In total hip arthroplasty, placement of the acetabular component within the classically described 'safe zone' reduces the risk of dislocation. According to Lewinnek, this safe zone corresponds to:

• A Abduction 30 degrees plus or minus 5 degrees, anteversion 20 degrees plus or minus 5 degrees
• B Abduction 35 degrees plus or minus 15 degrees, anteversion 10 degrees plus or minus 5 degrees
• C Abduction 45 degrees plus or minus 5 degrees, anteversion 25 degrees plus or minus 10 degrees
• D Abduction 40 degrees plus or minus 10 degrees, anteversion 15 degrees plus or minus 10 degrees ✓

Explanation

Lewinnek described the safe zone as 40 degrees plus or minus 10 degrees of abduction (inclination) and 15 degrees plus or minus 10 degrees of anteversion. Cups placed outside these limits have a significantly higher dislocation rate. Excessive abduction increases lateral edge loading and impingement, while retroversion predisposes to posterior dislocation. The other options shift both parameters outside the published range and are not supported by the original radiographic study of cup position.

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

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Written and medically reviewed by the StethoPrep medical team.