Updated: 1/25/2017

THA Acetabular Screw Fixation

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Evidence
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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 q
  • 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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Questions (4)

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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? Review Topic

QID: 3515
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1

Anterior superior quadrant

5%

(164/3345)

2

Through the medial wall

5%

(182/3345)

3

Anterior inferior quadrant

9%

(298/3345)

4

Posterior superior quadrant

77%

(2588/3345)

5

Through the femoral nerve

3%

(96/3345)

L 2

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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?
Review Topic

QID: 3428
FIGURES:
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1

A and C

63%

(2297/3670)

2

B and C

8%

(277/3670)

3

D and C

15%

(560/3670)

4

C and E

2%

(83/3670)

5

A and E

12%

(439/3670)

L 3

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SUBMIT RESPONSE 1
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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? Review Topic

QID: 1265
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1

anterior-inferior zone

15%

(381/2586)

2

anterior-superior zone

78%

(2018/2586)

3

posterior-inferior zone

4%

(103/2586)

4

posterior-superior zone

3%

(71/2586)

5

oblique zone

0%

(8/2586)

L 2

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