[Segmental hypermobility of the spine before and following discectomy]

In 145 patients with open dissectomies (virgin back) preoperative functional x-rays (flexion/extension) were available. 80 patients out of this group could be used for additional postoperative functional x-rays. The mean follow-up was 28 +/- 18 months. The segmental mobility was measured using the translation in the z- and the angular rotation about the x-axis (methods of Morgan/ King and Dupuis et al.). The patients were divided in 3 groups in respect to the level of operation. For each patient 3 segments (L3/4 to L5/S1) were analyzed. Segmental hypermobility was defined with a translation of more than 4 mm respectively a rotation of more than 18 degrees (ROM flexion/extension). In patients operated at the level of L4/5 (n = 62) segmental hypermobility was found in 12.9% at L3/4, in 8.1% at L4/5 and in 17.7% at L5/S1. Patients with a discectomy at the level of L5/S1 (n = 79) showed preoperative hypermobility in 10.1% at L3/4, in 15.1% at L4/5 and in 12.6% at L5/S1. In postoperative x-rays patients with discectomy at L4/5 (n = 34) showed no significant differences after operation, neither in translation nor in rotation. In the L5/S1-discectomy group (n = 45) the mobility for rotation at the level L4/5 increased significantly from 6.7 degrees to 10.2 degrees and in the level L5/S1 from 5.2 degrees to 8.4 degrees. There was no significant difference for the translation in all 3 segments. In both discectomy groups the number of segments with hypermobility didn't change significantly after operation.