Updated: 8/3/2018

THA Prosthesis Design

Topic
Review Topic
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Questions
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Evidence
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https://upload.orthobullets.com/topic/5033/images/key_image3.jpg
https://upload.orthobullets.com/topic/5033/images/cemented_stem.jpg
https://upload.orthobullets.com/topic/5033/images/cementless-femoral-stems-img-jisrf.jpg
https://upload.orthobullets.com/topic/5033/images/polyethylene_vs_metal.jpg
https://upload.orthobullets.com/topic/5033/images/bearing_surfaces.jpg
https://upload.orthobullets.com/topic/5033/images/austin_moore.jpg
Introduction
  • Biomechanics of total hip arthroplasty depend on
    • prosthesis design
    • bearing surface and lubrication characteristics
    • fixation method topic
  • Designs include
    • femoral component
      • cemented  
      • press-fit (uncemented)  
        • tapered stems
        • extensively porous coated stems
        • modular stems
    • acetabular components  
      • cemented
        • polyethylene
        • metal
      • press-fit (uncemented)
        • metal
    • bearing surfaces  
      • polyethylene
      • metal
      • ceramic
History
  • 1891
    • Dr. Gluck performs first reported attempt at a hip replacement with ivory used to replace the femoral head
  • 1940
    • Austin Moore performs first metallic hip replacement surgery (hemiarthroplasty) with a proximal femoral replacement bolted to the femur 
  • 1952
    • Austin Moore prosthesis developed  
  • 1960s
    • Sir John Charnley introduces concept of low friction arthroplasty
      • concept
        • termed "low friction" as a small femoral head was used to reduce wear
      • components  
        • metal femoral stem
        • polyethylene acetabular component
        • acrylic bone cement
Press-fit Femoral Stems
  • Overview
    • rely on biologic fixation topic
    • compression hoop stresses provide initial stability
  • Types
    • tapered stems
      • most are proximally coated stems that taper distally
      • examples
        • Tri-Lock (DePuy)  
        • M/L Taper (Zimmer)  
    • extensively coated stems
      • porous coating extends into the diaphysis for distal engagement
      • examples
        • AML (DePuy) 
        • VerSys Full Coat (Zimmer)  
    • modular stems
      • distal stem and proximal body can be "mixed-and-matched" 
      • examples
        • S-ROM (DePuy)  
        • ZMR (Zimmer) 
  • Unique complications 
    • intraoperative fracture
      • more likely in press-fit through lateral approach 
      • typically due to underreaming
    • loosening
      • high loosening rate when used in irradiated bone (due to lack of ingrowth)
    • junctional corrosion     
      • seen in modular components (including cemented modular components)
Cemented Femoral Stems
  • Overview 
    • rely on cement fixation topic
      • cement is a grout that provides initial and long-term stability
      • limited remodeling potential
      • preferred for irradiated bone due to the bone's limited ability for ingrowth
    • composition
      • cobalt-chrome
        • most common
        • reduce cement stresses
      • titanium
        • may be prone to micromotion and debonding
  • Unique complications
    • stem breakage
      • cemented stems are smaller than press-fit stems and unable to tolerate as much cantilever bending  
        • may occur in cementless stems as well
Bearing Surfaces
  • Metal-on-polyethylene
    • metal (cobalt-chrome) femoral head on polyethylene acetabular liner  
    • benefits
      • longest track record of bearing surfaces 
      • lowest cost
      • most modularity
    • disadvantages
      • higher wear and osteolysis rates compared to metal-on-metal and ceramics
      • smaller head (compared to metal-on-metal) leads to higher risk of impingement 
  • Metal-on-metal  
    • benefits
      • better wear properties than metal-on-polyethylene
        • lower linear wear rate
        • decreased volume of particles
      • larger head allows for increased ROM before impingement 
    • disadvantages
      • more expensive than metal-on-polyethylene
      • increased metal ions in serum and urine (5-10x normal) 
        • serum metal ion concentration highest at 12-24 months
          • correlates with the initial "wear in" or "run-in" phase of increased particle generation, but then followed by a "steady state" phase of decreased particle generation 
        • no proven cancer link 
      • may form pseudotumors  
      • hypersensitivity (Type IV delayed type hypersensitvity) 
        • mediated by T-cells
          • metals sensitize and activate T-cells (nickel > cobalt and chromium)
          • however, most participating cells are macrophages (only 5% are lymphocytes)
        • antigen-activated T-cells secrete cytokines that activate macrophages
          • activated macrophages have increased ability to present class II MHC and IL-2, leads to increased T-cell activation
          • the cycle continues
      • contraindications
        • pregnant women
        • renal disease
        • metal hypersensitivity due to metal ions
  • Ceramic on Ceramic  
    • benefits
      • best wear properties of all bearing surfaces 
      • lowest coefficient of friction of all bearing surfaces
      • inert particles 
        • no concern for cancer risk
    • disadvantages
      • more expensive than metal-on-polyethylene
      • worst mechanical properties (alumina is brittle, low fracture toughness)  
        • small 28mm heads only exist in zirconia because of alumina's inferior mechanical properties
      • squeaking  
        • increased risk with 
          • edge loading
          • impingement and acetabular malposition
          • third-body wear
          • loss of fluid film lubrication
          • thin, flexible (titanium) stems
      • less modularity with fewer neck length options
      • stripe wear 
        • caused by contact between the femoral head and rim of the cup during partial subluxation 
        • results in a crescent shaped line on the femoral head image
  • Ceramic on polyethylene
    • disadvantages
      • zirconia undergoes tetragonal to monoclinic phase transformation with time 
        • increased with 
          • prolonged in vivo implantation >8yr
          • pressure
          • temperature
            • has lower heat conductivity than alumina (joint temperature can reach 99oC for zirconia, and 50oC for alumina)
  • Titanium on Polyethylene
    • not recommended due to high wear rates 
 

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Questions (20)
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(SAE10HK.67) A patient with a severe nickel allergy and degenerative joint disease of the hip would be best served by which of the following prosthetic options? Review Topic

QID: 7055
1

Cemented titanium stem, ceramic (alumina) head, and press-fit titanium cup

8%

(37/471)

2

Cemented cobalt-chrome stem, ceramic (alumina) head, and press-fit cobalt-chrome cup

6%

(28/471)

3

Press-fit titanium stem, cobalt-chrome head, and press-fit titanium cup

3%

(13/471)

4

Press-fit titanium stem, titanium head, and press-fit titanium cup

7%

(31/471)

5

Press-fit titanium stem, ceramic (alumina) head, and cementless titanium cup

76%

(360/471)

ML 2

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PREFERRED RESPONSE 5
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(SAE07HK.12) Compared to metal-on-polyethylene total hip bearing surfaces, the debris particles generated by metal-on-metal articulations are Review Topic

QID: 5972
1

larger and less numerous.

5%

(19/406)

2

larger and more numerous.

6%

(23/406)

3

smaller and less numerous.

9%

(35/406)

4

smaller and more numerous.

81%

(327/406)

5

not detectable.

0%

(1/406)

ML 2

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PREFERRED RESPONSE 4

(SAE07HK.70) With the increasing availability of total hip arthroplasty (THA) to younger patients with hip osteoarthritis, there has been increased use of alternative bearing surfaces. Compared to a ceramic-on-ceramic articulation, which of the following is a specific advantage of a metal-on-metal bearing surface? Review Topic

QID: 6030
1

Increased wettability

6%

(9/160)

2

Increased hardness

8%

(12/160)

3

Increased fracture toughness

64%

(103/160)

4

Decreased surface roughness

4%

(7/160)

5

Lower coefficient of friction

17%

(27/160)

ML 3

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PREFERRED RESPONSE 3

(SAE07HK.55) Based on the type of articulation shown in Figure 32, wear is not affected by which of the following factors? Review Topic

QID: 6015
FIGURES:
1

Radial mismatch of the femoral head to the acetabular component

10%

(14/143)

2

Sphericity of the bearings

11%

(16/143)

3

Surface finish of the articulation

6%

(9/143)

4

Carbon content of the metal-on-metal bearing

17%

(25/143)

5

Head-to-neck ratio

55%

(79/143)

ML 3

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PREFERRED RESPONSE 5
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(OBQ09.78) An 80-year-old man has a Charnley all-polyethylene acetabular shell shown in Figure A. When defining failure as revision for any reason, what is the failure rate at 35 years for this type of prosthesis? Review Topic

QID: 2891
FIGURES:
1

Less than 10%

11%

(257/2356)

2

20% to 30%

58%

(1362/2356)

3

40% to 50%

10%

(241/2356)

4

50% to 75%

9%

(220/2356)

5

Greater than 75%

11%

(268/2356)

ML 3

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PREFERRED RESPONSE 2

(OBQ12.159) What surgeon is credited for designing the prosthesis seen in Figure A? Review Topic

QID: 4519
FIGURES:
1

John Charnley

14%

(574/4016)

2

San Baw

0%

(10/4016)

3

Sir Harry Platt

2%

(63/4016)

4

Austin T. Moore

82%

(3313/4016)

5

Charles Frederick Thackray

1%

(31/4016)

ML 2

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PREFERRED RESPONSE 4

(OBQ11.126) A patient undergoes the procedure depicted in Figures A and B with standard components (non-gender specific). Which of the following outcomes most appropriately describes the difference in females compared to males for this procedure? Review Topic

QID: 3549
FIGURES:
1

Greater implant survivorship

67%

(2304/3447)

2

Decreased WOMAC scores

15%

(502/3447)

3

Increased rate of extensor mechanism rupture

3%

(119/3447)

4

Increased postoperative pain

12%

(425/3447)

5

Increased component osteoloysis

2%

(84/3447)

ML 2

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PREFERRED RESPONSE 1

(SBQ07HK.3) A 56-year-old gentleman presents to your office one year after undergoing total hip arthroplasty with the implant seen in Figure A. He is concerned about the potential complications given the recent media attention his implant has received. He is currently asymptomatic. Which of the following statements is accurate regarding his prosthesis and future care? Review Topic

QID: 1588
FIGURES:
1

He should have bi-annual LFTs measured, as metal ions are metabolized by the liver.

22%

(565/2599)

2

His risk of developing cancer is dramatically increased.

1%

(23/2599)

3

There is no correlation between activity level and serum levels of metal ions.

70%

(1823/2599)

4

His prosthesis design is safe in women of child-bearing age as the ions cannot be transmitted via pregnancy.

3%

(88/2599)

5

His prosthesis design puts him at an increased risk for dislocation.

3%

(88/2599)

ML 3

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PREFERRED RESPONSE 3

(OBQ04.45) All of the following are true for a patient who underwent a metal-on-metal total hip arthroplasty (THA) EXCEPT? Review Topic

QID: 106
1

they will have production of ionically charged wear particles

3%

(86/2825)

2

there is a higher cancer risk than with metal-on-polyethylene THA

79%

(2231/2825)

3

they will have elevated levels of cobalt and chromium in the serum

3%

(85/2825)

4

they will have elevated levels of cobalt and chromium in the urine

5%

(155/2825)

5

there is a higher frictional torque than with ceramic on ceramic THA

9%

(262/2825)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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