Anterior Release Generates More Thoracic Rotation Than Posterior Osteotomy: A Biomechanical Study of Human Cadaver Spines

Study Design. Biomechanical testing of human cadaveric spines. Objective. To determine the effect of anterior and posterior anatomic structures on the rotational stability of the thoracic spine. Summary of Background Data. Historically, large and/or stiff spinal deformities were treated with anterior release to facilitate correction. However, anterior release increases risks and requires a 2-part procedure. Recently, large or rigid deformities have been treated with a single posterior procedure using pedicle screws and spinal osteotomies. No study has yet evaluated the effect of anterior release or posterior osteotomy on thoracic spinal column rotation. Methods. Thoracolumbar spines were obtained from cadavers and segmented into upper, middle, and lower specimens. Specimens were cyclically loaded with a ±5 N·m moment in axial rotation for 10 cycles. Specimens were tested intact and then retested after sectioning or removal of each structure to simulate those removed during anterior release and posterior osteotomy. The total increases in axial rotation after posterior and anterior resections were calculated using a 3-dimensional motion capture camera system. For each ligament resection, the absolute and percent change in degrees of rotation was calculated from comparison with the intact specimen. The median data points were compared to account for outliers. Results. Resection of anterior structures was more efficacious than resection of posterior structures. An 8.8% to 71.9% increase in the amount of axial rotation was achieved by a posterior release, whereas resection of anterior structures led to a 141% to 288% increase in rotation. The differences between the anterior and posterior resections at all levels tested (T2–T3, T6–T7, and T10–T11) were significant (P < 0.05). Conclusion. Anterior release generated significantly more thoracic rotation than posterior osteotomy in biomechanical testing of human cadaver spines. Level of Evidence: N/A

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