Spinal growth modulation with posterior unilateral elastic tether in immature swine model

Three-dimensional vertebral shape changes confirm growth modulation after anterior vertebral body tethering for idiopathic scoliosis

PURPOSE

To evaluate three-dimensional (3D) vertebra and disk shape changes over 2 years following anterior vertebral body tether (AVBT) placement in patients with idiopathic scoliosis (IS).

METHODS

Patients with right thoracic IS treated with AVBT were retrospectively evaluated. 3D reconstructions were created from biplanar radiographs. Vertebral body and disk height (anterior, posterior, left and right) and shape (wedging angle) were recorded over the three apical segments in the local vertebral reference planes. Changes in height and wedging were measured through 2 years postoperatively. Change in patient height was correlated with changes in the spine dimensions.

RESULTS

Forty-nine patients (Risser 0-3, Sanders 2-4) were included. The mean age was 12.2 ± 1.4 years (range 8-14). The mean coronal curve was 51 ± 10° preoperatively, 31 ± 9° at first postoperative time point and 27 ± 11° at 2-year follow-up (p < 0.001). The mean patient height increased 8 cm by 2 years (p < 0.001). The left side of the spine (vertebra + disc) grew in height by 2.2 mm/level versus 0.7 mm/level on the right side (p < 0.001). This differential growth was composed of 0.5 mm/vertebral level and 1.0 mm/disk level. Evaluation of the change in disk heights showed significantly decreased height anteriorly (- 0.4 mm), posteriorly (- 0.3 mm) and on the right (- 0.5 mm) from FE to 2 years. Coronal wedging reduced 2.3°/level with 1.1°/vertebral level change and 1.2°/disk level. There was no differential growth in the sagittal plane (anterior/posterior height). Patient height change moderately correlated with 3D measures of vertebra + disk shape changes.

CONCLUSIONS

Three-dimensional analysis confirms AVBT in skeletally immature patients results in asymmetric growth of the apical spine segments. The left (untethered) side length increased more than 3 × than the right (tethered) side length with differential effects observed within the vertebral bodies and disks, each correlating with overall patient height change.

Fusionless All-Pedicle Screws for Posterior Deformity Correction in AIS Immature Patients Permit the Restoration of Normal Vertebral Morphology and Removal of the Instrumentation Once Bone Maturity Is Reached

The aim of this study was to report the restoration of normal vertebral morphology and the absence of curve progression after the removal of instrumentation in AIS patients that underwent posterior correction of the deformity by a common all-screws construct without fusion. A series of 36 AIS immature patients (Risser 3 or less) were included in the study. Instrumentation was removed once the maturity stage was complete (Risser 5). The curve correction was assessed pre- and postoperatively, before instrumentation removal, directly post-removal, and more than two years after instrumentation was removed. Epiphyseal vertebral growth modulation was assessed by the coronal wedging ratio (WR) at the apical level of the main curve (MC). The mean preoperative coronal Cobb was corrected from 53.7° ± 7.5 to 5.5° ± 7.5° (89.7%) at the immediate postop. After implant removal (31.0 ± 5.8 months), the MC was 13.1°. T5-T12 kyphosis showed significant improvement from 19.0° before curve correction to 27.1° after implant removal (p < 0.05). Before surgery, the WR was 0.71 ± 0.06, and after removal, 0.98 ± 0.08 (p < 0.001). At the end of the follow-up, the mean sagittal range of motion (ROM) of the T12-S1 segment was 51.2 ± 21.0°. The SRS-22 scores improved from 3.31 ± 0.25 preoperatively to 3.68 ± 0.25 at the final assessment (p < 0.001). In conclusion, a fusionless posterior approach using common all-pedicle screws correctly constructed satisfactory scoliotic main curves and permitted the removal of instrumentation once bone maturity was reached. The final correction was highly satisfactory, and an acceptable ROM of the previously lower instrumented segments was observed.

Anterior vertebral body tethering for thoracic idiopathic scoliosis leads to asymmetric growth of the periapical vertebrae

PURPOSE

To evaluate 3D growth of the periapical vertebrae and discs in the 2 years after anterior vertebral body tether (AVBT) placement in patients with idiopathic scoliosis (IS).

METHODS

Patients with IS treated with AVBT, ≥ 2 years of follow-up, and 3D spine reconstructions created from simultaneous, biplanar radiographs were studied. Patients were divided into two groups: progressive scoliosis correction (PC) or no/limited correction (NPC). The average of the 3 apical vertebral and disc heights and angular measures were made. The rate of change for each measure (mm/mo, °/mo) from first erect to 2-year follow-up was compared between groups.

RESULTS

Fourteen (Risser 0, Sanders 2-3) patients aged 11.4 ± 1.4 years with right thoracic scoliosis of 52 ± 9° were included. There were 7 patients per group (6F, 1M). Mean follow-up was 3.6 ± 1.1 (range 2-5) years. PC left-sided vertebral height increased 0.13 mm/months compared to 0.05 mm/mo in the NPC group (p = 0.001). Right (tethered side) vertebral growth was not different (PC: 0.07 mm/mo, NPC: 0.05 mm/mo, p = 0.2). Coronal vertebral wedging occurred at - 0.11°/mo compared to - 0.02°/mo for the PC and NPC groups, respectively (p = 0.004). Coronal disc angulation change was - 0.12°/mo in the PC group and - 0.04°/mo in the NPC group (p = 0.03), and was associated with loss of right disc height (PC: - 0.06 mm/mo) with little effect on the left disc height (PC: -0.01 mm/mo).

CONCLUSIONS

AVBT in immature patients with thoracic scoliosis can asymmetrically modulate growth of the periapical vertebrae and discs. Progressive reduction in scoliosis after AVBT was associated with greater concave growth rates in the vertebrae and loss of disc height on the convex side.

Motion preservation surgery for scoliosis with a vertebral body tethering system: a biomechanical study

PURPOSE

There is a paucity of studies on new vertebral body tethering (VBT) surgical constructs especially regarding their potentially motion-preserving ability. This study analyses their effects on the ROM of the spine.

METHODS

Human spines (T10-L3) were tested under pure moment in four different conditions: (1) native, (2) instrumented with one tether continuously connected in all vertebrae from T10 to L3, (3) additional instrumented with a second tether continuously connected in all vertebrae from T11 to L3, and (4) instrumented with one tether and one titanium rod (hybrid) attached to T12, L1 and L2. The instrumentation was inserted in the left lateral side. The intersegmental ROM was evaluated using a magnetic tracking system, and the medians were analysed. Please check and confirm the author names and initials are correct. Also, kindly confirm the details in the metadata are correct. The mentioned information is correct RESULTS: Compared to the native spine, the instrumented spine presented a reduction of less than 13% in global ROM considering flexion-extension and axial rotation. For left lateral bending, the median global ROM of the native spine (100%) significantly reduced to 74.6%, 66.4%, and 68.1% after testing one tether, two tethers and the hybrid construction, respectively. In these cases, the L1-L2 ROM was reduced to 68.3%, 58.5%, and 38.3%, respectively. In right lateral bending, the normalized global ROM of the spine with one tether, two tethers and the hybrid construction was 58.9%, 54.0%, and 56.6%, respectively. Considering the same order, the normalized L1-L2 ROM was 64.3%, 49.9%, and 35.3%, respectively.

CONCLUSION

The investigated VBT techniques preserved global ROM of the spine in flexion-extension and axial rotation while reduced the ROM in lateral bending.

Preliminary Study of a New Growing Rod System in Immature Swine Model

BACKGROUND

Growing rod techniques have been demonstrated to be a valuable treatment in early-onset scoliosis; however, repeated surgeries and general anesthesia cannot be avoided.

METHODS

This study included 12 immature swine that were randomly assigned to receive either a novel growing rod system (experimental group) or a traditional growing rod system (control group). Lengthening was undertaken at 4-week intervals, for a total observation period of 12 weeks. Radiography, computed tomography, and motion analysis of the spine were conducted to evaluate rod extension, growth and nonfusion of the spine, and fixation.

RESULTS

One swine (control group) was excluded from the analysis because of a deep wound infection at 1 week after the initial operation. No complications were observed in the remaining 11 swine. In the experimental group, the average lengthening operation lasted 12.1 ± 3.1 minutes, and average incision length was 1.1 ± 0.2 cm; both values were significantly less compared with the control group (P < 0.001). No significant between-group differences in mean trunk length, body mass, or thickness of cephalad-instrumented or caudad-instrumented vertebrae and intervertebral disks were present before the initial operation or at the final assessment (12 weeks after operation; P > 0.05). Spinal growth and motion of instrumented spinal segments were conserved.

CONCLUSIONS

The novel growing rod system is safe and effective in immature swine, preserving spine growth potential and involving less surgical trauma.

Development of spinal deformities in the tight-skin mouse

Tight-skin (TSK) mice are commonly used as an animal model to study the pathogenesis of Marfan syndrome (MFS), but little is known of their skeletal phenotype and in particular of the development of the spinal deformities, common in MFS. Here we examined growth of the axial skeletons of TSK and wild-type(B6) mice during their period of rapid growth. The whole bodies of mice, 4–12 weeks of age, were scanned after sacrifice, by micro-computed tomography (microCT). We reconstructed three-dimensional models of the spine and ribs, and measured vertebral body heights and rib lengths using the Mac-based image-processing software “OsiriX”. Although the TSK mice were smaller than the B6 mice at 4 weeks, they experienced an early growth spurt and by 8 weeks the height, but not the width, of the vertebral body was significantly greater in the TSK mice than the B6 mice. Measurement of the angles of scoliotic and kyphotic curves post-mortem in the mice was problematic, hence we measured changes that develop in skeletal elements in these disorders. As a marker of kyphosis, we measured anterior wedging of the vertebral bodies; as a marker for scoliosis we measured asymmetries in rib length. We found, unlike in the B6 mice where the pattern was diffuse, wedging in TSK mice was directly related to spinal level and peaked steeply at the thoracolumbar junction. There was also significant asymmetry in length of the ribs in the TSK mice, but not in the B6 mice. The TSK mice thus appear to exhibit spinal deformities seen in MFS and could be a useful model for gaining understanding of the mechanisms of development of scoliosis and kyphosis in this disorder.

Local Epiphyseal Growth Modulation for the Early Treatment of Progressive Scoliosis: Experimental Validation Using a Porcine Model

STUDY DESIGN

Experimental study of a localized device for the control of the vertebral growth using an immature porcine model.

OBJECTIVE

The aim of the study was to experimentally evaluate a localized device acting on the epiphyseal growth plates without bridging the intervertebral disc of immature hybrid pigs over 3 months of growth.

SUMMARY OF BACKGROUND DATA

Based on current published literature, fusionless devices offer promising scoliosis treatment alternatives to conventional spinal instrumentation and fusion in the growing spine. Current compression-based devices achieve growth modulation while also compressing the intervertebral discs, increasing the risk of long-term disc degeneration.

METHODS

An intravertebral staple acting on both the superior and inferior growth plates was inserted locally over T7-T9 of seven healthy immature pigs. Four age-matched animals served as controls. Radiographs were acquired monthly to assess induced spinal curvature and vertebral wedging (inverse model). Global (spinal) and local (vertebral, discal) geometric changes were evaluated over 3-months follow-up. Final left/right vertebral height differences were also quantified.

RESULTS

The only postoperative complication observed was one pig that had a persistent deep infection and was excluded from the study. No significant changes in spinal alignment were reported in control animals. Final induced Cobb angle was 25.0° ± 4.2° measured over T7-T9, with no observable sagittal profile modification. Highest vertebral wedging occurred at T9 with 18.2° ± 2.7°. Cumulative vertebral wedging over T7-T9 accounted for 45.4°, demonstrating evidence of reversed disc wedge phenomenon. Vertebral height was 3.9 ± 1.0 mm shorter on the instrumented side suggesting full growth restraint. Local and regional induced deformities significantly differed from their control counterparts (P < 0.001).

CONCLUSION

In this animal model, the local epiphyseal device achieved significant localized growth modulation over as little as three instrumented levels, with explicit vertebral wedging exclusive of the intervertebral disc. By increasing the number of instrumented levels, one may achieve higher curvature control potentially providing a unique local correction method to correct spinal deformity without affecting the intervertebral disc.

LEVEL OF EVIDENCE

5.

Environmental aspects of congenital scoliosis

Growing evidence has proved that many aspects of our lifestyle and the environment contribute to the development of congenital disease. Congenital spinal deformities are due to anomalous development of the vertebrae including failure of formation and segmentation during embryogenesis. The causes of congenital scoliosis have not been fully identified. A variety of factors are implicated in the development of vertebral abnormalities. Previous studies have demonstrated that both genetics and environmental factors are implicated in the development of vertebral abnormalities. However, no specific cause for congenital scoliosis has been identified. In our review, we focus on the environmental factors for the development of congenital scoliosis. Various maternal exposures during pregnancy including hypoxia, alcohol use, vitamin deficiency, valproic acid, boric acid, and hyperthermia have been observed to be associated with the occurrence of congenital scoliosis. This review describes the major environmental contributors of congenital scoliosis with an emphasis on treatment aspects associated with environmental disposition in congenital scoliosis.