Basic Diagnostic Plan 
1. Radiograph lower right limb.
2. Perform arthrocentesis of affected  area  to  look for bacteria/fungi. 

Adjunct Diagnostics (if basic diagnostics do not reveal abnormalities) 
1. Ultrasound lower right limb to see soft tissue structures.
2. MRI.
3. Scintigraphy.
4. Thermography.