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https://upload.orthobullets.com/topic/5007/images/offset_900.jpg
https://upload.orthobullets.com/topic/5007/images/head-neck_ratio.jpg
https://upload.orthobullets.com/topic/5007/images/skirt.jpg
https://upload.orthobullets.com/topic/5007/images/jump..jpg
https://upload.orthobullets.com/topic/5007/images/liners.jpg
Introduction
  • Four important variables that help determine the stability of THA 
    • component design
    • component position
    • soft-tissue tensioning
    • soft tissue function
Component Design
  • Femoral component design
    • large femoral heads
      • decreased dislocation rates due to
        • head-neck ratio increased
          • definition
            • diameter of femoral head/diameter of femoral neck
          • importance
            • larger head-neck ratios allow greater arc range of motion prior to impingement  
        • skirts can be avoided
          • definition
            • skirts are attachments used to extend the length of the femoral neck
          • importance
            • skirts decrease the head-neck ratio
        • jump-distance is increased
          • definition
            • amount of translation prior to dislocation
          • importance
            • large femoral heads are seated deeper within the acetabulum, increasing jump-distance  
            • increase in jump-distance increases joint stability
    • femoral offset
      • see "soft tissue tensioning" below
  • Acetabular component design
    • elevated rim liner
      • a posteriorly placed elevated rim liner may increase joint stability  
    • lateralized liner
      • increases soft-tissue tension by increasing offset  
      • has been shown to increase the risk of acetabular component loosening 
Component Position
  • Acetabular position 
    • recommendations   
      • anteversion  
        • 5° - 25°
      • abduction  
        • 30° - 50°
    • caveats
      • surgical approach may affect optimal position of implants
        • posterior approach should err towards more anteversion
        • anterior approach should err towards less anteversion
      •  Hypertrophy of the anterior inferior iliac spine may cause component impingement and instability  
    • complications
      • excessive retroversion  
        • posterior dislocation
      • excessive anteversion
        • anterior dislocation
      • excessive abduction (high theta angle, vertical cup)
        • posterior superior dislocation  
        • eccentric polyethylene wear and late instability
      • excessive adduction (low theta angle, horizontal cup)
        • impingement in flexion
        • inferior dislocation
  • Femoral stem position
    • recommendations
      • 10°- 15° of anteversion
    • caveats
      • more difficult to adjust femoral component version in uncemented femoral components
  • Combined version
    • definition
      • femoral component anteversion plus acetabular component anteversion
    • recommendations
      • 37 degrees
Soft Tissue Tensioning
  • Restoration of offset
    • definition
      • perpendicular distance from femoral head center of rotation to the axis of the femur  
    • importance
      • increased offset leads to
        • increased soft-tissue tension
        • decreased impingement
        • decreased joint reaction force  
      • decreased offset may lead to 
        • instability
        • abductor weakness
        • gluteus medius lurch
      • increasing offset improves hip stability 
    • techniques to increase offset  
      • increasing length of femoral neck
      • decreasing neck-shaft angle
      • medializing the femoral neck while increasing femoral neck length
      • trochanteric advancement  
      • alteration of the acetabular liner (see "component design" above)
Soft Tissue Function
  • Three main factors controlling proper soft tissue function
    • central nervous system 
      • pathology that affects the central nervous system
        • stroke
        • cerebellar dysfunction 
        • dementia
        • MS
        • Parkinson's 
        • myelopathy
        • delirium
        • alcoholism
    • peripheral nervous system
      • pathology that affects the peripheral nervous system
        • spinal stenosis (gluteus medius is L5) 
        • peripheral neuropathy 
        • radiculopathy 
        • paralysis/paresis
    • local soft tissue integrity
      • trauma
      • myoligamentous disruption
      • deconditioning
      • aging process
      • poor health
      • irradiation
      • osteolysis 
      • collagen abnormalities
      • myopathy
      • malignancy
      • infection
 

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Questions (11)

(OBQ06.2) During total hip arthroplasty, which of the following techniques increases range of motion prior to impingement? Review Topic

QID: 13
1

Using implants with a smaller femoral head

4%

(98/2486)

2

Using implants with a larger femoral head to neck ratio

94%

(2340/2486)

3

Using a ultra high molecular weight polyethylene liner on the acetabulum

1%

(13/2486)

4

Decreasing femoral offset

1%

(22/2486)

5

Cementing the femoral stem

0%

(2/2486)

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(OBQ05.268) A surgeon is planning to revise a left hip resurfacing component to a total hip arthroplasty. He wishes to decrease the joint reaction force of the left hip by increasing the femoral offset. Which of the following labeled measurements found in Figure A best describes femoral offset? Review Topic

QID: 1154
FIGURES:
1

Line 1

2%

(25/1080)

2

Line 2

1%

(14/1080)

3

Line 4

95%

(1026/1080)

4

Line 5

0%

(2/1080)

5

Line A

1%

(7/1080)

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PREFERRED RESPONSE 3
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(OBQ04.269) Which of the following factors is most likely to increase the risk of hip dislocation after a total hip arthroplasty (THA)? Review Topic

QID: 1374
1

Large head-to-neck ratio

2%

(40/2264)

2

Use of a skirted femoral head

81%

(1835/2264)

3

Femoral component in 15 degrees of anteversion

3%

(73/2264)

4

Acetabular cup in 15 degrees of anteversion

3%

(66/2264)

5

Acetabular cup in 50 degrees of abduction

11%

(247/2264)

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PREFERRED RESPONSE 2

(OBQ05.245) The schematic shown in Figure A displays a ceramic-on-ceramic total hip arthroplasty articulation with impingement. Which of the following modifications would increase the primary arc range of motion? Review Topic

QID: 1131
FIGURES:
1

Addition of a collar on the femoral head

1%

(11/1528)

2

Exchanging the ceramic liner with a hooded polyethylene liner

1%

(10/1528)

3

Increasing the femoral head size

93%

(1418/1528)

4

Increasing the femoral offset

4%

(56/1528)

5

Increasing the acetabular anteversion

2%

(30/1528)

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PREFERRED RESPONSE 3

(OBQ07.213) In total hip arthroplasty, which of the following techniques will lead to improved stability by increasing the abductor tension? Review Topic

QID: 874
1

Use of a high offset femoral component

96%

(2751/2876)

2

Decreasing neck length

0%

(8/2876)

3

Use of a low offset femoral component

1%

(31/2876)

4

Increasing the head size

1%

(16/2876)

5

Medializing the acetabular component

2%

(63/2876)

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PREFERRED RESPONSE 1

(OBQ07.117) Figure A depicts an individual seen from behind during a single-leg stance on the left lower extremity. Which of the following modifications during a left-sided total hip arthroplasty would exacerbate the abnormal findings present in Figure A? Review Topic

QID: 778
FIGURES:
1

Decreasing femoral offset

86%

(1905/2224)

2

Changing from a standard offset neck to an extended offset neck

8%

(173/2224)

3

Increasing femoral head size

0%

(6/2224)

4

Increasing femoral neck length

4%

(99/2224)

5

Moving acetabular cup inferiorly

1%

(32/2224)

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PREFERRED RESPONSE 1

(OBQ10.75) A 67-year-old female underwent a total hip arthroplasty 6 months ago and has had recurrent prosthetic dislocations. Figure A is a representative drawing of the mechanism of her dislocation. During the time of surgery what is the most likely factor leading to the bone-on-bone impingement? Review Topic

QID: 3163
FIGURES:
1

Lateralizing the acetabular cup

1%

(13/1546)

2

Decreased femoral offset

83%

(1283/1546)

3

Increased femoral offset

5%

(75/1546)

4

Increased acetabular inclination (>55 degrees)

3%

(54/1546)

5

Small head-neck ratio (<2)

8%

(118/1546)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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