5. CLASSIFICATION, TYPES AND MOVEMENTS OF JOINTS, DISORDERS OF JOINTS

JOINTS (ARTICULATIONS)

The site where more than two bones meet to carry out the movement is known as a joint or articulation. There are movable and non-movable joints in the body. Only the movable joints allow different kinds of movements. The structure of the joint is the governing factor for the type, direction, and degree of movement. The joints serve a dual purpose, i.e., holding of bones together as well as allowing skeletal movement. The hyoid bone present in the neck is the only one which does not articulate with any of the bones.

CLASSIFICATION OF JOINTS

Functional Classification

Type	Synonyms	Mobility	Examples
Synarthrosis	Immovable	No mobility	Cranial sutures in adults, primary cartilaginous joints in growing children
Amphiarthrosis	Slightly movable	Some degree of mobility	Secondary cartilaginous joints, syndesmosis
Diarthrosis	Freely movable	Maximum degree of mobility	Synovial joints

Structural Classification

1. Fibrous joint (Immovable)
2. Cartilaginous joint (Slightly movable)
3. Synovial joint (Freely movable)

FIBROUS JOINTS

Fibrous joints join bones by fibrous connective tissue. There is no or very less degree of movement in these joints. The joint cavity is absent in the fibrous joints.

Types of Fibrous Joints

1. Sutures: Thin layer of connective tissue (sutural ligaments) connects articulating surfaces. Present only in skull; immovable. Sub-types: plane suture, serrate suture, denticulate suture, squamous suture, schindylesis.
2. Syndesmosis: Linking of two adjacent bones by considerable amount of connective tissue (interosseous ligaments and membranes). Permit slight movement. Examples: interosseous joints of radio-ulna and tibia-fibula, joints between adjacent laminae of vertebrae.
3. Gomphoses (Peg and Socket Joint): Special type of fibrous joint involved in fixing of teeth (peg) in alveolar sockets of maxillae and mandible.

CARTILAGINOUS JOINTS

In cartilaginous joints, the bones are attached to each other by hyaline cartilage or fibrocartilage. These joints are devoid of the joint cavity.

Types of Cartilaginous Joints

1. Primary Cartilaginous Joints (Synchondrosis): Bones joined by plate of hyaline cartilage; immovable; mostly temporary. Examples: sphenoccipital joint, first costosternal joint, joint between epiphysis and diaphysis of growing long bone.
2. Secondary Cartilaginous Joints (Symphysis): Bones joined by thin plates of hyaline cartilage; slightly movable. Examples: intervertebral discs, symphysis pubis.

SYNOVIAL JOINTS

Synovial joints (diarthrodial joints) are freely movable joints. They have a cavity enclosed in a fibrous capsule, containing synovial fluid. Articular surfaces are covered by hyaline cartilage.

Types of Synovial Joints

Joint Type	Examples	Description	Mobility
Ball and Socket	Shoulder, Hip	Ball-shaped head articulates with cup-like socket	Movement in three planes; greatest range of movement
Hinge	Elbow, Knee, Ankle	Cylindrical protrusion articulates with trough-shaped depression	Movement restricted to one plane (bending and straightening)
Pivot	Spine (Atlas-Axis), Radius-Ulna	Rounded structure articulates with ring-shaped structure	Rotation about longitudinal axis only
Condyloid	Wrist	Similar to ball and socket but with flatter surfaces	Movement in two planes; second greatest range
Gliding	Spine (between vertebrae)	Almost flat articulating surfaces of similar size	Movement in three planes but severely limited
Saddle	Thumb	One part concave (like saddle), other convex (like rider)	Flexion-extension and abduction-adduction

MOVEMENTS OF JOINTS

1. Gliding: Simplest motion; flat bone glides over other bone without angular or rotary motion.
2. Angular: Angle between two adjacent bones is decreased or increased.
   • Flexion: Decreases joint angle (e.g., bending trunk or knee).
   • Extension: Increases joint angle (e.g., straightening after flexion).
   • Abduction: Movement away from median plane (e.g., spreading fingers).
3. Rotation: Bone turns along its own axis (e.g., atlas-axis joint).
4. Circumduction: Movement in circular direction (360°).

DISORDERS OF JOINTS

Rheumatoid Arthritis

Rheumatoid arthritis is a chronic, progressive inflammatory musculoskeletal disorder affecting multiple joints, connective tissues, muscles, tendons, and fibrous tissues.

Causes of Rheumatoid Arthritis

• Genetic sensitivity
• Immunological reaction to synovial tissue
• Inflammation in tendon sheaths and joints
• Expression of rheumatoid factors
• Prolonged inflammatory reaction
• Destruction of articular cartilage
• Smoking and obesity

Signs and Symptoms of Rheumatoid Arthritis

• Articular: Synovitis, pain and stiffness in wrists and finger joints, joint swelling, synovial thickening, osteoporosis.
• Extra-Articular: Cardiac (pericarditis), haematological (amyloidosis), nervous (neuropathy), pulmonary (interstitial lung disease), skin (rheumatoid nodules).
• Systemic: Fatigue, weight loss, low-grade fever, depression.

Gout

Gout is a heterogeneous group of diseases characterised by increased serum uric acid and deposition of urate crystals in joints and kidneys, with acute or chronic arthritis.

Causes of Gout

• Primary Gout: Unknown cause; genetic and environmental factors implicated in purine metabolism defect.
• Secondary Gout: Underlying disease (hypertension, diabetes, renal disease) or side effect of drugs (hydrochlorothiazide, pyrazinamide, low-dose aspirin).

Stages of Gout

1. Asymptomatic Stage: Hyperuricemia without pain.
2. Acute Stage: Monoarticular acute attack (often metatarsophalangeal joint); severe pain, redness, inflammation.
3. Inter-Critical Stage: Asymptomatic period between attacks.
4. Chronic Stage: Hyperuricemia, chronic arthritis, tophus formation, recurrent attacks.

Osteoarthritis

Osteoarthritis (degenerative arthritis) involves inflammation, pain, and degeneration of joints due to deterioration of cartilage. Commonly affected areas: hands, fingertips, knees, hips, spine.

Causes of Osteoarthritis

• Hereditary/genetic factors
• Injury
• Inflammatory diseases
• Tendonitis and bursitis
• Injury to protective cartilage
• Development of bone spurs

Signs and Symptoms of Osteoarthritis

• Pain
• Tenderness
• Stiffness
• Inflammation

Osteoporosis

Osteoporosis means “porous bone.” It is a bone-weakening illness causing loss of bone mass and strength, leading to increased risk of fractures (hip, wrist, spine).

Risk Factors for Osteoporosis

• Sex: Women more likely than men
• Age: Risk increases with age
• Race: Asian or White heritage
• Family History: Parent or sibling with osteoporosis
• Body Frame Size: Small physical frames

Signs and Symptoms of Osteoporosis

• Kyphosis (stooped posture)
• Weight loss over time
• Bone breaks more frequently or easily
• Bone tissue loss leading to fragility
• Frequent back pain