|SYMPOSIUM: COMPLICATIONS IN SPINE SURGERY
|Year : 2023 | Volume
| Issue : 1 | Page : 27-36
Complications of growing rod technique for early onset scoliosis
Abhishek Srivastava, Anuj Gupta, Vikas Hanasoge, Arvind Jayaswal
Department of Spine Surgery, Max Super Speciality Hospital, Vaishali, Ghaziabad, Uttar Pradesh, India
|Date of Submission||14-Oct-2022|
|Date of Decision||15-Nov-2022|
|Date of Acceptance||04-Jan-2023|
|Date of Web Publication||11-Feb-2023|
Department of Spine Surgery, Max Super Speciality Hospital, W-3, Sector-1, Vaishali, Ghaziabad 201012, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Early onset scoliosis (EOS) is defined as scoliosis occurring in children less than 10 years of age. The EOS is a separate entity of discussion as development of lungs is restricted due to restricted growth of the chest wall, unlike in adolescent scoliosis which is more of a cosmetic problem. Therefore, in EOS, control of deformity at early stage and growth of the spine should go hand-in-hand. The most favored option in recent era is growing rods which allow growth of the spine but in a controlled manner. However due to fusionless nature, these techniques have high rate of complications. The complications primarily include implant related, wound related, and anesthetic complications. Recently impact of multiple surgeries on psychology of developing child has been reported. This narrative reviews the literature about complications associated with growing rod surgeries in EOS.
Keywords: Early onset scoliosis, growing rods, implant-related complications, MCGR, TGR
|How to cite this article:|
Srivastava A, Gupta A, Hanasoge V, Jayaswal A. Complications of growing rod technique for early onset scoliosis. Indian Spine J 2023;6:27-36
|How to cite this URL:|
Srivastava A, Gupta A, Hanasoge V, Jayaswal A. Complications of growing rod technique for early onset scoliosis. Indian Spine J [serial online] 2023 [cited 2023 Mar 27];6:27-36. Available from: https://www.isjonline.com/text.asp?2023/6/1/27/369578
| Introduction|| |
Scoliosis research society (SRS) defines early onset scoliosis (EOS) as scoliosis occurring in children less than 10 years of age irrespective of etiology. They may be associated with congenital vertebral body anomalies/dysplasia’s, neuromuscular disorders, connective tissue disorders, or idiopathic in nature which can present with or without thoracic insufficiency. Treatment of these cases is often challenging due to significant remaining growth potential of the spine and incomplete lung development. Non-operative or conservative treatment in terms of bracing in a progressive curve often leads to poor outcome and pulmonary function disorders., Historically used in EOS, early correction, and definitive fusion treatment strategies through anterior and/or posterior based approaches have been abandoned, due to a better understanding of their poor long-term outcomes. Early fusion in EOS leads to small fixed thoracic cage with underdeveloped lungs causing pulmonary complications and reduced average lifespan in addition to stunted growth of the spine. Therefore, to ameliorate the above-mentioned drawbacks, the growing rods were introduced which ushered in a paradigm shift in the management of this complex problem. The growing rod instrumentation allows spinal growth in guided fashion while allowing lung growth to happen by increasing the space available for lungs. Fusionless spinal instrumentation was first introduced by Paul Harrington in 1963 for early onset scoliosis and Moe reported after 20 years the first growing rod which was subcutaneous and used hooks as anchors. In 1982, Luque treated EOS with segmental wiring without external support and rods were placed next to the spine after complete sub-periosteal stripping. However, these technique despite initial encouraging results documented spontaneous fusion, high implant related complications, limited spinal growth, and control of deformity, and over the years are rarely used now. All the above techniques are not widely used and growing rods became popular after the advent of better spine instrumentation especially pedicle screws. Although many techniques have developed since then, pedicle screw anchor based submuscular dual growing rods remain popular worldwide.,, Fusionless surgeries postpone final fusion and keep the deformity controlled until the complete development of lungs and spine. This allows for immature lung alveoli to both multiply in number and also increase in size.
The salutary effect of these techniques has significantly decreased the complication rates arising out of natural history of EOS, which is of progression and in severe cases leads to thoracic insufficiency syndrome.
There has been a significant progress over the years in development and improvement in growing rod techniques. The newer development magnetically controlled growing rods (MCGR) is currently in spotlight, where after the initial application, the subsequent routine distractions are non-invasive and can be done in OPD on awake patient obliviating the need for repeated anesthetic exposure.
Goals of treatment in early onset scoliosis include:
- Guided spinal growth with control of the deformity
- Lung development
- Chest wall growth
- Improved pulmonary function and prevention of thoracic insufficiency syndrome
- Better quality of life
Treatment with growing rods also stimulates the growth of the individual bodies within the area of instrumentation making the patient’s alignment more balanced. Despite the improvements in technique and implants in EOS, the complication rates still remain high. More than half of EOS patients experience at least one complication following growing rod constructs. This is partly due to long duration of treatment and more frequency of required surgical procedures. This narrative review looks at the complications commonly associated with EOS surgical management.
| Implant Related Complications (IRC)|| |
IRC are the most common complications seen in patients with EOS. This is attributed to the divergent requirements of providing long-term spine alignment and deformity correction/alignment without fusion. Thus, the construct is positioned, in the absence of fusion, in load bearing rather than load sharing position making it prone for failure. This leads to repeated cyclical loading going on to metal/implant fatigue. This problem is further accentuated by higher incidence of compromised fixation due to poor bone quality, deformed or underdeveloped pedicles, and altered and immature anatomy, which precludes use of larger size and dense implant constructs. The metanalysis by Xu et al. shows dual rods have higher coronal correction and lengthening with fewer rates of implant related complications as compared to single rod construct but higher rate of surgical site complications.
Sagittal alignment also has an important role to play as the thoracic hyper kyphosis (>40°) has been associated with increased implant failure, commonly in the form of rod breakage. This can be attributed to increased forces due to hyper kyphosis at implant bone interface as well as the increased stress in the implant itself. This was correlated with amount of hyper kyphosis and was seen more commonly in syndromic cases. Although kyphosis has been proven to be associated with implant failure the combination of rod diameter and construct levels/anchored levels (CL/AL) ratio, (which is number of levels spanned by instrumentation divided by number of levels with bone anchor fixation), demonstrated significant correlation with implant related complications. The CL/AL ratio less than 3:5 decreases the risk of implant related complications by shortening the length of construct (CL) and or increase the number of anchored levels (AL). Rod diameter less than 5 mm is associated with increased risk of IRC even after controlling maximum kyphosis. It occurred more frequently in 2-level anchor foundation compared with 3 or more level at both cephalad and caudal levels.
Severe scoliosis where Cobbs angle is more than 90° leads to higher implant related complications. Similarly syndromic patients such as with neurofibromatosis treated with growing rods show higher incidence of IRC (57%), most commonly failure of proximal constructs, rod breakage, and prominent implants. Loosening of the implant is defined as loss of bone-implant contact without migration whereas pull out is loss of contact with migration.
Risk factors for IRC include,
- (1) Overzealous curve correction
- (2) Early age of onset
- (3) Higher degree of scoliosis
- (4) Kyphosis more than 50 degree
- (5) Location of the apex of the curve in the middle-to-caudal thoracic area.
- (6) Rod metal type and diameter [stainless steel and small diameter rods are more prone to breakage]
- (7) Location of rod insertion [subcutaneous rod insertion has more complication rates compared to submuscular]
- (8) Duration of lengthening intervals
- (9) Single growing rods
- (10) Etiology [syndromic has higher incidence of rod breakage]
- (11) Activity level of the child [rod breakage more common in independent ambulators]
The reported complication rate due to index surgery in growing rods is approximately 20%, but the complication rates increase during the treatment period (58%) as frequent lengthening are required. Early age at index surgery requires more duration of lengthening, thereby increasing the incidence of complications.
Construct wise, four pedicle screws implanted in two adjacent bodies at each anchor site provide strongest construct in pull out testing and crosslinks do not seem to enhance fixation.
Implant prominence is one of the disturbing features for the children while sleeping and during brace application. This can cause breakdown of the skin or can cause local pain. Subfascial/ Submuscular placement of the implant reduces implant prominence and number of unplanned surgeries. The rationale for putting growing rods subcutaneously is to prevent spontaneous fusion but wound related complications and IRC increases (31%) as compared to submuscular placement. It has also been observed that subcutaneous placement has lower control over the deformity as its effect is negated by intervening soft tissues.
Rod fracture implies fatigue fracture and location of the anchor site contributes significantly for these fractures. Rib based anchor fixation has lesser incidence compared to spine-based fixation as there is reduction in rigidity of construct and movement at rib-hook interface and costovertebral joint allows dissipation of forces across the rod. The rod fracture is the most common (15%) implant related complication seen in EOS treated with growing rods. Yang et al. reported the incidence of rod fracture in all hook constructs, all screws constructs, and hybrid construct containing both screws and hooks. The incidence was 12% in all hooks, 9% in all screws, and 10% in hybrid and it was not statistically significant.
The complication profile of the devices can differ as there are few differences in the application and lengthening techniques between different devices. Complications should be anticipated and should be explained in detail to the parents and care givers as children undergo multiple lengthening procedures in traditional growth rods (TGR) at every 4–6 months intervals.
MCGR rods due to its non-invasive mechanism of lengthening has gained popularity as a preferred procedure of choice among surgeons as well as parents, looking for treatment of EOS. However, in underprivileged healthcare system and in certain situation, traditional growth rods are still the first choice., The failure rates between these two rods are much similar when considering anchor pull out (11.8%) and rod breakage (10.6%). Nevertheless, MCGR has a higher chance of unplanned revision surgery. Distraction mechanism failure—Failure to distract non-invasively which is more common due to reduced force generation (due to high BMI of the patient/rigid curves) and breakage of actuator pin were the main causes of unplanned revisions., More the distraction magnitude, higher the distraction forces and the off-axis loading, resulting in higher wear and breakage of rod components. This can be reduced by applying minimum distractive forces such as 1.5 to 2 mm every 2–3 months as in MCGR rather than 4.5–6 mm every 6 months as in TGR. This also reduces the tissue trauma, spontaneous fusion, and in turn reduces “Law of diminishing returns.”,, First described in traditional growth rods, this law is applicable to MCGR from 4th distraction onwards and it is explained by tissue scarring and stiffening of the instrumented segment., The MCGR are difficult to contour as the major part of the implant is the actuator and hence implant related complications are frequent with incidence of almost 50% during initial 2–3 years. Despite the above drawbacks, an average of 2.03 surgical procedures per patient were avoided with non-invasive distraction at the end of follow-up when compared to management by traditional growing rods.
These unplanned revisions due to IRC in MCGR, are a serious burden for the patient and family, which increases the psychological trauma and cost dramatically.,,, Contrary to the expectation, the incidence of implant related complications such as screw pull-out and rod breakage remain unchanged with the use of MCGR.
Even in hybrid constructs where MCGR is a part, the most common complication noted was failure to distract and in 7 out of 20 cases, re-operation was performed in one study. Other complications in this study include failure of the actuator which was followed by driving pin fracture and in some cases radial bearing fracture.
Risks of rod breakage, junctional failure, pseudoarthrosis, screw loosening are higher in patients with neuromuscular scoliosis treated with MCGR similar to TGR, underscoring the role of etiology in growth rods failure.,,,
Overall complication rate was 57% which includes proximal screw loosening [Figure 1], failure to lengthen [Figure 2], rod and screw breakages [Figure 3], PJK [Figure 1], wound dehiscence with implant exposure, infections, secondary lumbar scoliosis, painful OPD distraction and medical complications such as pulmonary embolism, pulmonary insufficiency. As discussed previously these are more prevalent in syndromic and neuromuscular, although not significantly.[Table 1] summarizes the incidence of IRC in few prominent studies on TGR.
|Figure 1: A 4-year follow-up of magnetically controlled growing rods showing proximal junctional kyphosis (PJK) and proximal screw pull-out|
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|Figure 2: (a) Pre-operative X-rays of 8 years/F, progressive EOS. (b) Immediate post-op X-rays, magnetically controlled growing rods was applied. (c) After 3 years of follow-up, failure to distract on left side and lowering of apex. (d) Metallosis around actuator seen during final fusion. (e) Two years follow-up after final fusion|
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|Figure 3: (a) Pre-op X-rays of congenital scoliosis managed with traditional growth rods. (b) Proximal screw breakage. (c) Proximal screw replaced during planned lengthening|
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|Table 1: Implant related complications in various series of TGR (Original)|
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| Wound Related Complications|| |
Unlike idiopathic scoliosis, repeated surgery and complications are a norm in surgical management of EOS. Recurrent lengthening procedures with multiple surgeries increase the likelihood of wound complications [Figure 4]. This is the second most common complication after implant related in EOS surgery.
This problem is a major reason for unplanned return to operation room in TGR. Bess et al. reported 39% whereas Basu et al. reported only 17% of patient returning unplanned to OR for wound related issues/debridement. The wound-related complication rate per patient of the growing rod technique ranges from 9.1% to 24.3%. Majority of wound problems (80%) were due to surgical site infections (SSI) out of which deep infections constituted 61% followed by superficial infections in the rest. Younger children’s body habitus, including nominal soft tissue coverage, lead to prominent implants and may also contribute to more wound problems with dual growing rods.
Similarly, in VEPTR the wound-related complication rate per patient ranged from 8.3% to 69.6% (median 21.7%) in systematic review by Latalski et al. The incidence of unplanned surgery due to wound problems ranged from 31.3% to 57.1% (median 44.2%)., They further reported that SSI was higher compared to TGR at 85.7%, rest were classified as “other wound problems.” 62.5% were deep infections and SSI was superficial in 37.5% cases. In a direct comparison reported by Matsumoto et al. where they compared VEPTR with spine based TGR systems, he found significantly less surgical site complications in spine-based groups versus rib-based group for neuromuscular/syndromic patients. The most common presentation of SSI is wound drainage and dehiscence (71%) followed by fever, pain and tenderness over implant site (49%) with localized swelling/abscess. Laboratory values were not elevated in 2/3 of patients. The majority of infections were caused by gram positive bacteria and Staph Aureus was the specific organism isolated in most cases which was of methicillin sensitive variety., Crews et al. noted that the only factor which affected the propensity to develop SSI was administration of pre-operative antibiotic outside the 1–30 min window, rest other determinants such as demographic, surgery related and patient related factors had no major bearing. However, Striano et al. identified low body weight, immobility and distal surgical sites compared to proximal had higher association with SSI.
The techniques which intend to limit repeated procedures such as SHILLA and MCGR have reduced rates of infection at 16.7% and 7.7% respectively. This trend was also noted by Thakar et al. in their metanalysis where the overall incidence of deep infection in MCGR rod was 3.3% and 2.2% reported superficial wound infection.
| Junctional Kyphosis|| |
Proximal junction kyphosis (PJK) is defined as proximal junctional angle ≥10° or ≥10° increase from pre-operative value. The proximal junctional angle is calculated as angle formed between caudal end plate of upper instrumented vertebrae (UIV) and cephalad end plate of UIV+2. The phenomenon of PJK was first described in the cases of adult spinal deformity by Glattes et al. The incidence of PJK reported by authors ranges from 17% to 61.7%. The incidence in EOS is reported to be 42% by Shah et al. in their series of EOS growing rods with all screw construct. However, Watanabe et al. in their series reported an incidence of 26% but they considered more than 20-degree change from pre op as PJK. The risk factors for PJK were broadly divided into surgical risk factors, radiographic risk factors and patient related risk factors.
The surgical risk factors include choice of approach and disruption of posterior tension band. Since all growing rod techniques are done by posterior approach, hence there is an inherent risk of PJK. The disruption of posterior tension band and supporting structures like facet capsule form the major iatrogenic preventable cause of PJK. Another important cause seen in cases of EOS is lower instrumented vertebrae (LIV) at or cranial to L3. As we know, thoracic kyphosis and lumbar lordosis balance each other to maintain sagittal profile of a person. In deformity surgeries including growing rod, surgeons tend to overcorrect kyphosis. If the LIV is L3 or cranial to it, then lumbar lordosis remains unchanged whereas thoracic kyphosis is reduced and chances of PJK is increased. The distraction forces applied during distraction of growing rods exerts kyphogenic force which increases the proximal junctional angle and again predisposes the spine for PJK. It has been seen that chances of PJK increase after four or more rod lengthening procedures., A note should be made about the type of anchors used for proximal foundation. There has been no difference found in the incidence of PJK with the different anchors used.
The radiographic risk factors include proximal thoracic scoliosis ≥40°, main thoracic kyphosis ≥60° and high pelvic incidence (PI). The proximal thoracic scoliosis curve ≥40° imposes difficulty in applying proximal anchor resulting in overzealous exposure of soft tissues and damage of posterior tension band. Anderson et al. demonstrated that there is 12.62% loss of flexion stiffness after supraspinous and interspinous ligament transection combined with supralaminar hook preparation. Moreover, in growing rod constructs, after repeated lengthening, the proximal spine bears excessive forces, further predisposing for PJK. The main thoracic kyphosis ≥60° has increased proximal junctional angle and as explained above, the surgeons tend to overcorrect without disturbing lumbar lordosis and incidence of PJK is increased. The PI has been proven to be strongly associated with spondylolysis and spondylolisthesis. It has been reported that there is no difference in the PI due to scoliosis per se and is comparable with the normal population. Though the relation of PI has not been extensively studied but PJK is more commonly seen in patients with high PI (>60˚).
The patient related risk factors pertaining to EOS include older age and high BMI. Mac-Thiong et al. have reported correlation between age, pelvic parameters and thoracic kyphosis. The increasing age has been associated with increasing thoracic kyphosis. Also, correlation with high BMI and PJK has been reported in some studies but few studies discarded any correlation between them.
Inaparthy et al. have reported PJK incidence of 28% in a case series of MCGR in which they use tail gaiting technique of distraction. They found syndromic etiology, male sex, a greater number of distractions, pre operative hyperkyphosis and younger age as predisposing factors for PJK in MCGR patients. This is attributable in part to implant design where the non-malleable actuator part of MCGR stays in thoracic spine causing hypokyphosis and pushing pressure at end leading to increased risk of PJK while distraction.
In summation, the common risk factors responsible for PJK in EOS treated with growing rod surgery are:
- Proximal thoracic scoliosis ≥40°.
- Main thoracic kyphosis ≥60°.
- LIV at or cranial to L3.
- 4 or more rod-lengthening procedures.
- Syndromic etiology
| Complications of Repeated Anesthesia|| |
Early onset scoliosis requires repeated anesthetic exposure (AE) which may be in the stage of radiological diagnosis, index surgery, repeated distractions/lengthening, final fusion and any other unplanned procedures arising out of complications. The duration in index surgery, any unplanned return and final fusion can be long while short AE is required for diagnostic and lengthening procedures. In a study published by Goldstein et al., the percentage of total anesthetic exposure in children with growth rod was 55% in main procedures whereas associated care procedures accounted for 45% of total anesthetic time (TAT). The maximum share was taken by revision surgeries which was 27% where as planned distractions consisted only 14% of TAT. Anesthetic drugs have potential to histologically damage the neurons and retard development of circuits in brain, as outlined in various in vivo animal model studies.,, The increasing number of human studies are indicative of neurocognitive affection which is manifested in form of higher incidence of behavioral disorders and learning disabilities in these children. DiMaggio et al. in their large study on pediatric population determined that the hazard ratio for developing behavioral or developmental disorder associated with anesthesia was 1.6 for children under the age of 3 years. The ratio dramatically increased from 1.1 for one operation to 4.0 for three or more operations experienced by child. This finding was also supported by Wilder et al. in their study where the children below 4 years of age, had greater risk for learning disability if they underwent two or three episodes of anesthesia (35.1% vs. 20% for controls). Likewise, attention-deficit hyperactivity disorder with repeated AE (10.7% with single exposure vs. 17.9% with 2 or more exposures) has also been reported. The effects of anesthesia especially in children less than 4 years can translate to lower language comprehension and IQ as reported by Backeljauw and colleagues, in a matched neurocognitive assessment test scores. Based on growing body of evidence and publication in both animal and recent human studies outlined above, USFDA highlighted the concerns that repeated anesthesia exposure in very young children can affect the development of children’s brain. This effect is more pronounced when the exposure is more than three hours, repeated and in children less than 3 years of age. Hence, the decision to go down the path of growth rods, which cannot be taken without the risk of prolonged and repeated anesthesia exposure and its antecedent consequences, should be done at appropriate time when benefits outweigh the risks.
| Complications Specific for EOS Implants/Other Considerations|| |
Shilla technique—lowering of curve
Adjacent compensatory curve is defined as previously unidentified compensatory curve with more than 20° Cobb angle. When comparing preoperative radiographs before index procedure and post operatively at the end of follow-up at minimum 5 years, the apex migrated in 62 % of cases (13/21) at an average of 2.73 ± 0.88 vertebral levels. Of these the apex shifted distally in 12 patients and proximally in one patient. There was no significant difference between the diagnosis and apex migration. Although no significant difference was found in coronal translation and coronal apex migration from the midline in patients having apex migration and with those who did not, trends were seen in patients who had curve migration having greater apical translation and mean coronal imbalance. Development of secondary curve and apex migration threaten ultimate spinal height and pulmonary capacity.,,,, One theory explaining migration is crank shafting as it is a progressive rotatory angulation of the spine at the level of posterior fusion of immature skeleton. Another phenomenon for migration is “adding on” where children with open triradiate cartilage had more proximal and distal add on compared to children with closed triradiate cartilage with fusion. “Adding on” has been reported between 2% and 29% in immature scoliosis.,,
MCGR move in gliding fixtures allowing non-invasive lengthening. This friction has significant potential of metal debris generation (metallosis). The problem of metallosis has been well covered in pediatric spine deformity literature especially AIS and in arthroplasty. These metal debris can be absorbed in circulation via lymphatics, blood vessels, and general seepage. Despite having lower implant density, the EOS patients are subjected to repeated stresses at the implant interface due to the fusionless nature of surgery. More over multiple lengthening procedures add to the problem and leads to release of further metal ions/particles in and around the tissue surrounding the screw and moving parts such as actuator in MAGEC rods [Figure 2b]. This appears to be related to wear debris within the actuator and high rates of O-ring failure. These particles can enter blood circulation and lead to elevated concentration of which the long-term effects are still not clear. Recent study by Borde et al. measured serum levels of titanium and aluminum in patients who underwent MAGEC rod surgery for EOS. The titanium levels were raised especially in patients with complications whereas aluminum levels were normal in both patients with or without complications. These patients did not report any clinical presentation of metal toxicity. Further investigation and studies are need to assess the clinical relevance of metallosis in this population over long periods of time.
Psychological aspects on patients with EOS must be considered as it has significant impact affecting their quality of life. Moreover, natural progression of physical deformity has influence on their self-esteem and psychological outlook. They need lifestyle adjustments to cope up with the disease and surgical management which includes multiple medical visits, surgical interventions, hospitalizations, and with associated comorbidities. Depression and anxiety are more prevalent in these patients along with dysfunctional regions of daily living. Patients with thoracic insufficiency reported lower quality of life those scores than that of chronic medical conditions such as malignancy and cardiac disease. They are also exposed to harmful effects of anesthesia, due to repeated lengthening surgeries and management of complications cumulatively producing chronic stress.,, About 58% of patients with repeated surgeries exhibit psychological dysfunction having positive correlations with depression, anxiety, and anger management. Individuals surgically intervened earlier have the risk of developing aggression, rule breaking, and conduct problems more significantly than individuals undergoing multiple interventions. So, delaying the surgery is beneficial as they allow body to mature decreasing the negative psychological impact and limiting complications. Therefore, EOS needs multi-disciplinary team care, and accessing their mental health should be prioritized as part of a holistic approach to provide best possible outcomes in the management of patient care, treatment outcomes, and quality of life.
| Conclusion|| |
EOS is a challenging problem which requires a multidisciplinary approach, of which the child is the center. The choices for management are competing, as every implant and technique has its own unique sets of challenges. Despite long strides in understanding the disease, its manifestations, improvements in implants, the complication rates, surgeries and unplanned return to OR still remains uncomfortably high. Adequate education, two-way discussion, counseling, and consenting should be done before embarking on the route of surgical management of EOS with growing rods.
Ethical policy and institutional review board statement
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]