Photo Quiz: Septic Arthritis following a Fall

An 81-year-old man presented to the emergency department with sudden acute onset of hip pain following a fall. The patient had undergone an operation for a total left hip replacement 4 years earlier and suffered from chronic renal failure. At the time of physical examination, he had a fever (38°C) and was complaining of left hip pain. An inflammatory syndrome was observed, with a high serum C-reactive protein level (175 mg/liter; reference, ≤4 mg/liter) and neutrophilic polynucleosis (11.7 × 10⁹ cells/liter, with 90% neutrophils; reference, 4.1 × 10⁹ to 10.5 × 10⁹ cells/liter). The patient also described an episode of gastroenteritis with diarrhea a few days before the fall. Pelvic radiography did not show hip fracture or prosthetic loosening, but magnetic resonance imaging revealed a voluminous articular effusion with diffuse soft tissue infiltration. Synovial fluid was collected for bacteriological analysis. An examination of a Gram-stained sample of joint fluid showed many neutrophils and few aggregations of organisms (Fig. 1).

FIG 1.

Gram stain of the unknown organism. Magnification, ×1,000.

See https://doi.org/10.1128/JCM.00248-20 in this issue for answer and discussion.