Abstract: An assembly for the stabilisation of vertebral bodies (12, 14) of the spine is described. It comprises a pair of pedicle screws (20) each having a threaded shaft (20a) with a tapering first end (20b) for introduction into a vertebral body and a head portion (20c) with a second end (20d), and is characterised in that it further comprises a spring member (18, 22, 24, 40, 42, 44) of the following form. The spring member has first and second ends, substantially straight portions (18b) adjacent each end and a substantially curvilinear central portion (18a) therebetween, the straight portions and the substantially curvilinear central portion being substantially coplanar. The assembly also includes a pair of fixation mechanisms (26) for securing the first and second ends of the spring member to the pair of pedicle screws. Typically the assembly will be for stabilisation of two adjacent vertebral bodies of the spine, that is one motion segment.