skeletal

Bone Chapter Overview

This section summarizes key aspects of bone structure and function, highlighting concepts related to bone marrow, articulations, joints, and fractures.

Bone Marrow

  • Definition: Bone marrow is the tissue that fills the inner space of bones.

  • Types of Bone Marrow:

    • Red Marrow:

    • Characteristics: Active in producing components of blood.

    • Cell Types:

      • Red blood cells
      • White blood cells
      • Platelets

    • High Activity: Predominantly found in younger animals due to the need for increased blood cell production for growth.

    • Yellow Marrow:

    • Characteristics: Comprised mostly of fat; replaces red marrow as animals mature.

    • Function: Less active in blood production as needs decrease with age but can revert to red marrow in cases of significant blood loss.

    • Locations: Typically found in long bones of adults.

Articulations and Joints

  • Types of Joints: Three major classifications based on movement:

    1. Synarthrosis (immovable joints):
    • Definition: Fibrous joints.
    • Examples: Suture lines of the skull, splint bones in horses (e.g., third metacarpal).
    1. Amphiarthrosis (slightly movable joints):
    • Definition: Cartilaginous joints; allow limited movement.
    • Examples: Mandibular symphysis, pubic symphysis.
    • Radiographic Note: The appearance of non-bony symmetry on radiographs due to cartilage presence.
    1. Diarthrosis (freely movable joints):
    • Definition: Also known as synovial joints.
    • Characteristics:
      • Hyaline cartilage covering joint surfaces.
      • Joint capsule lined with synovial membrane producing synovial fluid (lubricant).
      • Typically, collateral ligaments for support (medial and lateral).
      • For the knee: additional ligaments (cranial, caudal) and fibrocartilage pads (menisci).

Synovial Joint Movements

  • Flexion and Extension:

    • Flexion: Reduces the angle between bones (e.g., flexing a horse's carpus from 180° to 90°).
    • Extension: Increases the angle (e.g., extending the carpus from 90° back to 180°).

  • Abduction and Adduction:

    • Abduction: Movement away from the midline of the body.
    • Adduction: Movement towards the midline of the body.

  • Rotation and Circumduction:

    • Rotation: Bone rotates around its own long axis.
    • Circumduction: Movement in a circular pattern at the distal end of a limb.

Types of Diarthrosis Joints

  1. Hinge Joint (Ginglymus):

    • Movement: Limited to flexion and extension only (e.g., elbow joint).

  2. Gliding Joint (Arthrodial):

    • Movement: Primarily flexion and extension with limited abduction/adduction (e.g., carpus/wrist).

  3. Pivot Joint (Trochoid):

    • Movement: One bone rotating around another (e.g., atlas and axis vertebrae for head rotation).

  4. Ball and Socket Joint (Spheroidal):

    • Movement: Most extensive range of motion; includes flexion, extension, abduction, adduction, rotation, and circumduction (e.g., shoulder and hip joints).

Fractures

  • Types of Fractures:

    • Complete vs. Incomplete:

    • Complete: Fracture extends completely across the bone.

    • Incomplete: Partial fracture (e.g., greenstick fracture common in young animals).

    • Open vs. Closed:

    • Open Fracture (Compound): Bone penetrates through the skin, increasing infection risk.

    • Closed Fracture: Does not penetrate the skin.

  • Fracture Patterns:

    • Transverse: Cut at a right angle.
    • Linear: Cut parallel to the bone's long axis.
    • Spiral: Caused by twisting forces (similar to twisting a cardboard tube).
    • Oblique: Cut at an angle.
    • Comminuted: Bone is shattered into multiple pieces; typically high-energy causes (e.g., car accidents).

  • Displaced vs. Nondisplaced:

    • Displaced: Fracture ends are not in alignment.
    • Nondisplaced: Fracture ends remain in alignment.

Fracture Repair Stages

  1. Inflammatory Stage:

    • Bleeding occurs, damaging capillaries and causing bruising.
    • Blood Clot Formation: Initiates inflammation.

  2. Repair Stage:

    • Collagen laid down by osteoblasts; begins formation of new bone.
    • Fibrous tissue forms scaffolding for osteoblast activity.

  3. Remodeling Stage:

    • Bone is slowly replaced by new bone; process continues throughout life.
    • Involves osteoblasts and osteoclasts for bone maintenance and adaptation.

Bone Healing and Fixation

  • Healing rates vary by age:

    • Young Animals: Rapid healing (5 - 8 weeks).
    • Older animals: May take over 12 weeks.

  • Importance of Proper Fixation:

    • Essential for healing; any movement can disrupt repair.

  • Methods of Fixation:

    • Casts, splints, intramedullary nails, plates, screws, or cerclage wires.

Calcium Regulation in Bone

  • Normal Plasma Calcium Levels:

    • Ideally between 8 to 12 mg/dL, critical for bone health and function.

  • Calcium Needs:

    • Young growing animals require higher calcium for growth.
    • Lactating females utilize calcium for milk production.

  • Hormones Involved:

    1. Vitamin D: Facilitates calcium absorption from diet.
    • Sources and Activation: Dependent on sunlight and conversion from cholesterol forms.

    1. Parathyroid Hormone: Released when blood calcium levels drop; promotes osteoclast activity.

    2. Calcitonin: Released to lower blood calcium levels; inhibits osteoclast activity to retain bone calcium.

Conclusion / Q&A Discussion

  • Discussed potential for metabolic bone disease in reptiles due to lack of vitamin D3.
  • Open to questions for further clarification on the material covered in the bone chapter.