Japan's highest court has ruled that a 19th-century law stipulating that couples should have the same surname does not violate the constitution, dealing a blow to the women's rights movement in the country.The rule does not specify whether the couple should adopt the man or the woman's surname, but in practice women take their husbands' names in 96 per cent of cases, which is seen as a manifestation of the country's patriarchal society.The ruling came in response to a lawsuit filed in 2011 by five women who argued that the requirement violated couples' civil rights.The claim encountered opposition from conservative politicians who argued that reversing the requirement could damage the country's traditional societal structures.