Updated: 9/14/2022

THA Acetabular Screw Fixation

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Evidence
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Videos / Pods
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Cases
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https://upload.orthobullets.com/topic/5029/images/safe 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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(OBQ11.92) A 64-year-old male undergoes acetabular revision of his failed total hip arthroplasty using a large uncemented component. Post-operatively he is noted to have a foot drop and radicular pain in the operative extremity. A CT scan of the hip is obtained and reveals screw penetration into the sciatic notch. Where was this screw most likely inserted in the acetabulum?

QID: 3515

Anterior superior quadrant

5%

(226/4370)

Through the medial wall

6%

(249/4370)

Anterior inferior quadrant

9%

(396/4370)

Posterior superior quadrant

77%

(3377/4370)

Through the femoral nerve

2%

(101/4370)

L 1 B

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(OBQ11.5) In order to determine the boundaries of the posterior-superior safe zone for acetabular screw placement during THA, a line is initially drawn through which of the following two anatomic landmarks, represented by dots on the illustration?

QID: 3428
FIGURES:

A and C

61%

(2918/4776)

B and C

8%

(365/4776)

D and C

16%

(763/4776)

C and E

3%

(123/4776)

A and E

12%

(586/4776)

L 1 B

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(OBQ04.160) When placing acetabular screws to supplement cementless acetabular fixation in total hip arthroplasty, placing screws in which zone poses the highest risk to damaging the external iliac vasculature?

QID: 1265

anterior-inferior zone

15%

(545/3646)

anterior-superior zone

77%

(2814/3646)

posterior-inferior zone

4%

(160/3646)

posterior-superior zone

3%

(106/3646)

oblique zone

0%

(12/3646)

L 1 C

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