Woke up withcalf cramping everytime i walk. went to urgent care. they did ultrasound said no clot. how accurate are ultrasounds? could si joint cause?

Muscle or nerve: Probably a muscle or nerve problem. Need MRI of lumbar spine to check for pinched nerve. Not likely SI problem.

High if Pos. & Yes.: Like all imaging tests, echo for vein clots=very equipment, operator & reader dependant. Get copy of images & review yourself to better understand. If clot found=likely high reliability; if not, good yet not absolute. Bigger issue: why the focus on this vs. many possible causes for calf muscle discomfort? (cause they had a test to sell?). SI joint? Calf muscles=controlled by nerves in spinal cord.

Very accurate: Unless you have a personal history of abnormal clotting or just got off a very long flight and have a very swollen leg that won't go down, the chance of a missed clot despite a negative ultrasound is very, very low. Cramps are difficult and often no cause is found, but yes, anything that causes you to walk funny (like SI joint pain) can strain muscles and contribute to cramping.