Anatomy Part 2

Osteogenesis and Infant Skeletal Development

• Osteogenesis defined: The development and formation of bones.

• Timeline of formation: Bones begin to form in the second month ($2\text{nd}$ month) of embryonic life.

• Skeletal components observed at birth:

  • Frontal bone

  • Superior maxilla (Sup. maxilla)

  • Mandible

  • Parietal bone

  • Occipital bone

  • Temporal bone

  • Clavicle

  • Scapula

  • Sternum

  • Shoulder joint

  • Humerous

  • Radius

  • Ulna

  • Elbow joint

  • Wrist joint

  • Bones of hand

  • Pelvic bones

  • Sacrum

  • Hip joint

  • Femur

  • Tibia

  • Fibula

  • Knee joint

  • Ankle joint

  • Bones of foot

  • Infant skeletal structure consists of cartilage and formed bone at birth.

• Two processes of bone growth:

  • Intermembranous Ossification

  • Endochondral Ossification

• Primary Ossification:

  • Timeline: Begins before birth.

  • Extent: Forms the entire bulk of short and irregular bones.

  • Long bone formation: Forms the central shaft of long bones.

  • Primary Ossification Center: Diaphysis (the main portion or shaft during development of long bones).

• Secondary Ossification:

  • Timeline: Occurs after birth when a separate bone begins to develop at the ends of long bones.

  • Secondary Ossification Center: Epiphysis (the end of long bones).

  • Epiphyseal Plate (Growth Plate): A plate of cartilage that develops between the diaphysis and epiphysis as growth occurs. It is a common site of fractures in pediatric patients.

  • Completion: Near the age of $21$, full ossification occurs, and the two areas (diaphysis and epiphysis) join.

  • Epiphyseal Line: A moderately visible line seen on the adult bone indicating the site of fusion.

  • Radiological age comparisons:

  • $6$ Year Old: AP Knee demonstrates distinct epiphysis, epiphyseal plate, and diaphysis.

  • $21$ Year Old: Demonstrates full fusion with a visible epiphyseal line.

Bone Classification and Anatomical Types

• Bone Age Assessment: Evaluated using a bone age study of the non-dominant hand (referenced from Standring S: Gray's anatomy, ed $40$, New York, 2009, Churchill Livingstone).

• General Classifications of Bones:

  • Long

  • Short

  • Flat

  • Irregular

  • Sesamoid (sometimes not listed as a standalone category, but instead included within irregular bones)

• Long Bones:

  • Location: Found only in the limbs.

  • Structure: Consists of a shaft or body (main portion) and $2$ articular ends.

  • Function: Provide support to the body.

  • Examples: Phalanges of the fingers and toes, radius, ulna, tibia, fibula, humerus, and femur.

• Short Bones:

  • Structure: Consists mainly of cancellous bone containing red marrow, surrounded by a thin outer layer of compact bone.

  • Examples: Carpal bones of the wrist and tarsal bones of the ankle (these represent the only short bones in the body).

• Flat Bones:

  • Structure: Consists mainly of $2$ tables of compact bone separated by cancellous bone and red marrow (termed diploe in flat bones).

  • Function: Provide protection and allow surface area for muscle attachment.

  • Examples: Cranium, sternum, and scapula.

• Irregular Bones:

  • Structure: Characterized by peculiar shapes, with compact bone on the exterior and cancellous bone in the interior.

  • Function: Serve as attachment sites for muscles, tendons, and ligaments, or attach to other bones to create joints.

  • Examples: Vertebrae, pelvic bones, and facial bones.

• Sesamoid Bones:

  • Structure & Location: Small, oval bones that develop inside and beside tendons.

  • Function: Precise role is not fully understood, but experts believe they alter the direction of muscle pull and reduce friction.

  • Examples: Patella (largest sesamoid bone in the body), and small sesamoids located at the $1\text{st}$ metacarpophalangeal ($1\text{st}$ MCP) joint in the hand and $1\text{st}$ metatarsophalangeal ($1\text{st}$ MTP) joint in the foot.

Arthrology and Joint Classifications

• Arthrology defined: The study of joints or articulations between bones ("Can it move?").

• Functional Classification of Joints (based on mobility):

  1. Synarthroses: Immovable joints.

  2. Amphiarthroses: Slightly movable joints.

  3. Diarthroses: Freely movable joints.

• Structural Classification of Joints (based on binding tissue types):

  1. Fibrous Joints:

  • Lack a joint cavity.

  • Immovable (functionally classified as synarthroses).

  • Subtypes and examples:

    • Skull Suture

    • Syndesmosis (e.g., Inferior Tibiofibular Joint)

    • Gomphosis (e.g., Roots of the teeth)

  1. Cartilaginous Joints:

  • Lack a joint cavity.

  • Virtually immovable (functionally classified as amphiarthroses).

  • Subtypes and examples:

    • Symphysis type (e.g., Pubic symphysis)

    • Synchondrosis (e.g., Epiphyseal plate)

  1. Synovial Joints:

  • Possess a wide range of motion.

  • All are freely movable (functionally classified as diarthroses).

Synovial Joint Anatomy and Functional Subtypes

• Structural Anatomy of Synovial Joints:

  • Articular Capsule: Completely surrounds and enfolds all synovial joints to join separate bones together.

  • Fibrous Capsule: Outer layer that connects the capsule to the periosteum of the two joining bones.

  • Synovial Membrane: Inner layer that surrounds the entire joint to form the joint cavity.

  • Synovial Fluid: A thick, yellow fluid produced by the synovial membrane that lubricates the joint and reduces friction.

  • Articular Cartilage: Smooth and slippery cartilage covering the ends of long bones to ease motion; separated by the synovial membrane and fluid.

  • Meniscus: An extra pad of cartilage present in specific synovial joints acting as a shock absorber (e.g., cross section in knee joint).

  • Bursa: Synovial fluid-filled sacs located outside the main joint cavity that function to reduce friction (e.g., suprapatellar bursa, infrapatellar bursa).

• Subtypes of Synovial Joints:

  • Gliding / Plane:

  • Motion: Simplest synovial joint, permitting the least amount of movement among synovial joints; involves sliding or gliding movement between articular surfaces.

  • Axis: Uniaxial movement.

  • Examples: Intercarpal joints of the wrist, intertarsal joints, carpometacarpal joints.

  • Hinge / Ginglymus:

  • Motion: Flexion and extension movements only.

  • Axis: Uniaxial movement.

  • Examples: Interphalangeal joints, elbow joint, knee joint.

  • Pivot / Trochoid:

  • Structure & Motion: Composed of one bone with a projection or rounded/pointed portion articulating with a ringlike structure formed by bone or ligaments; allows rotation around a single axis.

  • Axis: Uniaxial movement.

  • Examples: Atlas and Axis ($C1$ & $C2$), proximal radioulnar joint, distal radioulnar joint.

  • Ellipsoid / Condyloid:

  • Motion: Allows movement in two directions at right angles to each other, including flexion, extension, abduction, and adduction. Circumduction (a combination of both movements) also occurs.

  • Axis: Biaxial movement.

  • Examples: Radiocarpal joint of the wrist, $2\text{nd}$ through $5\text{th}$ metacarpophalangeal ($2\text{nd}\text{--}5\text{th}$ MCP) joints, metatarsophalangeal (MTP) joints of toes.

  • Saddle / Sellar:

  • Structure & Motion: Articular surfaces are concave-convex; permits flexion, extension, abduction, adduction, and circumduction.

  • Axis: Biaxial movement.

  • Example: First carpometacarpal ($1\text{st}$ CMC) joint of the thumb.

  • Ball + Socket / Spheroidal:

  • Structure & Motion: Round head of one bone rests within a cup-shaped depression of another bone; provides the greatest range of motion including flexion, extension, abduction, adduction, circumduction, and medial and lateral rotation.

  • Axis: Multiaxial movement.

  • Examples: Hip joint, shoulder joint.

Bone Fracture Mechanisms and Classification

• Fracture Definition: A break in the continuity of a bone.

• Healing Sequence and Mechanics:

  • Fracture tears and destroys blood vessels that carry nutrients to osteocytes.

  • Vascular damage initiates the repair sequence.

  • Fracture Hematoma: A blood clot occurring immediately after the fracture event, which is then reabsorbed and replaced by callus.

  • Callus: Specialized repair tissue that binds the broken ends of the fracture together.

• Fundamental Structural Classifications:

  • Closed Fracture: Fracture that does not break through the skin.

  • Open / Compound Fracture: Fracture in which the bone or bones break through the skin.

  • Non-displaced Fracture: Fracture in which the bone maintains its normal alignment.

  • Displaced Fracture: A more serious fracture in which the bones are not in anatomic alignment.

• Common Classification of Fractures:

  • Compression Fracture: Most common in the spine; bones get shorter.

  • Open / Compound Fracture: Breaks through the skin.

  • Simple Fracture: Closed fracture with normal alignment.

  • Greenstick Fracture: Bone bends or partially breaks while remaining attached.

  • Transverse Fracture: Horizontal fracture line across the bone.

  • Spiral or Oblique Fracture: Curves around the bone.

  • Comminuted Fracture: Fracture resulting in many pieces.

  • Impacted Fracture: Bone is smashed upon itself.

Anatomical Relationship Terminology

• Anterior (Ventral): Forward or front of body or organ.

• Posterior (Dorsal): Back of body or organ.

• Caudad: Away from the head toward feet.

• Cephalad: Toward the head.

• Inferior: Below or nearer the feet.

• Superior: Above or nearer the head.

• Central: Middle area or main part of organ.

• Peripheral: Near the surface or edge or outside.

• Contralateral: Opposite side of body.

• Ipsilateral: Same side of body.

• Lateral: Away from the median/midline.

• Medial: Towards the median/midline.

• Deep: Parts far from the surface.

• Superficial: Parts near the skin or surface.

• Distal: Furthest from point of attachment or away from center of the body.

• Proximal: Nearer the point of attachment or center of the body.

• External: Parts outside an organ or outside the body.

• Internal: Parts within or on the inside of an organ.

• Parietal: Wall or lining of a body cavity.

• Visceral: Lining of the organ.

• Dorsum: Top of the foot or back of hand.

• Palmer: Palm of the hand.

• Plantar: Sole of the foot.

Radiographic Projections

• Projection Definition: The path of the central ray (CR) as it exits the x-ray tube, goes through the patient, and enters the image receptor.

• Independence from Position: Projection classification is defined by the CR path and is not affected by patient's body position (e.g., upright, supine, lateral decubitus).

• Anteroposterior (AP) Projection:

  • CR enters anterior part of body and exits the posterior.

  • Can be achieved in upright, recumbent, seated, or lateral decubitus positions.

• Posteroanterior (PA) Projection:

  • CR enters the posterior body surface and exits anterior.

  • Can be achieved in upright, prone (ventral recumbent), seated, and lateral decubitus positions.

• Axial Projection:

  • Characterized by a longitudinal angulation of the central ray with the long axis of the body or a specific part.

  • CR is usually angled caudad or cephalad.

  • Typically uses the term axial projection when the angle is $10^\circ$ or more.

  • Would typically be classified further as an AP Axial or PA Axial Projection.

• Tangential Projection:

  • CR is directed toward the outer margin of a curved body surface to profile a certain body part just under the surface and frees it from superimposition.

• Lateral Projection:

  • CR enters one side of the body or part, passes transversely along the coronal plane, and exits the opposite side.

  • Clarified for limbs by the terms lateromedial or mediolateral to indicate where CR enters and exits.

  • Transthoracic Projection: A lateral projection through the thorax used for the humerus and shoulder.

• Oblique Projection:

  • CR enters the body from a side angle following the oblique plane.

  • AP Oblique Projection: CR enters anterior and exits posterior.

  • PA Oblique Projection: CR enters posterior and exits anterior.

• Complex Projections:

  • Projections defined by entrance and exit points and by central ray relationship to the body simultaneously.

  • Axiolateral Projection: Uses angulations of the CR where CR enters and exits through lateral surfaces of the body or part.

• True Projections:

  • Body part is placed in true anatomic position.

  • True AP or PA: CR is perpendicular to the coronal plane and parallel to the sagittal plane.

  • True Lateral: CR is parallel to the coronal plane and perpendicular to the sagittal plane.

• In-Profile:

  • Outlined or silhouette view of an anatomic structure with a distinctive shape.

  • The distinctive aspect is not superimposed over other anatomy.

• Comprehensive List of Projections:

  • Anteroposterior (AP)

  • Posteroanterior (PA)

  • Lateral

  • AP Oblique

  • PA Oblique

  • Axial

  • AP Axial

  • PA Axial

  • AP Axial Oblique

  • PA Axial Oblique

  • Axiolateral

  • Axiolateral Oblique

  • Transthoracic

  • Craniocaudal

  • Tangential

  • Inferosuperior

  • Superoinferior

  • Plantodorsal

  • Dorsoplantar

  • Lateromedial

  • Mediolateral

  • Submentovertical

  • Acanthoparietal

  • Parietoacanthial

Radiographic Positioning Definitions

• Position defined in 2 ways:

  1. General Body Position: Refers to the manner in which the patient is placed in relation to the surroundings.

  • Upright

  • Seated

  • Supine

  • Prone

  • Recumbent

  • Fowler's

  • Trendelenburg

  • Sim's [left semi-prone oblique]

  1. Radiographic Position: Specific placement of the body part in relation to the radiographic table or image receptor.

  • Lateral

  • Oblique

  • Decubitus

  • Lordotic