Anatomy of Joints
Structure of a Synovial Joint
Synovial joints are the most common type of joint in the body and allow for a wide range of motion. Their key structures include:
- Articular Cartilage: A smooth, white, resilient tissue that covers the ends of bones. It provides a low-friction surface for movement and acts as a shock absorber.
- Synovial Membrane: The inner lining of the joint capsule that secretes synovial fluid.
- Synovial Fluid: A viscous fluid that lubricates the joint and nourishes the articular cartilage.
- Joint Capsule: A fibrous sac that encloses the joint, providing stability.
- Ligaments: Tough, fibrous bands that connect bone to bone, further stabilizing the joint.
- Tendons: Fibrous cords that connect muscle to bone, enabling movement.
Inflammatory Joint Disorders
Rheumatoid Arthritis (RA)
Pathophysiology: RA is a chronic, systemic autoimmune disease characterized by symmetrical, destructive polyarthritis. The immune system mistakenly attacks the synovial membrane, causing chronic inflammation (synovitis). This leads to the formation of an aggressive, invasive tissue called pannus, which erodes and destroys articular cartilage and bone, resulting in joint deformities and loss of function. The presence of autoantibodies like Rheumatoid Factor (RF) and anti-CCP is common (seropositive RA).
Clinical Features: Symmetrical swelling, pain, and prolonged morning stiffness (>30 mins) in small joints (hands, wrists, feet). Systemic symptoms like fatigue and malaise are common. Characteristic deformities include ulnar deviation, boutonnière, and swan-neck deformities.
Seronegative Spondyloarthropathies
A group of inflammatory disorders that primarily affect the axial skeleton (spine) and are negative for RF and anti-CCP. The hallmark is enthesitis, inflammation where ligaments and tendons attach to bone.
- Ankylosing Spondylitis (AS): Primarily affects the sacroiliac joints and spine, leading to progressive stiffening and fusion ("bamboo spine"). Presents with chronic inflammatory low back pain that improves with activity.
- Reactive Arthritis: Arthritis that develops following an infection elsewhere in the body (typically GIT or urogenital). Often presents with the triad of arthritis, urethritis, and conjunctivitis.
- Psoriatic Arthritis (PsA): Inflammatory arthritis associated with the skin condition psoriasis. Can affect peripheral and axial joints, and is often associated with nail changes (pitting) and dactylitis ("sausage digits").
Degenerative and Metabolic Disorders
Osteoarthritis (OA)
Pathophysiology: OA is a degenerative "wear-and-tear" condition characterized by the progressive loss of articular cartilage. This leads to friction between the bones, causing pain and restricted movement. The underlying bone responds by forming bony spurs (osteophytes) and subchondral cysts. Inflammation is secondary to the mechanical damage.
Clinical Features: Asymmetrical joint pain that is worse with activity and relieved by rest. Morning stiffness is brief (<30 mins). Commonly affects large weight-bearing joints (hips, knees) and small joints of the hands (DIPs - Heberden's nodes, PIPs - Bouchard's nodes).
Gout
Pathophysiology: A form of inflammatory arthritis caused by hyperuricemia (high levels of uric acid in the blood). When uric acid levels are too high, it can precipitate as monosodium urate crystals in joints. These sharp crystals trigger an intense inflammatory response, leading to an acute gout flare.
Clinical Features: Sudden onset of severe pain, redness, swelling, and tenderness in a single joint, most classically the metatarsophalangeal joint of the big toe (podagra). Chronic gout can lead to the formation of tophi (deposits of urate crystals in soft tissues).
Osteoporosis
Pathophysiology: A metabolic bone disease characterized by low bone mass and micro-architectural deterioration, leading to increased bone fragility. It occurs when bone resorption by osteoclasts outpaces bone formation by osteoblasts. Postmenopausal estrogen deficiency is a major cause.
Clinical Features: Known as a "silent disease" as it is asymptomatic until a fragility fracture occurs. Common fracture sites are the vertebra (compression fracture), hip, and wrist.
Musculoskeletal Injuries
| Injury | Description | Common Locations & Features |
|---|---|---|
| Sprain | An injury to a ligament caused by overstretching or tearing. Graded I (stretch), II (partial tear), or III (complete tear). | Ankle: Most common, usually an inversion injury affecting the lateral ligaments. Knee: Often involves the ACL, PCL, MCL, or LCL. |
| Strain | An injury to a muscle or tendon caused by overstretching or excessive contraction. | Hamstrings, Back Muscles: Acute strains are common. Chronic overuse can lead to tendinosis (e.g., tennis elbow, Achilles tendinopathy). |
| Dislocation | Complete displacement of the articular surfaces of a joint. A subluxation is a partial dislocation. | Shoulder: Most commonly dislocated major joint, usually anteriorly. Causes severe pain, deformity, and loss of function. |
| Fracture | A break in the continuity of a bone. Can be classified as open (compound) or closed (simple), and by the pattern of the break (e.g., transverse, spiral, comminuted). | Presents with pain, swelling, deformity, crepitus, and loss of function. Healing involves hematoma formation, callus formation, and bone remodeling. |
Management Principles (RICE/MEAT)
RICE (Rest, Ice, Compression, Elevation) is the traditional approach for acute soft tissue injuries to limit swelling and inflammation.
MEAT (Movement, Exercise, Analgesia, Treatment) is an alternative protocol, particularly for ligament/tendon injuries, that emphasizes early, controlled movement to promote optimal healing.
Muscle Disorders
| Disorder | Pathophysiology | Key Clinical Features |
|---|---|---|
| Fibromyalgia | A chronic disorder of pain regulation, considered a central sensitization syndrome. There is no peripheral tissue damage or inflammation. | Widespread musculoskeletal pain, fatigue, non-restorative sleep, and cognitive disturbances ("fibro fog"). Characterized by multiple tender points on physical exam. |
| Myasthenia Gravis (MG) | An autoimmune disorder where antibodies block or destroy acetylcholine receptors at the neuromuscular junction, impairing nerve impulse transmission to muscles. | Fluctuating, fatigable muscle weakness that worsens with activity and improves with rest. Often presents initially with ocular symptoms (ptosis, diplopia). |
| Muscular Dystrophies | A group of genetic diseases characterized by progressive degeneration and weakness of skeletal muscles. Duchenne Muscular Dystrophy (DMD) is the most common and severe form, caused by a lack of the protein dystrophin. | Progressive muscle wasting and weakness, starting in the proximal muscles. Children with DMD often exhibit a characteristic Gowers' sign (using hands to "walk" up their legs to stand). |