Updated 27 August 2015

What's your diagnosis? – Case 25: swollen knee and fever

Mrs S takes her five-year-old son, Child A, to the doctor with a swollen left knee and a fever. Read the full case below and help to solve this week's case.


Child A's fever started the night before. Initially Mrs S thought the child had a bout of flu, but she became very concerned when he did not respond to fever medication, kept on crying and complained about knee pain.

General weakness

Two days earlier Child A fell on the playground at school and sustained an abrasion wound on his left lower leg. Mrs S didn't make much of it as the wound was very superficial. Since the night before, the child has refused to walk, vomited twice, and appears generally weak.

Read: Nausea and vomiting

Child A has no medical or surgical history, is not allergic to anything and does not take any supplements or medication. 

On examination, the GP finds the following:


Very irritated young child, warm to touch, refusing to walk, complaining about body pains

Chest exam:

Fast heart rate, lung fields clear


Swollen left knee with decreased ability to bend. Warm to touch, and redder than the right knee.

The rest of the examination was normal.

Side Room:

Temperature: 39,3°C

Urine: clear

Heart rate: 155 beats per minute

Based on the above, what is the most likely diagnosis, and how would you confirm it? How would you treat the child?

NOTE: Health24's on-site GP Dr Owen Wiese reveals new cases on Thursdays. The answer is posted with the story on Mondays, or you can get it in our Daily Tip – sign up here.

Previously on What's Your Diagnosis?

What's your diagnosis? -  Case 1: vomiting and weight loss

What's your diagnosis? -  Case 2: eye pain

What's your diagnosis? -  Case 3: strange behaviour and a bullet in the back

What's your diagnosis? -  Case 4: seeing odd things

What's your diagnosis? - Case 5: mysterious lungs

What's your diagnosis? - Case 6: runner with seizures

What's your diagnosis? - Case 7: swollen knee

What's your diagnosis? - Case 8: bloody semen

What's your diagnosis? - Case 9: confusing neurological signs

What's your diagnosis? - Case 10: diabetic teenager with unusual signs and symptoms

What's your diagnosis? - Case 11: bruising with no apparent reason

What's your diagnosis? - Case 12: severe tummy pain

What's your diagnosis? - Case 13: severe sore throat

What's your diagnosis? - Case 14: abdominal pain and swelling

What's your diagnosis? - Case 15: the world is spinning

What's your diagnosis? - Case 16: numbness in forearm

What's your diagnosis? - Case 17: burning urine

What's your diagnosis? - Case 18: boy with persistent fever

What's your diagnosis? – Case 19: lady who can't lose weight

What's your diagnosis? – Case 20: chest pain next to breastbone

What's your diagnosis? – Case 21: burning sensation in vagina

What's your diagnosis? – Case 22: vomiting and headaches

What's your diagnosis? – Case 23: frequent urination

What's your diagnosis? – Case 24: painful and swollen leg

Image: Sore knee from Shutterstock

Dr. Owen J. Wiese is Health24's resident doctor. After graduating from Stellenbosch University with additional qualifications in biochemistry and physiology he developed a keen interest in providing medical information through the media.


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