X-ray is only required in patients who have an<unk><unk>  and one or more of the following:
Age >55
Isolated tenderness of the patella
Tenderness at the fibular head
Inability flex to 90 degrees
Inability to walk 4 steps BOTH immediately after the<unk>  and in the ED
Anteroposterior and lateral views
Consider sunrise if pain over patella
Consider sunrise if pain over patella
Acute knee injury
Knee dislocation
Knee fractures
Patella fracture
Ankle sprain
Segond fracture
Ankle fracture 
Tibial plateau fracture