Endoscopic Mechanical Spinal Hemiepiphysiodesis Modifies Spine Growth

• (a - DePuy AcroMed)

Purpose: Staple hemiepiphysiodesis is a well-established method for treating lower limb deformities. Growth control combined with thoracoscopic methods may lead to much earlier and less invasive treatments for scoliosis. The purpose of this study was to determine whether a novel spine staple consistently altered spine growth in an animal model of scoliosis.

Methods: In seven live, skeletally immature domestic pigs, custom spine staples were implanted into the left side of the mid-thoracic vertebrae using video-assisted thorascopic procedures approved by an IACUC. Six staples were implanted per pig from T6-7 to T11-12. The staples were placed just anterior to the rib heads and spanned the intervertebral discs and two adjacent growth plates. The staples were fixed to the vertebral bodies using two bone screws. The animals were maintained for 8 weeks and anesthetized biweekly for radiography. Anteroposterior (AP) traction, lateral, and right oblique radiographs were taken immediately after surgery, at 2, 4, 6 and 8 weeks, and again after spine harvest. Cobb angles were measured by standard methods in all views. Paired two-tailed t-tests were used to determine differences between initial and final post-operative curvatures.

Results: Five of the seven animals were followed for the entire 8-week period. These gained an average of 413 N (92.9 lbs), or 149% of their starting weight. Cobb angles at 0, 2, 4, 6, and 8 weeks were 0.8 degrees (+/- 1.8), 5.1 degrees (+/- 2.0), 7.3 degrees (+/- 1.1), 9.1 degrees (+/- 2.3), and 16.4 degrees (+/- 5.4), respectively. Cobb angles at 8 weeks in vivo were significantly different than the immediate post-operative values (p=0.006). With clearer radiographic views after spine harvest, the angles measured 22.4 degrees (+/- 2.8), markedly different than initial values (p=0.0001). Mean angles in the lateral view did not change with time; the variability reflects that individual animals progressed to either hyperkyphosis or hypokyphosis.

Conclusion: Spinal hemiepiphysiodesis using surgically relevant, minimally invasive techniques repeatedly induced spine curvature in a normal porcine model. If eventually successful clinically, these techniques would allow the highly desirable outcome of slowing the progression, and perhaps even correction, of spine deformity without spinal arthrodesis.

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