Download Thoracic and Lumbar Spine Anatomy Handout

Thoracic and Lumbar Spine Anatomy Handout
Most of the information is from Miller’s Review of Orthopaedics and Netter’s Orthopaedic Atlas
General Spine Information:
33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal
Topographic Landmarks:
1) Mandible – C2-3
2) Hyoid Cartilage – C3
3) Thyroid Cartilage – C4-5
4) Cricoid Cartilage – C6
5) Vertebra Prominens – C7
6) Scapular Spine – T3
7) Distal Tip of Scapula – T7
8) Iliac Crest – L4-5
Thoracic Vertabrae:
1) Costal Facets
2) Rounded Vertebral Foramen
3) Articulation with Rib Cage
4) Most Rigid portion of Axial Skeleton
Lumbar Vertabrae:
1) Largest Vertebral Bodies
2) Increased Height Anteriorly = Lordosis
3) Lordosis is 55-60 deg with apex at L3
4) Short Laminae and Short Pedicles
5) Mammillary Processes (separate ossification center)
6) Spondylolysis is defect in pars interarticularis (Back Pain in Kids, Think Spondy)
Sacrum Vertabrae:
1) Five Fused Spinal Elements
2) Usually 4 pairs of Pelvic Sacral Foramina
3) Sacral Canal opens Caudally into the Sacral Hiatus
Coccyx
1) Fusion of the lowest 4 spinal elements
2) Attaches dorsally to the Gluteus Maximus, the External Anal Sphincter,and the
Coccygeal Muscles
Spinal Ligaments:
1) Anterior Longitudinal Ligament (ALL) – very strong and resists hyperextension
2) Posterior Longitudinal Ligament (PLL) – weaker, hour-glass shaped (wide over discs)
3) Ligamentum flavum – strong, yellow, elastic, connects laminae, runs from anterior
surface of superior laminae to posterior surface of inferior laminae, constantly in tension,
hypertrophy = nerve root compression
4) Supraspinous Ligament – begins at C7 and lies dorsal to spinous process
5) Interspinous Ligament – lies between spinous process
6) Iliolumbar Ligament – very stout ligament connects transverse process of L5 with ilium,
tension from vertical shear pelvic fractures can lead to avulsion fracture of TP
Facet Joints
Orientation dictates plane of motion at each level
Thoracic
Sagittal Facet Orientation – 60 degrees at T1 increasing to 70 degrees at T12
Coronal Facet Orientation – 20 degrees posterior
Lumbar
Sagittal Facet Orientation – 137 degrees at L1 decreasing to 118 degrees at L5
Coronal Facet Orientation – 45 degrees anterior
Intervertebral Discs
1) Consist of Fibrocartilage
2) Two components:
a. Annulus Fibrosus – obliquely oriented fibers composed of type I collagen
b. Nucleus Pulposus – softer central portion composed of type II collagen and has a
high polysaccharide content with 88% water.
3) Account for 25% of the total spinal columnar height
4) Attached to Vertebral Bodies by Hyaline Cartilage
5) Intradiscal Pressure is dependant on position – supine is lowest and sitting flexed forward
is the highest.
Spinal Cord
1) Spinal Cord Ends at L1
2) Conus Medullaris starts at L1 ends in small filum terminale
3) Sensation Dorsal and Motor Ventral
4) Incomplete Spinal Cord Injury Patterns
Injury Pattern
Functional Deficit
Recovery
Central (Most Common)
UE>LE, usually quadriplegic
75%
with sacral sparing. Flaccid
paralyis of UE and spastic
paralysis of LE
Anterior
Complete Motor Deficit
10% (worst prognosis)
Posterior
Loss of Deep Pressure, Deep
Pain and Proprioception
Brown-Sequard
Unilateral Cord Injury with
>90%
ipsilateral Motor Deficit and
Contralateral Pain and Temp
Deficit (2 levels below injury)
Nerve Roots
1) In Thoracic and Lumbar Spine, central and paracentral disc herniations affect the nerve
root of the lower vertebral level (eg L4-L5 = L5 nerve root involvement)
2) In Thoracic and Lumbar Spine, far lateral disc herniations affect the nerve root of the
upper vertebral level (eg L4-L5 = L4 nerve root involvement)
3) Neurologic Levels
Neurologic Level
C5
C6
C7
C8
T1
L4
L5
S1
Representative Motor
Deltoid
Wrist Extension
Wrist Flexion
Finger Flexion
Interossei
Tibialis Anterior
Extensor Hallicus Longus
Peroneal
Reflex
Biceps
Brachioradialis
Triceps
None
None
Patellar
None
Achilles
Dermatomes
Vascular Supply to the Spine
1) Usually derived from segmental arteries located at vertebral midbodies via the aorta
2) Dura and posterior elements - primary blood supply is dorsal braches of segmentals
3) Vertebral bodies blood supply is from ventral branches of segmentals
4) Artery of Adamkiewicz – enters through the left intervertebral foramen in the lower
thoracic spine from T8 to T12. It supplies the interior 2/3rds of the anterior cord.
5) Spinal cord blood supply from anterior and posterior spinal arteries and segmental
branches of the vertebral artery and dorsal arteries.
Anterior (Transthoracic) Approach to the Thoracic Spine
1) Transverse incision is made approx. 2 ribs above the levele of interest.
2) Dissection over the top fo the riv is carried out to avoid injuring the intercostal
neurovascular bundle.
3) The rib is further dissected and removed from the field.
4) Note: The right-sided approach is favored to avoid the aorta, segmental arteries, and
artery of Adamkiewicz, and thoracic duct.
5) The esophagus, aorta, vena cava, and pleura of the lungs should be identified and
protected.
Surgical Approaches
Posterior Approach to the Thoracolumbar Spine
1) Straight midline incision is made over the spinous processes and carried down through
the thoracolumbar fascia.
2) Plane between the two segmentally innervated erector spinae muscles is used
3) Paraspinal musculature is subperiosteally dissected from the attached spinous processes,
exposing the posterior elements.
4) Structures at risk include the posterior primary rami (near facet joints) and segmental
vessels (anterior to the plane connecting the transverse processes)
Anterior Approach to the Lumbar Spine (Transperitoneal)
1) Longitudinal incision from below the umbilicus to just above the pubic symphysis.
2) Spliet the rectus abdominis muscles and incise the peritoneum.
3) Protect and retract bladder distally and bowel cephalad and incise the posterior
peritoneum longitudinally over the sacral promontory.
4) The aorta bifurcation is revealed and the middle sacral artery is logated
5) Expose the L5-S1 disc space.
6) Note: Injury to the lumbar plexus, particulary the superior hypogastric plexus of the
sympathetic plexus that lies over the L5 vertebral body, can cause sexual dysfunction and
retrograde ejaculation.
Anterolateral Approach to the Lumbar Spine (Retroperitoneal)
1) Provides access from L1 to Sacrum.
2) Oblique incision is centered over the 12th rib to the lateral border of the rectus abdominis
muscle.
3) The external oblique, internal oblique, and transversus abdominis muscles are incised in
line with the skin incision.
4) Elevate the retroperitoneal fat revealing the psoas major muscle and genitofemoral nerve.
5) Ligate the segmental lumbar vessels and mobilize the aorta and vena cava to expose the
desired vertebral level.
6) Protect the sympathetic chain (medialto the psoas and lateral to the vertebral body) and
ureters (btwn peritoneum and psoas fasicia).
Spine Surgical Approaches Summary
Approach
Interval
Anterior Thoracic
Transverse btwn ribs 2 levels
above surgical site
Posterior Thoracolumbar
Midline approach over spinous
processes
Anterior Lumbar
(Transperitoneal)
Anterolateral Lumbar
(Retroperitoneal)
Btwn segmentally innervated
rectus abdominis
Oblique and through external
and internal oblique as well as
transversus abdominis
Risks
Dissect over top of rib to avoid
intercostal neurovascular
bundle
Posterior primary rami and
segmental vessels, Protect
nerve root
Presacral plexus of
parasympathetic nerve
Sympathetic chain and ureters
Pertinent Netter Images: