Michael Khazzam, MD
DALLAS – October 31, 2022 – The most common bacterial infection after revision shoulder replacement surgery can be more accurately diagnosed by considering how quickly samples of the microbe grow in hospital labs and the level of bacteria that grows, a study done in part at UT Southwest Spectacles.
The findings, reported in the Journal of Shoulder and Elbow Surgerycould lead to better post-operative care for the thousands of patients who require follow-up surgery each year for shoulder replacements, called shoulder arthroplasty revisions.
“Knowing which bacterial cultures are truly positive and which are not guides a surgeon in what treatments a patient should receive,” said study co-author Michael Khazzam, MD, associate professor of orthopedic surgery and chief of shoulder surgery at UT Southwestern. “Our study suggests that clinicians should consider using a shorter time to positivity and strength of positivity to determine if a tissue culture specimen is a true positive in joint replacement surgery revisions. shoulder.”
A postoperative X-ray shows revision of the reverse shoulder total prosthesis.
Cutibacterium acnes Infections after shoulder replacement surgery revisions can be difficult to diagnose, Dr. Khazzam explained. Although some patients show obvious signs of infection, such as draining wounds at the surgical site, others show more subtle signs, such as pain or stiffness. This bacterial species can also be difficult to grow in the laboratory, requiring specialized media and extended growth times – which can lead to confusion about whether positive or negative diagnoses are genuine.
To improve the interpretation of C. acnes diagnostics, Dr. Khazzam and his colleagues at 11 US hospitals each received 12 blinded samples to test for the presence of the bacteria. Ten were certain positives, with five samples each isolated from two patients who underwent shoulder arthroscopy revisions and diluted to different bacterial concentrations. Two were certain negatives.
The researchers found that all of the samples positive at the four highest concentrations were positive in the laboratory, and about 91% of the lowest concentration were also positive. In addition, 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 average time to a positive result for all known positive samples was around four days, while the obtaining a positive result for known negative samples was approximately twice. so long. Additionally, the strength of positivity – an outcome associated with the number of bacteria growing in the lab – was significantly higher for true positive samples than for false positives derived from known negative samples.
Dr. Khazzam and his colleagues suggest that surgeons keep these factors in mind when deciding whether to treat suspected patients C. acnes infections after shoulder prosthesis revision.
“UTSW’s Shoulder Service performs one of the highest volumes of primary and revision shoulder replacement surgeries in the country,” Dr. Khazzam said. “The results of this multicenter collaboration open the framework for the development of an evidence-based decision-making protocol for the treatment of these often difficult shoulder problems.”
About UT Southwestern Medical Center
UT Southwestern, one of the nation’s leading academic medical centers, integrates pioneering biomedical research with exceptional clinical care and education. The institution’s faculty has received six Nobel Prizes and includes 24 members of the National Academy of Sciences, 18 members of the National Academy of Medicine, and 14 researchers from the Howard Hughes Medical Institute. Full-time faculty of more than 2,900 are responsible for groundbreaking medical advances and committed to rapidly translating scientific research into new clinical treatments. UT Southwestern physicians provide care in more than 80 specialties to more than 100,000 inpatients, more than 360,000 emergency room cases, and oversee nearly 4 million outpatient visits annually.