Canine Vertebral Column - Comprehensive Study Notes

Vertebral Column: Overview and Functions

• Unpaired, irregular bones (vertebrae) forming the canine vertebral column
• Functions:
  • Support body and maintain posture
  • Aid progression/movement
  • Protect the spinal cord
  • Shield structures of the neck, thorax, abdomen, and pelvis
• Number varies by species; in dogs/cats generally 50+ vertebrae in total
• Divided into 5 regions: Cervical (Neck), Thoracic (Back), Lumbar (Loin), Sacral (Croup), Caudal/Coccygeal (Tail)

Vertebral Regions and Formula

• Regions: 1) Cervical, 2) Thoracic, 3) Lumbar, 4) Sacral, 5) Caudal/Coccygeal
• Vertebral column formula (typical in dogs and cats):
  • Dog: $ext{C7 T13 L7 S3 Cd 20-23}$
  • Cat: $ext{C7 T13 L7 S3 Cd 21-23}$
• Note: C = cervical, T = thoracic, L = lumbar, S = sacral, Cd = caudal (coccygeal); counts indicate how many vertebrae per region and caudal vertebrae range

Anatomy of a Typical Vertebra

• Components of a typical vertebra:
  • 1) Body (basal part)
  • 2) Arch (pedicle & lamina)
  • 3) Vertebral foramen/canal
  • 4) Spinous process
  • 5) Transverse process
  • 6) Cranial and caudal articular surfaces
• The vertebral arch forms the vertebral foramen; together with adjacent vertebrae creates the vertebral canal housing the spinal cord
• Laminectomy involves removal of the lamina to access the spinal canal

Cervical Vertebrae

• C1: Atlas
  • No spine and no body
  • Modified articular processes (foveae)
  • Thick shelf-like transverse processes (wings) and a lateral vertebral foramen
• C2: Axis
  • Elongated ridge-like spine (the spine is cnnective to the axis)
  • Body projects cranially as the dens (odontoid process)
  • Cranial articular surface located in the body and continuous with the articulation area of the dens
• Remaining five cervical vertebrae are more typical; sequentially: C3–C6 typical vertebrae; C7 has notable features
• C7 (and some others):
  • Spinous processes increase gradually with C7 having the highest spine
  • C7 lacks a transverse foramen like the other cervical vertebrae
• Summary: 7 cervical vertebrae (C1–C7)

Foramina and Vertebral Anatomy

• Lateral vertebral foramen: for the first cervical spinal nerve
• Transverse foramen: for the vertebral artery and vein
• Intervertebral foramen: for spinal nerves and spinal vessels
• Key anatomy: arch, pedicle, lamina, body, transverse process, and articular surfaces

Thoracic Vertebrae and Ribs

• Thoracic vertebrae articulate with ribs
• Costs/Facets:
  • Cranial and caudal costal foveae (demifacets) on vertebral bodies form the rib head articulations with adjacent vertebrae
  • Transverse costal facets articulate with rib tubercles on the corresponding vertebra
  • Each rib head articulates with the demifacets of two adjacent vertebrae
• The 11th vertebra is often described as anticlinal in some species; thoracic vertebrae carry the rib articulations
• Ribs: total 13 pairs (costae)
  • Dorsal bony parts and ventral cartilaginous parts
  • 1st to 9th ribs articulate directly with the sternum (true ribs)
  • 10th–12th form the costal arch (false ribs)
  • 13th rib is floating

Lumbar Vertebrae

• Characteristics:
  • Longer, more uniform bodies
  • Long transverse processes
  • Absence of costal facets
  • Short cranially pointing spine
  • Mamillary and accessory processes (present in thoracic and lumbar regions)

Sacrum and Caudal Vertebrae

• Sacrum:
  • Three vertebrae are fused
  • Median sacral crest is palpable
  • Dorsal and ventral sacral foramina for dorsal and ventral nerve roots
  • First and second sacral spinal nerves pass through the foramina
  • Auricular surface articulates with the ilium (sacroiliac joint)
• Sacroiliac joints:
  • Synovial and/or fibrous joints
  • Shock absorption and added firmness via articular capsules and ligaments (dorsal sacroiliac ligaments, supraspinous ligaments, yellow ligaments, sacrotuberous ligaments)
• Caudal (coccygeal) vertebrae:
  • Vary by species; average ~20 in dogs
  • Distinctive features become less pronounced caudally

Joints of the Vertebral Column

• Two main joint types:
  • Cartilaginous joints: Intervertebral disks (IVD) between adjacent vertebral bodies
  • Synovial joints: between articular processes (plane joints)
• Specific synovial joints:
  • Atlanto-occipital: hinge/ginglymus type
  • Atlanto-axial: pivot type

Intervertebral Disks (IVD)

• Present between all vertebrae in neck, back, and tail except between the first two cervical vertebrae (C1-C2)
• Two components:
  • Annulus fibrosus: outer thick fibro-cartilaginous ring
  • Nucleus pulposus: inner gel-like core containing fluid and cartilage
• Function: absorb shock and allow limited movement between vertebrae

Ligaments of the Vertebral Column

• Nuchal ligament (absent in cats)
• Yellow ligament (Interarcuate/Flava)
• Interspinous ligament
• Supraspinous ligament
• Ventral longitudinal ligament (VLL): from the 8th thoracic vertebra to the sacrum
• Dorsal longitudinal ligament (DLL): from axis to sacrum; well developed in the cervical region
• Intercapital ligaments (ICL): between rib heads T2–T10; help limit lateral sliding of adjacent vertebrae

Clinical Considerations: Spinal Tap and Common Disorders

• Spinal tap (collecting CSF) considerations:
  • Vertebral arches fit dorsally with spaces open only at:
  • Atlanto-occipital space
  • Atlanto-axial space
  • Lumbosacral space
• Common conditions:
  • Intervertebral Disk Diseases (IVDD)
  • Wobbler Syndrome (Cervical Spondylomyelopathy)
  • Lumbosacral Stenosis (cauda equina syndrome)

Intervertebral Disk Diseases (IVDD)

• Synonyms: disc rupture, herniation, slipped disc
• Pathology:
  • Compression of spinal cord, blood vessels, and/or nerve roots
  • Predominantly affects chondrodystrophoid breeds (e.g., Dachshunds, Beagles, Basset Hounds, Poodles)
• Characteristics:
  • Degenerative disorder due to age, genetics, vigorous activity, trauma, or aging
  • Nucleus pulposus degenerates; annulus fibrosus cracks; nuclear material extrudes and compresses the spinal cord or nerve roots
• Distribution: ~85 ext{%} of cases in the thoracolumbar region and ~15 ext{%} in the neck region

Wobblers Syndrome (Cervical Spondylomyelopathy)

• Degenerative disorder associated with vertebral malformation leading to narrowing of the vertebral canal
• Results in compression of spinal cord and/or nerve roots
• Commonly affects Great Danes and Doberman Pinschers
• Clinical signs:
  • Ataxia in the hind limbs
  • Neck flexion or a flexed neck posture sometimes observed

Lumbosacral Stenosis (Cauda Equina Syndrome)

• More common in large breeds; typical onset around 3–7 years
• Arthritic changes between L7 and the sacrum
• Narrowing of the vertebral canal with nerve root compression
• Clinical signs: severe pain in back and tail, difficulty rising, urinary incontinence, muscle paresis/paralysis

Treatment Options for IVDD and Stenosis

• Medical management (mild cases with low-grade pain/neurological deficits):
  • Anti-inflammatory drugs, muscle relaxants, rest
• Surgical management (persistent/severe pain or deficits):
  • Remove extruded disc material to relieve pressure

Decompressive Surgical Procedures

• Fenestration: open disk space and remove nucleus pulposus without entering the spinal canal
• Ventral Slot (cervical disk cases): approach ventrally through bone to access disk space
• Hemilaminectomy: approach spinal cord from one side (right or left); common for thoracolumbar disk cases
• Dorsal Laminectomy: approach dorsal aspect; used in certain cervical, thoracolumbar, or lumbar disk cases

Thoracic Anatomy: Ribs, Sternum, and Joints of the Thorax

• Ribs (costae):
  • Typical rib has head, tuberculum, and a body
  • Head articulates with costal foveae of two adjacent vertebrae (demifacets)
  • Tubercle articulates with transverse costal facets
• Sternum (manubrium and xiphoid process):
  • 8 unpaired sternebrae (sternbrae)
  • Intersternebral cartilages between sternebrae
  • 1st sternebra: Manubrium; last sternebra: Xiphoid process; xiphoid cartilage at distal end
• Joints of the thorax:
  • Costo-vertebral joints (ball-and-socket)
  • Costo-transverse joints (plane)
  • Costo-sternal joints (synovial hinge)
  • Intersternal joints (cartilaginous)

Ligaments and Connections in Thoracic Region

• Costovertebral ligaments (head of rib to vertebrae)
• Radiate sternocostal ligaments (sternum to costal cartilages)
• Costotransverse ligaments (between rib tubercle and transverse process)
• Related structures and connective tissue cross-links help stabilize thoracic cage mechanics

Muscles of the Vertebral Column (Epaxial and Hypaxial)

• Epaxial muscles: three longitudinal systems, subdivided by region:
  1) Iliocostalis (lumborum & thoracis regions)
  2) Longissimus (lumborum, thoracis, cervicis, & capitis)
  3) Transversospinalis (splenius & semispinalis muscles)
• Principal action: extend the vertebral column
• Representative muscles and relationships:
  • Longissimus system includes longissimus capitis, cervicis, thoracis, and lumborum portions
  • Iliocostalis includes iliocostalis thoracis and lumborum portions
  • Transversospinalis includes spinalis and semispinalis groups; visible as components of the deep back musculature
• Hypaxial muscles: involved in neck and thoracic wall movement and vertebral flexion
  • Neck: longus capitis, longus colli
  • Thoracic/neck region: sternocephalicus, sternohyoideus, sternothyroideus
  • Thoracic wall: scalenus, serratus ventralis, serratus dorsalis (cranialis & caudalis), external intercostal, internal intercostal, rectus thoracis

Summary: Key Connections and Practical Takeaways

• The vertebral column provides structural support, protects the spinal cord, and supports propulsion and movement; its regional variation reflects functional demands (e.g., rib articulation in thoracic vertebrae)
• The cervical region houses specialized vertebrae (atlas and axis) enabling head and neck motion; C7 has distinctive features among the typical cervical vertebrae
• Thoracic vertebrae uniquely articulate with ribs via costal facets; the integrity of the thoracic cage is essential for respiration and protection of thoracic organs
• Lumbar vertebrae emphasize strength and mobility without rib articulation
• The sacrum fuses with the ilium to form the sacroiliac joint, pivotal for pelvic stability
• Intervertebral disks (IVDs) provide cushioning; nucleus pulposus and annulus fibrosus have distinct roles in disk mechanics and pathology
• Ligaments provide passive stability and limit excessive motion; intercapital ligaments help stabilize the rib-head articulations across T2–T10
• Clinical conditions such as IVDD, Wobbler syndrome, and lumbosacral stenosis have breed, regional, and functional implications; management ranges from medical to decompressive surgical approaches
• Surgical decompression techniques are selected based on disk location and severity: Fenestration, Ventral Slot, Hemilaminectomy, and Dorsal Laminectomy
• The thoracic cage (ribs and sternum) forms a protective and mechanical unit; its joints and ligaments allow coordinated movement with the vertebral column
• Epaxial muscles extend and stabilize the vertebral column; their organization reflects regional function; hypaxial muscles contribute to neck flexion, thoracic movement, and rib stabilization

Key Terminology (Concise Glossary)

• Annulus fibrosus: outer fibrous ring of an intervertebral disk
• Nucleus pulposus: inner gel-like core of an intervertebral disk
• Demifacet: half facet on adjacent vertebrae for rib head articulation
• Anticlinal vertebra: a thoracic vertebra (often T11 in some species) with special anatomical orientation
• Intercapital ligament (ICL): ligaments between heads of adjacent ribs in T2–T10
• Ginglymus: hinge-type joint (uniaxial)
• Planar joint: joint with flat surfaces allowing gliding movement
• Fenestration: surgical creation of an opening in a disk space while avoiding entry into the spinal canal

End of Notes