Skeletal System: Structure, Trauma, Articulations, and Disorders

Skeletal System Study Guide

Bone Structure and Anatomy

The skeletal system is composed of various types of bones and associated structures that provide support, protection, and movement for the body. Understanding the basic anatomy of bones is essential for studying the musculoskeletal system.

• Compact bone: Dense, strong outer layer of bone that provides strength and structure.

• Spongy (cancellous) bone: Porous, lightweight bone found at the ends of long bones and inside vertebrae.

• Diaphysis: The shaft or central part of a long bone.

• Epiphysis: The rounded end of a long bone, which articulates with another bone.

• Metaphysis: The region between the diaphysis and epiphysis; site of bone growth in children.

• Endosteum: Thin membrane lining the medullary cavity of bones.

• Periosteum: Dense connective tissue covering the outer surface of bones (except at joints).

• Medullary cavity: Central cavity within the diaphysis, containing bone marrow.

• Articular cartilage: Smooth, white tissue covering the ends of bones at joints, reducing friction.

Bone Processes, Depressions, and Openings

Bones have various markings that serve as sites for muscle attachment, passage of nerves and blood vessels, and articulation with other bones.

• Foramen: Opening or passageway (e.g., foramen magnum in the skull).

• Fossa: Shallow depression (e.g., supraspinatus fossa of scapula).

• Sulcus: Groove (e.g., vascular sulcus).

• Meatus: Tube-like passageway (e.g., external auditory meatus).

• Sinus: Cavity within a bone (e.g., frontal sinus).

• Crest: Narrow ridge (e.g., iliac crest of pelvis).

• Spine: Sharp, slender process (e.g., scapular spine).

• Process: Extension or projection (e.g., spinous process of vertebrae).

• Condyle: Rounded eminence for articulation (e.g., femoral condyle).

• Epicondyle: Process above a condyle (e.g., medial epicondyle of humerus).

• Tuberosity: Large process for anchorage (e.g., tibial tuberosity).

• Tubercle: Small rounded process (e.g., greater tubercle of humerus).

• Trochanter: Very large process (e.g., greater trochanter of femur).

Appendicular Skeleton

Lower Extremity

The lower extremity includes the bones of the pelvis and legs, which support body weight and enable locomotion.

• Pelvis: Composed of ilium, ischium, and pubis. Key landmarks include:

  • Anterior superior iliac spine (ASIS)

  • Posterior superior iliac spine

  • Iliac fossa

  • Ischial tuberosity

  • Pubic symphysis

  • Acetabulum (hip socket)

• Femur: Thigh bone; features include head, neck, greater and lesser trochanters, medial/lateral condyles, and linea aspera.

• Tibia: Shin bone; features include tibial tuberosity, medial malleolus, medial/lateral condyles, and anterior crest.

• Fibula: Lateral bone of the lower leg; notable for its neck.

• Patella: Kneecap.

• Foot/Ankle: Includes calcaneus (heel), talus, navicular, cuboid, cuneiforms (medial/intermediate/lateral), metatarsals, and phalanges (proximal, middle, distal).

Upper Extremity

The upper extremity consists of the bones of the shoulder, arm, forearm, and hand, allowing for a wide range of motion and dexterity.

• Scapula: Shoulder blade; features include acromion, coracoid process, glenoid cavity, spine, supraspinous/infraspinous/subscapular fossae.

• Humerus: Upper arm bone; features include head, neck, greater/lesser tubercles, deltoid tuberosity, medial/lateral epicondyles, trochlea, capitulum, coronoid/olecranon fossae.

• Radius: Lateral forearm bone; features include head, neck, radial tuberosity, styloid process.

• Ulna: Medial forearm bone; features include head, styloid process.

• Hand/Wrist: Carpal bones (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate), metacarpals, and phalanges (proximal, middle, distal).

Axial Skeleton

Skull

The skull protects the brain and supports facial structures. It consists of cranial and facial bones with various foramina and processes.

• Frontal, Parietal, Occipital, Temporal, Sphenoid, Ethmoid: Major cranial bones with features such as foramina, processes, and fossae.

• Facial bones: Include maxilla, zygomatic, nasal, lacrimal, palatine, vomer, mandible.

• Key features: Supraorbital foramen, external auditory meatus, mastoid process, mandibular condyle, foramen magnum, occipital condyles, sella turcica, crista galli, and others.

Spine

The vertebral column supports the body and protects the spinal cord. It is divided into regions with distinct vertebrae.

• Cervical vertebrae (7): Features include vertebral body, lamina, pedicle, transverse/spinous processes, superior/inferior articular surfaces, intervertebral foramen.

• Thoracic vertebrae (12): Features include vertebral body, lamina, pedicle, articular surface for ribs.

• Lumbar vertebrae (5): Features include vertebral body, lamina, pedicle, transverse/spinous processes, superior/inferior articular surfaces, intervertebral foramen, spinal foramen.

• Sacrum: Includes superior articular facet, articular surface for ilium, body, sacral promontory, sacral foramina, sacral canal, sacral hiatus.

• Coccyx: Tailbone.

• Intervertebral disc: Composed of annulus fibrosus (outer ring) and nucleus pulposus (inner core).

• Axis (C2): Notable for dens (odontoid process).

Thorax

• Ribs (1-12): True ribs (1-7), false ribs (8-12), head, neck, tubercle, body.

• Sternum: Manubrium, body, xiphoid process, costal facets.

• Clavicle: Sternal and acromial articular surfaces.

LAB – Skeletal Trauma

Fracture Types

Bone fractures are classified based on the nature of the break and whether the skin is penetrated.

• Closed (simple): Bone does not penetrate the skin.

• Transverse: Fracture line is at a right angle to the long axis of the bone.

• Oblique: Fracture line is at an angle to the long axis.

• Spiral: Fracture line encircles the bone, often due to twisting forces.

• Fissured: Incomplete, linear split.

• Open (compound): Bone penetrates the skin.

Fracture Complications

• Arterial injury

• Compartment syndromes

• Fat embolism

• Hardware failure

• Refracture

• Degenerative joint disease

• Osteoporosis

• Nonunion/mal-union

Bone Healing Stages

• Repair: 2-3 weeks post-trauma, soft callus forms, mineralization begins, hard callus forms.

• Remodeling: 4-8 weeks post-trauma, bone is reshaped, normal contour and angulation restored.

Nutritional Support for Healing

• Calcium: 1,000-1,500 mg/day

• Magnesium: 500-750 mg/day

• Vitamin C: 500 mg/day

• Vitamin D: 400 IU/day

• Chondroitin sulphate: 500 mg/day

• Glucosamine sulphate: 1,500 mg/day

• Boron: 10 mg/day

• Green food supplements: 1 tbsp/day

LAB 9 – Articulations (Joints)

Classification by Degree of Movement

• Immovable (Synarthroses): Bones joined by fibrous connective tissue or cartilage.

  • Sutures (skull)

  • Synchondroses (epiphyseal plates in children)

  • Gomphoses (teeth in sockets)

• Slightly Movable (Amphiarthroses): Bones joined by cartilage.

  • Symphyses (pubic symphysis, intervertebral discs)

  • Syndesmoses (distal tibia/fibula)

• Freely Movable (Diarthroses/Synovial Joints): Most joints in the body; have a synovial cavity and are stabilized by ligaments and tendons.

  • Articular cartilage covers bone ends

  • Articular capsule encloses joint

  • Synovial fluid lubricates joint

Types of Freely Movable (Synovial) Joints

• Ball and socket: Multidirectional movement (e.g., shoulder, hip)

• Hinge: Movement in one plane (e.g., elbow, knee)

• Pivot: Rotation around a single axis (e.g., atlas/axis in neck)

• Gliding: Sliding movements (e.g., intercarpal joints)

• Saddle: Both concave and convex areas (e.g., thumb)

• Movement but no rotation (e.g., wrist)

Knee Joint Anatomy

• Anterior cruciate ligament (ACL)

• Posterior cruciate ligament (PCL)

• Lateral (fibular) collateral ligament

• Medial (tibial) collateral ligament

• Lateral and medial meniscus (fibrocartilaginous pads)

• Transverse ligament (connects menisci)

• Patellar ligament

• Quadriceps tendon

• Suprapatellar bursa

Arthritic Disorders

Arthritis refers to inflammation of the joints, with several types based on etiology and clinical features.

• Osteoarthritis (OA): Degenerative, non-inflammatory, "wear and tear" type affecting articular cartilage.

• Rheumatoid Arthritis (RA): Systemic, autoimmune, inflammatory disorder affecting synovial tissue.

• Gout: Metabolic disorder due to purine metabolism, resulting in deposition of sodium urate crystals in joints.

Classification of Arthritis (Table)

The following table summarizes the classification of arthritis based on the number of joints involved and etiology:

Type	Monoarthritis	Polyarthritis
Inflammatory	Traumatic, Infective, Crystal-induced (gout), Rheumatoid (rare), Degenerative	Rheumatoid types (symmetric, small joints), Systemic lupus erythematosus
Degenerative	Primary osteoarthrosis (joint swelling)	Primary/Secondary osteoarthrosis, Lumpy bony joint deformity
Metabolic	Gout	Gout (multiple joints)
Rheumatoid Variants	Large joints, asymmetric	Ankylosing spondylitis, Psoriatic arthritis

Additional info: Polyarthritis involves more than four joints, while monoarthritis affects a single joint. Rheumatoid arthritis typically presents as a symmetric polyarthritis, while gout often presents as monoarthritis of the big toe (podagra).