Scoliosis instrumentation alters primary and coupled motions of the spine: An in vitro study using entire thoracolumbar spine and rib cage specimens

Abstract

Abstract Background Effects of rigid posterior instrumentation on the three‐dimensional post‐operative spinal flexibility are widely unknown. Purpose of this in vitro study was to quantify these effects for characteristic adolescent idiopathic scoliosis instrumentations. Methods Six fresh frozen human thoracic and lumbar spine specimens (C7‐S) with entire rib cage from young adult donors (26–45 years) without clinically relevant deformity were loaded quasi‐statically with pure moments of 5 Nm in flexion/extension, lateral bending, and axial rotation. Primary and coupled motions of all segments were measured using optical motion tracking. Specimens were tested without instrumentation and with posterior rod instrumentations ranging from T2 to L1 (for Lenke Type 2) and from T8 to L3 (for Lenke Type 5) based on survey results among spinal deformity surgeons. Statistical differences were evaluated using the pairwise Friedman test. Results Primary ranges of motion were significantly (p 0.05). Conclusions Instrumentation reduces the primary flexibility and diminishes the natural coupling behavior between lateral bending and axial rotation, primarily in the upper thoracic spine, potentially causing correction loss and junctional deformity in the long‐term.

Keywords

• adolescent idiopathic scoliosis
• biomechanics
• coupled motions
• in vitro study
• lumbar spine
• posterior instrumentation