Raised initial total white cell count and lower post-operative decline of C reactive protein increases the risk of secondary surgery in septic arthritis of the native knee

Purpose: Septic arthritis is an orthopaedic emergency with high morbidity and mortality. The aim of this study is to determine the risk factors associated with secondary surgery for septic arthritis of the native knee joint.

Methods: This is a retrospective study reviewing all patients who underwent surgery for septic arthritis of the knee from 2012 to 2019 in a single institution. A total of 117 patients were recruited. Patients were divided into 2 groups: Group I (79/117, 67.5%) underwent one surgery and Group II (38/117, 32.5%) underwent more than one surgery.

Results: Patients with a raised initial total white (TW) cell count of > 20 × 10⁹/L had a significantly higher risk of secondary surgery. (Adjusted hazard ratio 2.42, p < 0.05) A decline of CRP level of less than 20% within 24 h from initial operation was also a risk for secondary surgery. (Adjusted hazard ratio 0.34, p < 0.01) Patients in group II also had significantly higher post-operative median TW cell count and neutrophil count. There was no significant difference in the offending microbe, surgical approach, and duration of operation from initial presentation between the groups.

Conclusions: Patients with septic arthritis of the native knee joint who present with raised initial total white cell count of > 20 × 10⁹/L and decline of CRP level of less than 20% within 24 h from initial operation are at higher risk of secondary operation. In these patients, more aggressive treatment strategies and appropriate counselling on the risks of repeated surgery are recommended.

Level of evidence: Level IV.