Thank you for your query,
Your child seems to have a post viral myalgia and arthralgias involving the joints and muscles of the lower limbs.
is done whenever the doctor suspects meningitis
in a child depending on clinical symptoms, clinical findings like stiff neck
, and the other meningeal signs of irritation.
Routine lumbar puncture is not required to rule out meningitis in every case of fever or sore knees without the clinical suspicion of meningitis.
Is there any joint swelling? Or any muscle tenderness?
So consult your Pediatrician
for the examination and for the proper advise.
Hope I have answered your query.