Infection is one of the major reasons leading to early revision of total hip joint replacements. Traditionally, samples have been taken for microscopy, culture and sensitivity at the time of surgery. However, this doesn’t always reveal a causative organism. Molecular techniques have now been refined to improve sensitivity in bacterial detection.

In this study, samples were taken from acetabular and femoral components at the time of revision hip surgery for suspected infection. These underwent conventional culturing and also PCR and DNA sequencing. The white cell count, CRP and ESR were also recorded.

Results are available for 6 cases. All of these patients had an elevated CRP level (17–169). Microscopy at the time of surgery showed scanty white cells and no organisms on at least 1 sample from 2 cases. Subsequent culture was negative. When sonication techniques were used to remove bacterial DNA, followed by PCR and sequencing, one of these cases yielded Stenomophonas sp. A further 4 cases were positive for Stenophomonas using molecular techniques despite conventional culture being negative.

Stenophomonas sp is a gram negative bacillus. Its ability to adhere to plastic and to produce a bacteraemia are of significance in its proposed role in hip arthroplasty infection. It is also known to be resistant to most commonly used broad spectrum antibiotics.

This study demonstrated that we may be under-diagnosing infection in hip revision patients. These new techniques could prove invaluable in detecting low yet significant levels of bacteria which may lead to a change in current antibiotic policy for joint replacements and subsequently a reduction in the number of revisions required for loosening due to infection.