Madhok, Rajan, et al. “Urban Vs Rural Increase in Hip Fracture Incidence: Age and Sex of 901 Cases 1980-89 in Olmsted County, U.S.A”. Acta Orthopaedica, vol. 64, no. 5, Jan. 1993, pp. 543-8, doi:10.3109/17453679308993689.