Osteology and Radiographic Fundamentals

Cranial: Toward the head.
Caudal: Toward the tail.
Dorsal: Replaces cranial at and distal to the carpus (forelimb) and tarsus (hindlimb).
Palmar: Replaces caudal at and distal to the carpus.
Plantar: Replaces caudal at and distal to the tarsus.

Anatomical Functions:
- Mineral & Lipid Storage: Maintains mineral homeostasis.
- Hematopoiesis: Production of red and white blood cells within bone marrow.
- Protection: Encloses vital structures (cranium protects brain, ribs protect thoracic organs, pelvis protects pelvic viscera).
- Support: Supports body weight and pregnancy.
- Leverage: Anchors muscles across joints to facilitate movement.
Skeletal Components:
- Bones: Primary structural elements.
- Cartilage:
- Hyaline Cartilage: Covers joint surfaces at the ends of bones.
- Fibroelastic Cartilage: Functions as a shock absorber in intervertebral discs and joint menisci.
- Ligaments: Connective tissue connecting bone to bone.

Five Bone Types:
- Long Bones: Elongated bone featuring a shaft and expanded ends (e.g., humerus, femur).
- Short Bones: Small, cube-shaped bones (e.g., carpal and tarsal bones).
- Flat Bones: Broad, flattened surfaces (e.g., scapula, ribs, cranial/facial bones).
- Irregular Bones: Bilaterally symmetrical bones with complex shapes (e.g., vertebrae, facial bones).
- Sesamoid Bones: Embedded within muscle tendons to provide smooth surfaces and act as pulleys to increase muscular leverage (e.g., patella).
Anatomy of a Long Bone:
- Diaphysis: Central shaft of the bone.
- Epiphysis: End section of a long bone developing separately from the shaft.
- Metaphysis: Widened transition zone between diaphysis and epiphysis.
- Physis (Growth Plate): Cartilaginous line between epiphysis and metaphysis in young animals that closes at maturity; visible on radiographs and distinct from fractures.
Skeletal Divisions:
- Axial Skeleton: Forms the longitudinal axis (skull, hyoid bones, vertebral column, ribs, pelvis).
- Appendicular Skeleton: Appendages used for locomotion (forelimbs and hindlimbs).

X-Ray Physics:
- Discovered in 1895 by Wilhelm Conrad Roentgen.
- High-frequency, short-wavelength electromagnetic radiation; ionizing and carcinogenic.
- Production: High-speed electrons from a heated filament (cathode) strike a metal target (anode) inside a glass vacuum tube.
- Control Factors:
- kVp: Controls energy and penetrating power of x-rays.
- mA: Controls total quantity of x-rays emitted.
- Collimation: Limits beam scope to reduce scatter and radiation exposure.
Radiographic Opacities (Ordered from least to most dense / darkest to whitest):
1. Air / Gas: Darkest (maximum x-rays reach detector plate).
2. Fat: Dark grey.
3. Soft Tissue / Water: Mid-grey.
4. Bone: Light grey to white.
5. Metal / Barium: Whitest (fewest x-rays reach detector plate).

Key Concepts:
- Summation: Superposition of multiple overlapping 3D structures into a single 2D projection.
- Orthogonal Views: Taking two perpendicular ( $90^\circ$ ) views to evaluate 3D spatial geometry and localize structures accurately.
Naming Conventions:
- Right Lateral: Subject positioned with right side against table.
- Ventrodorsal (VD): Beam enters ventral aspect and exits dorsal aspect.
- Dorsopalmar (DP): Beam enters dorsal aspect and exits palmar aspect of distal forelimb.
- Oblique Views: Angled beam orientations to separate superimposed bones:
- Dorsolateral-palmaromedial (DLPM / Lateral Oblique)
- Dorsomedial-palmarolateral (DMPL / Medial Oblique)
- Skyline Views: Tangential projections used to isolate specific bony surfaces clear of superimposition.

Why does a skeleton exist?
- Muscle attachment provides mechanical leverage for movement.
- Overcomes size and speed limits of terrestrial invertebrates, facilitating rapid quadrupedal distance travel.
Why must orthogonal views be taken?
- Because radiographs compress 3D anatomical structures into a 2D image causing summation, perpendicular ( $90^\circ$ ) views are necessary to determine the exact 3D position of foreign objects, fractures, or pathologies.