This document discusses mechanical stability of the lumbar spine. It can be achieved through intra-abdominal pressure generated by muscles like the transverse abdominis, co-contraction of trunk muscles, external supports, and surgery. The transverse abdominis plays a key role in stabilizing the spine by increasing intra-abdominal pressure. Co-contraction of flexor and extensor muscles also provides stability. Common spine issues include injuries from accidents like whiplash, as well as overuse injuries, disc issues, and fractures.

1. Mechanical stability of lumber
spine
Dr.Rao Muhammad Mohsin

2. MECHANICAL STABILITY
OF THE LUMBAR SPINE
• Mechanical stability for the lumbar spine can
be achieved through several means:
• lAP (intra-abdominal pressure)
• Co contraction of the trunk muscles
• external support
• and surgery.

3. Intra-Abdominal Pressure
• lAP is one mechanism that may contribute to
both unloading and stabilization of the lumbar
spine.
• IAP is the pressure created within the abdominal
cavity by a coordinated contraction of the
diaphragm and the abdominal and pelvic floor
muscles
• lAP serves as a "pressurized balloon“ attempting
to separate the diaphragm and pelvic floor
• This creates an extensor moment that decreases
the compression forces on the lumbar discs

4. The Role of Intraabdominal Pressure?
McGill, author of our text chapter, thinks it stiffens trunk which reduces
tissue strain and tendency to buckle – but not pressure in the IVDs

5. • Recent studies using fine-wire EMG of the deeper abdominal
muscles found that the transverses abdominis is the primary
abdominal muscle responsible for lAP generation
• Transverse abdominis horizontally oriented ,it creates
compression and increase IAP
• Evidence suggested that elevated IAP produced extensor
moment
• Mechanical stability is maintained by co-activation between
antagonistic trunk flexors and extensors
• As the abdominal musculature contracts, IAP increases and
converts the abdomen into a rigid cylinder that greatly
increases stability as compared with the multi-segmental spinal
column
• Current research suggests that the transverses abdominis
muscle, together with the diaphragm, plays an important role
in stabilizing the spine in preparation for limb movement,
regardless of the direction in which movement is anticipated

7. Trunk Muscle Co-Contraction
• With higher levels of movement, co-contraction,
spine compression and trunk muscle stiffness
increases
• Loss of spine stability results from repetitive
continuous motions that fatigue the trunk muscles
• The reduction in the functional capacity of the
flexors & extensors was compensated by secondary
Muscle groups and led to an increased couple
motion pattern that is more prone to injury.

8. External Stabilization
• Restriction of motion at any level of the spine may
increase motion at another level.
• The use of back belts to prevent low back injury
remains controversial.
• Originally it was believed to assist in increasing lAP
as a way of unloading the spine during lifting,
however, inconclusive evidence exists for
biomechanical effectiveness of these devices
• Investigation into the effect of back belts on muscle
activity has revealed no significant EMG activity
differences in the back extensors during lifting with
or without a back belt

9. Low Back Pain
• 75-80% of population will experience it at some time in
their life
• psychological and social factors in some low back pain
cases.
• Mechanical stress plays a significant role.
• In Children incidence of back pain increases 30% with
age.
• Cause in children may be increase physical activity
stronger back flexor muscles .The main causes in children
are believed to be musculo-tendinous strains and
ligamentous sprains
• More incidence in athletes as compared to non athletes
• High incidences of low back pain have been found in
workers who sit for prolonged periods and in those
unable to sit at all during the work day

10. • High-risk occupations include, laborers, truck drivers,
garbage collectors, warehouse workers, mechanics,
nursing aides, materials handlers, lumber workers,
practical nurses, and construction laborers
• Cigarette smokers have increased incidence of low
back pain compared to non-smokers,due to the
contributions of smoking to disc degeneration
• Relative Stability of Spine
• In the absence of contraction of the surrounding
musculature, buckling of the lumbar spine occurs
under compressive loads as small as 4 N .Although
bone structure, discs, and ligaments all contribute to
stability, but surrounding muscles have been shown
to be primary contributors to spinal stability
• 60% of cases is idiopathic (unknown origin)
• Abdominal exercises help in treatment

11. Soft Tissue Injuries
• Contusions
• Muscle Strains
• Ligament Sprains
• Usually result from sustaining a blow or
overloading the muscles.
• Spasms and knot-like contractions of the back
muscles may also develop as a sympathetic
response to spinal injuries, and symptom for
underlying problems.

12. Acute Fractures
• Transverse or spinous process fractures may result from
extremely forceful contraction of the attached muscles or
• a hard blow to the back of the spine, which may occur
during participation in contact sports such as football,
rugby, soccer, basketball.
• The most common cause of cervical fractures is indirect
trauma involving force applied to the head or trunk rather
than to the cervical region itself.
• common mechanism for cervical injuries is an axial force to
the top of the head with the neck in slight flexion
• Extremely serious because of fragile spinal cord.
• Rib fractures usually due to blows from sports or accident ,
cause pain with each inhalation.
• Potential for serious damage to underlying soft tissues
(lungs)

13. Stress Fractures
• The most common type of vertebral fracture is a stress
fracture of pars interarticularis, the region between the
superior and inferior articular facets, which is the weakest
portion of the neural arch
• spondylolysis
• presence of a fracture in the pars interarticularis of the
vertebral neural arch
• spondylolisthesis
• complete bilateral fracture of the pars interarticularis,
resulting in the anterior slippage of the vertebra
• Spondylolysis and spondylolisthesis don’t tend to heal with
time
• Common with sports involving repeated hyperextension of
the lumbar spine.

16. Pathology of Intervertebral Disc Injuries
a) Disc Herniations
• General term used when there is any change in the shape
of the annulus that causes it to bulge beyond its normal
perimeter
• consists of the protrusion of part of the nucleus pulposus
from the annulus. But contained by the outer layers of
the annulus and supporting ligamentous structures
• Cause of 1-5% back pain cases.
• Traumatic or stress related.
• Common sites: between 5th-6th and 6th-7th cervical
vertebrae and 4th-5th lumbar and 5th lumbar and 1st
sacral.
• Sensory nerves supplying anterior and posterior
longitudinal ligaments generate pain signals.

17. Disk Prolapses
• Rupture of the nuclear
material into the vertebral
canal.
• Persistent and
chronic back pain
Disk Extrusion
• Extension of nuclear
material beyond the
confines of the posterior
longitudinal ligament or
above and below the disk
space, as detected on
magnetic resonance
imagine (MRI)but still in
contact with the disk

18. Free sequestration
• The extruded nucleus has separated from the
disk and moved away from the prolapsed
area.

21. Airbag Injuries
• Motor vehicle accidents continue to be the leading
cause of injury-related deaths in the United States.
• Studies generally concluded that front seat
occupants are adequately Protected against frontal
impact if belts are worn in an airbag equipped
vehicle
• Device meant for our safety
• An airbag is made from light fabric. The driver’s air
bag is in the steering wheel, and the passenger’s air
bag is behind a panel on the dashboard.
• The airbag is connected to a crash sensor, which will
deploy the airbag if the car gets into a sufficiently
severe crash

22. Airbag Injury Types
• A malfunctioning crash sensor can cause very serious
injuries or death ,But any deployment of an airbag can
cause injury.
• Abrasion to the face, chest or upper extremities
• Contusion of the face, chest, upper extremities, knees
or internal organs
• Strain, fracture or blunt trauma to the cervical spine
• Burns on the chest, upper extremities or hands
• Fracture or break in the face, upper extremities or
wrists
• Fracture in the skull or rib cage
• Loss of consciousness or concussion injuries
• Bruising or swelling of the brain

23. • Passenger-side airbags pose a lethal threat to
children riding in the front seat of an
automobile
• The back seat is the safest place for children of
any age to ride.
• Never put an infant (less than 1 year old) in the
front of a car with a passenger-side airbag.
Infants must always ride in the back seat, facing
the rear of the car.
• Make sure everyone is buckled up.
• Unbuckled occupants can be hurt or killed by an
airbag

24. Whiplash Injuries
• Relatively common injury to cervical region.
• Usually from automobile collisions, where neck undergoes
sudden acceleration and deceleration.
• Shear force and extension moment at the junction
between the cervical and thoracic spines are the underlying
mechanism causing neck motion and potential injury
The cervical spine assumes an S-shape, with the upper
segments in flexion and the lower segments in extension
• The cervical muscles contract rapidly in such situations, with
potential for forced eccentric tension development
• Symptoms
• Neck pain, muscle pain, pain or numbness radiating from neck
to shoulders, arms, hands and a headache (present in 50-60% of
most cases)
• Women appear to be at greater risk for whiplash injury
than men