The Relationship Between Postoperative Variation of Adjacent Segment Three-Dimensional Kinematics and Postoperative PI-LL in Patients With Degenerative Lumbar Scoliosis After Short Segment Fixation.

OBJECTIVE: The etiology of adjacent segment diseases and proximal junctional kyphosis has been related to biomechanical alterations after spinal operation. This study investigated the variation in pre- and postoperative range of motion in adjacent segments in patients with degenerative lumbar scoliosis (DLS) following posterior lumbar interbody fusion. PATIENTS AND METHODS: Eight patients with symptomatic DLS were analyzed using a biplane radiographic imaging system while adopting different postures. Synchronized biplane radiographs from L1 to S1 and the motions of each vertebra were acquired pre- and postoperatively. Six degrees of freedom (DOF) of kinematic data were compared between different postoperative pelvic incidence-lumbar lordosis (PI-LL) groups (group A: PI-LL = -10°-~10°; group B: PI-LL = 10°-~20°). RESULTS: After surgery, the axial rotational movement (primary rotation) during flexion-extension, bending, and torsion in the first adjacent segment at L3-4 decreased significantly in three patients (8.14 ± 2.78 vs. 15.13 ± 6.71; 8.36 ± 5.59 vs. 9.08 ± 3.57; 5.07 ± 0.56 vs. 9.25 ± 5.06). At this level, the torsion around the crania-caudal (CC) axis during bending (1.48 ± 1.01 vs. 7.05 ± 5.84, p < 0.05) and flexion around the mediolateral (ML) axis and bending rotation around the anterioposterior (AP) axis during torsion decreased postoperatively (6.37 ± 6.01 vs. 13.83 ± 8.12, 4.53 ± 1.97 vs. 13.06 ± 6.65; p < 0.05, p < 0.05). After surgery, in the L1-2 segment, translation along the ML direction decreased during bending (3.69 ± 2.12 vs. 14.76 ± 7.99, p < 0.05). In the adjacent L5-S1 segment, primary flexed rotation around the ML axis increased in group B postoperatively during flexion-extension, but decreased in group A (6.08 ± 1.17 vs. -13.41 ± 2.99, p < 0.05). Coupled flexed rotation around the ML axis decreased and showed the opposite trend during bending (-10.76 ± 5.51 vs. 18.12 ± 39.83, p < 0.05). CONCLUSIONS: Postoperative coupled motion at the adjacent segment decreased, which indicates an improved balance of the spinal order compared to before the surgery. However, primary motion changed according to the location of the upper instrumented vertebrae. Our results indicate that postoperative PI-LL values between 10° and 20° were associated with lower coupled motion and higher primary motion at L5-S1.