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Updated: Sep 14 2022

THA Acetabular Screw Fixation

Images zones 3.jpg
  • 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"
          • if screw exceeds 20mm the following structures are at risk
            • sciatic nerve
            • inferior gluteal nerve and vessels
            • internal pudendal nerve and vessels
      • anterior-inferior quadrant
        • "danger zone"
          • obturator nerve, artery, and vein at risk
      • anterior-superior quadrant
        • "death zone"
          • external iliac vessels at risk
    • 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
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