C-reactive protein (CRP) is an acute-phase biomarker responding to surgical trauma. Typically, a first peak is observed at day 2 with a reduction at day 4 and normalization 3-6 weeks after surgery. CRP is often linked to prosthetic joint infection when elevated values are present longer time after surgery. The aim of this study was to analyse the kinetics of CRP in different types of minimally invasive (MI) arthroplasty and to observe if there were significant differences in between MI total knee arthroplasty (TKA), patient-specific instruments (PSI) TKA and unicompartmental arthroplasty (UKA).
Three hundred and seventy-two patients were prospectively studied with a blood test measuring CRP at day 2, 4, 21 and 42 in 3 different groups of patients: 257 MI TKA, 55 PSI TKA and 60 UKA. Mean peak values and kinetics were compared in between different groups of MI arthroplasty.
There was a significant age difference in the three MI arthroplasty groups. The difference in mean age for the conventional MI TKA group of 68.8 ± 9.8 years, 58.5 ± 11.7 years for the unicompartmental group (P < 0.05) and 63.3 ± 9.6 years for the PSI group (P < 0.05) was significant. Mean CRP level, for the entire study group, on day 2 was 16.7 ± 8.8 mg/dl that gradually decreased to 13.6 ± 7.8 mg/dl on day 4. On day 21 and 42, median CRP level was 0.6 (0-20) and 0.4 (0-7) mg/dl, respectively. Peak CRP values were lower for UKA compared to TKA at day 2 (11.6 vs. 17.5 mg/dl) and day 4 (8.0 vs. 15 mg/dl), but this was not observed for PSI-assisted arthroplasty (18.9 vs. 17.5 mg/dl). There was a trend for faster CRP normalization in UKA compared to the two other groups at day 21 and at day 42 and for PSI TKA to have a lower mean level at 4 days (12.9 vs. 15 mg/dl). There was no statistical difference in the normalization rate of PSI-assisted versus MI TKA.
Kinetics of CRP in MI arthroplasty are identical to the published kinetics of conventional TKA. Most patients normalize CRP at 3 weeks; however, 18 % does not by 6 weeks. This is not a sign of early prosthetic joint infection. Peak values are significantly lower for UKA but not for PSI TKA.