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Pathology - Osteoarthritis
I. Definition & Epidemiology:
I. Definition & Epidemiology:
- Definition: Osteoarthritis (OA) is a group of diseases causing joint degradation. Crucially, it's not a single disease but a collection of similar conditions.
- Epidemiology: OA is the most common joint disease. In the UK, approximately 2 million people experience symptomatic OA. It primarily affects the elderly population.
- Primary OA: In most cases, the cause of OA is unknown (primary OA). This highlights the complexity of the disease and the challenges in pinpointing a single cause.
- Secondary OA: OA can also develop as a consequence of other joint disorders (secondary OA). Examples include rheumatoid arthritis and gout, where pre-existing joint damage sets the stage for OA development. Understanding this distinction is vital – treatment differs depending on the underlying cause.
- Cartilage Damage: The primary pathological change is damage to the articular cartilage, the smooth tissue covering joint surfaces. This damage is central to understanding OA's progression.
- Inflammation & Metalloproteinases: Low-grade inflammation within the joint plays a crucial role. This inflammation causes chondrocytes (cartilage cells) to release metalloproteinases, enzymes that break down the cartilage matrix, leading to further cartilage loss.
- Subchondral Bone Response: As cartilage is lost, the underlying bone becomes exposed. The bone responds by thickening (sclerosis) – a compensatory but ultimately unhelpful response. This bone thickening contributes to the pain and stiffness experienced by patients.
- Pain, Tenderness, Stiffness: The classic symptoms are pain, tenderness, and stiffness in the affected joint(s). It's important to note that symptom severity varies greatly between individuals.
- Activity-Related Worsening: Symptoms typically worsen throughout the day, particularly with increased activity. This contrasts with some other inflammatory arthritides where stiffness is worse in the morning.
- Commonly Affected Joints: OA most commonly affects the hip, knee, spine, and small joints of the hands, but it can affect any joint. Knowing the typical locations helps in differential diagnosis.
- Cartilage Loss & Thinning: Microscopic examination reveals thinned and lost articular cartilage. This confirms the central role of cartilage degeneration in the disease process.
- Subchondral Bone Sclerosis: Thickening and sclerosis (increased density) of the subchondral bone are also observed. This supports the clinical observation of bone changes in OA.
- Progressive Worsening: OA generally worsens over time. This emphasizes the need for early diagnosis and management to slow progression.
- Analgesics & Joint Replacement: Management typically involves analgesics (pain relievers) to manage symptoms. In severe cases, joint replacement surgery may be necessary. This highlights the potential long-term impact of the disease.
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