What type of doctor can order a lower extremity joint mri?

Various. Evaluation of a joint is done to look for ligament and bony disruption in the case of unexplained pain, ongoing disease (like arthritis) or trauma. A joint MRI can be ordered by your family doctor, an er doctor, an orthopedic surgeon or a rheumatologist. It is performed by a radiologist who will evaluate the results.
Most. Almost any Doctor can order an MRI for a patient, although some state regulations vary. MDs, DOs, Chiropractors, Dentists, Podiatrists, and others can order MRI in my State. The limiting factor in my area is the insurance company and workman's compensation, which sometime pre-screen the order and will only pay for MRI done at specific locations and interpreted by specifically trained Doctors.

Related Questions

Where do I go to get a lower extremity joint MRI without dye done?

MRI without "dye" Some hospitals have a permanent MRI unit; others share one with other hospitals; there are also free-standing imaging offices that do ct's & mri's. Unless you are allergic to contrast (dye) or have severe kidney disease, contrast is used for an optimal study. Discuss that issue with the doc ordering the mri. Read more...
Many places. Many hospitals, medical centers, imaging centers or even some doctor's offices have MRI machines. Ask your Doctor for the centers nearest you, or do a google search for MRI centers in your area. Read more...