The use of cementless threaded cups in THA is a well-established treatment. Fractures of the cups are rare complications recorded
in individual cases with material defects being discussed as the primary cause. We analyzed three cases of fractured cups.
Although all three cups were well fixed to existing bone, we observed deficient osseous backing dorsocranially and abrasion
particles. There were no signs of femoroacetabular impingement or infection. The cups showed corrosion debris. Scanning electron
microscopic investigations showed characteristics of fretting and fretting-related corrosion. We concluded the fractures occurred
because of fretting combined with inadequate bony support leading to fatigue of the material and subsequent fracture.
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