• arthroplasty;
  • cellulitis;
  • knee;
  • late infection;
  • risk factors


Background:  Infection after primary knee arthroplasty is devastating. The aim of this study was to determine the significance of sentinel infective events prior to the development of haematogenous prosthetic knee infection.

Methods:  A retrospective single-centre case control study of 1641 primary knee arthroplasties was conducted between 1998 and 2006. Seventeen haematogenous prosthesis infections were identified and were matched with 51 controls. Perioperative data were collected prospectively, and co-morbidities, infection parameters and sentinel events were collected from patient files and questionnaires. Analysis was performed between controls and the 17 haematogenous infections.

Results:  The overall prosthetic infection rate was 2.2%. Acute infections accounted for 1.2% with late haematogenous accounting for 1%. The mean time to infection in the haematogenous infection group was 2.3 years (range 3 months to 11 years), and the mean follow-up was 3.8 years (range 7 months to 11 years). Significant risk factors included the number of co-morbidities (relative risk 3.4) and a sentinel event of cellulitis (relative risk 2.7). Fifteen of 17 cases described a sentinel event prior to infection compared with 31 of 51 controls (P= 0.041). The commonest preceding event was skin or soft tissue infection in nine (53%) cases. The most common infecting organism was Staphylococcus aureus in 12 patients (four methicillin-resistant Staphylococcus aureus, eight methicillin-sensitive Staphylococcus aureus).

Conclusions:  Fifteen of 17 (88%) patients who developed late haematogenous infection had a preceding sentinel event with the commonest source being skin and soft tissue infection. Haematogenous infections are more likely to occur in patients with multiple co-morbidities.