Biomechanics of Spinal Hemiepiphysiodesis for Fusionless Scoliosis Treatment using Titanium Implant

Coombs, Matthew T.; Glos, David L.; Wall, Eric J.; Kim, Jay; Bylski-Austrow, Donita I.

Spine., POST ACCEPTANCE, 18 July 2013

Abstract:

Study Design. In vitro study of effect of hemiepiphyseal implant on biomechanical properties of porcine thoracic motion segments.

Objective. Determine whether implantation of a titanium clip-screw construct alters spine biomechanical properties.

Summary of Background Data. Growth modification is under investigation as a treatment for early adolescent idiopathic scoliosis. Biomechanical property changes due to device implantation are essential to characterize immediate post-operative treatment effects.

Methods. In vitro biomechanical tests were conducted on 18 thoracic functional spinal units. Specimens were tested before and after implantation of a clip-screw construct in lateral bending, flexion-extension, or axial rotation (n = 6 per loading direction). Pure moments were applied, and range of motion, stiffness, and neutral zone were measured. Axial translations were determined bilaterally.

Results. Implantation of the clip-screw construct decreased range of motion in lateral bending by 19% (p<0.0003), flexion-extension by 11% (p<0.04), and axial rotation by 8%. Mean stiffness in lateral bending toward and away from the treated side increased 20% (p<0.007) and 33%, respectively. In flexion and extension, mean stiffness increased 10% and 16%, respectively. Treatment decreased the neutral zone in lateral bending toward and away from the instrumented side by 30% (p<0.0003) and 47% (p<0.02). In flexion and extension, neutral zone decreased 20% (p<0.04) and 26% (p<0.007). In axial rotation toward and away from the treated side, mean neutral zone decreased by 22% (p<0.04) and 7%. Range of axial translation decreased on the ipsilateral side by 49% (p<0.001), and increased on the contralateral side by 17%.

Conclusions. Implantation of a titanium clip-screw construct decreased range of motion by less than one-fifth, increased stiffness by one-third or less, and decreased the neutral zone by less than one-half. Range of axial translation decreased on the instrumented side and increased contralaterally. This study suggests that most of the flexibility of the spine is preserved in the immediate post-operative period after implantation of the spinal hemiepiphyseal construct.

(C) 2013 by Lippincott Williams & Wilkins