“…Fewer studies demonstrated the criterion valid-ity and construct validity [3,4,[23][24][25]34,38,47,51,[57][58][59][60][61][62][63][64][65][66][67][68][69][70] where comparators were clinical examination, MRI, XRay, and histology. The lack of information is partially explained because of the difficulties in finding the best comparator, the relatively new use of ultrasound in SpA, and a slow rate of disease progression [5,71,72].…”