Are Nucleated Cell Counts Useful in the Diagnosis of Infection in Periprosthetic Fracture?

Abstract

Background Evaluating for the possibility of prosthetic joint infection in the setting of periprosthetic fracture is important because it determines the course of treatment. However, fracture-related inflammation can make investigations used in the diagnosis of infection less reliable. Questions/purposes The purpose of our study was to evaluate synovial fluid nucleated cell counts as a diagnostic test for deep prosthetic infection in patients with periprosthetic fractures around hip and knee arthroplasties. Specifically, we wished to determine the test's properties (sensitivity, specificity, positive predictive value [PPV], and negative predictive value [NPV]) using threshold levels of nucleated cell counts as they are otherwise used in the diagnosis of periprosthetic infection. Methods Billing codes were used to identify all cases of revision total hip arthroplasty (THA), revision total knee arthroplasty (TKA), open reduction and internal fixation (ORIF) of the femur, and ORIF of the tibia at our institution between 2005 and 2013. A total of 2537 charts were identified and reviewed to reveal 269 patients with 269 periprosthetic fractures about a THA or TKA (10.6% of charts reviewed). Of these, 27 fractures in 27 patients (10% of the periprosthetic fractures identified) underwent aspiration of their total joint arthroplasty to rule out infection before surgical intervention. The decision to aspirate was made by the treating surgeon based on clinical suspicion of infection from the patient history, physical examination, and radiographic findings. Nucleated cell counts from joint aspirates were recorded for all 27 patients. Synovial fluid culture results were then used to calculate the sensitivity, specificity, PPV, and NPV of an elevated nucleated cell count in the diagnosis of infection. Results The specificity, sensitivity, PPV, and NPV of an elevated nucleated cell count in the diagnosis of infection were 64% (95% confidence interval [CI,.57]), 100% (95% CI, 19.29-100), 18% (95% CI, 2.37-45.46), and 100% (95% CI, 76.66-100), respectively. Eleven of 27 patients (41%) with joint aspirates had elevated nucleated cell counts. Only two of the 11 patients (18%) with elevated nucleated cell counts had positive synovial fluid cultures. None of the patients with normal nucleated cell counts had positive synovial fluid cultures. Conclusions Although quite common, an elevated nucleated cell count has moderate specificity and poor PPV in the diagnosis of infection in the setting of periprosthetic fracture. Level of Evidence Level IV, therapeutic study.

Utility of synovial calprotectin lateral flow test to exclude chronic prosthetic joint infection in periprosthetic fractures: a prospective cohort study

“…Similarly, such a readjustment in the other direction might be helpful to adjust for the inflammation caused by the fracture (or other pathologies). Unfortunately, there is no final consensus on the definitive thresholds for calprotectin currently, especially not in the setting of PFF 11 , 25 . We therefore highlight the low specificity of calprotectin with a threshold of 50 mg/dl and advise to take particular caution as false positive results can likewise cause extensive overtreatment.Eventually, the diagnosis of a PJI in PPF continues to be the subject of research and the validation of calprotectin as a novel biomarker must be critically reviewed under these circumstances.…”

Periprosthetic Fractures following Total Knee Arthroplasty

“…40) 이때 발생하는 골절에 대해서는 잠금 금속판을 이용 한 지지 금속판 고정이 추천되고 있다. 41) 기존에 감염의 병력 이 있는 경우나 외상력에 비해 심한 골절 양상이 보이는 경우 는 항상 감염의 동반 여부를 확인해야 한다 42).…”