One aspect of the invention relates to a flexible drive assembly (12) which includes drive elements (14) connected to one another in series. Each drive element has a body (16) with a central axis (18) and male and female ends (20, 22). The male end includes a projecting rib (26) of non-circular cross-section and the female end defines a socket (36) with a groove (44) therein which is of non-circular cross-section. The drive elements are connected to one another in series by location of the male end of one element in the series in the socket at the female end of a neighbouring element in the series with the rib of the male end received as a snap fit in the groove of the socket. The male ends and sockets are configured to allow limited pivotal movement to take place between adjacent elements, in each case about an axis transverse to the central axes of the elements, while also allowing the connected elements to transmit rotational torque in either direction from one to the other. Another aspect of the invention relates to a bone distraction apparatus (10) that incorporates such a flexible drive assembly.
