Safety in the use of ultrasound in rheumatology during the COVID-19 pandemic. Spanish Society of Rheumatology positioning paper Lucía Mayordomo; Juan Molina Collada; Félix M. Francisco Hernández; Ángel Bueno; Santos A. Insua Vilariño; Francisco Gabriel Jiménez-Núñez; Rosalía Martínez Pérez; Ingrid Möller; Jacqueline Usón Jaeger; José Francisco García-Llorente; José M. Álvaro-Gracia; Eduardo Aparicio Ruiz; Liliana Asaro Daverio; Esperanza Naredo;