Background: The radiographic criteria for identification
of loose cementless acetabular components have not been well established.
The purpose of this study was to compare the radiographic appearance
of a hemispheric porous-coated cementless cup fixed with screws
with the intraoperative findings with regard to the fixation status.
Methods: The quality of the cup fixation was evaluated
at fifty-two hip revisions that were performed, for reasons other than
infection, at an average of 89.9 months (range, 33.8 to 150.1 months)
after the primary operations. The fixation status at the revision
surgery was compared with the findings on sequential anteroposterior
and lateral radiographs of these sockets. Sequential radiographs
of an additional 100 total hip replacements that had not required
a reoperation and that had been followed for an average of 121 months
were also measured.
Results: Loosening of the socket was radiographically
identified by (1) radiolucent lines that initially appeared after
two years, (2) progression of radiolucent lines after two years,
(3) radiolucent lines in all three zones, (4) radiolucent lines
2 mm or wider in any zone, or (5) migration. The sensitivity of
these criteria was 94%, and the specificity was 100%.
The criteria had a positive predictive value of 100% and
a negative predictive value of 97%.
Conclusions: The most predictive radiographic findings
for early diagnosis of loosening of a hemispheric porous-coated cup
were progression of radiolucent lines more than two years after
the operation and any new radiolucent line of 1 mm or wider that
appeared more than two years postoperatively. Sequential anteroposterior
and lateral radiographs are necessary to assess the time of onset and
progression of radiolucent lines in order to identify loose hemispheric
porous-coated cups accurately.