ObjectiveTo investigate the expression changes of the receptor activator of nuclear factor-κB ligand (RANKL) in the peripheral blood of patients with aseptic loosening of the implant after total hip arthroplasty (THA) by comparing with that of patients with femoral neck fracture and to analyze the correlation between RANKL expression and aseptic loosening. MethodsBetween January 2008 and January 2013,the peripheral blood were harvested from 58 patients with aseptic loosening of the implant after THA (trial group) and 63 patients with femoral neck fracture (control group).The 2 groups were well matched,with no significant differences in age and gender (P>0.05).The expressions of the RANKL mRNA and RANKL protein were evaluated by quantitative real-time PCR and Western blot respectively.At the same time,the concentration of RANKL was also measured by ELISA. ResultsThe expression of the RANKL mRNA in the trial group was 18.30±1.09,which was significantly higher than that of control group (1.00±0.05)(t=125.390,P=0.000).The relative RANKL protein expression values in trial group and control group were 0.856±0.254 and 0.404±0.102 respectively,showing significant difference (t=13.032,P=0.000).The results of ELISA showed that the concentration of RANKL in trial group [(3.553 5±0.129 7) ng/mL] was significantly higher than that of control group [(1.912 3±0.126 2) ng/mL] (t=18.124,P=0.000). ConclusionThe high RANKL expression in peripheral blood is probably correlated with aseptic loosening of the implant in patients undergoing THA,which possibly is the prognostic factor of aseptic loosening of the implant.