Minimally Invasive Surgery for Neuromuscular Scoliosis

Results and Complications at a Minimal Follow-up of 5 Years

Mathilde Gaume, MD; Claudio Vergari, MD; Nejib Khouri, MD; Wafa Skalli, MD, PhD; Christophe Glorion, MD, PhD; Lotfi Miladi, MD

Disclosures

Spine. 2021;46(24):1696-1704. 

In This Article

Discussion

In this study, the outcomes and complications of bipolar minimally invasive surgery in children with neuromuscular scoliosis were reviewed with a mean follow-up of 6.5 years. Results showed stable correction of spinal deformity and pelvic obliquity over time, including patients at skeletal maturity. PSF was not required for any patient at last follow-up.

This technique was initially used as an alternative to TGR to reduce mechanical and infectious complications while waiting for PSF planned at skeletal maturity for all of them. However, stable clinical and radiological evolution were noticed with a reduced rate of mechanical complications that did not require performing PSF as initially planned while obtaining an acceptable growth of the spine. Moreover, fibrosis and spontaneous fusion around the implants and along the rods was observed during revision surgeries for rod lengthening (Figure 2) and on complementary examinations such as computed tomography (CT) scan (Figure 3) or x-rays.

Figure 2.

Fibrosis and spontaneous fusion observed around the implants during a rod lengthening procedure.

Figure 3.

Computed tomography scan after 5 years' follow-up with autofusion around the rods.

This delayed spontaneous fusion was asserted by lateral bending x-rays performed after hardware removal because of chronic infection, in one patient 8 years after initial surgery. The dynamic x-rays showed the total stiffness of the spine completely fused (Figure 4A–D). These observations lead to hypothesize that a progressive stiffening of the spine occurs over time under the influence of the permanent presence of rigid metallic rods (Figure 3). However, this concept of autofusion is not new. In 1984, Moe et al[16] noted spontaneous fusion at the curve extremities and/or at the curve apex in young children treated for severe deformities with subcutaneous Harrington rod without fusion. Mard-jetko et al[17] observed extensive fibrosis and laminar spontaneous fusions under the instrumented regions with Luqué rods, frequently involving the entire thoracic spine but also extending across the thoracolumbar spine. In Cahill et al[18] series, the rate of autofusion in children treated with growing rods (GR) was 89%. This autofusion was characterized by solid sheet of bone similar to a mature fusion mass and lead to only moderate correction at the time of definitive fusion. Jain et al[19] also noticed a progressive ankylosis after GR surgeries and suggested to avoid PSF at skeletal maturity for patients with satisfactory final alignment and trunk height, and no clinical or radiographic evidence of implant-related problems. Recently, Bouthors et al[20] considered retaining dual GR instead of PSF in patients at skeletal maturity with satisfactory deformity correction.

Figure 4.

A 15-year-old girl with cerebral palsy. (A and B) Initial AP and lateral x-rays; (C and D) after initial surgery; (E and F) lateral bending after removal of instrumentation for chronic infection, 8 years after initial surgery.

The autofusion in traditional GR occurs at early stage due to the damage of the intermediate area secondary to repetitive rod lengthening procedures. This autofusion is unwanted and participates to the "law of diminishing return."[21] That is why rod-lengthening procedure was recommended with an interval of 6 months. The PSF realized at the end of traditional GR series with large autofusion was required because the deformity correction was unsatisfactory. In these cases, PSF were frequently performed earlier, before skeletal maturity.

In the bipolar minimally invasive technique, the autofu-sion is expected. It occurs at a delayed stage thanks to the preservation of the intermediate area between the two bipolar fixations and also thanks to the permanent presence of metallic rods. This phenomenon was experienced with Luqué-Trolley technique in the 70 s in which rods were sliding despite spontaneous fusion.[22,23]

The avoidance of PSF is particularly beneficial in this fragile neuromuscular population characterized by medical comorbidities, impaired bone quality, and poor nutritional status. Compared with other types of scoliosis, complication rates of PSF procedures in neuromuscular scoliosis show the highest rate of complications (24 to 75%), followed by congenital (10.6%) and idiopathic (6.3%) scoliosis.[24] More specifically, Connie Poe-Kochert et al[25] reported a mean of 1.5 complications per patient after PSF following treatment with the use of GR.

Unlike others GR techniques that are mainly provisory to wait for arthrodesis at skeletal maturity, this bipolar technique may be considered as an alternative to arthrodesis as it is strong enough to be definitive. The avoidance of PSF in our series relies on two main advantages of the instrumentation.

The first one is the relatively large deformity corrections of the Cobb angle (61%) and the pelvic obliquity (83%) which remained stable at latest follow-up (Figures 5A–D and 6). These amounts of correction were similar or better to TGR series[25,26] and even PSF.[27–31]

Figure 5.

(A–D) Radiographs of a boy with cerebral palsy operated at 7 years' old. (A and B) Preoperative x-rays. (C and D) x-rays after 8 years' follow-up.

Figure 6.

(A–D) Pre- and latest photographs after 8 years follow-up of the patient treated by the minimally invasive fusionless surgery.

The second one is the strength and the stability of this type of fixation over time allowing PSF avoidance with a reduced mechanical complication rate. The bipolar construct differs from TGR by the stability of the proximal and distal fixations, the frame sliding construct, and the absence of intermediate area damage. Sponseller et al[9] reported a rate of 16.6% rod breakages in their series of 36 neuromuscular/syndromic patients treated with TGR extended to the pelvis. A rod breakage rate of 15% to 42% in TGR was published in early onset scoliosis from all etiology without pelvic fixation.[32–34] 10.6% were related to magnetically controlled GR.[10] In Mc Elroy series of GR for the treatment of scoliosis in cerebral palsy,[4] mechanical complications occurred in 19 of 27 (70%) patients including rod exchange (six), rod fracture (five), anchor revision (four), or anchor dislodgement (two).

In the present series, despite the absence of PSF, rod breakage occurred in five patients at risk (cerebral palsy with dystonia or hyperactivity, ambulatory patients and high body weight). They were managed by simple rod replacement or the use of four rods construct in the lumbar area as shown in Figure 7A–D. For one of them, it was decided peroperatively not to replace the broken rod because of the observation of extensive auto fusion around the rod. The removal of the rod could have generated important damages. At 3 years after the rod breakage, the spinal deformity of this patient remained stable without any complaint. Three cases of proximal hook dislodgement were experienced, one due to a severe osteoporosis and the others because of a lack of rod contouring at the beginning of our learning curve. This low rate of proximal mechanical complications can be explained biomechani-cally by the stability of the double claw-hook construct.[35] We experienced nine cases of proximal junctional kyphosis (11%) in our series without the need for revision surgery. This low incidence compared to other series[36] can be explained first by the type of the proximal fixation made of a solid double hooks claws; secondly by an adequate proximal bending of the rods; and finally by the high level of proximal limit of fixation (C7 or T1) in poor head control, sagittal trunk imbalance, and hyperkyphotic cases.

Figure 7.

Nonambulatory 14-year-old girl suffering from dystonic cerebral palsy. (A/B) x-ray of rod fracture 4.5 years after initial surgery; (C/D) x-ray after revision surgery and additional rod implantation.

The construct also draws its strength and stability from its pelvic fixation technique using iliosacral screws, which have proved their efficiency and reliability for >40 years of experience.[29,37] No screw pullout or breakage was reported. Osteolysis around iliosacral screws was observed radiologically in 25 patients but no screw migration, pull-out, or adverse clinical outcomes was associated. The screw loosening was due to the microrotation of the screw concomitant to flexion/extension motion of the trunk of the patient. Iliosacral screw malposition was reported in four cases operated with freehand technique. No new case of misplaced screw was reported since the use of peroperative CT scan control.

Finally, the infectious rate of 18% was lower than TGR treatment in patients with cerebral palsy (30%)[4] or spinal muscular atrophy,[38] probably thanks to the minimally invasive approach preserving the intermediate area. The number of repeated surgical procedures is known as a high-risk factor especially in this population.[39] Three of 15 infections occurred after initial surgery and 12 after rod-lengthening procedures. This rate of infections after rod lengthening procedures could be reduced using self-expanding devices that avoid repeated surgeries.

One of the weakness of this study was the absence of comparative treatment to assess the lower rate of complications of the present surgical technique. Further work is under way to analyze long-term lung function and quality of life. Preliminary results suggest minimal impact of surgery on pulmonary management, and an overall patient satisfaction. All patients still did not achieve their skeletal maturity and the study still needs long-term follow-up (>10 years) to evaluate the effectiveness of this treatment to confirm the stability of the construct allowing the avoidance of PSF. Secondly, there were no radiological evidence to quantitatively assess the quality of the progressive ankylosis of the spine. These results open the way for further studies to evaluate spinal ankylosis using noninvasive examinations (e.g., magnetic resonance imaging and ultrasound).

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