Aims: To determine whether certain motion parameters could be linked to clinical signs and symptoms of instability in a group of chronic LBP patients. Methods: Thirty-four patients enrolled for an external þxation (ESF) test performed active ßexion-extension, axial rotation, and lateral bending motions, during which the relative motion between marker carriers attached to the Schanz screws was measured with an optoelectronic camera. The rotations of the vertebrae were analysed with special reference to ranges of motion, motion asymmetries, and coupled motions. Studentñs t-test was used to determine whether these parameters were signiþ cantly different between the patient groups that did and did not receive pain relief from the stabilization of the suspected painful segment/s. Results: The improvement of the patientñs functional status during the external þxation as well as after subsequent lumbar fusion surgery was signiþcantly correlated with the extension ROM (p=0.049 and p=0.036), and the ratio of extension to ßexion ROM (p=0.035 and p=0.044) at the index levels before surgery. No signiþcant correlations with the other motion pattern parameters were observed. Conclusions: In case of a positive ESF test, preserved motion at the symptomatic level/s before the surgery seemed to predict a favorable fusion outcome. On the other hand, abnormal patterns of asymmetry and coupled motion did not seem to be associated with pain relief after stabilization of the suspected painful segment/s.