Lewinnek’s ‘safe zone’ for acetabular component positioning in total hip arthroplasty was historically established via radiographic analysis to minimize the catastrophic risk of postoperative dislocation. What are the exact angular parameters that define this classic zone?

Explanation:
The correct option is d. In 1978, Lewinnek et al. published a landmark paper analyzing the relationship between acetabular cup orientation and dislocation rates. They defined a 'safe zone' target of 40 degrees of inclination (abduction) with an acceptable variance of plus or minus 10 degrees, combined with 15 degrees of anteversion with an acceptable variance of plus or minus 10 degrees. While modern biomechanical modeling and spinopelvic dynamic analysis have proven that many hips still dislocate even when placed strictly within this zone, it remains the foundational target framework taught globally for baseline primary THA component orientation. Reference: Lewinnek GE et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am.