Explanation:
Correct Option: C. The posterior wall is the most frequently fractured region of the acetabulum, commonly occurring secondary to a posteriorly directed force on a flexed knee (the classic dashboard injury mechanism). The decision to pursue operative fixation versus non-operative management is primarily dictated by the resultant stability of the hip joint. Extensive clinical and biomechanical studies have demonstrated that posterior wall fractures involving less than 20% of the articular surface are typically stable, whereas those involving greater than 20% to 25% predictably lead to catastrophic posterior instability of the femoral head and definitively require open reduction and internal fixation (ORIF). Dynamic stress fluoroscopy can be utilized to definitively assess borderline cases (fragment sizes falling between 20-40%). (Ref: Letournel and Judet, Fractures of the Acetabulum; Moed et al., J Bone Joint Surg Am, 2000)