Saturday, October 21, 2017

Periprosthetic shoulder infection - is sonication of implants helpful in the diagnosis

Performance of implant sonication culture for the diagnosis of periprosthetic shoulder infection

These authors sough to evaluate the utility of implant sonication in the diagnosis of periprosthetic joint infection in patients undergoing revision shoulder arthroplasty between August 2010 and April 2013.  There were 5 patients with 2 cultures, 12 patients with 3 cultures, 9 patients with 4 cultures, 9 patients with 5 cultures, 14 patients with 6 cultures, 3 patients with 7 cultures, and 1 patient with 8 cultures. Preoperative fluid was obtained in 36 of 53 cases, and intraoperative fluid was obtained in 36 of 53 cases. Of the 53 revision cases that underwent implant sonication fluid culture, 25 (47%) were classified as infected. Their results are shown below

They concluded that implant sonication fluid culture in revision shoulder arthroplasty showed no significant benefits over standard intraoperative cultures in diagnostic utility for periprosthetic joint infection.

Conclusion: Sonication has been proposed as a means for removing organisms in the biofilm of retrieved implants. It is an expensive process and at present is without substantial evidence supporting its use. Our practice is to culture retrieved implants by vortexing them in 3 cc of sterile saline and submitted the saline for standard culturing for Propionibacterium and other organisms.

In contrast to their cases from the era presented here, these authors now carefully standardize their culturing protocol for revision shoulder arthroplasty to include the harvest of 5 intraoperative specimens: a synovial fluid sample and four tissue samples with all specimens sent for 14 day anaerobic culture hold. This degree of standardization is essential for interpreting the culture results. 

The topic of sonication is also discussed here:

The authors of Sonication versus Vortexing of Implants for Diagnosis of Prosthetic Joint Infection
compared sanitation (shaking) versus vortexing (stirring) with respect to the biofilm removal efficacy of vortexing alone in 135 removed prostheses, 35 were diagnosed with infection and 100 with aseptic failure. They used two different cutoffs for a positive result: 1 colony forming unit (CFU) or 50 CFU.

Using a cutoff of >50 CFU/ml, sonication showed higher sensitivity than vortexing (60% versus 40%) (p = 0.151), while the specificities remained equal (99%). Using the lower cutoff value (>CFU/ml), the sensitivities of vortexing and sonication fluid were similar (69% to 71%); however, the specificities decreased to 92% to 93%. In the table below PJI were cases they defined as infection and AF were thought to be aseptic failure.

It is of note that only two of these cases involved the shoulder and only 5 of the recovered organisms were Propionibacterium.

Comment: These authors provide a nice commentary on their work : "Interestingly, vortexing alone demonstrated acceptable sensitivity and specificity, especially in acute PJI, and may be used for the diagnosis of PJI in laboratories where sonication is not available. In addition, vortexing fluid represents a single clinical sample, with such analyses reaching sensitivity comparable to that of analyses using multiple periprosthetic tissue cultures (∼70%). Furthermore, sonication may kill bacteria, especially Gram-negative bacilli and anaerobes, whereas vortexing has not been shown to be harmful to bacteria. In addition, vortexing is an easy and simple procedure which can be performed in most laboratories without additional costs. Despite vortexing having originally been introduced as a preparatory step before sonication to generate microbubbles, which increase the cavitation effect, it seems to be a powerful removal method. High shear forces generated on the interface between the prosthesis and the vortexing fluid may explain the biofilm removal effect. These shear forces could be increased by a pulsatile change of the fluid movement direction (as used in Stomacher analysis). The removal efficiency may be also increased by addition of detergents (e.g., polysorbate 80) or anticoagulants (e.g., EDTA) to the vortexing fluid. Another possibility is the addition of beads to vortexing fluid, as is used for processing tissue samples in a bead mill. However, the contamination risk, increased workload, and costs need to be considered"

Our laboratory has determined that the potential incremental benefit of sonication does not offset the incremental cost and time.

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