Kinesiology The Spine

Spinal Column Structure Base of support. Link between upper and lower extremities. Protects spinal cord. Stability vs. mobility Example: cervical vs. thoracic spine

5 Regions of Vertebral Column Cervical Thoracic Lumbar Sacral Cocygeal 33 bones and 23 disks

Curvatures Viewed Laterally Prior to birth “C-shaped”. 4 distinct curves in an adult.

Cervical Lordosis Thoracic Kyphosis Lumbar Lordosis

Spinal Motion Spinal movement is the combination of: Intervertebral joints Facet joints

Intervertebral Joints

Intervertebral Disc Intervertebral disk make up 20-30% of the height of the column and thickness varies from 3mm in cervical region, 5mm in thoracic region to 9 mm in the lumbar region. Ratio between the vertebral body height and the disk height will dictate the mobility between the vertebra – Highest ratio in cervical region allows for motion Lowest ratio in thoracic region limits motion

Disc Structure Nucleus Pulposus (NP) is located in the center except in lumbar lies slightly posterior. Gelatinous mass rich in water binding PG (proteoglycan) AKA (glycoaminoglycos) GAG-protein molecule. Chondrotin-4 sulfate in PG molecule gives the disc a fluid maintaining capacity (hydrophyllic) - decreases with age. Hydration of the disc will also decrease with compressive loading - this loss of hydration decreases its mechanical function.

Disc Structure 80-90% is H2O – decreases with age. Disc volume will reduce 20% daily (reversible) which causes a loss of 15-25 mm of height in the spinal column. Acts as a hydrostatic unit allowing for uniform distribution of pressure throughout the disc.

Disc Structure Compressive stresses on the disc translate into tensile stresses in the annulus fibrosis This makes the disc stiffer which adds stability and support to the spine. Bears weight and guides motion. Avascular - nutrition diffusion through end-plate.

Annulus Fibrosis Collagen arranged in sheets called lamellae (outer layers). These lamellae are arranged in concentric rings -10-12 layers that lessen in number with age and thicken (fibrose). Enclose the nucleus and oriented in opposite directions at an angle of 120 degrees (or 45-65 degrees). Controls the tensile loading from shear, accessory motions in the anterior compartment and disc forces which can be up to 5x the external compression force.

Annulus Fibrosis Mostly avascular and lacking innervation but the outermost layers are probably innervated (sinovertebral nerve). Thickest anteriorly. Outermost 1/3 connects to vertebral body via Sharpie’s fibers. Outer 2/3 connect to the end plate.

Disc Pathology - Herniation Highest incidence at C5-6, C6-7, L4-5, and L5-S1. Disc herniation Disc protrusion or bulge - contained Annulus intact. Localized – usually lateral Diffuse – usually posterior Prolapsed – not contained Annular fibers disrupted – inner layers Extrusion - migration through all layers

Longitudinal Ligaments Anterior longitudinal Supraspinous Posterior longitudinal Ligamentum flavum (elastic) PLL diverts herniation posteriolaterally

Posterior Structures (Elements) of Motion Segment Pedicles and lamina form the neural arch. Facet joints between the superior and inferior articulating surfaces. Transverse and spinous processes. Interspinous and supraspinous ligaments. Ligamentum lavum. Intervertebral foramina.

Facet Joint Articulation between the superior (concave) and inferior (convex) facets. Guide intervertebral motion through their orientation in the transverse and frontal planes.

Facet Joint Capsule Limit motions. Strongest in thoracolumbar and cervicothoracic regions where the curvatures change. Resist flexion and undertake tensile loading in the superior portion with axial loading or extension. Resists rotation in lumbar region.

Intervebral Foramina Exit for nerve root. The size is dictated by the disc heights and the pedicle shape. Will lose space with osteophytic formation, hypertrophy of ligaments and loss of disc height with aging – lateral stenosis. Decreases by 20% with extension and increases 24% with flexion

Spinal Stability The column’s ability to react to multiple forces placed on it. Degeneration increases instability. Body reacts to restore through fibrosus and osteophytic changes.

Types of Segmental Loading Axial Compression Bending Torsion Shear

Axial Compression Caused by gravity, ground reaction forces, muscle contraction and ligaments reaction to tensile forces. Intradiscal loads can range from 294N to 3332N depending upon position. Most load in anterior segment, posterior can load from 0-30% depending upon segments position. Compression at the disk causes tension at the annulus, changing the angle of the fibers and increasing the stability.

Axial Compression (cont’d) Creep will occur in the disc, will be larger with increased force and aging. 5-11% of H2O is lost through creep. Creep is rapid 1.5-2mm in 10 min. Plateaus at 90 minutes.

Bending Combination of compression, shear and tensile forces on the segment from translation. Bending into flexion will be resisted by posterior annulus, PLL and the facet capsule and anterior compressive forces on the anterior structures causing disc displacement. For extension posterior compressive forces in anterior segment and there is a tensile load in facet capsule and ALL.

Torsion Caused by axial rotation and coupled motions. Stiffness may increase due to facet compression with certain motions i.e., flexion increases torsional stiffness at L3-4. Annulus fibrosus resists, 1/2 fibers CW other 1/2 CCW facets may help depending upon the orientation (resists in a tensile manner). When combined with flexion the amount of force required for tissue failure is decreased.

Shear Facet joint resists especially in the lumbar area. Annulus will undergo some tensile forces depending upon direction and the fiber orientation or angle. Discs also resist but if creep occurs - the facet may undergo more loading.

Mobility Amount and direct of motion in a segment is determined by: Vertebral body/disc size. Facet orientation frontal vs. sagittal.

Flexion Superior vertebra will anterior tilt and forward gliding will occur: Widening the intervertebral foramina 24%. Adds compressive forces on the anterior aspect of the anterior segment moving the nucleus pulposus posteriorly. Tensile forces placed on posterior annulus, flavum, capsule and PLL. Central canal is widened Rationale for some of William’s flexion exercises

Extension Superior vertebra will tilt and glide posteriorly and the intervertebral foramina narrowed up to 20%. The central canal is also narrowed. Nucleus pulposus moves anteriorly

Lateral Flexion Superior vertebra will translate, tilt and rotate over inferior - direction will differ. Concavity towards, convexity opposite Tensile forces on convexity, compressive forces on concavity Extension in ipsilateral facet. Flexion in contralateral facet.

Rotation Accessory motions are like lateral flexion due to same coupling in cervical and upper thoracic spine. Exception with lower T/S and L/S in neutral coupling then opposite (in most references). If the motion segment is flexed or extended spine (in most references) the coupling will be the same.

Regional Structural and Functional Differences Differences are apparent due to connection requirements, sacral, upper C-spine, all junctions Vertebral body size increases with support requirements. Cervical, thoracic,lumbar, and sacral/cocygeal.

Cervical CO - occipital C1 - Atlas C2 - Axis C3-6 - general basic structure

Cervical Region Function Mobility > Stability. Upper cervical unit – C0-2 Lower Cervical unit C2-7

C0-1 C0 – occiput – containing the occipital condyle – convex. C1 - no body, disk and spinous process allows for free space and a large neutral zone and cord protection - this means more motion. Lateral facets of CO on C1 - concave C1 on convex CO - flex/ext or nodding and minimal to no lateral flexion/rotation.

C1-2 2 facets laterally and 1 medially with dens and anterior arch transverse ligament helps control (C1 on C2 anterior displacement), stabilizes – allows nodding also provides cartilaginous surface as does the alar ligament - limits flex/ext so right rotation requires left lateral facet to slide anterior and right lateral facet to slide posterior – so rotation is coupled with extension. Can account for up to 50% of rotation in the neck and most of the initial ROM.

C2-7 50% wider than they are deep. Transverse process holds foramen for vertebral artery, vein and plexus, and grove for the spinal nerve. Facet orientation is roughly 45 degrees(35-65) in the transverse plane w/ loose capsule - allows for motion in all planes and more rotation and lateral flexion than other regions.

Thoracic Spine Function Articulation for the ribs Least mobility Increasing load bearing Lat flex flex/Ext

Thoracic Spine Body T1 - similar to cervical in (C7a). Normally the vertebral body equals width and depth. The ratio of disc diameter to height is highest. This will: Decrease tensile forces Decrease possibility of disc injury Posterior aspect becomes thicker as you go lower - ribs bigger (articulates) and more compressive forces. End-plates become larger (higher compressive forces) as you go caudally.

Thoracic Spine Less flexible due to rib articulation, smaller disc to body ratio, spinous process. Flavum and ALL are thicker; facet capsule less flexible. Upper thoracic spine facet orientation Limits flexion extension - 60/20 transv/front Allows coupled lat/rot. (rot of spinous process to the convex side) Facets are more sagittal in T9-12 to allow flex/ext and rot of spinous process will be toward concavity (lumbar coupling).

Thoracic Spine Rib articulation consists of 2 articulations to the thoracic vertebra – Anterior surface of the lateral process Lateral aspect of the vertebral body. Bucket handle motion of the ribs with breathing. Extension and contralateral lateral flexion ribs separate. Flexion and lateral flexion ipsilaterally compresses ribs.

Thoracic Spine Scoliosis will cause a rib hump. Combination of tranverse plane rotation and frontal plane sidebend – contralateral coupling. Convex side will occur on the ipsilateral rotated side – causing hump.

Lumbar Spine Most load bearing structures in the skeletal system Sagittal plane motion Largest body/disc, lamina and pedicles short and thick for load bearing.

Lumbar Spine L5 transitional, wedge shape of body and disc – Anterior > posterior. L5-S1 most flexion extension. Coupling of motion - right lateral flexion will result in right sidebend and left rotation of vertebral body (when L/S in neutral)

Spinal Musculature Mobility vs. Stability Slow twitch SO vs. fast twitch FOG Energy storage Consider the line-of-pull of all spinal muscles

Spinal Muscles

Common Theme Small angle of insertion Therefore: Rotary component Compressive component

Common Theme Small angle of insertion Therefore: Rotary component Compressive component When are active vs. passive exercised indicated? When are they not?

Hip Flexors & Abdominals

General Comment Regarding Function Contracture vs. contraction

General Comment Regarding Function Contracture of hip flexors and effect on lumbar spine

General Comment Regarding Function Abdominals Pelvic stability/balance Guy-support system