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Occult PJI Periprosthetic Fracture — SCE Infectious Diseases MCQ

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HardBone & Joint InfectionOccult PJI Periprosthetic FractureSCE Infectious Diseases

A 50-year-old man develops a periprosthetic fracture 5 years after total hip replacement. Intraoperative cultures taken during fracture fixation surgery grow S. epidermidis from 3 out of 5 tissue samples. CRP is mildly elevated at 18 mg/L. He had no symptoms of infection before the fracture. What does the positive culture indicate?

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Correct answer: D — Likely low-grade/occult PJI — growth of the same organism from ≥3 out of 5 tissue samples meets the MSIS/ICM diagnostic threshold for PJI even in the absence of pre-fracture symptoms

The Musculoskeletal Infection Society (MSIS) and International Consensus Meeting (ICM) criteria define PJI as: growth of the same organism from ≥2 out of ≥5 tissue samples (or ≥3 out of 6 — varies by guideline). This patient has 3/5 positive samples with S. epidermidis — meeting the PJI threshold. Low-grade CoNS PJI can be occult for years. The periprosthetic fracture may have been partly caused by underlying low-grade infection (osteolysis). Management requires infectious diseases and orthopaedic MDT discussion regarding implant strategy and prolonged antibiotics.

Reference: BSAC 2023 – PJI; MSIS 2018 – PJI definition; NICE NG157 2024