Introduction to Osteology & Arthrology

Introduction to Osteology

• The Human Skeleton
• Bilaterally Symmetrical
• Endoskeleton
• Divided into axial skeleton - vertebral column, skull, ribs and sternum
• …and Appendicular Skeleton - pectoral and pelvic girdles and bones of Upper Limb & Lower Limb

Bone Tissue

• Bones differ macroscopically but are similar microscopically
• Bone tissues are classified as a specialised form of Connective Tissue and consists of a blend of:
• Organic components
• Collagen - provides pliability and resists tensile forces
• Cells - continual building and resorption of bone tissue

• Inorganic components:
• Ca salts provide rigidity and compressive strength
• Microscopic appearance may vary with age - balance of organic and inorganic content changes….
• (Young bones - not yet mineralised - pliable / Old bones - ↓ mineralised tissue mass - weak & brittle)
• All bones are formed from differing amounts of connective tissues
• Perosteum - external fibrous tissue covering for nutrition and attachment of soft tissue structures
• Endosteum - loose areolar tissue found in cavities of some bones
• Bone Tissue Proper:
• Compact bone - dense, hard layer of bone (external)
• Spongy (Trabecular) bone - light framework of bone filaments (internal)
• Trabeculae arranged along lines of stress
• Macroscopic (gross) appearance of bones vary from one to the next
• Influenced by:
• Genetics - role of DNA etc.
• Metabolism and nutrition
• Function and mechanical stress
• All bones will have:
• Articular surfaces - usually smooth and at ends of bone to form joints
• Identifiable prominences - ridges, crests, tubercles and tuberosity - points of attachment for ligaments, muscles, tendons etc.

Anatomical Classification

• According to gross shape:
• Long bones - diaphysis (shaft) and epiphysis (expanded ends)
• Short bones - small, regular shape (e.g. carpus and tarsus)
• Irregular bones - many exaggerated prominences (e.g. vertebrae)
• Flat bones - thin and curved around body (e.g. scapula, skull, ribs)
• Sesamoid bones - small and regular shaped - situated in tendons or ligaments at sites of stress

Functions of Bone

• Protection - body organs (e.g. skull, ribs)
• Support - suspension and attachment of soft tissue structures (e.g. muscles, ligament, thoracic structures)
• Permit Movement - joint formation and muscle attachment
• Blood Formation - marrow cavities of long bones
• Storage - fat and can act as reserves of Ca when needed
• Bone is a living tissue & requires a blood supply via the Nutrient Artery
• and a nerve supply - small sensory supply for pain (mostly in periosteum) 

Introduction to Arthrology

• Joints are formed when 2 or more bones come together 
• Role of joints is to allow movement (to varying degrees)
• The design of a joint will relate to its function

Primary Classification

• Joints are primarily classified according to tissue filling joint space:
• Fibrous
• Cartilaginous
• Synovial
• Each class has its sub classifications

Secondary Classification - Fibrous Joints

• Suture - Joint surfaces are serrated and close fitting (e.g. cranial sutures united by layer of fibrous tissue)
• Role is developmental and allow deformation of head during birth - usually disappear in 3^rd or 4^th decades
• Gomphosis - Peg & socket arrangement - fibrous ligament holds peg in socket e.g. teeth
• Syndesmosis - plane joint surfaces united by inter-osseous ligament e.g. inferior tibio-fibular joint

Secondary Classification - Cartilaginous

• Pad of Cartilage interposed between bone segments

• Primary Cartilaginous (Synchondrosis)

• Role is for longitudinal growth of bones
• Hyaline cartilage between bone ends
• No appreciable movement (e.g. Epiphyseal plates)

• Secondary Cartilagenous (Symphysis)

• Lie in midline of body
• Bone ends covered in hyaline cartilage, fibrocartilage pad interposed between joint surfaces
• Reinforced by ligaments, permit motion but very stable

Secondary Classification – Synovial Joints

• Majority of body joints are synovial
• Extremely mobile - motion limited by tension in overlying structures or apposition of anatomical structure
• Chief Characteristics
• Articular surfaces covered in Hyaline Cartilage for weight bearing and reduce friction between bones
• Fibrous Capsule attached to or just beyond articular margins
• Synovial Membrane attached to articular margins, lines capsule and covers any intra-articular bone. Highly vascular
• Joint Cavity
• Ligaments provide stability - may be thickenings in capsule or separate from capsule
• Bursae - occasional synovial pouches form outside the boundaries of the capsules - reduce friction or pressure
• Synovial Fluid is secreted by the Synovial Membrane - nutritional and lubricant
• Occasional intra-articular fibrocartilage Disc or Meniscus - role is to increase congruency and dissipate weight

Movements

• Role of synovial joints is to permit movement. Normal joint motion may occur:
• Actively - due to muscle contraction
• Passively - due to external forces (e.g. PT, gravity etc)
• Movements possible at a joint:
• Physiological - movements which can be produced actively (e.g. flexion / extension)
• Accessory - movements which cannot be produced in isolation by primary muscle action (e.g. AP / PA glides, distraction)
• Note: Accessory motion may occur during and are essential for a physiological motion 
• Close Packed vs Loose Packed position - position of greatest Stability vs Instability 

Secondary Classification - Synovial Joints

• Synovial Joints are subclassified according to the shape of Articular Surfaces:
• Ball & Socket - permit multiaxial motion - e.g. hip, shoulder
• Condyloid - modified B & S joint -
• Permit active motion about 2 axes…
• Passive motion may occur about 3^rd axis - e.g. MCP joints 
• Ellipsoid - another form of B & S joint - biconcave component is elliptical in shape
• Active motion about 2 axes - e.g. wrist (radiocarpal) joint 
• Hinge - permit uniaxial motion
• Often associated with good articular fit and strong collateral ligaments - e.g. elbow joint
• Pivot - permit rotation about long axis of bone
• Associated with bone moving within osseo-fibrous ring - e.g. superior radio-ulnar joint
• Plane - joint surfaces are flat (or close to it)
• Permit gliding or twisting motion - e.g. Acromio-Clavicular joint
• Saddle - reciprocally CONCAVO-CONVEX articular surfaces
• Permit active biaxial motion - e.g. 1^st carpo-metacarpal joint

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