High failure rate of cementless threaded acetabular cups: a radiographic and histologic study in the goat.

We studied the fixation of the Mecron cementless titanium screw cup radiographically and histologically in 20 dwarf-goats after periods of 0, 6, 26 and 52 weeks. In only 3 goats did histology show good bone-implant contact, whereas in the other 17 goats a fibrous membrane interface was seen. This high failure rate is caused by the poor primary fixation and should be a warning against the use of this implant.