Background: Previous studies have suggested that the balance between
receptor activator of nuclear factor-?B ligand (RANKL) and its
decoy-receptor osteoprotegerin (OPG) in local tissue seems to play a crucial
role in the loosening of the total hip replacement. The aim of this study was
to evaluate whether the circulating levels of OPG and RANKL, as well as their
ratio, could be different in patients with aseptic loosening compared with
patients with stable implants.
Methods: One hundred and twenty-eight subjects were recruited. They
included thirty-nine patients with osteoarthritis who had not yet undergone
total hip arthroplasty, thirty-three patients who had undergone total hip
arthroplasty and had clinically and radiographically stable implants,
thirty-six patients with aseptic loosening of total hip arthroplasty
components, and twenty healthy volunteers. Serum levels of OPG and RANKL were
measured with use of an immunoenzymatic method, and in each individual the
OPG-to-RANKL ratio was calculated.
Results: In every group, a significant correlation was detected
between OPG concentration and age (r = 0.58, p < 0.0001), especially in
individuals older than fifty years, while gender and underlying disease were
not found to influence serum levels of the tested parameters. In comparison
with the levels in healthy donors and patients with a stable total hip
replacement, the serum levels of OPG were increased in the patients who had
not yet had an arthroplasty, those with aseptic loosening of a total hip
replacement, and those with a cemented total hip replacement. Moreover, the
OPG serum level provided good diagnostic accuracy in detecting the implant
failure. A correlation was found between the sum of the osteolytic areas seen
radiographically around the femoral stem and the RANKL level (r = 0.38, p =
0.02) and the OPG-to-RANKL ratio (r = —0.29, p = 0.04).
Conclusions: An increase in OPG levels may reflect a protective
mechanism of the skeleton to compensate for the osteolytic activity that
occurs in severe osteoarthritis and in aseptic loosening. Prospective studies
are needed to determine whether serum OPG levels could be used as markers for
monitoring the stability of the implant, as well as for predicting aseptic
loosening.
Level of Evidence: Diagnostic study, Level III. See
Instructions to Authors for a complete description of levels of evidence.