Aims

Biopsy of the periprosthetic tissue is an important diagnostic tool for prosthetic joint infection (PJI) as it enables the detection of the responsible microorganism with its sensitivity to antibiotics. We aimed to investigate how often the bacteria identified in the tissue analysis differed between samples obtained from preoperative biopsy and intraoperative revision surgery in cases of late PJI; and whether there was a therapeutic consequence.

Aims

Fungal prosthetic joint infections (PJIs) are rare and account for about 1% of total PJIs. Our aim was to present clinical and microbiological results in treating these patients with a two-stage approach and antifungal spacers.

We investigated whether the indentation of bone cement spacers used in revision of infected joint arthroplasty with a MacDonald dissector increased the elution of antibiotic in vitro. A total of 24 cement discs containing either 0.17 g (0.88% w/w), 0.25 g (1.41% w/w), or 0.33 g (1.75% w/w) gentamicin of constant size were made. Of these, 12 were indented with the dissector. Each disc was immersed in ammonium acetate buffer in a sealed container, and fluid from each container was sampled at zero, one, three, six, 24, 48 and 72 hours and at one, and two weeks. The concentration of gentamicin in the fluid was analysed using high performance liquid chromatography mass spectrometry.

The fluid sampled at 72 hours from the indented discs containing 0.17 g gentamicin (0.88% w/w) contained a mean of 113 mcg/ml (90.12 to 143.5) compared with 44.5 mcg/ml (44.02 to 44.90) in the fluid sampled from the plain discs (p = 0.012). In discs containing 0.33 g gentamicin (1.75% w/w), the concentration eluted from the indented discs at 72 hours was a mean of 316 mcg/ml (223 to 421) compared with a mean of 118 mcg/ml (100 to 140) from the plain discs (p < 0.001).

At two weeks, these significant differences persisted. At nine weeks the indented discs eluted a greater concentration for all gentamicin doses, but the difference was only significant for the discs containing 0.17 g (0.88% w/w, p = 0.006). However if the area under the curve is taken as a measure of the total antibiotic eluted, the indented discs eluted more gentamicin than the plain discs for the 0.17 g (0.88% w/w, p = 0.031), the 0.25 g (1.41% w/w, p < 0.001) and the 0.33 g (1.75% w/w, p < 0.001) discs.

When preparing antibiotic spacers for use in staged revision arthroplasty surgery we recommend indenting the spacer with a MacDonald dissector to increase the elution of antibiotic.

Cite this article: Bone Joint J 2015;97-B:1519–24.