summary THA Trunnionosis is a complication of hip arthroplasty caused by metal ion release from tribocorrosion at the femoral head-neck interface morse taper leading to hip pain and adverse local tissue reactions. Diagnosis can be suspected in a patient with elevated serum metal ions with cobalt levels being elevated more substantially than chromium levels. MRI studies can be helpful to assess for pseudotumors. Treatment is observation for patients without symptoms. Single stage revision THA is indicated for patients with a painful THA in the absence of an infection. Epidemiology 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 (ppb) should lead to consideration for mechanically assisted crevice corrosion (MACC) mixed alloy components Etiology 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 contributes to trunniononsis Crevice corrosion physicochemical interaction between a metal and environment leading to altered mehcanical properties stainless steel most prone to crevice corrosion 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 are elevated substantially more than chromium levels ratio of at least 2:1 Treatment Operative revision total hip indications painful THA with the above risk factors and elevated serum cobalt level compared to serum chromium level elevation technique frozen-sections and intraoperative cultures extensive synovectomy inspection of the taper and decision for retention of stem versus revision stem to ceramic head with titanium sleeve and new polyethylene liner