## Most Common Site of Hip Osteoarthritis ### Anatomical Distribution **Key Point:** The superolateral aspect of the femoral head is the most common site of osteoarthritis in the hip joint, accounting for approximately 70–80% of primary hip OA cases. ### Why Superolateral? The superolateral region bears the greatest load during weight-bearing and bipedal locomotion. This area experiences the highest contact pressures during standing, walking, and climbing stairs. ### Biomechanical Basis 1. **Load distribution**: The superolateral quadrant of the femoral head articulates with the superolateral acetabulum, which is the primary weight-bearing zone. 2. **Shear forces**: Maximum shear and compressive forces concentrate in this region during normal gait. 3. **Cartilage thickness**: Although cartilage is thicker superolaterally, chronic repetitive stress leads to progressive degeneration. ### Progression Pattern | Stage | Location | Features | |-------|----------|----------| | Early OA | Superolateral femoral head | Focal cartilage loss | | Moderate OA | Extends to superolateral acetabulum | Osteophyte formation | | Advanced OA | Entire weight-bearing surface | Bone-on-bone contact | **Clinical Pearl:** Patients with superolateral hip OA typically present with groin pain and limited internal rotation, reflecting the anatomical distribution of cartilage loss. **High-Yield:** In imaging (X-ray, MRI), look for joint space narrowing and osteophytes at the superolateral pole—this is the classic pattern of primary hip osteoarthritis.
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