it will disappear at 13 months.
From 1.5 years onwards, the lumbar lordosis begin to
appear becoming obvious by 8 years and assuming
the adult state at 10 years.
During ontogeny
Those curves that are naturally present at he time of birth(thoracic and sacral) are known as primary curvatures and those curvatures that are acquired later on, are named assecondary curvatures.
▪ Those curves that can change according to body position or posture are named as dynamic curves and those which are fixed and do not change, are termed as static curves (sacral).
The curvatures of the spinal column increase its
resistance to axial compression forces. The
resistance is directly proportional to the square of
the number of curvatures plus one.
The significance of these curvatures can be
quantified by the DELMAS INDEX as follows:
• The higher the delmas index (over 94%), the more
rigid the vertebral column and vice versa.
The body of a vertebra is composed of a dense bony content surrounding a spongy medulla. The cortex of the superior and inferior aspects is called
VERTEBRAL PLATEAU
A frontal section of the body shows clearly the thick cortex on either side, the cartilage lined vertebral plateau superiorly and inferiorly, and the spongy center of the vertebral body with bony trabeculae disposed along the lines of force
These lines are vertical, horizontal, or oblique.
In a sagittal section you can find two more sheaves of oblique trabeculae in fan like arrangement.
These trabeculae start from superior or inferior plateau
and fan out to the spinous process and the articular processes.
The criss-crossing of these trabecular systems constitutes zones of maximum resistance as well as a triangular area of minimum resistance.
This explains the wedge-shaped compression
fracture of the vertebra (19) under an axial compression equal to 600 Kg. a similar force up to 800 Kg is required to crush the whole vertebra.
When viewed laterally the functional component of the column are easily distinguished.
Anteriorly lies the anterior pillar which is the essential supporting structure.
Posteriorly lies the posterior
pillar which contains the two minor pillars.
While the anterior pillar plays a
STATIC role, the posterior pillar has a
DYNAMIC function.
In the vertical plane, the alteration of bony and ligamentous structures allows one to distinguish a
PASSIVE segment formed by the vertebra
itself and an ACTIVE segment, bounded in
the diagram by a heavy black line.
It consists of intervertebral disk, the intervertebral foramen the articular processes the ligamentum flavum, the interspinous ligament.
Ligaments of the Spinal Column and Intervertebral Disk
• A horizontal section and a lateral view of the the vertebral column show the following ligaments:
1) Anterior longitudinal ligament
2) Posterior longitudinal ligament
3) The ligamentum flavum
4) The interspinous ligament
5) The supraspinous ligament
6 & 7) The annulus fibrosus
8) The nucleus pulposus
9) The anterior and posterior zygapophyseal ligaments
10) The inter transverse ligament
The joint between two vertebrae is a symphysis. It is formed by the two vertebral plateaus connected by the intervertebral disk.
The structure of this disk consists of two parts
A central part
A peripheral part
- a gelatinous substance containing 88 percent of water.
It is strongly hydrophilic.
No blood vessels or nerves penetrate the nucleus which is tightly bounded peripherally by fibrous tracts.
A central part– the nucleus pulposus (N)
– made up of concentric fibers which appear to cross one another obliquely.
Thus the nucleus is enclosed within an inextensible casing formed by the vertebral plateaus and the annulus.
the annulus fibrosus (A) A peripheral part
This type of joint is known as a SWIVEL joint
allows three degrees of freedom
• The nucleus pulposus is roughly spherical.
Therefore to a first approximation, one can consider the nucleus as a ball placed between two planes.
The Intervertebral Disc Function
intervertebral disc movement
- )TILTING: in sagittal and frontal planes ( flexion or extension & lateral flexion );
2) ROTATION: of one plateau relative to the other;
3) GLIDING: of one plateau over the other.
intervertebral disc
-The compression forces applied to the disk assume greater significance the nearer the disk is to the sacrum, which supports the bulk of the body weight. These forces may include:
1) Body weight (P)
2) The tone of para-vertebral muscles (M1 & M2)
3) Extra load (E)
4) Violent overload (S).
The loss of thickness of the disk depends on whether the disk is healthy or diseased. The progressive flattening of the diseased disk has an effect on the joints between the articular processes. In this case the inter-space of the joint opens posteriorly.
This articular distortion by itself will lead to osteo arthrosis in the long run.
important than its thickness is the ratio of
disk thickness to the height of the vertebral
body.
In fact it is this ratio that accounts for the mobility of the particular segment of the column since the greater the ratio the greater the mobility.
This ratio for lumbar, thoracic and cervical segments is
1/3, 1/5, and 2/5 respectively.
On the other hand the position of the
nucleus within the intervertebral disk is
not the same in all levels.
The intervertebral disk is thickest in the
lumbar region amounting to 9 mm;
in the thoracic region it is 5 mm thick
in the cervical region 3 mm
Each vertebra articulates with the upper and lower vertebrae in two ways:
1) Bodies of the vertebrae articulate with the body of the upper and lower vertebra via intervertebral disc.
2) The articular processes of each vertebra articulate with theupper and lower vertebrae articular processes. (Synovial joints called zygapophysial (facet) joints).
Articulations of vertebral bodies are functionally
amphiarthrodial and structurally cartilaginous symphysis joints.
The individual vertebrae move only slightly on each other.
When, however, this slight degree of movement between the pairs of bones takes place in all the joints of the vertebral column, the total range of movement is very considerable.
The ligaments of these articulations are the following:
The Anterior Longitudinal Ligament (ALL)
The Posterior Longitudinal Ligament (PLL)
is a broad and strong band of fibers, which extends along the anterior surfaces of the bodies of the vertebrae, from the axis to the sacrum. The ALL limits backward bending, and supports the anterior convexity in the lumbosacral area.
The Anterior Longitudinal Ligament (ALL)
is situated within the vertebral canal, and extends along the posterior surfaces of the bodies of the vertebrae, from the body of the axis, to the sacrum. The PLL does not attach to the body but covers a plexus of arteries, veins, and lymphatics and the nutrient foramina through which these vessels pass to the cancellous bone of the body.
The PLL has a relatively low tensile strength and does not significantly restrict forward bending. It does however become taut and closes the nutrient foramina and traps fluid in the cancellous vertebral body with forward bending. This mechanism is thought to increase the body’s ability to withstand compression forces.
The Posterior Longitudinal Ligament (PLL)
Intervertebral disc: A fibrocartilaginous structure, that intervene between the bodies of the adjacent vertebrae and bind them together. It is made of three parts:
- The nucleus pulposus fills the central part of the disc and is gelatinous in nature which absorbs compression forces between the vertebrae.
- The anulus fibrosus is made of collagen fibers which forms the peripheral part of the disc.
- and two hyaline cartilaginous plates, which separate the nucleus and the anulus from the vertebral bodies.
Degenerative changes in anulus fibrosus can lead to herniation of nucleus pulposus
Postero-lateral herniation can impinge on
the roots of a spinal nerve in the intervertebral foramen.
In most of the vertebral joints, 6 DOF are permitted:
- Flexion-extension
- Lateral flexion
- Rotation
- Anterior-posterior shear
- Lateral shear
- Distraction-compression
The zypapophysial (facet) joints belong to the diarthrodial (synovial) variety (planar) and are enveloped by capsules lined by synovial membranes.
The articular capsules are longer and looser in the cervical than in the thoracic and lumbar regions .
The major functions of the facet joints are:
A.to control vertebral motions.
B. to protect the disk from excessive shear, flexion, side bending, and rotation.
connect the laminae of adjacent vertebrae,
from the axis to the first segment (vertebra) of the sacrum.
Their marked elasticity serves to preserve the upright posture, and to assist the vertebral column in resuming it after flexion
The Ligamenta Flava
A strong fibrous cord, which connects together
the apices of the spinous processes from the seventh cervical vertebra to the sacrum. It is continued upward to the external occipital protuberance as the ligamentum nucha
The Supraspinous Ligament
thin and membranous, connect adjoining spinous processes and extend from the root to the apex of each process.
The Interspinous Ligaments
are interposed between the transverse
processes.
The Intertransverse Ligaments
is a fibrous membrane, which, in the neck, represents
the supraspinous ligaments of the lower vertebrae. It extends from the external occipital protuberance to the spinous process of the seventh cervical vertebra.
The Ligamentum Nucha
It is a pivot articulation between the odontoid process of the axis and the ring formed by the anterior arch and the
transverse ligament of the atlas
Atlanto – Axial Joint
