Oral Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

INTRODUCTION:

Adult spinal deformity (ASD) patient outcomes from sagittal realignment surgery have relied on associations between static alignment measurements from standing radiographs, patient-reported and clinical outcomes supporting the notion that improving standing alignment will correspond with patient improvement [1]. Correcting sagittal balance follows the ‘cone of economy’ theorem [2] based on static measurements which do not completely represent the spine’s function during activities. Maintaining dynamic trunk control is important for patients during functional tasks where active muscles and dynamic forces are contributing to postural stability and spinal loading that influence post-operative success. Less is known about how longitudinal pre- to post-operative changes in trunk control relate to changes in static sagittal balance measurements and clinical outcomes. We hypothesize that post-operative improvements in dynamic trunk control during gait are better associated with clinical outcomes than static radiographic measurements.

METHODS:

Thirty-two ASD patients (IRB: 15-17095) undergoing realignment surgery with measurements at pre- and 6-week post-operation were chosen. Measurements of sagittal vertical alignment (SVA), spinal kyphosis and lordosis were taken from bi-plane radiographs (EOS). Trunk kinematics were collected using IMU sensors (Movella; 60 Hz) placed on the anterior thorax at the T8 level. Following familiarization, patients were asked to perform a five meter “out-and-back” walking trial. From the IMU data, the global transverse orientation of the thorax was calculated. The sagittal and frontal angles were analysed from initial heel strike after quite standing to final toe-off before the 180° turn. Two-dimensional Kernel Density Estimates (Gaussian bandwidth selector) of the transverse angles timeseries were completed for each patient’s pre- and 6-week post-operative walking trials. The 25-100% data probability range were measured as areas on the plots to estimate dynamic trunk control. The ASD patients were split into non-incident (N-IN) and incident (IN) groups if mechanical or radiographic failure was observed, or they reported a fall up to 6-months post-operatively. Data is presented as Median (Inter Quartile Range).

RESULTS:

Nine patients (4 PJK, 1 sagittal imbalance re-operation and 4 falls) were identified in the IN [age: 68 (66-74)] and 23 in N-IN [age: 70 (65-75), p=0.79]. Post-operative dynamic trunk control KDE area and static SVA decreased in both groups (KDE: IN=-43% p=0.25, N-IN=-4% p=0.37; SVA: IN=-73% p<0.01, N-IN=-86% p<0.01). Post-operative alignment measures increased similarly in both groups (Kyphosis: IN=27% p=0.16, N-IN=28% p=0.02; Lordosis: IN=72% p=0.12, N-IN=77% p<0.01).

DISCUSSION:

Stability and alignment measures followed similar trends for both groups pre- to post-operatively. The IN group however maintained larger KDE area demonstrating lower dynamic trunk control and resulted in larger static SVA measurements than the N-IN group post-operatively supporting our hypothesis. Reduced dynamic trunk control pre- and post-operatively combined with increased SVA post-operatively may reduce spine tissue tolerance due to repetitive suboptimal loading during activities of daily living, putting patients at higher risk of complications. Dynamic trunk control metrics could complement static clinical imaging measures of the spine’s structure and help improve ASD patient outcome assessment and forecasting by assessing patient’s spine function during more “real-world” tests.