Evolution of C-reactive protein values in the first month after anterior cruciate ligament reconstruction: reference values

C-reactive protein (CRP) is often used as an infection marker in orthopaedic patients and in particular after anterior cruciate ligament (ACL) reconstruction surgery. The aim of this study is to obtain the reference values of CRP during the first month after an ACL reconstruction and to analyse the epidemiological and surgical parameters that affect these values. One hundred and twenty ACL reconstructions were included. A CRP determination was performed preoperatively and 1, 7, 14, 21 and 28 days after surgery. CRP values under 5 mg/l were considered to be normal. One patient developed a septic arthritis in the second week postoperatively and was excluded. One hundred and seventeen patients [93 males and 24 females; mean age (standard deviation) 31.6 years (7.6)] underwent 119 ACL reconstructions with different techniques and grafts. Preoperative CRP (n = 119) was 1.80 mg/ml (2.6). Mean values at 1, 7, 14, 21 and 28 days were, respectively, 8.5 mg/ml (11.6), 10.5 mg/ml (17.0), 4.5 mg/ml (3.43), 4.4 mg/ml (7.59) and 3.4 mg/ml (3.03). Multivariate analysis showed that males had postoperative CRP levels 1.7 higher than females (p < 0.0001; 95 % CI 1.8-2.5); the patients operated by less experienced surgeons had levels 2.5 times higher than those operated by a highly experienced surgeons (p = 0.007; 95 % CI 1.2-3.4) and that if microfracture of a chondral lesion was associated, the levels increased 1.9 times (p = 0.021; 95 % CI 1.1-3.4). There are significant variations in CRP levels after ACL reconstruction in half of patients without infectious complications. Males, patients operated by less experienced surgeons and those with chondral lesions treated with microfracture had increased postoperative CRP levels. CRP values up to five times the normal limit are common in the month after an ACL reconstruction and are not necessarily associated with infection, especially in these groups. Diagnostic study, Level IV.