## Most Common Sites of Osteoarthritis in Lower Limb **Key Point:** The knee is the most frequently affected weight-bearing joint in osteoarthritis, followed by the hip and then the spine. ### Why the Knee is Most Common 1. **Weight-bearing load** — The knee bears 3–6× body weight during walking and stair climbing, making it highly susceptible to degenerative changes. 2. **Biomechanical vulnerability** — The knee joint has less inherent stability than the hip and relies heavily on muscular support and ligaments. 3. **Prevalence data** — Radiographic knee OA affects 10–15% of adults >60 years; symptomatic knee OA is the leading cause of disability in older adults. ### Frequency Hierarchy in OA | Site | Frequency | Notes | |------|-----------|-------| | **Knee** | Most common (40–50% of all OA) | Weight-bearing, high mechanical stress | | **Hip** | Second most common (20–30%) | Weight-bearing, but more stable joint | | **Spine (cervical/lumbar)** | Common (30–40%) | Often asymptomatic; high prevalence on imaging | | **Ankle** | Uncommon (5–10%) | Usually post-traumatic | | **Subtalar joint** | Rare | Rarely affected in primary OA | **Clinical Pearl:** Knee OA is the most common reason for total joint replacement in the world, reflecting both its frequency and functional impact. **High-Yield:** In NEET PG, when asked about the "most common site" of primary OA without further specification, the answer is **knee**, followed by hip and spine.
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