According to the classic safe zone described by Lewinnek for acetabular component orientation in total hip arthroplasty, the target ranges are:

• A Abduction 40 plus or minus 10 degrees, anteversion 15 plus or minus 10 degrees ✓
• B Abduction 45 plus or minus 5 degrees, anteversion 25 plus or minus 5 degrees
• C Abduction 35 plus or minus 10 degrees, anteversion 20 plus or minus 15 degrees
• D Abduction 50 plus or minus 5 degrees, anteversion 10 plus or minus 5 degrees

Explanation

Lewinnek described the safe zone as 40 plus or minus 10 degrees of abduction (inclination) and 15 plus or minus 10 degrees of anteversion; components outside this range carry higher dislocation risk. Excessive abduction increases edge loading and wear, while insufficient abduction permits impingement and dislocation in adduction. This remains the standard figure quoted in Indian postgraduate examinations even though contemporary practice sometimes targets slightly lower inclination with larger heads.

Reference: Miller's Review of Orthopaedics, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.