The patient

A 9 year old girl with a history of conservatively managed left sided Perthes' (Legg-Calvé-Perthes) disease presented to her orthopaedic team via her general practitioner with onset of right hip pain and subsequent limp. She was otherwise well. On clinical examination she had a limp with moderate pain and some limitation of abduction and internal rotation. She did not have a fever, and routine haematology and biochemistry gave normal results.

Differential diagnosis and prognosis

Assuming the disease can confidently be localised to the hip (rather than knee, pelvis, or lower back), a presumptive diagnosis of the painful hip is reasonable, based on age and presentation.

• In a younger, febrile, or unwell child, septic arthritis needs to be excluded urgently.

• Perthes' disease typically affects children aged between 3 and 10 years (peaking between 5 and 7 years); it affects about four boys for each girl affected; and it occurs bilaterally in about 10% of cases1.

• Slipped upper femoral epiphysis tends to occur in adolescents (aged 10-16 years), again more commonly in boys (ratio 3:1), patients of Afro-Caribbean origin, and obese patients.

• Transient synovitis typically has an acute onset, and spontaneous recovery with no radiological abnormality or systemic upset. It occurs between the ages of 2 and 10 years (peaking between 5 and …