A biopsy trocar (1) is provided for performing bone marrow biopsies. The trocar comprises a biopsy needle (2) having a cannula (4), and a mandrel (3) having a shaft (6), the shaft (6) being suitable for sliding in the biopsy needle (2). The cannula (4) has, at its distal end, at least one internal rib (12, 21) forming a helix portion on the internal wall of the cannula (4), and the shaft (6) has a helical groove (16, 26) that is able to cooperate with the internal rib (12, 21), the internal rib (12, 21) being suitable for retaining a sample of marrow in the needle (2).
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