KS40: CHARACTERISTICS OF ‘LATE’ INFECTIONS IN 1641 TOTAL KNEE ARTHROPLASTIES

Abstract

Infection after Total Knee arthroplasty is devastating. The primary aim of this study was to characterise deep prosthesis infection in patients presenting greater than 3 months from index surgery. A retrospective single centre case control study of 1641 primary knee arthroplasties conducted between 1998 and 2006. All infected patients were identified (n=35) and those occurring within 3 months of surgery (n = 12) were excluded. All remaining infections (n=23) were classified into “latent” and “haematogenous”. Latent infections (n=7) were classified as having symptoms persisting from the time of surgery. Haematogenous infections (n=16) were those with an uneventful recovery and then a sudden onset of symptoms immediately prior to diagnosis of deep prosthetic infection. Each haematogenous infection was matched with 2 controls. Statistical analysis was performed between controls and the 16 haematogenous infections to determine any differences.

The overall prosthetic infection rate was 2.13%. Early infections accounted for 0.73% of the total and “haematogenous” infections for 0.98% of the total. The median time to infection in the “haematogenous” group was 1.6 years (Range 103 to 1803 days) and the median follow up time was 3.3 years (Range 230–3410). 94% (n=15) of the “haematogenous” group described a sentinel event prior to infection compared with 66% (n=21) of patients in the control group who reported an event with no subsequent progression to infection (P=0.04). Common preceding events included traumatic haemarthrosis in 31%, distant infections (eg dental abscess, intrathecal pump site infection, infected permacath, sternal wound infection, UTI) in 31% and cellulitis in 19%. The most common infecting organism was staphylococcus aureus in 56.5% (2 MRSA, 11 MSSA). Significant risk factors included the presence of diabetes (P=0.042), obesity and diabetes (P=0.044) and the number of co-morbidities (P=0.07). Infections were managed with debridement and washout (n=9) or removal of the implant with or without revision (n=7).

A significant number of patients who develop haematogenous infection have a preceding sentinel event. Haematogenous infections are more likely to occur in patients with diabetes or those with multiple co-morbidities. This group should be counseled regarding the ongoing risk of deep prosthetic infection.