In total hip arthroplasty (THA), the acetabular component is placed at a target inclination (abduction angle) and anteversion. The 'safe zone' described by Lewinnek is:

• A Inclination 40–60° and anteversion 10–30°
• B Inclination 20–40° and anteversion 0–10°
• C Inclination 50–70° and anteversion 15–35°
• D Inclination 30–50° and anteversion 5–25° ✓

Explanation

Lewinnek et al. (1978) defined the 'safe zone' for acetabular component placement to minimise dislocation risk: cup abduction (inclination) of 40±10° (i.e., 30–50°) and cup anteversion of 15±10° (i.e., 5–25°). Cups outside this zone have significantly higher dislocation rates. More recent literature suggests the concept of a patient-specific 'combined anteversion' (cup + stem anteversion targeting ~35–40°) is more accurate than the Lewinnek safe zone alone, particularly given variation in spinopelvic mobility. Nonetheless, Lewinnek's classic safe zone remains the standard NEET examination reference.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.