Incidence of late bead shedding from uncemented porous coated cups. A radiographic evaluation.

A radiographic study was performed on late head separation from the porous surface of clinically well functioning and radiographically stable Arthropor uncemented acetabular components. Of 104 cups in 102 patients, 11 (10.6%) showed bead separation from the porous coated surface. Bead shedding occurred at an average of 4.2 years (range, 2-7 years). In each case the phenomenon was progressive. In the group that shed beads, there was a higher prevalence of acetabular radiolucencies (63.6% versus 25.8%) and of osteolysis (45.5% versus 10.8%). These differences were statistically significant. The group that shed beads also had a higher polyethylene wear rate (0.21 mm/year versus 0.16 mm/year) and were younger (49.5 years versus 59.5 years). All cups that shed beads remained clinically and radiographically stable. Thus, the clinical impact of these observations is uncertain. However, the higher prevalence of acetabular lucencies and osteolysis in these patients, in combination with an increased polyethylene wear rate, require thorough clinical and radiographic followup to uncover potential loosening problems of these acetabular components.