ARTHROPLASTY

COMPONENT TYPES • metal on polyethylene Earliest implants Issue of polyethylene wear and wear particle disease

Wear shown as reduced distance between head and acetabular margin • ceramic on polyethylene Low wear ratio Ceramic head can fracture

• ceramic on ceramic Ceramic fracture risk • metal on metal Metal ions released

ARMD Reaction to metal ions Also called ALVAL or Pseudotumor • Uncemented • Hybrid (cemented stem uncemented cup)

• Reverse hybrid REPORT SHOULD CONSIDER ACETABULAR COMPONENT • Abduction or Inclination angle

30-50 degrees See figure adjacent.

Angle varies according to desired mobility.

Angle proportional to dislocation risk • Anterversion

10-30 degrees See figure above.

Simple calculation of angle theta useful for quick assessment.

May require 'guestimate' of margin of cup if obscured by metal head Ackland method more accurate if cup partially obscured but requires tables (below) CT better if accurate assessment required FEMORAL COMPONENT

• Limb length Various methods but teardrop line to lesser troc easy Less than 1cm difference acceptable • Offset (centre of rotation)

Compare with contraletaral side Quick method: compare distance from head center to teardrop cal center of rotation is distance from head center to interischial line • Tip position. Valgus/Neutral/Varus

Is tip in centre of medulla? Center (Neutral) or Medial (Valgus) are optimal • Concentric to acetabular component

Circle on Femoral head, insert & Cup ..

Should be isocentric • Femoral anteversion RESURFACING • Stem 5-10 degrees valgus wrt the femoral neck

ie Stem lies below axis of femoral neck • Cup 30-50 degrees abduction 15 to 25 degrees ante version COMPLICATIONS TO LOOK FOR • Aseptic loosening

Use Gruen's zones to describe 1-7 from lateral on AP 8-14 from posterior on lateral 1-3 from superior for acetabular cup

more than 2mm significant • Infection (septic loosening) • Metal fatigue (Trunnionosis) • Heterotopic bone formation

• Failure of incorporation of uncemmented components ACKLAND ANTEVERSION TABLES