[Correlation between C-reactive protein and pain in periprosthetic infection after total hip arthroplasty]

To explore the difference in level of pain experienced by patients with total hip arthroplasty between aseptic loosening and periprosthetic infection, and to examine the correlation between C-reactive protein (CRP) and pain.

Fifty-one patients (recruited from our hospital between March 2010 and November 2011) suffering aseptic loosening or periprosthetic infection after total hip arthroplasty were included in this study: 24 males and 27 females, with mean age 68.13 years. The patients were divided into an aseptic loosening group (n=31) and a periprosthetic infection group (n=20). Both the visual analog scale (VAS) and Harris pain score were used to estimate the level of pain experienced by the patients. CRP levels in serum were measured. The difference in assessment of pain by VAS and Harris pain score was compared between the two groups, and the correlation between pain and CRP was analyzed.

The mean VAS in the aseptic loosening group was 5.39 (2.10-8.13) compared with 5.48 (2.09-8.30) in the periprosthetic infection group; however, the difference was not statistically significant (P=0.85). The mean rank of Harris pain score was 26.23 in the aseptic loosening group and 25.65 in the periprosthetic infection group, but again there was no significant difference (P=0.88). The CRP level in the periprosthetic infection group (36.20-101.40 mg/L, mean 72.86 mg/L) was obvious higher than that in the aseptic loosening group (1.37-13.70 mg/L, mean 6.53 mg/L), and the difference was statistically significant (P<0.01). The VAS was related with the CRP level in the periprosthetic infection group (r=0.87, P<0.01), and the correlation between Harris pain score and CRP level was conspicuous (r=0.92, P<0.01) in this group. However, those correlations were not evident in the aseptic loosening group (r=0.25, P=0.17; r=0.19, P=0.65).

There is no difference in perception of pain in patients after total hip arthroplasty between those with aseptic loosening and those with periprosthetic infection. It is therefore unreliable to make a initial diagnosis only according to the level of pain. However, the level of CRP is a sensitive and effective way of differentiating the two conditions. The positive correlation between CRP and pian exists in patients with periprosthetic infection but not with aseptic loosening.