A novel fusionless vertebral physeal device inducing spinal growth modulation for the correction of spinal deformities

Abstract

Current fusionless scoliosis surgical techniques span the intervertebral disc. This alters the spine stiffness, disc pressure equilibrium and possibly may lead to disc degeneration. A new fusionless physeal device was developed that locally modulates vertebral growth by compressing the physeal ring, while maintaining maximum segmental spinal mobility without spanning the intervertebral disc. This study's objective was to test the feasibility of the device on a small animal model by inducing a scoliotic deformity (inverse approach) while analyzing the growth modifications. This study was conducted on caudal vertebrae of 21 rats (26-day-old) divided into 3 groups: (1) "experimental" (n = 11) with 4 instrumented vertebrae, (2) sham (n = 5) and (3) control (n = 5). Radiographs were taken at regular intervals during the 7-week experimental period. Tissues were embedded in methyl metacrylate (MMA), prepared by the cutting/grinding method, and then stained (Toluidine blue). The discs physiological alterations were qualitatively assessed and classified by inspection of the histological sections. A mean maximum Cobb angle of 30 masculine (+/-6 masculine) and a mean maximum vertebral wedge angle of 10 masculine (+/-3 masculine) were obtained between the 23rd and 35th day postoperative in the subgroup that underwent a long-term response from the device. The sham group underwent no growth alterations when compared to the control group. Descriptive histological analyses of the operated segments showed that 69% had no alterations to the intervertebral disc. This study presents experimental evidence that the device induces a significant and controlled wedging of the vertebrae while maintaining regular flexibility. In most discs, there were no visible morphological alterations induced. Further analysis of the discs and testing of this device on a larger animal is recommended with the long-term objective of developing an early treatment of progressive idiopathic scoliosis.

Fig. 1

Cobb angles versus time postoperative for all the rats of the experimental group

Fig. 2

Effective growth modulation of the 7th caudal vertebra in Rat 18 (3D reconstruction of micro CT Scan images, after sacrifice)

Fig. 3

Vertebral wedging of versus time. Seventh to tenth vertebrae are plotted for the four rats from long-term response subgroup

Fig. 4

Global growth deformations in the tail of rat 5 presenting a long term growth modulation response. The fives pictures show the evolution of the curvature in time

Fig. 5

Growth rate estimation versus days postoperative for the rats from all three experimental groups

Fig. 6

High resolution radiographs showing the position of 3 devices. a Efficient position. b Position of the device being pushed out by the vertebra. c Inefficient position

Fig. 7

a Intervertebral disc showing no visible alteration. b Deformed intervertebral disc showing no visible alteration. c Intervertebral disc with fibrous tissues. d Intervertebral disc with a hernia