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Introduction
  • Definition
    • the process of anticipating the size and position of implants prior to surgery
  • Importance
    • allows surgeon to anticipate potential difficulties
    • to reproduce hip biomechanics
    • minimizes leg length inequality
  • Accuracy
    • 52-98% accurate +/- one size
    • related to experience and practice
  • Steps
    • obtain appropriate radiographs
    • record vital patient information on template (age, height, weight, etc)
    • establish radiographic landmarks
    • establish limb length discrepancy
    • template acetabular component
      • do this first to determining center of rotation of new hip
    • template femoral component
  • Tips 
    • best to achieve a good template with sizes in the middle range of the component system  
    • different system may be a better choice if this cannot be achieved
Radiographic Analysis
  • Necessary radiographs
    • AP pelvis
      • centered over pubic symphysis
    • AP hip
      • taken with 10-15 degrees of internal rotation
        • places femoral neck parallel to cassette
        • external rotation on radiographs will 
          • falsely decrease offset
          • create valgus appearing femoral neck
          • falsely decrease femoral canal diameter
    • frog lateral hip
  • Magnification
    • 20% is standard
      • most templates account for this
    • magnification markers are helpful
  • Secondary assessment of radiographs
    • pelvic obliquity
      • may be secondary to spinal deformity
      • may cause leg-length issues
    • acetabular retroversion
      • makes appropriate positioning of acetabular component more difficult intraoperatively
Radiographic Landmarks
  •  Femoral side
    • medullary canal
    • greater trochanter
    • lesser trochanter
    • saddle point
      • most distal part of the junction between the superior aspect of the femoral neck and the greater trochanter  
  • Acetabular side
    • acetabular roof  
    • tear drop 
      • created by superposition of the most distal part of the medial wall of the acetabulum and the tip of the anterior/posterior horn of acetabulum
  • Pelvis
    • ischial tuberosities  
      • important to determine limb length discrepancy
Establish Limb Length Discrepancy
  • Steps
    • on AP pelvis, draw horizontal line connecting the ischial tuberosities 
      • ensure the line extends beyond the medial femoral cortices bilaterally
    • mark the top (proximal-most point) of both lesser trochanters on the AP pelvis radiograph 
    • measure the distance between the inter-tuberosity line and the line drawn at the most proximal aspect of the lesser trochanters  
  • Alternatives
    • a line connecting the teardrops may be used instead of the ischial tuberosity line
      • this may be more accurate
Template the Acetabulum
  • Steps
    • place appropriately sized acetabular template with roughly 40 degrees of abduction
      • medial border of cup should approximate the ilioischial line and lie close to the teardrop
      • inferior border of cup should be at level of inferior teardrop line
    • mark center of rotation of acetabular component
Template the Femur
  • Steps
    • choose an appropriate sized femoral implant to fill medullary canal
    • insertion depth is determined to optimize limb length inequality 
      • placing the new femoral head center of rotation superior to the acetabular center of rotation will lengthen the limb 
      • placing the new femoral head center of rotation inferior to the acetabular center of rotation will shorten the limb (example shown here )
      • mark the intended femoral neck resection level
        • use lesser trochanter for posterior approach
        • use saddle point (see above) for anterior approaches
    • restore offset 
      • may be restored by
        • choosing a stem with more or less offset
        • choosing a stem with a different neck-shaft angle
        • modifying the length of the femoral neck
 

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Questions (4)
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(OBQ12.128) Which of the following templates, seen in Figures A-E, will increase the offset while keeping the leg lengths the same? Review Topic

QID: 4488
FIGURES:
1

Figure A

7%

(328/4999)

2

Figure B

6%

(290/4999)

3

Figure C

23%

(1174/4999)

4

Figure D

15%

(759/4999)

5

Figure E

48%

(2402/4999)

ML 5

Select Answer to see Preferred Response

PREFERRED RESPONSE 5
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