Why prosthesis exchange is important: biofilms protect bacteria from antibiotics

Antibiotic-tolerant Staphylococcus aureus Biofilm Persists on Arthroplasty Materials.

These authors cultured methicillin-sensitive Staphylococcus aureus biofilm on total knee arthroplasty materials and exposed these biofilms to increasing concentrations of cefazolin (control, 0.5, 1.0, 10.0, 100.0 μg/mL) to determine if the biofilm could be treated with antibiotics.

Quantitative confocal microscopy and quantitative culture were used to measure viable biofilm cell density.

At the highest concentration tested (100 µg/mL), residual viable biofilm was present on all three materials, and there were no differences in percent biofilm survival among cobalt-chromium (18.5% ± 15.1%), polymethylmethacrylate (22.8% ± 20.2%), and polyethylene (14.7% ± 10.4%). They found that tolerance was a phenotypic phenomenon, because increasing cefazolin exposure did not result in changes in minimum inhibitory concentration as compared with controls.

They concluded that antibiotics are inadequate at complete removal of the biofilm from the surface of arthroplasty materials.

Comment: Biofilms provide a protective niche for bacteria. The biofilms impede antibiotic access by providing a barrier to diffusion. They also allow bacteria to persist at a lower metabolic rate, again making them less susceptible to the effects of antibiotics. 

These results help explain the ineffectiveness of washout and partial prosthesis exchange in managing  colonized implants.

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Total joint FDA approvals and recalls

Analysis of FDA-Approved Orthopaedic Devices and Their Recalls.

These authors note that there are two paths by which medical devices, such as shoulder implants, can obtain approval for use by the U.S. Food and Drug Administration (FDA).  The more stringent Premarket Approval (PMA) review requires clinical trials, and the Premarket Notification 510(k) process generally exempts devices from clinical trials if they prove to be "substantially equivalent" to existing devices.

They hypothesized that because 510(k) approval was less stringent, it would be more commonly used on one hand and devices approved by this mechanism would be more likely to be recalled.

They searched for the following: PMA and 510(k) clearances for orthopaedics and non-orthopaedic specialties from 1992 to 2012. They also searched for all device recall events from 2002 to 2012. For the top-twenty recall companies, they calculated the odds ratio that compares the likelihood of recall for 510(k)-approved devices with that for PMA-approved devices.

While non-orthopaedic devices are increasingly approved by PMA:

Orthopaedic devices continue to be approved principally by 510(k):

The type of approval process is strongly related to the frequency of recall:from 2002 to 2012, the percentage of recalled devices was 17.8% for 510(k)-cleared devices and 1.6% for PMA-approved devices. 

They conclude that 510(k)-cleared devices were 11.5 times more likely to be recalled than PMA-approved devices; therefore is concerning that most orthopaedic devices are cleared through the 510(k) process with limited clinical trials data.

Comment: These data suggest that the 510(k) process, being easier and less expensive, is being used for devices that are not, in fact, "substantially equivalent to existing devices. " If they were "substantially equivalent", the recall rate discrepancy would not be what it is. It may be time to re-look at what it takes to qualify for 510(k) approval.

When we see data, such as that shown below from the AOA registry, it makes us wonder how "new" implants come to market, and which ones were claimed to be "substantially equivalent".

A recent article discusses the surgeon's responsibility for the use of new technologies:

Introduction of New Technologies in Orthopaedic Surgery. The bullet points are

➢ The introduction of new devices, biologics, and combination products to the orthopaedic marketplace is increasing rapidly.


➢ The majority of these new technologies obtain clearance to market by demonstrating substantial equivalence to a predicate (previously approved device) according to the U.S. Food and Drug Administration (FDA) 510(k) process.


➢ Surgeons play a critical role in the introduction of new technologies to patients and must take a leadership role in promoting safe, efficacious, appropriate, and cost-effective care, especially for operative procedures.


➢ Surgeons should monitor and document their patients’ clinical outcomes and adverse events when using new technology, to ensure that the new technology is performing as desired.

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