How to differentiate between symptoms of sacroiliitis and piriformis syndrome?

Piriformis syndrome: the symptoms of piriformis syndrome and sacroilitis may be similar. They both involve the irritation of the sciatic nerve. The pain of piriformis syndrome may be increased with rotating the foot away from the body and palpation over the piriformis muscle

Skilled Examiner: Piriformis Synd often causes pain in the buttock region & can also cause sciatica-type symptoms with pain down the back of the thigh to just above the knee. Sacroilitis is not known to cause pain down the back of the thigh. A skilled examiner, such as an osteopath trained in hands-on diagnosis & manipulation can easily tell the diff: tenderness over the piriformis vs. tenderness along the SI jt.