Metallic Discoloration on the Right Shin Caused by Titanium Alloy Prostheses in a Patient with Right Total Knee Replacement
A 75-year-old woman had a large blue patch on the right shin for 3 years. She underwent a left total knee replacement 18 years ago and a right total knee replacement 14 years ago due to severe osteoarthritis of both knees. Each of the operations was carried out successfully without any serious adverse events. Eleven years after the right total knee replacement, she noticed a discoloration of her right shin, and the lesion continued to enlarge slowly over time. She was referred to a dermatology clinic where a large, well-demarcated bluish-gray patch was noted on her right shin. The surface of the skin was smooth with no palpable infiltration. For 1 year, she experienced pain when walking on the right shin. She had a 10×15 cm well-demarcated bluish-gray patch on the extensor surface of her right shin (). Routine laboratory tests, including complete blood count, liver function tests and urine analysis, yielded normal findings. Histopathologic findings from the skin lesion showed perivascular, fine black particles in the dermis (). The black particles were stained positive with both melanin and demelanin stains. Polarizing microscopy of the skin specimen revealed refractile foreign materials in the perivascular area of the dermis (). Further, energy-dispersive X-ray spectrophotometry revealed the presence of titanium and aluminium (). Metallic discoloration was diagnosed on the basis of clinical, histopathological, polarizing microscopy and energy dispersive X-ray spectrophotometer findings. The radiographs revealed loosened and dislocated tibial components of the right knee prostheses. Preoperative and intraoperative cultures were negative for bacteria. During surgical revision, marked loosening of the tibial component and wearing of polyethylene were found. Additionally, an intense black staining of a substantial amount of wear debris adjacent to the tibial components and tibial bone defect was observed (). The patient was treated by debridement, and the right tibial component was replaced. After the revision procedure, metallic discoloration disappeared and has not reoccurred over the past 4 years.