A six-year-old boy presents to the emergency department with a painful limp. Clinical examination reveals tenderness in the femoral triangle and some limitation of hip movements. An X-ray was done which was normal. Which of the following should be the next course of action?
Some of the guides have given option (MRI scan) as the answer by stating that this is a case of Perthe's disease. I do not agree with them.
Two most common causes of limp in a child between 4-10 years are :-


Transient synovitis of hip
Perthe's disease


The child in question has painful limp, tenderness in the femoral triangle and limitation of hip movement with normal X-ray. All of these can occur in both transient synovitis of hip and early stage of perthe's disease. However, the most favourable diagnosis here is transient synovitis because :-



Transient synovitis of hip is the most common cause of painful limp in a child between 4-10 years.
X-rays of transient synovitis are typically normal; however they may reveal subtle changes (widening of joint space). On the other hand x-rays are normal only in the initial stage of Perthe's; most of the time when patients present, the x-ray changes are there.
Child with perthe's disease may present with painful limp, but maximum patients present when pain has subsided and only limp is there, i.e. painless limp (in chronic stage).


Therefore, most probable diagnosis here is transient synovitis and management includes observation, bed rest and NSAIDs.
And this is the protocol, which is followed in most of the hospitals. In a suspected case of transient synovitis, we give conservative treatment, i.e. bed rest, NSAIDs and observation. If the child does not improve in 3-5 days, then we think of further investigation.
So, according to me option 'a' is the best answer here. You can choose your answer according to your thought process.
Wait and Watch/Observation
Ultrasonogrpahy
Aspiration
MRI Scan