The Spanish registry of hip and proximal femur fractures (SPARE-HIP): baseline characteristics of the first patients and participating centres - Prieto-Alhambra, D; Aguado-Maestro, I; Andres Cano, I; Asenjo Cambra, M; Balfagon Ferrer, A; Branas Baztan, F; Bravo Bardaj, M; Climent-Peris, V; Diaz Minarro, J; Diez Rodriguez, A; Escudero Martinez, E; Etxebarria-Foronda, I; et al. (Springer Verlag, 2016)