[Septic arthritis due to meningococcus. Report an atypical case presentation].

We have observed the case of a 73-years-old man with a septic monoarthritis affecting the left knee due to Neisseria meningitidis serogroup B, without previous traumatism, fever, headache or meningeal symptoms. The patient didńt present risk factors of meningococcal infection. The infection was resolved satisfactorily with parenteral ceftriaxone during 2 weeks and oral ciprofloxacin during 1 month.