Revision after knee arthroplasty due to Mycoplasma hominis infection: A case report and literature review.

RATIONALE

Mycoplasma hominis is an opportunistic pathogen commonly found in the human genitourinary system. However, infections caused by Mycoplasma hominis following knee arthroplasty are relatively rare.

PATIENT CONCERNS

A 68-year-old male patient underwent bilateral total knee arthroplasty 2 years ago due to osteoarthritis. Over the past 3 months, he developed persistent swelling and pain in both knees, along with the formation of a mass in the left knee. The patient also has a history of type 2 diabetes and hypoalbuminemia.

DIAGNOSES

Joint fluid samples from both knees were collected for metagenomic sequencing (mNGS), which detected Mycoplasma hominis infection. Histopathological examination confirmed chronic infection.

INTERVENTIONS

The patient underwent 1-stage revision surgery for the left knee, followed by intravenous doxycycline (100 mg, q12h) and intra-articular injections of vancomycin (0.5 g/d) and meropenem (0.5 g/d) for 2 weeks. Afterward, the patient was switched to oral rifampin (450 mg daily) and moxifloxacin (400 mg daily) for six weeks. Following improvement in the left knee symptoms, 1-stage revision surgery was performed on the right knee. The same antibiotic regimen was used postoperatively.

OUTCOMES

The patient experienced significant postoperative improvement, with marked pain relief and no signs of recurrent infection. The knee remained stable, and functional recovery was observed. To date, there have been no signs of infection recurrence during follow-up.

LESSONS

After joint arthroplasty, if a patient has persistent infection symptoms, does not respond to beta-lactam antibiotics, and has negative blood cultures, Mycoplasma infection should be considered. In this instance, the use of mNGS proved highly effective in diagnosing this atypical pathogen. The patient improved significantly after 1-stage revision surgery and targeted antibiotic therapy, though longer follow-up is needed to confirm long-term outcomes. Additionally, limited access to mNGS in some regions may delay diagnosis and treatment.