All skeletal

Skeletal System Overview

• The skeletal system consists of two main parts:

  • Axial Skeleton: includes the skull, vertebral column, and thorax.

  • Appendicular Skeleton: includes the upper limbs, pectoral girdle, lower limbs, and pelvic girdle.

• Functions of the skeletal system:

  1. Protection: encases vital organs (e.g., skull protects brain).

  2. Support: provides structural framework for the body.

  3. Movement: facilitates movement through joints and muscle attachment.

  4. Storage: reserves minerals such as calcium and phosphorus.

  5. Blood Cell Production: hematopoiesis occurs in the bone marrow.

Bone Types

• Long Bones:

  • Shaft (diaphysis) with heads at both ends (e.g., femur, humerus).

• Short Bones:

  • Cube-shaped (e.g., carpal bones).

• Flat Bones:

  • Thin, curved (e.g., skull, ribs).

• Sesamoid Bones:

  • Small, round bones found in tendons (e.g., patella).

• Irregular Bones:

  • Bones that don't fit into other categories (e.g., vertebrae).

Bone Structure

• Two types based on density ratio:

  1. Compact Bone: dense and smooth, withstands stress.

  2. Spongy Bone: lighter, with an open structure; contains trabeculae.

Bone Cells

1. Osteocytes:

   • Mature cells that regulate calcium levels and repair bone.

2. Osteoblasts:

   • Responsible for new bone production (osteogenesis).

3. Osteoclasts:

   • Large cells that break down bone tissue to regulate calcium levels.

Bone Formation & Growth

• Intramembranous Ossification: forms flat bones from fibrous membranes (e.g., skull).

• Endochondral Ossification: begins with hyaline cartilage, most bones develop this way.

• Increasing Bone Length: happens at the epipheseal line. The growth plate is split into 4 zones:

  1. Resting Cartilage: nearest to the epiphysis, randomly arranged, slowly dividing cells

  2. Proliferation: produces new cartilage, cells are dividing and form columns like stacks of coins

  3. Hypertrphy: Cells mature and enlarge

  4. Calcification: Cells die and cartilage calcifies

• Increasing Bone Diameter: Appositional growth, a new osteon is formed when cells secrete enough matrix

• Bone Remodeling: occurs due to activity and diet

  • Activity: Bones adapt to changes in forces pulling on bone by laying down new matrix at sites of stress or by atrophying

  • Diet: When blood calcium levels drop, PTH is released and osteoclasts break down bone to release stored Calcium. When blood calcium is too high, excess calcium is deposited into the matrixx

Spinal Column Sections

• The vertebral column has five sections:

  Cervical Vertebrae (7): These vertebrae have a small, oval-shaped body that is smaller than the large triangular foramen; the spinous process is short and bifid, forming an angle that is generally parallel to the transverse processes.

  Thoracic Vertebrae (12): Characterized by a larger, heart-shaped body and a circular foramen, the spinous process is long and extends downward at a sharp angle compared to the transverse processes.

  Lumbar Vertebrae (5): These have the largest, kidney-shaped body with a triangular foramen; the spinous process is thick and short, projecting horizontally and less angled than in thoracic vertebrae.

  • Sacrum: composed of fused vertebrae.

  • Coccyx: tailbone, also fused.

Abnormal Spinal Curvatures

1. Scoliosis: lateral curvature of the spine.

2. Kyphosis: excessive outward curvature, hunchback appearance.

3. Lordosis: excessive inward curvature, swayback appearance.

Cranial and Facial Bones

• Cranial Bones: occipital, parietal, frontal, temporal, sphenoid.

• Facial Bones: nasal, zygomatic, maxilla, mandible.

• Sutures: connections between cranial bones (e.g., coronal, sagital, lambdoid).

Thoracic Cage Components

• Includes the sternum and ribs (true & false ribs).

• True ribs connect directly to the sternum; false ribs connect indirectly or not at all.

The Upper Limb

• Bones include: clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, and phalanges.

• Functions and features of each bone:

  • Clavicle: collarbone, only bony connection between arm and trunk.

  • Scapula: shoulder blade, features include the glenoid fossa for humeral articulation.

Glenoid Fossa: A shallow socket located on the scapula that articulates with the head of the humerus, allowing for shoulder joint mobility.

Supraspinous Fossa: A concave area located above the spine of the scapula, serving as an attachment site for the supraspinatus muscle.

Infraspinous Fossa: A shallow cavity located below the spine of the scapula, providing attachment for the infraspinatus muscle.

Acromion Process: A bony projection on the scapula that forms the highest point of the shoulder, articulating with the clavicle.

Coracoid Process: A small hook-like structure on the scapula that serves as an attachment point for muscles and ligaments, located below the acromion.

Greater Tubercle: A prominent projection on the humerus that provides attachment for rotator cuff muscles, located on the lateral side near the head.

Deltoid Tuberosity: A roughened area on the humerus where the deltoid muscle attaches, situated on the lateral aspect of the humerus shaft.

Radial Groove: A shallow longitudinal depression on the humerus that accommodates the radial nerve, located on the posterior side of the bone's shaft.

Coronoid Fossa: A depression on the anterior surface of the humerus that receives the coronoid process of the ulna during elbow flexion.

Olecranon Fossa: A large depression on the posterior aspect of the humerus that accommodates the olecranon process of the ulna when the elbow is extended.

Trochlear Notch: A deep notch on the ulna that articulates with the trochlea of the humerus, forming the hinge joint of the elbow.

The Lower Limb

• Bones include: femur, tibia, fibula, patella.

• The tibia is the weight-bearing bone of the lower leg; the fibula supports but is not weight-bearing.

• Tibial Tuberosity: A prominent bony projection on the front of the tibia that serves as the attachment point for the patellar ligament, essential for knee extension.

• Anterior Crest: A sharp ridge located on the anterior surface of the tibia that provides structure and stability to the lower leg.

Carpal and Tarsal Bones

• Carpal Bones: proximal (scaphoid, lunate, triquetrum, pisiform) and distal rows (trapezium, trapezoid, capitate, hamate).

• Tarsal Bones: includes talus, calcaneus, cuboid, navicular, and cuneiforms.

Coxal Bones:

• Posterior Superior Iliac Spine: A bony projection on the posterior aspect of the ilium that serves as a landmark for various anatomical references; located at the back of the pelvis.

• Greater Sciatic Notch: A large indentation located on the ilium beneath the posterior inferior iliac spine that allows the passage of the sciatic nerve and other structures from the pelvis to the lower limb.

• Anterior Superior Iliac Spine: An important bony landmark at the front of the ilium that serves as an attachment point for ligaments and muscles; located at the anterior end of the iliac crest.

• Iliac Crest: The uppermost ridge of the ilium that forms the prominence of the pelvis and serves as an attachment site for the abdominal muscles and fascia; located along the top of the ilium.

• Obturator Foramen: A large opening in the pelvis formed by the ischium and pubis that is covered by a membrane and allows for the passage of nerves and blood vessels; located inferior to the acetabulum.

• Acetabulum: A deep, cup-like structure on the lateral aspect of the pelvis that articulates with the head of the femur to form the hip joint; located on the side of the pelvis.

• Ischial Tuberosity: A roughened area on the ischium that bears weight when sitting and serves as an attachment point for muscles and ligaments; located at the lower and back part of the pelvis.

• Male pelvis is generally narrower and has a more robust structure, with a larger and more prominent iliac crest.

• Female pelvis is wider and more circular to facilitate childbirth, featuring a broader pelvic inlet and a greater distance between the ischial spines.

Hormonal and Nutritional Effects on Bone

• Hormones play critical roles in bone growth and maintenance:

  • Calcitriol: The active form of vitamin D; essential for calcium absorption in the intestines and helps to maintain adequate serum calcium and phosphorus levels for normal bone mineralization.

  • Growth Hormone: Stimulates overall growth and development. It enhances the lengthening of bones during childhood and adolescence by promoting the proliferation of chondrocytes at the growth plates.

  • Sex Hormones:

    • Estrogen: In females, estrogen is crucial for bone density and helps to prevent bone loss post-menopause. It inhibits osteoclast activity, lowering the rate of bone resorption.

    • Testosterone: In males, testosterone contributes to bone density and strength by promoting osteoblast formation and function.

• Nutrients necessary for bone health include:

  • Vitamin C: Important for collagen synthesis, which provides structure and strength to bones and connective tissue.

  • Vitamin D: Works synergistically with calcium to promote bone health; enhances absorption of calcium from the gut and maintains proper blood levels of calcium and phosphate.

  • Calcium: The primary mineral found in bones; essential for maintaining bone rigidity and strength. A consistent intake of calcium is vital throughout life to support bone structure.

  • Phosphorus: Works with calcium to form hydroxyapatite, the mineral component of bone, thereby aiding in bone development and repair.

Bone Disorders & Fractures

• Osteoporosis: loss of bone density, leads to fractures.

• Osteomalacia: softening of bones due to Vitamin D deficiency.

• Rickets: A pediatric condition due to vitamin D, calcium, or phosphate deficiency, leading to weakened bones and deformities like bowed legs.

• Scurvy: Caused by vitamin C deficiency, it results in weakened collagen synthesis, leading to joint pain, bruising, and problems with bone integrity.

• Osteogenesis Imperfecta (OI): A genetic disorder of collagen defects causing fragile bones that break easily, also associated with blue sclera and dental issues.

• Osteomyelitis: A severe infection of the bone that causes pain and inflammation, potentially requiring antibiotics or surgery for persistent cases.

• Osteopetrosis: A rare disorder with excessive bone density due to dysfunctional osteoclasts, leading to brittle bones and potential nerve compression.

• Heterotopic Bone Formation: The abnormal development of bone in soft tissues, causing pain and limited movement.

• Fibrodysplasia Ossificans Progressiva (FOP): A rare genetic disorder that causes soft tissues to gradually turn into bone, particularly after minor injuries.

  • Fracture Types

    • Open: The bone breaks through the skin, increasing the risk of infection. Also known as a compound fracture, it requires surgical intervention.

    • Closed: The bone fractures without breaking the skin, meaning it is less likely to become infected. This type of fracture typically heals well with appropriate treatment.

    • Incomplete: The bone is partially fractured but not broken all the way through; often seen in children. This type usually heals quickly as the bone isn't fully separated.

    • Greenstick: A type of incomplete fracture where the bone bends and breaks on one side without breaking completely through, resembling a green twig. It is commonly observed in children due to their softer bones.

    • Complete: The bone is fractured all the way through, dividing it into two or more pieces. This type may require immobilization or surgery to ensure proper alignment during healing.

    • Communited: The bone breaks into several fragments at the fracture site. Treatment often necessitates surgical intervention to stabilize the pieces.

    • Impacted: This occurs when the ends of the broken bone are pressed together, often due to a fall from a height. It usually requires immobilization and sometimes surgical treatment to stabilize the bone.

    • Spiral: A fracture that occurs when a twisting force is applied to the bone, causing a helical break. This type often results from sports injuries or falls and can be more severe due to the nature of the injury.

• Four stages of healing:

  1. Hematoma Formation: In this initial stage, blood vessels at the fracture site break, leading to the accumulation of blood and the formation of a hematoma around the fracture.

  2. Callus Formation (Internal and External): A soft callus forms around the fracture, providing a bridge between bone ends while new bone begins to develop underneath, eventually creating both internal and external calluses.

  3. Callus Ossification: The soft callus is gradually replaced with hard bone through the process of ossification, strengthening the fracture site.

  4. Bone Remodeling: Over a period of up to a year, the new bone is reshaped and strengthened through remodeling, optimizing its strength and function.