You might have had internal derangement of the knee at the time of initial injury.
If you are feeling pain or instability after activity, it is a sign ligament or meniscus injury.
Next Steps
Consult an orthopedic surgeon near you for detailed history, examination and relevant investigations.
Till then, use a knee support or a hinged knee brace for support while walking.
Also, please specify why are you on Deflazacort- is it for the knee issue or something else.