To investigate the predictive value of α-defensins (DEFA) and lipopolysaccharide (LPS) for periprosthetic infection and aseptic loosening in elderly patients after hip replacement.

From February 2015 to February 2018, a total of 105 elderly patients who received hip replacement in the Department of Orthopaedics, the Second People’s Hospital of Liangshan Yi Autonomous Prefecture were selected, and were divided into control group (36 cases), aseptic loosening group (41 cases) and infection group (28 cases) according to whether complications occurred one year after operation. The strains of the extracted synovial fluid were identified by VITEK-2 Compact automatic microbial identification system, the level of DEFA in synovial fluid was measured by enzyme-linked immunosorbent assay (ELISA), the levels of LPS were detected by immunoturbidimetric assay. The diagnostic values of DEFA and LPS in synovial fluid after operation for aseptic loosening and periprosthetic infection was analyzed by Receiver operating characteristic curve (ROC).

A total of 31 pathogenic bacteria were isolated from the synovial fluid of 28 infected patients, among which, 18 strains (58.06%) were Gram-positive, and the coagulase-negative Staphylococci accounted for the largest proportion (5/31, 16.13%); the other 13 strains (41.94%) were Gram-negative bacteria, and Pseudomonas aeruginosa accounted for the largest proportion (4/31, 12.90%). There were significant differences in the levels of DEFA and LPS in synovial fluid among three groups (F = 141.328, 84.922, all P < 0.001), the levels of DEFA [(3.70 ± 1.18) mg/L and (8.14 ± 2.65) mg/L] and LPS [(0.47 ± 0.14) ng/ml and (0.69 ± 0.22) ng/ml] in synovial fluid of aseptic loosening group and infected group were significantly higher than those of control group [(1.52 ± 0.49) mg/L and ( 0.21 ± 0.06 )ng/ml] (t_DEFA = 10.324, 14.701; t_LPS = 10.334, 12.531; all P < 0.001), and the levels of DEFA [(8.14 ± 2.65) mg/L] and LPS [(0.69 ± 0.22) ng/ml] in synovial fluid of infected group were significantly higher than those of aseptic loosening group [(3.70 ± 1.18) mg/L and (0.47 ± 0.14) ng/ml] (t_DEFA = 9.465, t_LPS = 5.080; both P < 0.001). The level of DEFA [(8.50 ± 2.19) mg/L] in synovial fluid of patients with positive Gram-positive infection was higher than that of Gram-negative bacteria infection group [(6.89 ± 1.31) mg/L] (t = 2.114, P = 0.044), and the level of LPS [(0.57 ± 0.09) ng/ml] was lower than that of Gram-negative bacteria infection [(0.80 ± 0.10) ng/ml], with significant difference (t = 6.231, P < 0.001). The areas under ROC curve of joint synovial fluid DEFA level and LPS level for diagnosis of aseptic loosening were 0.934 and 0.873, respectively, while the areas under ROC curve for diagnosis of periprosthetic infection were 0.941 and 0.895, respectively. The area under ROC curve for diagnosis of aseptic loosening predicted by DEFA and LPS was 0.986, the sensitivity and specificity were 95.10% and 94.40%, respectively. The area under ROC curve for diagnosis of periprosthetic infection was 0.990, the sensitivity and specificity were 100.00% and 92.70%, respectively.

The level of DEFA joint synovial fluid combined with LPS in elderly patients after hip replacement was more sensitive and specific for the diagnosis of periprosthetic infection and aseptic loosening.