THA Trunnionosis - Recon

Introduction

Overview
- metal ion released from tribocorrosion at the femoral head-neck interface morse taper leading to adverse local tissue reactions (ALTRs)
Risk factors
- Modular designs
- Large cobalt chrome femoral heads
  - larger heads may put more torsional forces on the trunnion.
- Taper design
  - shorter taper length may afford less interference fit and more micromotion
  - greater rigidity of the taper may lead to less wear
- Metal on metal
  - serum metal ions may contribute to taper wear
  - no pathognomonic serum metal ion level for trunnionosis
  - serum cobalt >1 ng/ml (ppm) should lead to consideration for mechanically assisted crevice corrosion (MACC)
Pathophysiology
- Galvanic corrosion
  - corrosion caused by an electrochemical transfer of electrons between dissimilar metals
    - i.e. cobalt-chromium (CoCr) alloy femoral head on a titanium alloy stem
- Fretting corrosion
  - corrosion from relative micromotion between two materials causing wear
    - i.e. tolerance between male and female morse taper allows for micromotion and wear
- Crevice corrosion
  - physicochemical interaction between a metal and environment leading to altered mehcanical properties

Presentation

History
- pain and limp are the most common complaints
Physical exam
- occasionally if ALTR is large enough a palpable pseudocyst can be felt
- abduction weakness if ALTR has caused soft tissue destruction of abductors

Imaging

AP and lateral hip views should be obtained
- imaging studies may be normal in the setting of trunnnionosis
Judet views and/or CT scan may be obtained if advanced osteolysis is present
MARS MRI
- findings may include periarticular pseudotumors and/or soft tissue destruction

Studies

Infection should be ruled out
- ESR, CRP, WBC
- Aspiration
  - consider manual cell count as metal debris can cause a false elevation of automated cell count
Metal ion levels
- cobalt and chromium ion levels
- cobalt levels may be elevated more substantially (4-5x) than chromium levels

Treatment