The thoracic spine has several distinguishing biomechanical characteristics: 1) It contains articular facets for rib attachment and long, thin spinous processes that overlap and direct the vertebrae. 2) Range of motion is limited, especially in flexion/extension, due to the rib cage and facet orientation. More mobility occurs in the lower thoracic spine. 3) The intervertebral disks are wedge-shaped and provide stability while allowing some movement, restricted primarily by ligaments.

1. BIOMECHANICS OF
THORACIC SPINE
DR ABU SHOHAIL NIZAME

2. CHARACTERISTIC
 Presence of articular facets on vertebral bodies for ribs attachment
 Long/thin spinous process directed backward/downward in relation to
motion segment & overlap each other.
 Tip of spinous process lies posterior & inferior to the body of the
vertebrae.
 Act as lever to rotate the vertebral body.
 Results in gliding of facets joints during flexion & extension

6. SPINOUS PROCESS
 T1,T2,T3 are projected backward & the tip is on the same line as transverse
process.
 T4,T5,T6 are located half a vertebra below the one to which they are
attached.
 T7,T8,T9 are located a full vertebra lower than the vertebra to which they
are attached.
 T10,T11,T12 are palpable at the same level as the vertebral body to which
they are attached.

8. THORACIC SPINE
VERTEBRAL BODY
 Roughly equal in transverse/ AP diameter
FACET JOINTS
 Vertical & at 60◦ angle from horizontal plane
 Superior facets faces upward/backward
 Inferior facets faces downward/forward
ATYPICAL THORACIC VERTEBRA
 T1 & T12

10. ATYPICAL THORACIC VERTEBRAE(T1)
 The midway between cervical & thoracic spine
 Inferior facet surface orientation is typically thoracic and superior facet
surface is cervical.
 T1 dysfunction greatly affects the functional capacity of thoracic outlet
(blood vessels or nerve in the space between collar bone & 1st rib) &
related structures.

11. ATYPICAL THORACIC VERTEBRAE (T12)
 Superior facet surface is usually thoracic & inferior facet is lumbar
 Location of change between thoracic kyphosis & lumbar lordosis.
 Location of change in mobility of 2 areas of spine.
 Point of frequent dysfunction
 T3 the axis of rotation for the shoulder girdle.
 T6 the axis of rotation for entire thoracic spine.

12. Intervertebral Disks
 The intervertebral disks are somewhat wedge shaped, with the posterior
height greater than the anterior height, which contributes to the thoracic
kyphosis.
 The thoracic intervertebral disks are primary restraints to movement and
are considered the primary stabilizer of the mobile segment.
 The ratio of disk size to vertebral body size is smallest in the thoracic
region, which results in greater stability and less mobility for this region.

14. Ligaments

15. Kinematics
 All motions are possible, but the range of flexion and extension is
extremely limited in the upper thoracic region (T1 to T6).
 the rigidity of the rib cage and
 the zygapophyseal facet orientation in the frontal plane.
 In the lower part of the thoracic region (T9 to T12), the zygapophyseal
facets lie more in the sagittal plane, allowing an increased amount of
flexion and extension.
 Lateral flexion and rotation are free in the upper thoracic region.
 The ROM in lateral flexion is always coupled with some axial rotation.

16.  The amount of accompanying axial rotation decreases in the lower part of
the region because of the change in orientation of the zygapophyseal
facets at T10 or T11.
 In the upper part of the thoracic region, lateral flexion and rotation are
coupled in the same direction, whereas rotation in the lower region may
be accompanied by lateral flexion in the opposite direction.
 In this region, however, the direction of coupled rotation may vary widely
among individuals.

17.  Flexion in the thoracic region is limited by tension in the PLL, the
ligamentum flavum, the interspinous ligaments, and the capsules of the
zygapophyseal joints.
 Extension of the thoracic region is limited by contact of the spinous
processes, laminae, and zygapophyseal facets and by tension in the
anterior longitudinal ligament, zygapophyseal joint capsules, and
abdominal muscles.
 Lateral flexion is restricted by impact of the zygapophyseal facets on the
concavity of the lateralflexion curve and by limitations imposed by the rib
cage.
 Rotation in the thoracic region is limited by the rib cage.

18. 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.
 The line of gravity falls anterior to the thoracic spine.
 This produces a flexion moment on the thoracic spine that is counteracted
by the posterior ligaments and the spinal extensors.

19. BIOMECHANICS OF
LUMBAR SPINE
DR ABU SHOHAIL NIZAME

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