TOTAL HIP ARTHROPLASTY

01 Nov TOTAL HIP ARTHROPLASTY

Posted at 05:20h in Uncategorized by drneerajkumar 0 Comments

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Biomechanics of THR implant relies on prosthesis design, bearing surface and type of fixation (cemented vs uncemented)
THR components include
- femoral component
  - cemented
  - uncemented (press-fit) High cost, difficult to control version, calcar fracture,
    - Modular stem
    - taper stem
    - extensively porous coated stem
- Acetabular component
  - cemented
  - uncemented (press-fit)
- Bearing surface
  - polyethylene
  - metal
  - ceramic
Type of fixation
- Cement(PMMA)
- Biological fixation( uncemented) – young, older patient with good bone quality and in revision THR
  - bone ingrowth- bone grows into the porosity of implant
  - bone ongrowth- bone grows onto the divots in the implant
Depuy Charnley 10A
- 22.2mm mono-block stainless steel head and stem
- Matt-finish
- stability depends on strong bonds between bone and implant
- Stress shielding in proximal femur
- Collared to prevent stress shielding
Exeter(Stryker)
- Double taper stainless steel
- Modular
- Self locking sliding per or forced-closed design
- Subsidence 1.5 mm in 12months
- no neck collar
CPT stem (Zimmer)
- Collarless, polished, Tapper stem
- similar to Exeter
- Made of cobalt chrome or stainless
C-Stem(Depuy)
- Triple taper and thicker laterally.
- Loads medial cement mantle
- Produces proximal bone remodelling
Stanmore(Zimmer)
- Similar design to charnley.
S-ROM stem(Depuy)
- revision stem
- distal fixing modular uncemented stem
Restoration Stem (Stryker)
- modular revision stem

X-RAY AP and frog leg lateral view of both hips done in 15 degree of internal rotation
CT scan as prep planning if there is protrusio acetabulum or bone loss
MRI in case of AVN of hip
Alignment view of both limbs
Xray ls spine to rule out referred pain from degenerative spine

Minimally invasive THR
- No added advantage over convention in RCT
- B/L THR has increased infection rate and increased chances of bleeding

Skirted vs non skirted decreases the range of motion and head neck ratio so should be avoided
Small vs large head – 22.2mm vs 28mm vs 32mm, large head give more range of motion and decreases dislocation rate due to increased head and neck ratio.

Metal on poly
- metalic (cobalt chrome) femoral head on polyethylene acetabular liner
- longest track record, low cost and most modular
- High wear rate and osteolysis
- revision rate 5% in male and 3% in female at 15 years in 75 years age group
Ceramic on ceramic
- Best wear properties
- Inert particle
- expensive
- Squeaking
- low rate of revision 5.6% in male and 4.3% in female
Ceramic on poly
- reduced fracture and squeaking risk
- revision in male 2.3% and 2.9% in female at 15 year follow-up in 75 years age group.
Metal on metal
- better wear properties than metal on poly
- type 4 hypersensitivity
- increased metal ions in urine and serum

Cemented cup
- All poly
- thicker poly can be used for reduce stress transmission on the cement mantle
- commonly used cups are Exeter rimfit/contemporary, ZCA ally poly cemented cup Zimmer and marathon (depuy)
Uncemented cup
- Trident stryker available in hemispherical shell with multilocking hole option and peripheral self locking option
- Trilogy by Zimmer
- Pinnacle(depuy)
  - most commonly used
- Exceed(Biomet)