Wiegers, E. J. A., C. A. Sewalt, E. Venema, N. W. L. Schep, J. A. N. . Verhaar, H. F. Lingsma, and D. . Den Hartog. “The volume–outcome Relationship for Hip Fractures: A Systematic Review and Meta-Analysis of 2,023,469 Patients”. Acta Orthopaedica, vol. 90, no. 1, Feb. 2019, pp. 26-32, doi:10.1080/17453674.2018.1545383.