Curve Progression in Children with Spinal Deformity after Removal of Vertical Expandable Prosthetic Titanium Ribs

Curve Progression in Children with Spinal Deformity after Removal of Vertical Expandable Prosthetic Titanium Ribs

Corresponding author: Dr. Anna-Kathrin Hell, Pediatric Orthopedics, Department of Trauma, Orthopedic and Plastic Surgery, Universi- ty Medical Center Goettingen, Goettingen, Germany, Tel: 0049-551-39-8701, Fax: 0049-551-39-20558; Email : anna.hell@med.uni-goet- tingen.de

Abstract

Purpose

Vertical expandable prosthetic titanium rib (VEPTR) implants may be used in children with severe spinal deformities during the growth period before definite spinal fusion.

The purpose of this study was to evaluate spinal deformities before, during and after VEPTR treatment, with special focus on potential differences between congenital and neuromuscular scoliosis.

Methods

Retrospective cohort study on a population of 15 children with a continuous documentation starting before VEPTR treatment and ending with the removal of hardware prior to spinal fusion. Radiologic measurements of scoliosis and of pelvic obliquity were performed in anteroposterior radiographs, while kyphosis, lordosis and spinal length were evaluated in lateral radio- graphs. Measurements were conducted before and after initial VEPTR implantation, in two years intervals during VEPTR treat- ment as well as before and after final VEPTR explanation.

Results

Initial implantation of VEPTR was able to significantly reduce the main curve, which increased again over time. Howev- er, scoliosis in children with congenital spinal deformity re- mained stable after implant removal, whereas neuromuscular scoliosis showed a significant deterioration of the main curve immediately after VEPTR removal. Bending films pre VEPTR and after explanation showed 50% and 24% curve flexibility, respectively. The primary achieved correction of pelvic obliq- uity remained unchanged after implant removal in patients with congenital scoliosis, but deteriorated in neuromuscular children.

Conclusions

After removal of long-standing VEPTR implants, spinal de- formity in children with congenital scoliosis remained un- changed, suggesting an observing approach in the future. Bilateral VEPTR treatment using rib-to-pelvis constructs with- out touching the spine preserved some spinal flexibility in chil- dren with neuromuscular scoliosis.

Level of Evidence

Therapeutic Level IV

Keywords: Vertical Expandable Prosthetic Titanium Rib; Con- genital Scoliosis; Neuromuscular Scoliosis; Spinal Flexibility; Veptr Removal

Introduction

Progressive spinal deformity in children often requires early and repetitive surgical treatment. In the last decades, several growth-friendly devices such as vertical expandable prosthetic titanium rib (VEPTR) implants [1, 2], magnetically controlled devices [3, 4], growing rods [5, 6] and other growth-guided im- plants [7, 8] have been used to achieve this goal. However, the majority of these constructs serve as interim solutions, requir- ing definitive spinal fusion in puberty [9].

Recently, several problems connected with these pediatric im- plants have been reported [10–13]. Many of these devices may lead to stiffness of the spine due to auto fusion and ossifica- tions, thus making the definitive spinal fusion more complex [9, 10]. Additionally, this may also lead to a longer fusion area than initially assumed.

Another major problem poses the recently identified asymp- tomatic bacterial colonization of the implant [12, 13]. Rou- tinely, growth-friendly implants are removed at the same surgery as definitive spinal fusion. If bacteria colonizing the growth-friendly implants infect the final spondylodesis devic- es, severe local infection with multiple surgeries, septicemia and potentially life-threatening events may occur [14].

To avoid the latter complications, juvenile patients had their definitive spinal fusion in average 8 months after explanation of long-standing VEPTR devices allowing analysis of the flexi- bility of spinal deformity after VEPTR treatment. In this group,

curve pattern changes were analyzed focusing on the behavior of frontal and sagittal profiles in adolescents with neuromus- cular or congenital scoliosis after VEPTR treatment.

Material and Methods

In accordance with the ethical standards of the institution- al and national research committee and with the 1964 Hel- sinki declaration, we conducted a retrospective case study on children who underwent surgical implantation of VEPTR implants, several expansion surgeries and removal of VEPTR implants before final fusion. Fifteen patients met the inclusion criteria, which comprised (1) diagnosis as either neuromus- cular or congenital scoliosis (2) evident indication for a sur- gical intervention and (3) complete documentation of VEPTR treatment from the point before intervention to removal of implants. Twelve patients received definite spinal fusion after VEPTR treatment.

Patients underwent implantation of VEPTR devices between ribs and the lumbar spine with a second lateral implant from rib-to-rib or bilateral devices between ribs and the pelvis. Re- petitive expansion surgeries were performed approximately every six months. Clinical data such as gender, diagnosis, age at initial VEPTR implantation, type of construct and ability to walk were obtained.

Measurements of digitally available radiographs were per- formed using the radiologic processing program Centricity (GE Healthcare). All radiographs matching the following crite- ria were analyzed: standing or sitting anteroposterior, lateral and bending radiographs pre- and post-VEPTR implantation, anteroposterior and lateral radiographs in two-year-intervals during VEPTR treatment as well as pre and post VEPTR remov- al at the latest possible follow-up. Again, after final implant re- moval bending films were obtained.

Measurements of the Cobb angle [15] of the main curve (main- ly thoracic or thoracolumbar) and the associated cranial (mainly cervical) and caudal (mainly lumbar) curve and pelvic obliquity were conducted in every anteroposterior radiograph. Curve angles on bending film were also obtained. In the lat- eral radiographs, measurements of the kyphosis and lordosis and spinal length were performed. For the latter, the distance between the center of T1 and the sacrum was measured. Pel- vic obliquity was measured by evaluating the angle between a horizontal line and a straight line between the iliac crests.

For evaluation of inter-observer errors, all measurements were done by two independent investigators. The acquired data were analyzed statistically using the computer program Statistica 13.0 (Dell, USA). Analysis of variance and post-hoc tests were adopted. All data are presented as mean ± standard error of the mean and statistical significance was defined with levels as p<0.05 (*), p<0.01 (**) and p<0.001 (***).

 

Result

Patient demographics

Data of 15 scoliotic children (12 female, 3 male) were reviewed pre and post VEPTR implantation, half-time of VEPTR treat- ment (average 2.9 years), last measurement with the VEPTR devices implanted (average 5.5 years) and latest examination after removal of all VEPTR implants (average 6.3 years). In the ten cases of neuromuscular scoliosis, diagnosis was spinal muscular atrophy, cerebral palsy and type-IV collagen defi- ciency. All of them were non-ambulatory. The mean age of this group at initial VEPTR surgery was 8.7 years. The five cases of congenital scoliosis had typical vertebral body malforma- tion with unilateral unsegmented bars, failure of formation and segmentation as well as fused ribs. All of them were able to walk. Their mean age at VEPTR implantation was 4.3 years (figure 1). Patients were treated with rib-to-lumbar spine im- plants (n=6), bilateral rib-to-pelvis implants (n=7), or had de- vice conversions from the first to the second VEPTR construct (n=2) (table 1).

Radiographic results Curve progression

The main curve was corrected from mean angles of 72° (con- genital) and 52° (neuromuscular) prior to VEPTR treatment to 48° (p=0.024) and 37° (p<0.001) respectively immediately af- ter surgery (figure 2). This correction was maintained during the first 2.9 years, but deteriorated again to 61° and 49° at the

5.5 years follow-up. In neuromuscular children, the main curve increased significantly (p<0.001) directly after VEPTR expla- nation, whereas this curve remained stable in congenital scoli- otic patients after VEPTR removal.

Furthermore, analyzing the bending films pre implantation and after removal of the implants in ten children, a correction of the main thoracic curve of 50% (67.7° to 36°) could be ini- tially achieved versus 24% (77.7° to 59.3°) correction, respec- tively (p=0.06).

Pelvic obliquity

Development of pelvic obliquity displayed significant differ- ences between congenital and neuromuscular children. Chil- dren with congenital scoliosis did not have a relevant pelvic obliquity and this did not change throughout the treatment (figure 3). In children with neuromuscular scoliosis, pelvic obliquity was initially corrected by VEPTR implantation (from 12° to 4°) and during the first follow-up (5°). However, longer follow-up (8°) and explanation of VEPTR devices (9°) dimin- ished the positive effects on pelvic position.

Kyphosis and lordosis

In the sagittal plane, kyphosis measured around 45° for both patient groups before the first surgery. Kyphosis could not be reduced by spinal implantation, but instead even worsened during VEPTR treatment exceeding baseline values during fol- low-up.

Lordosis values averaged 36° prior to surgical intervention.

Again, VEPTR treatment failed to achieve any correction in both patient groups either directly after surgery or during fol- low-up. In contrast to kyphosis values, lordosis remained on a constant level.

Spinal length

The spinal length averaged 262 mm for congenital and 287 mm for neuromuscular patients before surgery. For congenital sco- liosis, spinal length increased steadily in the course of VEPTR treatment representing roughly a normal growth curve. In contrast, children with neuromuscular scoliosis experienced a sudden increase (32 mm) of spinal length immediately upon VEPTR surgery, but had an unchanged curve thereafter.

 

Discussion

Distraction based spinal implants such as the VEPTR device are commonly used in children with spinal deformities and thoracic insufficiency syndrome. Several studies have shown that implantation and repetitive lengthening of VEPTR im- plants achieve correction of the scoliotic curves [1, 16–19], as well as possibly improve thoracic insufficiency syndrome [1] and support spinal growth in congenital scoliosis [20]. In these children, definite spinal fusion remains the standard surgical treatment endpoint at puberty. Most clinicians perform VEPTR removal and definitive spondylodesis within one surgery. However, recent data suggest a two-staged procedure with at least some weeks in between when converting from the VEPTR system to spondylodesis to minimize implant-transmitted in- fection from one to the other implant system [12, 13].

To our knowledge, there are no studies available regarding the changes in spinal deformities after VEPTR explanation. Therefore, we observed spinal curve changes in children with long-standing VEPTR implants after explanation and prior to definitive spinal fusion.

Interestingly shown for the first time, the main curve of chil- dren with congenital scoliosis remained stable after removal of the VEPTR implants. In contrast, kyphotic deformity was poor- ly controlled over a long-term VEPTR treatment as described before [17, 19, 21]. However, kyphosis in congenital scoliosis did not progress after implant removal, thus suggesting an overall stiff spinal situation. In case of an acceptable kyphosis therapeutic management of congenital scoliosis after VEPTR removal should be reconsidered and possibly, congenital pa- tients could be spared from subsequent spinal fusion surgery with the risk of severe complications. Spinal length increased slowly over time during VEPTR treatment as described previ- ously [20].

Contrary, neuromuscular patients experienced marked initial curve correction by VEPTR implantation and deterioration of scoliosis immediately after explanation reflecting the flexibil- ity of neuromuscular spinal deformities. Analysing bending films pre VEPTR implantation and after removal, curve reduc- tion reflecting spinal flexibility was 50% versus 24% respec- tively. Previously reported increased stiffness and limited cor-

rection potential over time in children with spinal deformity and growing rod treatment [10] does not seem to apply to the same extend to flexible scoliosis in neuromuscular patients with VEPTR devices. In these patients, this spinal “no-touch technique” is beneficial in order to prevent stiffness and auto fusion and to reduce the risks in definitive spinal fusion as de- scribed by Lattig et al. [9]. Flexibility of neuromuscular spines was also confirmed by analysing the spinal length, which re- sponded significantly to VEPTR implantation only in neuro- muscular patients. The commonly seen increased pelvic obliq- uity in neuromuscular patients due to hip dislocation could be sufficiently controlled with bilateral VEPTR constructs and in- creased during long-term treatment and after implant removal Our study shows different outcomes of spinal deformities in congenital scoliosis compared to neuromuscular children af- ter implant removal at the beginning of puberty. However, the reported data only base on a congenital subset of five and a neuromuscular subset of ten children and result from hetero- geneous patient groups regarding age at VEPTR implantation, length of treatment and underlying etiology. Therefore, further studies analyzing different impact of treatment in neuromus- cular and congenital patients might be helpful.

 

Conclusion

Bilateral VEPTR treatment without touching the spine retains spinal flexibility in children with neuromuscular scoliosis. In congenital scoliosis, however, spinal deformity remains un- changed after removal of long-time VEPTR implants, indicat- ing an overall stiff spinal situation. In these cases, subsequent spinal fusion surgery should be reconsidered.

Conflicts of Interest and Source of Funding

Authors Andrea S Gantner, Lena Braunschweig, Konstantinos Tsaknakis, Heiko M Lorenz and Anna K Hell declare that they have no conflict of interest and no source of funding was re- ceived for this study.

Figure 1. Poster anterior (A-C) and lateral radiographs (D-F) of a 14-year-old girl with congenital scoliosis and a thoracic curve of 40 ° at the end of VEPTR treatment (A), which re- mained stable 4 months (B) and 16 months (C) after VEPTR removal.

Figure 2. Development of the main curve in patients with congenital (n=5, circles) and neuromuscular (n=10, squares) scoliosis pre and post VEPTR surgery, half-time of treatment, final measurement with VEPTR implant and after explanation of the VEPTR device. Data show the mean ± standard error of the mean and p-values refer to the pre-surgical value, if not indicated otherwise.

Figure 3. Development of pelvic obliquity in patients with congenital (n=5, circles) and neuromuscular (n=10, squares) scoliosis pre and post VEPTR surgery, half-time of treatment, final measurement with VEPTR implant and after explanation of the VEPTR device. Data show the mean ± standard error of the mean and p-values refer to the pre-surgical value.

Table 1 Overview of patient characteristics

Variable Neuromuscular Congenital
no. of patients 10 5
females 9 3
males 1 2
average age at VEPTR implanta- tion in years 8.7 4.3
(range) (6.6-12.6) (1.6-10.5)
average duration of VEPTR treat- ment in years 5.2 8.5
(range) (2.3-8.0) (4.4-11.0)
implant type (no. of patients)
rib to pelvis 6 1
rib to lumbar spine 3 3
change of im- plant types 1 1

VEPTR = vertical expandable prosthetic titanium rib; no. =

number

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