TITLE:
Bilateral Knee Septic Arthritis Associated with Mycoplasma pulmonis Following Intra-Articular Umbilical Cord-Derived Stem Cell Injection: A Case Report
AUTHORS:
Zee Sze-Tsing Jonpaul, Wu Wing-Cheung Stephen, Chan Wai-Sing Raymond
KEYWORDS:
Mycoplasma pulmonis, Septic Arthritis, Intra-Articular Stem Cell Injection
JOURNAL NAME:
Case Reports in Clinical Medicine,
Vol.15 No.3,
March
12,
2026
ABSTRACT: Background: Stem cell therapy has emerged as a potential treatment for knee osteoarthritis. Infective complications arising from stem cell therapy are uncommon. We report an unusual case of bilateral knee septic arthritis following intra-articular umbilical cord-derived stem cell injections. Case Presentation: A 78-year-old man with a history of degenerative knee disease presented with acute arthritis of both knees after receiving intra-articular umbilical cord-derived stem cell injections into both knees. Mycoplasma pulmonis, a murine pathogen, was identified in bilateral knee effusion and granulation tissue. He improved with arthroscopic debridement and combination antibiotic therapy. Conclusion: Mycoplasma pulmonis infection involving sterile sites in humans has never been reported. Although a definitive causal relationship between Mycoplasma pulmonis and septic arthritis cannot be established from a single case, this report highlights the need for rigorous quality control in stem cell product preparation and the potential for serious complications associated with novel therapies. Further study of the pathogenic role of M. pulmonis in humans is warranted.