Thoracic Vertebrae Anatomy

• Vertebrae articulate into a functional column.
• Thoracic ribs ossify separately as costal elements.
• The kyphosis results in upper thoracic vertebrae leaning forward, affecting transverse process tilt and rib neck slope.
• The neck of the first rib slopes upwards from head to tubercle.
• Concave facets on upper transverse processes face somewhat downwards.
• Flat facets on lower transverse processes face somewhat upwards.
• Spinous processes slope downwards, with increasing declivity to T7, then gradually level out to T12.
• Tips of upper four spines are opposite tubercles of ribs one lower in series.
• T5-8 spines are opposite tubercles two ribs lower.
• Lower thoracic spines are opposite ribs one lower in series.
• The 'vertebra prominens' process can originate from C7 or T1.
• Narrow space separates wide, imbricated laminae.
• Transverse processes are uniform except for shorter T12 (sometimes T11).
• Bodies become more massive from top to bottom.
• Middle four bodies may show asymmetry due to the aorta.

Typical Thoracic Vertebra

• Characterized by costal facets.
• Demifacets located on each side of the body.
• The upper demifacet is at the junction with the pedicle's upper border and is semicircular.
• A lower, smaller demifacet faces downwards from the body's lower border.
• Demifacets are on the neural arch, not the centrum.
• Covered in hyaline cartilage, each facet forms a synovial joint with a rib head facet.
• The body is concave around its circumference and perforated by vessels.
• Anterior convexity attaches to the anterior longitudinal ligament.
• Below T4, the body has a sharper anterior curve, creating a heart-shaped outline.
• Asymmetry results from a left-sided excavation caused by the descending aorta.
• The posterior surface is concave from side to side, forming an almost circular vertebral foramen.
• The lumbar and cervical vertebrae have more triangular foramina.
• Two large foramina for basivertebral veins open centrally on the posterior body.
• They appear like a pair of small nostrils.
• The posterior longitudinal ligament loosely attaches at body borders (firmly to discs).
• Compact bone encloses each surface in a heart-shaped ring, forming the fused epiphyseal ring.
• Cancellous bone reaches the surface within the ring and is covered by hyaline cartilage.
• The annulus fibrosus attaches to the hyaline cartilage.
• The pedicle projects back from the body's upper half.
• The body doesn't form part of the intervertebral foramen above it.
• Upper border of the pedicle curves up to the superior articular process, forming the superior vertebral notch.
• Lower border curves down to the inferior articular process, creating the inferior vertebral notch.
• Concave inferior vertebral notch forms the upper boundary of the intervertebral foramen.
• The thoracic nerve number corresponds to the vertebra it accommodates.
• Flat laminae slope down from pedicles to unite in the midline, completing the neural arch.
• Deep notch at the upper border of the laminae.
• Groove along the posterior lamina surface for ligamentum flavum attachment.
• Deep groove at the lower border of the lamina along the anterior surface.
• Groove allows for ligamentum flavum attachment coming up from below.
• Alternate laminae and ligamenta flava are imbricated.
• The superior articular process projects from the pedicle-lamina junction.
• Oval articular facet is steep, facing backward and slightly laterally.
• Two articular surfaces are on a circle's arc, facilitating body rotation.
• Inferior articular facets face forward and medially.
• These facets project below the pedicle at the lamina's inferior angle.
• Cartilage-covered upper and lower facets form synovial joints.
• Capsules and synovial membranes attach to articular margins.
• The ligamentum flavum extends from one capsule to the other, filling the bony hiatus between laminae.
• Intervertebral foramina serve as the main exit from the vertebral canal.
• Small midline veins may unite internal and external vertebral venous plexuses between ligamenta flava.
• Spinous process tapers from a broad base to an expanded tip.

Spinous Process

• Weak interspinous ligaments and muscles connect adjacent sharp borders of the processes.
• Thick supraspinous ligament connects expanded tips.
• Thoracolumbar fascia attaches here, overlaid by trapezius, splenius, and latissimus dorsi.
• Base receives rotator muscle from vertebra below.
• Multifidus, semispinalis, and spinalis muscles insert into each side up to the tip.
• Transverse process projects backward and laterally from the pedicle-lamina junction.
• The anterior surface expands distally to form the costal facet.
• Upper six costal facets are concave; lower ones are flat.
• Tip attaches to the lateral costotransverse ligament.
• Root gives origin to the rotator muscle.
• Upper and lower borders connect to intertransverse ligaments and muscles.
• Lower margin gives origin to a levator costae muscle and receives the superior costotransverse ligament.
• Posterior surface has erector spinae attachments (semispinalis, longissimus).
• Anterior surface is covered by the costotransverse ligament attachment.

First Thoracic Vertebra

• The body is broad, not heart-shaped.
• The longus colli is attached to its anterior convexity over the anterior longitudinal ligament.
• Large round facet for the single articular surface of the first rib head.
• Demifacet for the second rib at the lower border of the body.
• Pedicle attaches below the upper margin of the body, similar to cervical vertebrae.
• The body takes part in the formation of the intervertebral foramen
• Foramina allows exit of C8 and T1 spinal nerves.

Eleventh Thoracic Vertebra

• Single costal facet behind the body on the upper part of the broad pedicle.
• Articular facets exhibit typical thoracic features.
• Transverse process stunted.
• At times, T10 vertebra also shows these features.

Twelfth Thoracic Vertebra

• The broad pedicle carries a single costal facet near its lower margin.
• Transverse process is stunted.
• Its base projects upwards into a mamillary process and downwards into an accessory tubercle.
• Posterior ramus of T11 nerve lies in the groove between them.
• Superior articular facet looks backwards, like a typical thoracic facet.
• Inferior articular facet is lumbar in type, a vertical cylinder facing laterally.
• Upper limit of psoas major attachment is at the lower border of this vertebra.
• Psoas minor arises just above this.

Lumbar Vertebrae

• Normal lordosis of the lumbar vertebrae is between L5 and the sacrum
• Best appreciated via examination of a fresh specimen.
• Bodies may be wedge-shaped (especially the fifth).
• No wedging in the bodies, spinous processes make a backward convexity when piled
• Wedge-shaped discs produce the normal lordosis.
• Bodies increase in breadth downwards.
• Reflected posteriorly by widening between articular processes.
• In LI and 2 the four processes make a rectangle set vertically.
• In L3 they may also make a vertical rectangle, or they may be like those of L4 and make a square.
• In L5 they make a horizontal rectangle.
• The transverse processes are variable in length.
• The fourth is usually the longest.
• In the upper four they are spatulate.
• Processes are set well back on the pedicle.
• The transverse process of the fifth is characteristic.
• Short, massive, pyramidal, and attached from the pedicle forward on the body's side.
• L5 is unique in that the transverse process joins the body, easily recognizable.
• The body shares characteristics with smaller thoracic vertebrae.
• Pedicles attached to its upper half.
• Perforated by a pair of basivertebral veins posteriorly.
• Differs from the thoracic vertebra as its kidney, not heart-shaped.
• The posterior surface is flatter, creating a triangular vertebral canal section.
• Anterior and posterior longitudinal ligaments attach as in thoracic vertebrae.
• Psoas major attaches to the upper and lower borders.
• Psoas spans the concavity of the body on a fibrous arch.
• Lumbar vessels and sympathetic rami curve around beneath the fibrous arch.

Pedicles

• Pedicles enclose intervertebral foramina, like thoracic foramina.
• Laminae lack the downward slope, but have grooves for ligamenta flava attachment.
• The spinous process is roughly horizontal.
• Upper border is straight; lower border curves down, creating a hatchet shape.
• Interspinous ligaments attach to adjacent upper and lower borders.
• Posterior border is thickened for the supraspinous ligament.
• Interspinales and multifidus muscles attach to the spines.

Transverse Processes

• Upper four, spatulate, have a vertical ridge for psoas fascia and anterior layer of lumbar fascia attachment.
• The medial and lateral arcuate ligaments attach to the ridge on LI transverse process.
• Psoas attaches medial to the ridge, while quadratus lumborum inserts lateral to it.
• Tip receives the middle layer of the lumbar fascia.
• Adjacent borders carry intertransverse ligaments and muscles.
• Posterior surface receives attachments of erector spinae.
• The articular processes are characteristic.
• The upper pair rise up and carry articular facets that face medially .
• The upper facets of L4 and 5 will face posteriorly as well as medially.
• Articular surfaces are cylindrical and concave from front to back.
• Lower pair project down from the lateral laminae angles.
• Lower pair are mortised into the superior processes of the vertebra below.
• Each carries a reciprocal convex facet, a section of a vertical cylinder.
• The true transverse element of the lumber vertebra is visible.
• True transverse element consists of two elevations.
• There's a groove between them made by the medial branch of the posterior ramus of the lumbar nerve
• The mamillary process is a 'breast-shaped' convexity.
• Projecting back from the superior articular process behind the articular facet margin.
• The accessory tubercle lies below, at the root of the transverse process.
• The lumbar nerve is located in the accessory tubercle.
• Mamillary process and accessory tubercle represent the stunted transverse process of a thoracic vertebra.
• Mamillary process and accessory tubercle carry similar attachments for back muscles (multifidus, longissimus).

Fifth Lumbar Vertebra

• Pyramidal transverse process.
• Transverse process carries the strong iliolumbar ligament.
• Quadratus lumborum arises from both the iliolumbar ligament and transverse process.
• Anterior and middle layers of the lumbar fascia attach to the process and ligament.
• Inferior articular processes face well forwards and received into backward-facing facets on the sacrum.
• Disc strongly unites the adjacent bodies, and this locking prevents L5 vertebra from sliding down SI vertebra.
• Sloping lumbosacral joint carries the body weight with stability.
• A contracting erector spinae acts as a supporting strap posteriorly.
• The fifth lumbar vertebra may be fused on one or both sides to the first sacral vertebra (sacralization).

Sacrum

• Five smaller sacral vertebrae and costal elements fuse to form the sacrum.
• The sacrum is triangular and curved to concavity towards the pelvis.
• Sacrum carries the body weight.
• It articulates with the ilium and forms the upper posterior wall of the pelvic basin.
• Slung on ligaments carries the body weight.
• The sacrum tapers off down to its apex.
• The cylindrical surfaces are curved from side to side but flat from above down
• The upper surface of the first sacral body slopes down at 30° or more.
• The sacrum is directed backwards before curving down over the pelvic cavity.

Pelvic Surface

• Smooth and concave surface.
• Five fused bodies with four ridges marking ossification lines (intervertebral discs).
• Each side has four diminishing large anterior sacral foramina.
• Rounded bars of bone between the foramina (costal elements).
• The medial boundaries of the anterior sacral foramina are formed by the bodies of the sacral vertebrae.
• Costal elements form the rest of their circumference.
• Rounded bar of bone above the first sacral foramen continues the arcuate line of the ilium.
• This forms the posterior part of the pelvic brim.
• Continues medially to the sacral promontory (anterior lip of the first sacral body).

Lateral Mass

• Mass of bone lateral to the foramina is formed by fusion of costal elements.
• Lateral mass is indented by grooves for the anterior rami of the upper sacral nerves.
• Piriformis arises from the ridges and lateral mass.
• Peritoneum drapes over the upper two bodies, while the retroperitoneal rectum lies against the lower three.
• The fascia of Waldeyer and the superior rectal vessels lie between the sacrum, peritoneum, and rectum.
• The superior hypogastric plexus extends onto the promontory.
• The midline of the sacral hollow contains the median sacral artery, vein, and lymph nodes.
• The sacral sympathetic trunk crosses alongside the promontory to lie medial to sacral foramina.
• Lies the sacral plexus on the piriformis muscle.
• Plexus and muscle covered by parietal pelvic fascia.
• The lateral sacral artery and vein lie lateral to the foramina.

Dorsal Surface

• Convex, irregular, and rough surface.
• Closed by fusion of adjacent laminae in the midline.
• Sacral canal due to caudal slope of first sacral laminae.
• Closed by the ligamenta flava attached to the laminae of L5 vertebra.
• Sacral hiatus below indicates failure of fusion of laminae of S5 and S4 vertebrae.
• Closes via fibrous tissue.
• Spinous processes fuse to produce the median sacral crest.
• The superior articular process on SI vertebra carries a concave cylindrical facet for the joint with L5 vertebra.
• Lateral margin of fused laminae, a line of irregular tubercles represent fused articular processes.
• The low ridge forms the intermediate sacral crest.
• projects below alongside the sacral hiatus.
• Ridge ends in the rounded sacral cornu, which articulates with the coccyx.
• The transverse processes fuse with each other and makes the lateral sacral crest.
• Bony bosses mark the fused transverse processes tips.
• Fused sacral vertebrae enclose the posterior sacral foramina.
• Erector spinae fills the the Lumbar fascia attaches to both crests.
• Fossae presence gives an undulating irregularity to the lateral mass.
• Area carries the attachments of the weight-bearing sacroiliac ligaments.
• Articular cartilage on the auricular surface has tubercles and depressions.
• Sacrum is slender below the postauricular surface.
• Lateral crest meets the lateral border of the sacrum at the level of S4 vertebra.
• Part of the sacrotuberous ligament and gluteus maximus arises from the triangular area.
• Sacrospinous ligament and coccygeus muscle attach to the border of the sacrum.
• The apex of the sacrum is attached by an intervertebral disc to the body of the coccyx.
• Cornua make synovial joints with the cornua of the coccyx.

Sacral Ala

• Projects laterally from the upper surface of SI vertebra.
• Margin forms the brim of the pelvis.
• Attaches to the ventral sacroiliac ligament.
• Iliacus arises from the ligament over the ala.
• Base is crossed by the sympathetic trunk.
• The lumbosacral trunk lies medially, the obturator nerve lies laterally.
• Iliolumbar artery is between the lumbosacral trunk and obturator nerve.
• Fusion of SI and 2 vertebrae may be incomplete, producing unilateral 'lumbarization' of SI vertebra.
• The triangular sacral canal curves with the sacrum.
• Pedicles create intervertebral foramina.
• The pedicle forms lateral exits as in the rest of the vertebral canal.
• The lateral mass is circumvented via the body of the sacrum the anterior or posterior sacral foramina if necessary.
• The fifth sacral foramen is formed by the cornua of sacrum and coccyx.
• The S5 and coccygeal nerves emerge from the fifth sacral foramen.
• Meninges extends down to S2 vertebra.
• The dura mater contains cerebrospinal fluid.
• Tubular sheaths surround the sacral nerve roots, which unite distal to the root ganglia.
• The filum terminale runs via dura to blend with the coccyx periosteum.
• Space around dura mater is filled with loose fat and the internal vertebral venous plexus.

Sex Differences

• In males, the body is wider than the ala.
• Male vertebrae are rugged and has a narrower pelvis.
• In females, the body is narrower than the ala.
• Female vertebrae are slender and broad.
• The anterior male surface is gently and uniformly concave.
• With females the anterior surfaces are relatively flat above and turns forward more prominently below, with the auricular surface occupies.

Coccyx

• Represents the tail of other vertebrates.
• Contracts into four pieces fused together.
• Joined by its base to the sacrum apex via the sacrococcygeal joint.
• Midline symphysis is reinforced by ligaments.
• The ventral and dorsal sacrococcygeal ligaments lie at the front and back.
• A lateral sacrococcygeal ligament joins the transverse process of the first coccyx piece to the sacrum.
• Lateral ligament completes the foramen for S5 nerve and sometimes ossifies.
• Upper surface is in the pelvic floor; lower surface is in the buttock.
• The tip gives attachment to the anococcygeal raphe and the external anal sphincter.
• Borders attach to the coccygeus muscle, sacrospinous ligament fibers of iliococcygeus and pubococcygeus (levator ani).