Normal red marrow signal in the metaphyses. 

The periosteum is separated from the cortex by fibrovascular tissue, most evident at the metaphyses (e.g., fibular neck on axial PDFS), and should not be mistaken for subperiosteal hematoma or "stripping".
It is hyperintense on T2WI, demonstrates vivid contrast enhancement (not shown here), and is no longer seen after physeal closure.

Subchondral curvilinear hypointensity at the medial and lateral femoral condyles reflects irregular ossification, and should not be confused with osteochondritis dessicans. There is no significant marrow edema signal, and the overlying cartilage is intact. No undermining fluid or cystic change to suggest the latter.

Accessory ossification center at the inferior patella pole. No marrow hyperintensity, patellar tendon swelling/tendinosis, or surrounding soft tissue inflammation to suggest traction apophysitis (Sinding-Larsen-Johanssen disease).