English

Abstract

Introduction Periprosthetic joint infection is a frequent and dreadful complication after total joint arthroplasty. Serological inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are widely available and easy to use. As such, they are often used as preliminary diagnostic as well as follow-up tools during the course of treatment. The information they carry is not the same in every clinical scenario, and they should be interpreted accordingly. This review confronts the reader with different doubtful clinical situations and then provides the necessary tools to interpret ESR and CRP in each of them: the immediate postoperative period, the chronic painful arthroplasty and between two-staged revision of infected cases. Conclusion Serological inflammatory markers have different diagnostic thresholds in acute and chronic situations. Follow-up measurements during treatment are informative, but complete normalization is not a mandatory requirement for successful outcome. Introduction Total joint replacement, especially hip and knee, is one of the most successful surgeries in orthopaedics. The demand for total hip and knee joint arthroplasty is increasing and is expected to grow even further over the coming decades1. Infection is arguably the most challenging and certainly one of the most frequent complications after joint replacement2,3. Despite modern surgical prophylaxis, the incidence of this complication is rising worldwide4,5. It is therefore likely that an increasing number of orthopaedic surgeons and other clinicians will encounter this problem. Periprosthetic joint infection (PJI) is typically classified according to the timing of symptom development and the mechanism of bacterial contamination as acute postoperative, acute delayed (haematogeneous) or chronic. This simple classification scheme greatly influences treatment options. Timely recognition of this grievous complication is crucial as it may make the difference between successful and failed outcome. Definitive diagnosis is often challenging as a real ‘gold standard’ has yet to be determined6.Currently, it can only be determined after culture results of samples taken during surgery. As such, preoperative diagnosis is forced to rely on clinical suspicion as well as on careful scrutiny of laboratory and imaging modalities7. In this setting, serological inflammatory markers, specifically erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are often used as initial tests even when there is a low suspicion of PJI6. They are also commonly used in monitoring response to therapy since they are inexpensive, non-invasive and widely available tests. This review confronts the reader with real daily practice doubtful clinical situations and then provides the necessary tools to interpret ESR and CRP values in three different key periods: the immediate postoperative period, diagnosis of a suspected chronic infection and between stages of treatment of an infected total joint arthroplasty. The different thresholds and diagnostic accuracy in each instance will be presented. Discussion Immediate postoperative period Clinical case An otherwise healthy 73-year-old man underwent right total knee arthroplasty (TKA) for primary knee osteoarthritis. The first few days after the procedure were uneventful and the patient was discharged on the fifth postoperative day. On discharge, ESR and CRP values were 100 mm/h and 49.2 mg/L respectively. On the 18th postoperative day, the patient presented to the outpatient clinic with scarce serous wound drainage through a small area of maceratedlooking skin wound. Blood tests revealed normal leukocytes and elevated ESR and CRP: 84 mm/h and 6.2 mg/L respectively. The patient was sent home with no antibiotics and was seen again a week later. Small and seemingly superficial area of skin necrosis was present, and there was no drainage or obvious inflammatory signs (Figure 1). ESR was 102 mm/h and CRP was 7.9 mg/L. Is it normal? ESR is the rate at which red blood cells sediment in 1 h. It is a nonspecific haematological test routinely used as an indirect measure of inflammation. CRP is a major acute-phase protein produced by the liver and increases as a response to * Corresponding author Email: ricardojgsousa@gmail.com Department of Orthopaedics, Centro Hospitalar do Porto – Hospital de Santo Antonio, Porto, Portugal