Chapter 9: The Biomechanics of The Human Spine

What is true about intervertebral discs?

-act as cushions between the vertebrae -account for approximately 1/4 of the height of the spine -are responsible for spinal movement due to compression

Transverse or spinous process fractures may result from what?

-extremely forceful contraction of the attached muscles -the sustenance of a hard blow to the back of the spine

Unusually high incidences of pars interarticularis fractures have been documented in what groups of athletes?

-female gymnasts -interior football linemen -weight lifters

In what muscle groups can lack of flexibility cause anterior pelvic tilt?

-hip flexors -erector spinae -quadratus lumborum

Which muscle(s) cause spinal rotation to the left (i.e. left lateral rotation)?

-left internal oblique -right external oblique

What is true about lordosis? What is not true?

-often accompanied by anterior pelvic tilt -often a result of weight gain and/or pregnancy It is NOT caused by poor abdominal flexibility.

What are potential consequences of spinal fractures?

-paralysis -death

Movement of the spine occurs in which plane(s)?

-sagittal -frontal -transverse

What helps the spine absorb shock?

-spinal curves -intervertebral discs

What is the most common type of vertebral fracture?

-stress fracture of the pars interarticularis

What kind of joints are the articulations between the adjacent vertebral bodies?

-symphysis joints (cartilaginous)

What is kyphosis?

-the condition of exaggerated throacic curvature

cervical region

1. Cervical Region: The cervical region has triplanar movement. Flexion and extension are as high as 17 degrees in the C5-C6 vertebral joint which takes place in the sagittal plane. ROM for hyperextension in the cervical spine is also allowed which takes place in the sagittal plane as well. Lateral and medial rotation of the cervical spine is also allowed, where there is up to 12 degrees of motion allowed at C1-C2 which occurs in the transverse plane. The largest lateral flexion in the spine occurs at the cervical spine where it is about 9-10 degrees of motion at C4-C5 which occurs in the frontal plane.

Describe the range of motion in all three planes for each vertebral region relative to the other regions.

1. Cervical Region: The cervical region has triplanar movement. Flexion and extension are as high as 17 degrees in the C5-C6 vertebral joint which takes place in the sagittal plane. ROM for hyperextension in the cervical spine is also allowed which takes place in the sagittal plane as well. Lateral and medial rotation of the cervical spine is also allowed, where there is up to 12 degrees of motion allowed at C1-C2 which occurs in the transverse plane. The largest lateral flexion in the spine occurs at the cervical spine where it is about 9-10 degrees of motion at C4-C5 which occurs in the frontal plane. 2. Thoracic Region: The thoracic region allows lateral flexion with a ROM of about 6 to 8-9 degrees depending on the height of the segments. This takes place in the frontal plane. The thoracic region also contains lateral and medial rotation. Here, there is 9 degrees of rotation in the upper motion segments, but ROM seems to decrease in rotational capability from T7-T8 downward. This takes place in the transverse plane. ROM for flexion and extension is only in 4 degrees at T1-T2 and 10 degrees at T11-T12 which is in the sagittal plane. 3. Lumbar Region: The lumbar regions allows extension and flexion. There is a ROM of about 20 degrees from the L5-S1. This takes place in the sagittal axis. Hyperextension also takes place in this plane. Lateral flexion of the lumbar spine is 6 degrees, but is only about 3 degrees at the L5-S1. Lateral flexion takes place in the frontal plane. There is limited rotation in the lumbar, where there is only about 5 degrees allowed at the lumbosacral joint which is in the transverse plane. 4. Sacral Region: Movement of the sacral region is fixed due to the fact that the vertebrae are fused to the pelvic girdle. 5. Coccygeal Region: Movement of the coccygeal region is fixed due to the fact that the vertebrae are fused together.

How do we help to prevent lower back pain?

1. Help individuals who are overweight and obese to loose weight. 2. Teach workers who have to handle heavy materials how to properly lift heavy objects. 3. Abdominal exercises such as partial curl-up exercises so that abdominal muscle strength is sufficient enough to contribute to spinal stability. 4. Train the trunk muscles for endurance rather than strength because fatigue of the spinal extensor muscles with reduced force output increased bending moment on the lumbar spine and reduces the ability of the muscles to protect the spine.

lordosis

1. Lordosis is extreme lumbar curvature. It associated with weak abdominal muscles and anterior pelvic tilt. It also places added compressive stress on the posterior elements of the spine. A risk factor for lordosis is obesity where there is reduced ROM of the entire spine and pelvis. Causes are congenital spinal deformity, weakness of the abdominal muscles, poor postural habits, and overtraining in sports that require repeated lumbar hyperextension.

List and describe the three abnormal deviations in the spinal curvature.

1. Lordosis is extreme lumbar curvature. It associated with weak abdominal muscles and anterior pelvic tilt. It also places added compressive stress on the posterior elements of the spine. A risk factor for lordosis is obesity where there is reduced ROM of the entire spine and pelvis. Causes are congenital spinal deformity, weakness of the abdominal muscles, poor postural habits, and overtraining in sports that require repeated lumbar hyperextension. 2. Kyphosis is extreme thoracic curvature. Its causes are congenital abnormality, a pathology such as osteoporosis, or Scheuermann's disease where abnormal epiphyseal plate behavior leads to one or more wedge-shaped vertebrae. In milder cases, it appears that an individual's posture is slouching. It may be treated by exercises that strengthen the posterior thoracic muscles as well as bracing or surgical corrections, depending on the severity of the condition. 3. Scoliosis is lateral spinal curvature/ lateral deviation in spinal curvature. It is coupled with deformity of the involved vertebrae. It can have a C- or S- curve in either the thoracic or lumbar spine, or both. There are two forms of scoliosis: structural scoliosis and nonstructural scoliosis. Structural scoliosis has inflexible curvature that persists even with lateral bending of the spine that can be caused by congenital abnormalities and selected cancers. Nonstructural scoliosis is flexible and are corrected with lateral bending. This type of scoliosis may be secondary to leg length discrepancy or local inflammation.

rectus abdominis

1. Rectus abdominis: The rectus abdominis allows spinal flexion in the sagittal plane when functioning bilaterally. It also allows lateral flexion of the spine when there is unilateral tension development which occurs in the frontal plane.

List and discuss the primary abdominal muscles, explaining how they perform motion in all three planes.

1. Rectus abdominis: The rectus abdominis allows spinal flexion in the sagittal plane when functioning bilaterally. It also allows lateral flexion of the spine when there is unilateral tension development which occurs in the frontal plane. 2. External obliques: The external obliques allow spinal flexion when they function bilaterally in the sagittal plane. They also allow lateral flexion of the spine when there is unilateral tension in the frontal plane. Rotation of the spine toward the opposite side also occurs in the transverse plane from unilateral tension development. 3. Internal obliques: The internal obliques produce sagittal plane movement through spinal flexion when it functions bilaterally. Lateral flexion of the spine also takes places in the frontal plane when there is unilateral tension development. Rotation of the spine toward the same side occurs in the transverse plane from unilateral tension development.

How many pairs of ribs do humans have? Does this differ from the number of thoracic vertebrae?

12 pairs of ribs; No it does not differ - we have 12 thoracic vertebrae

external obliques

2. External obliques: The external obliques allow spinal flexion when they function bilaterally in the sagittal plane. They also allow lateral flexion of the spine when there is unilateral tension in the frontal plane. Rotation of the spine toward the opposite side also occurs in the transverse plane from unilateral tension development.

kyphosis

2. Kyphosis is extreme thoracic curvature. Its causes are congenital abnormality, a pathology such as osteoporosis, or Scheuermann's disease where abnormal epiphyseal plate behavior leads to one or more wedge-shaped vertebrae. In milder cases, it appears that an individual's posture is slouching. It may be treated by exercises that strengthen the posterior thoracic muscles as well as bracing or surgical corrections, depending on the severity of the condition.

thoracic region

2. Thoracic Region: The thoracic region allows lateral flexion with a ROM of about 6 to 8-9 degrees depending on the height of the segments. This takes place in the frontal plane. The thoracic region also contains lateral and medial rotation. Here, there is 9 degrees of rotation in the upper motion segments, but ROM seems to decrease in rotational capability from T7-T8 downward. This takes place in the transverse plane. ROM for flexion and extension is only in 4 degrees at T1-T2 and 10 degrees at T11-T12 which is in the sagittal plane.

internal obliques

3. Internal obliques: The internal obliques produce sagittal plane movement through spinal flexion when it functions bilaterally. Lateral flexion of the spine also takes places in the frontal plane when there is unilateral tension development. Rotation of the spine toward the same side occurs in the transverse plane from unilateral tension development.

lumbar region

3. Lumbar Region: The lumbar regions allows extension and flexion. There is a ROM of about 20 degrees from the L5-S1. This takes place in the sagittal axis. Hyperextension also takes place in this plane. Lateral flexion of the lumbar spine is 6 degrees, but is only about 3 degrees at the L5-S1. Lateral flexion takes place in the frontal plane. There is limited rotation in the lumbar, where there is only about 5 degrees allowed at the lumbosacral joint which is in the transverse plane.

scoliosis

3. Scoliosis is lateral spinal curvature/ lateral deviation in spinal curvature. It is coupled with deformity of the involved vertebrae. It can have a C- or S- curve in either the thoracic or lumbar spine, or both. There are two forms of scoliosis: structural scoliosis and nonstructural scoliosis. Structural scoliosis has inflexible curvature that persists even with lateral bending of the spine that can be caused by congenital abnormalities and selected cancers. Nonstructural scoliosis is flexible and are corrected with lateral bending. This type of scoliosis may be secondary to leg length discrepancy or local inflammation.

A typical geriatric disc has a fluid content that is reduced by approximately how much?

35%

sacral region

4. Sacral Region: Movement of the sacral region is fixed due to the fact that the vertebrae are fused to the pelvic girdle.

coccygeal region

5. Coccygeal Region: Movement of the coccygeal region is fixed due to the fact that the vertebrae are fused together.

How can we properly breathe (and brace) while lifting?.

One should breathe from their diaphragm when lifting. When bracing to lift, one should inhale in this eccentric phase. The diaphragm contracts during this phase, which stabilizes the core. Breathing in also creates intraabdominal pressure in the abdominal cavity which helps stiffen the lumbar spine against buckling. One should also stabilize their trunk in a neutral position to avoid sternal elevation. During the hardest part of lifting, one should exhale in the concentric phase.

Explain proper spinal position while lifting. Also, explain why twisting should be avoided when lifting.

When lifting, one must maintain normal lumbar curvature by lifting this the legs. This is thought to minimize trunk flexion which minimizes the torque generated on the spine by body weight. This allows the active lumbar extensor muscles to partially offset the anterior shear produced by body weight as well as uniformly load the lumbar discs rather than place a tensile load on the posterior annulus of the discs. Lordotic lumbar posture must be eliminated in lifting because it increases the loading of the posterior annulus and the fact joints. Full lumbar flexion also must be diminished because it changes the line of action of the lumbar extensor muscles in which they cannot counteract the anterior shear. Twisting should be avoided when lifting because it places about three times more stress on the back than lifting in the sagittal plane.

In anatomical position, where is the center of gravity located relative to the spine?

anterior

What does contraction of the rectus abdominis cause?

bilateral flexion of the spine

What causes the pumping action (influx and outflux of water containing nutrients and waste) of the intervertebral discs in adults?

body motion

What vertebral region has the best range of motion?

cervical

What is the most common type of spinal loading during daily activities?

compression

What type of joint occurs between the superior and inferior articulating facets of adjacent vertebrae?

gliding (synovial)

What is the result when part of the nucleus pulposus of the disc protrudes and presses on a nerve?

herniated disc

What do obese individual display?

increased anterior pelvic tilt and lumbar lordosis

What is scoliosis?

lateral deviations in spinal curvature

What action(s) do posterior trunk muscles cause when they contract unilaterally?

lateral flexion

What musculoskeletal problem causes the most absences from work?

low back pain

How does a back pack load be placed so that it does not minimize postural adaptations?

lower

What vertebrae are the largest?

lumbar

What gender is lumbar spondylolysis more prevalent in?

men

In what plane do the spinous processes of the thoracic vertebrae limit movement?

sagittal

Which part of the vertebrae bears the most weight?

the body

What is the atlas?

the most superior cervical vertebrae

Attachment to the ribs limits range of motion in which vertebrae?

thoracic

What spinal curves are present at birth?

thoracic and sacral curves