Heparin/dihydroergotamine for venous thrombosis prophylaxis: comparison of low-dose heparin and low molecular weight heparin in hip surgery - Lassen, M R; Borris, L C; Christiansen, H M; Møller-Larsen, F; Knudsen, V E; Boris, P; Nehen, A-M; de Carvalho, A; Jurik, A-G; Nielsen, B W; Lucht, U (Br J Surg, 1988)