Background: Although periprosthetic bone
loss remains a major concern in total hip arthroplasty, radiographic assessment
of such loss is both difficult and subjective. In the present study,
we assessed the ability of orthopaedic surgeons to reproducibly recognize
changes in periprosthetic bone density on radiographs. We hypothesized
that assessment of periprosthetic bone loss on plain radiographs
is not reliable enough to justify its use in outcomes research.
Methods: Twenty-nine unilateral total hip replacements
and the surrounding bone were retrieved at autopsy, and radiographs
were made; radiographs of the contralateral, normal femur were also
made after implantation of an identical prosthesis and used as a
control. Three orthopaedic surgeons independently examined the specimen
radiographs and classified bone loss in each of sixteen femoral zones.
Bone loss was recorded as present if the bone of the femur that
had had in vivo implantation showed evidence of cortical thinning,
increased porosity, or decreased density (either cortical or trabecular)
when compared with the control femur. The kappa coefficient was
used to quantify interobserver and intraobserver reproducibility
in determining bone loss for the 464 zones examined and in determining
the Engh and Bobyn stress-shielding classification of each femur.
In fourteen femoral pairs, bone loss was also quantified with dual-energy
x-ray absorptiometry, and the resulting value was then compared
with the bone-loss classification that had been determined radiographically.
Results: First, the surgeons agreed on the presence
or absence of bone loss in 73 percent (337) of the 464 zones. The
interobserver kappa value of 0.58 denoted only good reproducibility.
The intraobserver reproducibility was better; the surgeon's initial evaluation
of bone loss agreed with his second evaluation for 90 percent of
the zones (kappa = 0.74). Second, the three surgeons agreed on the
degree of stress-shielding, according to the Engh and Bobyn classification,
in 66 percent (nineteen) of the twenty-nine femora. The kappa value
for this comparison was only 0.27, indicating marginal reproducibility.
Third, although there was some agreement among reviewers when there
was 20 to 60 percent reduction in bone-mineral content as determined
with dual-energy x-ray absorptiometry, excellent agreement among
the examiners (kappa = 0.85) was not achieved until bone loss averaged
Conclusions: On the basis of these results,
we suggest caution in interpreting results from studies of femoral
bone loss that have used plain radiographic analysis if the authors
have not provided interobserver reliability data. We question the
utility of evaluating periprosthetic bone loss on radiographs, since
the loss is not reproducibly recognized until 70 percent of the
bone is gone.