Ten year follow-up of Jarcho–Levin syndrome with thoracic insufficiency treated by VEPTR and MCGR VEPTR hybrid

Posterior Column Release and Lengthening with a Magnetic Growing Rod Construct in Severe Congenital Thoracic Fusion: A Report of 2 Cases

CASE

We describe treatment of severe multilevel congenital thoracic fusion in a 3-year-old girl with Apert Syndrome by posterior element excision, posterior column osteotomies, and gradual distraction with magnetically controlled growing rods (MCGR) with 3-year follow-up. We also describe short-term follow-up with similar management in an 8-year-old patient with a congenitally fused thoracic spine from Jarcho-Levin syndrome.

CONCLUSION

Posterior element resection and targeted posterior column osteotomies combined with gradual distraction with MCGR offers a promising treatment course for children with severe thoracic insufficiency syndrome derived from congenital fusions.

Thoracic insufficiency syndrome: Approaches to assessment and management

Thoracic insufficiency syndrome (TIS) was described in 2003 as the inability of the thorax to support normal respiration or lung growth. TIS includes a broad and disparate group of typically degenerative thoracospinal conditions. Although TIS arises due to a heterogeneous group of disorders and thus its incidence is not well quantified, general approaches to management and treatment exist. Evolving imaging techniques and measurements of health-related quality of life augment tests of pulmonary function to quantify disease burden, longitudinally and pre- and post-intervention. Intervention is primarily via growth-sparing surgery, for which several device options exist, to preserve vertical growth prior to a definitive spinal fusion at skeletal maturity.

"Law of Temporary Diminishing Distraction Gains": The Phenomenon of Temporary Diminished Distraction Lengths With Magnetically Controlled Growing Rods That Is Reverted With Rod Exchange

STUDY DESIGN

Prospective study.

OBJECTIVES

To study the increasing divergence between targeted and achieved distractions observed with magnetically controlled growing rod (MCGR)lengthening, and the relationship of this reduced rate of achieved lengthening with remaining rod length.

METHODS

Patients with early onset scoliosis (EOS) who underwent MCGRs with minimum 2-year follow-up were consecutively enrolled. Targeted and achieved lengths were compared. Correlation between percentage of lengthening achieved from targeted length was identified with the timing of rod exchanges.

RESULTS

A total of 20 patients fulfilled the inclusion criteria. The mean age at index surgery was 9.5 years and mean postoperative follow-up was 68 ± 28 months. Of these, 8 patients had at least one rod exchange that occurred at 23 ± 4 months. A decrease in rate of achieved lengthening was observed when compared with targeted distractions. The achieved lengthening drops from 86% of targeted length at the first distraction to only 58.8% at the 21st distraction episode for the first set of rods. After rod exchange, the average achieved lengthening went back up to 81.3% of the targeted length but subsequently had a gradual reduction to 35% at the 19th distraction episode.

CONCLUSIONS

We propose a "law of temporary diminishing distraction gains" that MCGR users should be aware of when monitoring rod lengthening. Diminishing distraction length gains is observed as the rod is lengthened and is a phenomenon independent of patient factors. It is only temporary as the rates of achieved lengthening returns to baseline after rod exchange.

A biomechanical study on the effect of lengthening magnitude on spine off-loading in magnetically controlled growing rod surgery: Implications on lengthening frequency

Purpose: To assess whether the magnitude of lengthening in magnetically controlled growing rod (MCGR) surgeries has an immediate or delayed effect on spinal off-loading. Methods: 9 whole porcine spines were instrumented using two standard MCGRs from T9 to L5. Static compression testing using a mechanical testing system (MTS) was performed at three MCGR lengthening stages (0 mm, 2 mm, and 6 mm) in each spine. At each stage, five cycles of compression at 175N with 25 min of relaxation was carried out. Off-loading was derived by comparing the load sustained by the spine with force applied by the MTS to the spine. Micro-CT imaging was subsequently performed. Results: The mean load sustained by the vertebral body before lengthening was 39.69N, and immediately after lengthening was 25.12N and 19.91N at 2 mm and 6 mm lengthening, respectively; decreasing to 10.07N, 8.31N, and 8.17N after 25 minutes of relaxation, at 0 mm, 2 mm, and 6 mm lengthening stages, respectively. There was no significant difference in off-loading between 2 mm and 6 mm lengthening stages, either instantaneously (p = 0.395) or after viscoelastic relaxation (p = 0.958). CT images showed fractures/separations at the level of pedicle screws in six spines and in the vertebral body's growth zone in five spines after 6 mm MCGR lengthening. Conclusion: This study demonstrated MCGRs cause significant off-loading of the spine leading to stress shielding. 6 mm of lengthening caused tissue damage and microfractures in some spines. There was no significant difference in spine off-loading between 2 mm and 6 mm MCGR lengthening, either immediately after lengthening or after viscoelastic relaxation.

The first magnetically controlled growing rod (MCGR) in the world - lessons learned and how the identified complications helped to develop the implant in the past decade: case report

Background

The first magnetically controlled growing rod (MCGR) was implanted in 2009. Since then multiple complications have been identified that have helped drive the development of the MCGR and its surgery. The aim of this report is to illustrate how identified complications in the first MCGR helped with developments in the past decade and to report a unique failure mechanism with stud fracture close to the barrel opening.

Case presentation

A 5-year old girl with a scoliosis of 58.5 degrees at T1–9 and 72.8 degrees at T9-L4 had a single MCGR inserted and anchored at T3–4 and L3–4. At postoperative 13 months the MCGR was noted to have lost of distraction between lengthening episodes due to unrestricted turning of the internal magnet. To prevent further loss of distraction, an external magnet was placed outside the skin to prevent the magnet from turning back. The overall balance was suboptimal and after the rod was fully distracted, proximal junctional kyphosis occurred. Subsequently, the MCGR was modified with an internal keeper plate to prevent loss of distraction and a dual set of these rods were implanted when the patient was 9 years old. Extension proximally to C7-T1 was done to manage the proximal junctional kyphosis. Her spinal balance improved and distractions continued. She subsequently developed add-on below and the piston rod was not aligned with the actuator. The lumbar spine was also observed to have autofusion. She subsequently had final fusion surgery performed at the age of 15 from C7-L4 leaving a residual tilt below to avoid fusion to the pelvis. The final extracted rod on the left side indicated the “crooked rod sign” on X-ray and rod dissections revealed a new failure mechanism of stud fracture close to the barrel opening. Body fluids and tissue may infiltrate the rod despite no obvious deformation or fractures resulting in hastened wearing of the threads.

Conclusions

There are various complications associated with MCGRs that are related to rod design and surgical inexperience. Repeated rod stalling is not recommended with potential stud fracture and “crooked rod sign”. Rotor stalling and thread wearing which indicates rod failure still require solutions.

Current status of the magnetically controlled growing rod in treatment of early-onset scoliosis: What we know after a decade of experience

The magnetically controlled growing rod (MCGR) has had approximately 10 years of clinical experience worldwide. Clinical effectiveness to control early-onset scoliosis is consistent even at final surgery. MCGRs have significantly lower relative percentage of infection or wound complications as compared to traditional growing rods. Most common complications include foundation failure and failure of distraction. Contouring of the rod especially at the proximal segment while accommodating for the straight actuator remains a difficult task and its failure may lead to proximal junctional kyphosis. Unique complications of MCGR include clunking, temporary diminishing distraction gains, and metallosis. Temporary reductions in distraction gains are observed as the MCGR lengthens but return to normal baseline distraction gains after rod exchange. Lack of standardization for rod configuration, distraction strategies and decisions of whether to keep the rods in situ, remove without fusion surgery or to perform spinal fusion at skeletal maturity will require further study.

The effect of magnetically controlled growing rods on three-dimensional changes in deformity correction

STUDY DESIGN

Prospective radiographic study.

OBJECTIVES

To determine the three-dimensional (3D) changes in deformity correction with magnetically controlled growing rod (MCGR) distractions. MCGRs can achieve similar coronal plane correction as traditional growing rods. The changes in the sagittal and axial planes are unknown and should be studied as these factors reflect potential for proximal junctional kyphosis and rotational deformity. Frequent MCGR distractions may potentially improve axial plane deformities to the same extent as coronal and sagittal plane deformities.

METHODS

Early onset scoliosis (EOS) patients who underwent dual MCGRs with minimum 2-year follow-up were included in this study. 3D reconstructions of 6-monthly biplanar images were used to study changes in coronal, sagittal and axial planes. Changes in growth parameters (body height and arm span) were scaled to changes in coronal Cobb angles, sagittal profile (T1-12, T4-12, L1-L5, L1-S1), and rotational profile at the proximal thoracic, main thoracic and lumbar curves, and pelvic parameters (sagittal pelvic tilt, lateral pelvic tilt and pelvis rotation).

RESULTS

A total of 10 EOS patients were studied. The mean age at index surgery was 8.2 ± 3.0 years and mean postoperative follow-up of 34.3 ± 9.5 months. Six patients had rod exchange at mean 29.5 ± 11.8 months after initial implantation. Despite consistent gains in body height and arm span, the main changes in coronal and rotational profiles only occurred at the initial rod implantation surgery with only small changes occurring with subsequent follow-ups. Patients with higher preoperative proximal junctional angles had flattening of the sagittal plane occurring at initial surgery with early rebound. No changes in pelvic parameters were observed.

CONCLUSIONS

The 3D changes with MCGR are mainly observed with initial rod implantation and no significant changes are observed with distractions. The MCGR can prevent deformity progression in the axial plane.

LEVEL OF EVIDENCE

IV.