Joints

JOINTS

INTRODUCTION

A joint (articulation) is any connection between bones. Joints allow varying degrees of movement and are composed of bone ends plus connective tissues (cartilage, ligaments, tendons).

• Tendons attach muscle to bone.
• Ligaments connect bone to bone.
• Cartilage cushions and reduces friction at joint surfaces.

The study of joints is called arthrology.

CLASSIFICATION OF JOINTS

Joints are classified structurally and functionally. Structurally:

• Fibrous joints (synarthroses) - bones joined by fibrous tissue; little or no movement.
• Cartilaginous joints (amphiarthroses) - bones joined by cartilage; limited movement.
• Synovial joints (diarthroses) - freely movable joints with a synovial cavity.

FIBROUS JOINTS (SYNARTHROSES)

• Immovable or very limited movement.
• Examples: sutures of the skull, gomphosis (tooth in socket).

CARTILAGINOUS JOINTS (AMPHIARTHROSES)

• Bones united by hyaline cartilage or fibrocartilage.
• Examples: intervertebral discs (fibrocartilage), pubic symphysis; allow limited movement and absorb shock.

SYNOVIAL JOINTS (DIARTHROSES)

Freely movable joints with common features:

• Articular surfaces covered by hyaline (articular) cartilage.
• Bones held together by ligaments.
• Enclosed by a fibrous capsule lined internally by a synovial membrane.
• Joint cavity contains synovial fluid for lubrication.
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Types of Synovial Joints and Examples

MOVEMENTS OF JOINTS

Joints permit various movements described by directional terms:

Gliding Movements

• Two relatively flat surfaces slide past one another (e.g., between carpal bones).

Angular Movements

• Flexion: Decreases the angle between bones (bending elbow).
• Extension: Increases the angle (straightening elbow).
• Abduction: Movement away from midline (raising arm laterally).
• Adduction: Movement toward midline (lowering arm toward body).
• Circumduction: Circular movement combining flexion, extension, abduction and adduction.

Rotational Movements

• Medial (internal) rotation: Turning a limb toward the midline.
• Lateral (external) rotation: Turning a limb away from midline.
• Pronation / Supination (forearm): Pronation turns palm posteriorly/downward; supination turns palm anteriorly/upward.

JOINTS OF THE UPPER LIMB

Sternoclavicular Joint

• A gliding joint between sternum and clavicle; includes a cartilage pad for shock absorption. Supports wide shoulder movement.

Acromioclavicular Joint

• Between acromion of scapula and lateral clavicle; has limited motion and helps scapular rotation.

Shoulder (Glenohumeral) Joint

• A ball-and-socket joint: head of humerus in glenoid cavity.
• Very mobile, stabilized by rotator cuff muscles, ligaments and capsule.
• Permit flexion, extension, abduction, adduction, rotation, circumduction.

Elbow Joint

• Primarily a hinge joint between humerus, radius and ulna.
• Components: humero-ulnar, humero-radial and superior radioulnar articulations.
• Movements: flexion and extension.

Radio-ulnar Joints

• Proximal and distal radioulnar joints allow pronation and supination of the forearm via pivot-like movement of radius around ulna.

Wrist Joint (Radiocarpal)

• A condyloid joint between distal radius and proximal carpal bones (mainly scaphoid and lunate).
• Movements: flexion, extension, abduction (radial deviation), adduction (ulnar deviation).

Metacarpophalangeal & Interphalangeal Joints

• MCP joints are condyloid allowing flexion/extension, abduction/adduction.
• IP joints are hinge joints allowing flexion and extension.

JOINTS OF THE LOWER LIMB

Hip Joint

• A deep ball-and-socket joint: head of femur in acetabulum; deeper socket than shoulder, making it more stable but less mobile.
• Reinforced by strong ligaments (iliofemoral, pubofemoral, ischiofemoral).
• Movements: flexion, extension, abduction, adduction, rotation, circumduction.

Knee Joint

• The largest, most complex hinge joint; consists of femorotibial and femoropatellar articulations.
• Important structures:
• Menisci (medial & lateral): semilunar cartilages that deepen the tibial surface and absorb shock.
• Cruciate ligaments (ACL & PCL): control anterior-posterior stability and rotational movement.
• Collateral ligaments: stabilize medial and lateral sides.
• Largest synovial membrane with bursae around the joint.

Movements: Flexion and extension (with slight rotation when flexed).

Ankle Joint (Talocrural)

• A hinge joint formed by tibia, fibula and talus.
• Stabilised by medial (deltoid) and lateral ligament complexes.
• Movements: dorsiflexion (toes toward shin) and plantarflexion (pointing foot downward).

JOINTS OF THE FOOT

• Tarsal joints: Gliding joints among tarsals (talus and calcaneus bear most weight).
• Tarsometatarsal joints: Slight gliding movements that help foot stiffness or flexibility.
• Metatarsophalangeal joints: Allow flexion/extension and some abduction/adduction.
• Interphalangeal joints: Hinge joints allowing flexion/extension of toes.

DISORDERS OF JOINTS

ARTHRITIS

General term for inflammation of joints. Common in middle and older age but may occur at any age.

• Rheumatoid arthritis (RA)
• An autoimmune polyarthritis often affecting small joints (hands, feet).
• Characterised by inflammation of the synovial membrane, pain, stiffness, progressive joint deformity, and systemic symptoms (e.g., fever).
• Management commonly includes anti-inflammatory drugs, disease-modifying agents and physiotherapy.
• Osteoarthritis (OA)
• Degenerative “wear-and-tear” disease of articular cartilage.
• Cartilage thins, bone surfaces may rub together causing pain, stiffness and reduced movement.
• Conservative management: physiotherapy, weight reduction, analgesics; severe cases may require joint replacement.

GOUT

• Caused by deposition of uric acid (sodium urate) crystals in joints and soft tissues.
• Presents as acute painful inflammatory attacks (commonly first metatarsophalangeal joint, ankle, knee).
• Related to high uric acid—due to overproduction or reduced excretion. Long-term management aims to lower uric acid levels.

DISLOCATIONS

• Occur when joint surfaces are completely displaced, often tearing the joint capsule and ligaments.
• Common sites: shoulder, hip (posterior most common), elbow.
• Require prompt reduction (medical) and rehabilitation.

KNEE SPECIFIC DISORDERS

• Slipped (torn) meniscus: Injury or detachment of semilunar cartilage causing pain, locking or restricted movement.
• Acute synovitis: Inflammation of synovial membrane after trauma, causing swelling (notably around the knee).
• Bursitis: Inflammation of bursae (fluid-filled sacs), commonly prepatellar bursitis (in front of the kneecap) causing swelling and pain.

BASIC PRINCIPLES OF JOINT CARE AND MANAGEMENT (GENERAL GUIDANCE)

• Maintain healthy body weight to reduce joint load.
• Regular exercise (strengthening, flexibility) to maintain joint function.
• Early medical evaluation for persistent joint pain, swelling, or deformity.
• Use of supportive aids (splints, braces) and physiotherapy for rehabilitation.
• Referral to specialists (orthopaedics, rheumatology) when needed.