The research could lead to better postoperative care for patients requiring revision shoulder arthroplasty

The research could lead to better postoperative care for patients requiring revision shoulder arthroplasty

The most common bacterial infection that occurs after revision shoulder arthroplasty can be more accurately diagnosed by considering how quickly samples of the microbe grow in hospital labs and how much bacteria grows, a study conducted in part at UT Southwestern shows.

The findings, reported in the Journal of Shoulder and Elbow Surgery, could lead to better postoperative care for thousands of patients who need follow-up shoulder replacement surgery, known as shoulder arthroplasty revisions.

Knowing which bacterial cultures are truly positive and which are not guides a surgeon in deciding which treatments a patient should receive. “Our study suggests that clinicians should consider using a shorter time to positivity and strength of positivity to determine whether a tissue culture sample is a true positive in shoulder arthroplasty revisions.”

Michael Khazzam, MD, Study co-author,Associate Professor of Orthopedic Surgery and Chief of Shoulder Surgery at UT Southwestern

Cutibacterium acnes infections after shoulder arthroplasty revisions can be difficult to diagnose, explained Dr. Khazzam. Although some patients show obvious signs of infection such as: B. weeping wounds at the surgical site, have other more subtle signs, such as: B. Pain or stiffness. This type of bacteria can also be difficult to grow in the lab because it requires special media and longer growth times - which can lead to confusion about whether positive or negative diagnoses are real.

To improve the interpretation of C. acnes diagnoses, Drs. Khazzam and colleagues from 11 U.S. hospitals each sent 12 blank samples to test for the presence of the bacteria. Ten were positive positive, with five samples each isolated from two patients undergoing revision shoulder arthroscopy and diluted to different bacterial concentrations. Two were definite negatives.

The researchers found that all positive samples tested positive at the four highest concentrations in the laboratory, and about 91% of the lowest concentration also tested positive. Additionally, approximately 14% of negative samples tested positive for C. acnes.

When the researchers looked for factors to distinguish true positives from false positives, they found that the median time to a positive result for all known positive samples was about four days, while the time for a positive result for the known negative samples was about twice as long. In addition, the strength of positivity - a result related to the number of bacteria growing in the laboratory - was significantly higher for the true positive samples than for the false positives that came from known negative samples.

Dr. Khazzam and his colleagues suggest that surgeons should consider these factors when deciding whether to treat patients with suspected C. acnes infections after shoulder arthroplasty revisions.

“The shoulder service at UTSW performs some of the highest volumes of primary and revision shoulder arthroplasties in the country,” said Dr. Khazzam. “The results of this multicenter collaboration provide the framework for the development of an evidence-based decision-making protocol for the treatment of these often difficult shoulder problems.”

Source:

UT Southwestern Medical Center

Reference:

American Shoulder and Elbow Surgeons (ASES) Periprosthetic Joint Infection (PJI) Multicenter Group.,(2022)What do positive and negative Cutibacterium culture results mean in periprosthetic shoulder infection? A multi-institutional control study. Journal of Shoulder and Elbow Surgery. doi.org/10.1016/j.jse.2022.01.127.

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