Acetabular Screw Placement and Safe Zones Draw quadrants first line drawn from ASIS to center of acetabulum second line drawn perpendicular to first line Quadrant posterior-superior quadrant "target zone" is the ideal place for supplemental component screws. elevating the hip center in revisions can place sciatic nerve at risk in this quadrant posterior-inferior quadrant "caution zone" login to view 4 more bullets anterior-inferior quadrant "danger zone" login to view 1 more bullet anterior-superior quadrant "death zone" login to view 1 more bullet Exceptions in the "high hip" the structures in the anterosuperior and anteroinferior quadrants are often found in the posterosuperior quadrant Avoiding Prosthesis Impingement Leaving the anterior rim of the acetabular component proud above the native acetabulum may result in anterior iliopsoas tendon impingement evaluate with cross-table lateral radiograph and anesthetic injection of the iliopsoas tendon sheath Causes of impingement medializing and raising acetabulum cup center of rotation will increase risk of bone-on-bone impingement by decreasing femoral offset lateralizing cup will increase risk of metal femoral neck-on-metal acetabulum impingement femoral head-to-neck ratio (<2:1) will increase risk of impingement femoral head skirts small femoral head