ISSLS PRIZE IN BIOENGINEERING SCIENCE 2019: biomechanical changes in dynamic sagittal balance and lower limb compensatory strategies following realignment surgery in adult spinal deformity patients

Abstract

Study design A longitudinal cohort study. Objective To define a set of objective biomechanical metrics that are representative of adult spinal deformity (ASD) post-surgical outcomes and that may forecast post-surgical mechanical complications. Summary of background data Current outcomes for ASD surgical planning and post-surgical assessment are limited to static radiographic alignment and patient-reported questionnaires. Little is known about the compensatory biomechanical strategies for stabilizing sagittal balance during functional movements in ASD patients. Methods We collected in-clinic motion data from 15 ASD patients and 10 controls during an unassisted sit-to-stand (STS) functional maneuver. Joint motions were measured using noninvasive 3D depth mapping sensor technology. Mathematical methods were used to attain high-fidelity joint-position tracking for biomechanical modeling. This approach provided reliable measurements for biomechanical behaviors at the spine, hip, and knee. These included peak sagittal vertical axis (SVA) over the course of the STS, as well as forces and muscular moments at various joints. We compared changes in dynamic sagittal balance (DSB) metrics between pre- and post-surgery and then separately compared pre- and post-surgical data to controls. Results Standard radiographic and patient-reported outcomes significantly improved following realignment surgery. From the DSB biomechanical metrics, peak SVA and biomechanical loads and muscular forces on the lower lumbar spine significantly reduced following surgery (− 19 to − 30%, all p < 0.05). In addition, as SVA improved, hip moments decreased (− 28 to − 65%, all p < 0.05) and knee moments increased (+ 7 to + 28%, p < 0.05), indicating changes in lower limb compensatory strategies. After surgery, DSB data approached values from the controls, with some post-surgical metrics becoming statistically equivalent to controls. Conclusions Longitudinal changes in DSB following successful multi-level spinal realignment indicate reduced forces on the lower lumbar spine along with altered lower limb dynamics matching that of controls. Inadequate improvement in DSB may indicate increased risk of post-surgical mechanical failure. Graphical abstract These slides can be retrieved under Electronic Supplementary Material. Electronic supplementary material The online version of this article (10.1007/s00586-019-05925-2) contains supplementary material, which is available to authorized users.

Alteration of the Sitting and Standing Movement in Adult Spinal Deformity

“…On further examination of the corresponding kinematic curve ( Figure 4 ), peak hip flexion seems to be the most affected in ASD-sag. This corroborates results by Bailey et al who had previously demonstrated that ASD patients had a decreased peak of hip flexion during sit-to-stand, along with an increased energy expenditure at this level ( Bailey et al, 2019 ). Limitation in hip flexion could serve to prevent additional forward bending of the trunk in the sitting position and during the transition from sitting to standing, since ASD-sag already present with an increased trunk flexion during motion.…”

“…In particular, Bailey et al used a 3D depth-camera to describe motion kinematics and kinetics from 15 ASD patients, both pre- and postoperatively, compared with 10 controls. They showed that ASD patients had increased peak sagittal vertical axis (SVA) during sit-to-stand as well as increased lumbar and lower limb torques, which could be corrected by surgical interventions ( Bailey et al, 2019 ). However, the segmental motion of the spine was not analyzed and further subdivision of the ASD population according to the type of spinal deformity was not possible due to the small sample size.…”

Direct Lateral Corpectomy and Reconstruction Using an Expandable Cage Improves Local Kyphosis but Not Global Sagittal Alignment

“…Second, due to the lack of apparatus, we did not take whole spine X-rays including the lower extremity. Hence, we could not evaluate knee and hip joint flexion, which might have been used to compensate for sagittal imbalance [34]. Despite these limitations, this is the first report describing the correlation between anterior spinal surgery and changes in sagittal alignment, which might contribute to preoperative planning in OVF patients.…”

Computation of Intersegmental Moments during Standing Posture: Can We Neglect the Horizontal Ground Reaction Force? Results from an Experimental Study

“…Analyzing intersegmental moments in these patients could be of great interest. Recently, Bailey et al [25] reported the results of a biomechanical study that evaluated peak sagittal vertical axis, forces, and muscular moments at various joints. According to their results, a significant improvement of dynamic sagittal balance metrics was observed after surgical correction in the setting of adult spinal deformity.…”