Human Anatomy: Spine Overview

Normal Spine Curves

• Lordotic: Inward curvature of the spine
  • Located in the cervical (neck) and lumbar (lower back) regions
  • Normal function: Helps distribute weight and absorb shock
  • Excessive curve: May lead to lordosis (swayback)
• Kyphotic: Outward curvature of the spine
  • Located in the thoracic (upper back) and sacral (pelvic) regions
  • Normal function: Provides stability and supports the body's upright posture
  • Excessive curve: May lead to kyphosis (hunchback)

Spine Segments

• 7 cervical, 12 thoracic, 5 lumbar, 5 sacrum (fused), 4 coccygeal (fused)
• Cervical (C1-C7)
  • More flexible, supporting the head
  • Wide range of motion
  • Flexion: 45-50°
  • Extension: 60-70°
  • Lateral flexion (side bending): 40-45°
  • Rotation: 70-90°
• Thoracic (T1-T12)
  • Relatively immobile
  • Ribs attach
  • Plays with the balance of mobility vs. stability
• Lumbar (L1-L5)

Sacrum and Coccyx

• Sacrum: Triangle base of spine connects spine to pelvis
• Coccyx: Delivers nerves to pelvic organs, few small bones, remnant of tail

Mobility and Stability

• 3 aspects
  • Neurological control
  • Bone structure (passive)
  • Muscle (active)
• Body is great at compensating, making it difficult to diagnose chronic back pain.
• Recruiting bigger muscles instead of smaller stabilizers sacrifices mobility.

Spinal Column

• Stability
  • Protect spinal cord
  • Maintain upright posture
  • Transmit weight to lower limbs
• Mobility
  • Provide motion for head and trunk
  • Absorb force
  • Provide space for muscle attachments
• Functional spinal unit
  • Allows for movement
    • 2 adjacent vertebrae, Intervertebral disc, Intervening disc, Intervening ligaments

Vertebrae Motion

• 6 degrees of freedom
  • Distraction, Compression, Translation, Extension, Side flexion

Intervertebral Joints

• Allow for small motion between segments
• Separated by fibrous-cartilaginous discs
• Ratio between vertebral body and disc dictates mobility
  • Higher ratios = thicker discs = more motion, especially in cervical regions
  • Lower ratios = thinner discs = limited motion, especially in thoracic regions
• Also, motion can vary during the day

Vertebral Disc

• Fluid-filled (jelly donut)
  • Outer layer: annulus fibrosus (fibrous ring)
  • Inner layer: nucleus pulposus (gel)
• Shock absorption: maintains space between vertebrae and maintains height
• Avascular (nutrition via endplate) = thin cartilage layer between vertebral body and intervertebral disc

Disc Anatomy

• Spongy center = nucleus pulposus
• Fibrous ring = annulus fibrosus
• Annulus = whole thing
  • Annulus Fibrosus: entire outer fibrous ring
    • Concentric layers of collagen and fibrocartilage
  • Annular Wall: outer layer
    • 12-14 layers altering obliquities of about 30°

Disc Under Compressive Loads

• Nucleus pulposus absorbs water and expands
• Hydration decreases with increased load, increasing internal pressure
• Compressive stress on disc causes tensile stress in annulus fibrosis
• Increased stiffness = stability but sacrifices mobility
• Laterally against annulus, and against end vertebrae
• Increased stiffness superiorly/inferiorly

Disc Kinematics

• Nucleuses flatten under axial compression
• Forces are distributed throughout the layers.
• Protects the spine from localized damage

Intradiscal Pressure

• Rises with annular stress increases and uneven loading
• Nuclei are driven away from closure of space to allow material to distribute evenly

Anterior Longitudinal Ligament

• Resists extension forces, limits excessive lordosis
  • Fiber span: several segments (superficial) and single segment (deep)

Posterior Longitudinal Ligament

• Resists flexion

Atlanto-occipital Joint & C1-C2

• “Yes” nodding motion
  • Condyles of occipital bone (convex)
  • Facets of atlas (concave)
• “No” head joint- rotation
  • Atlas = bony ring without body, pivot joint
  • 50% rotation of transverse plane

Cervical Motion

• Most flexible region
• Anatomical position: approximately 80° extension, 50° flexion, 30-35° lordosis, and 20-25° sagittal plane motion

Lateral Flexion

• Down and back slide = same side we're going to
• Rotation is still down and back

Cervical Coupling

• Combines all motions
• C1-C2 not involved

Cervical Flexion Muscles

• Rectus capitis anterior, Rectus capitis lateralis, Longus capitis, Longus colli, Sternocleidomastoid, Scalenes

Cervical Extension Muscles

• Rotators, Splenius capitis, Splenius cervicis, Rectus capitis posterior major/minor, Obliquus capitis superior/inferior

Thoracic Spine

• Least mobile due to ribs
• Sacrifices mobility for stability
• Articulates with ribs

Thoracic Spine Curve

• 40° kyphotic curve
• Curve from wedge-shaped vertebral bodies
• T1 similar to C7
• Disc to height ratio highest
• Decreases in tensile forces
• Decreases possibility of disc injury as you move to lower regions of spine

Rib Anatomy

• Three classifications (12 pairs)
  • True ribs
    • Direct connection
  • False ribs
    • Cartilage connection
  • Floating ribs
    • No connection
• Costotransverse joint: Takes a lot of effort to displace

Thoracic Motion

• Extension is primarily caused by lumbar extensors
• Muscles:
  • Erector spinae group
  • Quadratus lumborum

Axial Rotation

• Abdominal muscles and trunk rotators
• Abs are farther away from spine than rotators, increase the arm's moment
• Rotators have high sensory cells
• Side bending is initiated by ipsilateral abs + erectors and continued by gravity.

Lumbar Flexion

• Muscles:
  • Rectus abdominis
  • Internal obliques
  • External obliques

Lumbar Extension

• Layering effect of muscles
• 2 classes of muscles
  • Erector spinae (spinae, longissimus, iliocostalis)
    • Middle (semispinalis) connects adjacent
• Deep spinal muscles; connects adjacent muscles, Multifidus, Rotatores, and some other muscles that aren't the primary

Lateral Flexion

• Involved quadratus lumborum, psoas major, and unilateral flexors / extensors
• The opposite side of the motion is involved in eccentric contraction, holding a position

Lumbar Stability

• Efficient stabilizers
  • Obliques, Transverse abdominis, Multifidus, Quadratus lumborum
• Inefficient stabilizers
  • Rectus abdominis, Longissimus, Latissimus dorsi

Rectus Abdominis

• Isometric contraction increases abdominal pressure
• Resist extension forces
• Controls against hyperextension
• Stabilizes spine; holding breath during squatting increases intra-abdominal pressure

Psoas

• Function depends on the position of the lumbar spine
• Hip flexion/external rotation
• Unilateral contraction = side bending
• Bilateral contraction = flexes trunk toward hip & arches lower back

External Oblique

• Stabilizer vs. neutralizer
• Pulls chest down, compresses abdominal cavity, increases intra-abdominal pressure
• Involved in flexion and rotation (opposite side) working against each other.

Internal Oblique

• Antagonist to the diaphragm, compresses organs and produces trunk rotation
• Works with opposite side external oblique

Quadratus Lumborum

• Unilateral = laterally flexes vertebral column; Bilateral = extends lumbar column
• Provides lateral stability

Sacrum

• 1-3° motion relative to ilium
• Supports weight of spine and entire upper body
• Acts as a keystone

Loads on the Spine

• Body weight acts anterior to the spine
  • Creates forward bending loads
• Erectors & spine extensors are always active to some level

Disc Failure

• Pressure elevated by bending, coughing, sneezing, straining
• Intradiscal pressure
  • Sitting (forward lean)
  • Standing
  • Side lying
  • Supine lying
  • Order of most to least pressure

Disc Injuries

• Degenerative disc disease: flattening over time, fissures
• Herniated discs: nucleus pulposus migration, can apply pressure on nerves

Walking Speed

• 6th major vital sign
  • Cardiorespiratory,
  • Musculoskeletal,
  • Neurological
• Scores in any major deficits will likely show up in walking speed
• Reliability: consistency of a measurement
• Validity: if the test is measuring what it is intended to assess

Cadence, Stride Length, Gait Rhythm, and ONE STRIDE

• Cadence: number of steps per minute (men: ~108, women: ~118)
• Stride length: foot-to-foot
  • Men: ~1.51 m, Women: ~1.32 m
• One stride is 1 complete gait cycle
  • Step: initial contact of one foot to the other
  • Stride: 2 steps (initial contact of one limb to the next contact of the same limb)

Gait Cycle Phases

• Stages of the stride cycle
  • Double support
  • Single support
  • Double support (again)
• Initial contact
• Loading Response
• Single support - Mid Stance
• Terminal stance
• Pre-swing
• Double Support
• Initial, Mid, and Terminal swing

Sagittal Plane Kinematics

• Initial contact
  • Thigh - 25° flexion, knee - 0-5°flexion, Ankle - neutral
• Mid-stance
  • Thigh - 0°, knee - 0°, Ankle- 5° dorsiflexion
• Terminal stance
  • Thigh - 15° extension, knee - 0°, Ankle- 10° dorsiflexion
• Initial swing
  • Thigh -15° flexion, kneee-60°flexion
  • Ankle - 5° plantar flexion
• Mid swing
  • Thigh + knee- 25° flexion, Ankle-neutral
• Terminal swing
  • Thigh -25° flexion, knee -0°, Ankle- 15° plantar flexion

Frontal Plane Kinematics

• Total motion:
  • 7° eversion, 6° inversion, 13° total ROM
  • Pronated = more flexion
  • Supinated = more rigid
  • Initial Contact (rigid supinated)
  • Loading response (flex pronate)
• Walking GRFs peak eversion is 7°during mid-stance