Efficacy of Biphasic Calcium Phosphate Ceramic With a Needle-shaped Surface Topography Versus Autograft in Instrumented Posterolateral Spinal Fusion: A Randomized Trial.

STUDY DESIGN: A multicenter randomized controlled noninferiority trial with intrapatient comparisons. OBJECTIVE: The aim of this study was to determine noninferiority of a slowly resorbable Biphasic Calcium Phosphate with submicron microporosity (BCP<µm, MagnetOs™ Granules) as an alternative for autograft in instrumented posterolateral fusion (PLF). SUMMARY OF BACKGROUND DATA: Successful spinal fusion with a solid bone bridge between the vertebrae is traditionally achieved by grafting with autologous iliac bone. However, the disadvantages of autograft and unsatisfactory fusion rates have prompted the exploration of alternatives, including ceramics. Nevertheless, clinical evidence for the standalone use of these materials is limited. METHODS: Adults indicated for instrumented PLF (one to six levels) were enrolled at five participating centers. After bilateral instrumentation and fusion-bed preparation, the randomized allocation side (left or right) was disclosed. Per segment 10cc of BCP<µm granules (1-2 mm) was placed in the posterolateral gutter on one side and 10cc autograft on the contralateral side. Fusion was systematically scored on 1-year follow-up CT scans. The study was powered to detect >15% inferiority with binomial paired comparisons of the fusion performance score per treatment side. RESULTS: Of the 100 patients (57 ± 12.9 years, 62% female), 91 subjects and 128 segments were analyzed. The overall posterolateral fusion rate per segment (left and/or right) was 83%. For the BCP<µm side only the fusion rate was 79% vs. 47% for the autograft side (difference 32 percentage points, 95% CI = 23-41). Analysis of the primary outcome confirmed the noninferiority of BCP<µm with an absolute difference in paired proportions of 39.6% (95% CI = 26.8-51.2, < 0.001). CONCLUSION: This clinical trial demonstrates noninferiority and suggest several attractive features of MagnetOs™ Granules as a standalone ceramic when compared to autograft for posterolateral spinal fusion. These results suggest the need for larger trials with longer duration of follow-up.

Maturation of the vertebral ring apophysis is delayed in girls with adolescent idiopathic scoliosis compared to the normal population.

PURPOSE: The ring apophysis is a secondary ossification center on both sides of each vertebral body, to which the annulus of the intervertebral disc inserts. Recently, its pattern of ossification and fusion to the vertebral body was described for the normal growing spine. The aim of the present study was to investigate the ossification and fusion of the ring apophysis in patients with adolescent idiopathic scoliosis (AIS) and compare it to the normal growing population. METHODS: Ring apophysis maturation along the entire thoracic and lumbar spine was analyzed on CT scans of 99 female, pre-operative AIS patients and compared to 134 CT scans of non-scoliotic girls, aged 12 to 20. RESULTS: The ring apophysis maturation in AIS patients was delayed at all spinal levels in AIS patients compared to non-scoliotic controls. Ossification starts at T4-T11 at age 12, followed by T1-T5 and L3-S1 at age 15. The fusion process in AIS patients continues longer in the midthoracic region as compared to the other regions and as compared to non-scoliotic controls, with many incomplete fusions still at age 20. CONCLUSION: The ring apophysis maturation in AIS is delayed compared to that in the normal population and lasts longer in the mid/low thoracic spine. Delayed maturation of the spine's most important stabilizer, while the body's dimensions continue to increase, could be part of the patho-mechanism of AIS.

Comment on Grabala et al. Radiological Outcomes of Magnetically Controlled Growing Rods for the Treatment of Children with Various Etiologies of Early-Onset Scoliosis-A Multicenter Study. J. Clin. Med. 2024, 13, 1529.

We read with great interest the study titled "Radiological Outcomes of Magnetically Controlled Growing Rods for the Treatment of Children with Various Etiologies of Early-Onset Scoliosis-A Multicenter Study" by Grabala and colleagues [...].

Safety and efficacy of growth-friendly instrumentation for early-onset scoliosis in patients with spinal muscular atrophy type 1 in the disease-modifying treatment era.

Purpose: To evaluate the safety of growth-friendly instrumentation for early-onset scoliosis (EOS) in patients with spinal muscular atrophy (SMA) type 1 who received disease-modifying treatment (DMT) and analyze short-term efficacy. Methods: Retrospective search was conducted between 2017 and 2023. Patients with genetically confirmed SMA type 1 who were surgically treated for spinal deformity and receiving DMTs (nusinersen, risdiplam, or onasemnogene abeparvovec) were included. SMA types 2 and 3 and patients who do not receive DMTs were excluded. Clinical and radiographic data were collected at preoperative, postoperative, and latest follow-up visits. Results: Twenty-eight patients (mean follow-up: 16 months (range 2-41)) were included. The mean age at surgery was 60 months (range 29-96). Fifteen were treated with dual magnetically controlled growing rods (MCGR), four with unilateral MCGR and a contralateral guided growth system, three with Vertical Expandable Prosthetic Titanium Rib (VEPTR®) implants, five with self-distracting systems, and one with traditional dual growing rods. The mean amount of correction was 57% (44°± 17) for scoliosis and 83% (13°± 11) for pelvic obliquity. The mean T1-12 height gain during surgery was 31 mm (±16 mm), while the mean T1 S1 height gain was 51 mm (±24 mm), and instrumented growth was observed during follow-up. Five patients (18%) developed six serious adverse events: three surgical site infections, two anchor failures, and one rod fracture, and all required unplanned reoperations. No neurologic complication, difficulty during nusinersen injections, or respiratory decline was recorded. Conclusion: We report that spinal deformity in this population can be safely treated with growth-friendly instrumentation, with similar complication rates when compared with SMA type 2.

Radiologic Assessment of Interbody Fusion: A Systematic Review on the Use, Reliability, and Accuracy of Current Fusion Criteria.

BACKGROUND: Lumbar interbody fusion (IF) is a common procedure to fuse the anterior spine. However, a lack of consensus on image-based fusion assessment limits the validity and comparison of IF studies. This systematic review aims to (1) report on IF assessment strategies and definitions and (2) summarize available literature on the diagnostic reliability and accuracy of these assessments. METHODS: Two searches were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Search 1 identified studies on adult lumbar IF that provided a detailed description of image-based fusion assessment. Search 2 analyzed studies on the reliability of specific fusion criteria/classifications and the accuracy assessed with surgical exploration. RESULTS: A total of 442 studies were included for search 1 and 8 studies for search 2. Fusion assessment throughout the literature was highly variable. Eighteen definitions and more than 250 unique fusion assessment methods were identified. The criteria that showed most consistent use were continuity of bony bridging, radiolucency around the cage, and angular motion <5°. However, reliability and accuracy studies were scarce. CONCLUSION: This review highlights the challenges in reaching consensus on IF assessment. The variability in IF assessment is very high, which limits the translatability of studies. Accuracy studies are needed to guide innovations of assessment. Future IF assessment strategies should focus on the standardization of computed tomography-based continuity of bony bridging. Knowledge from preclinical and imaging studies can add valuable information to this ongoing discussion. LEVEL OF EVIDENCE: Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Health-related quality of life in early onset scoliosis patients treated with the spring distraction system: what to expect in the first 2 years after surgery.

PURPOSE: The Spring Distraction System (SDS) is a novel "growth-friendly" implant for the treatment of Early-Onset Scoliosis (EOS). This prospective study aims to determine the evolution of the "24-Item Early-Onset Scoliosis Questionnaire" (EOSQ-24) scores during 2-year follow-up after SDS surgery. Secondary aims include investigating the relation between EOSQ-24 scores and EOS etiology, and evaluating the impact of an unplanned return to the operating room (UPROR) on HRQoL. METHODS: All SDS patients with at least 2-year follow-up were included. Caregivers completed the EOSQ-24 pre-operatively, post-operatively, and at 6, 12, and 24 month follow-up. Mean total and -domain scores were graphed over time. Repeated-measures ANOVA analyzed the influence of etiology on EOSQ-24 scores. Multiple regression analyzed associations between UPRORs and EOSQ-24 scores. RESULTS: Forty-nine patients were included. Mean total EOSQ-24 scores decreased from 70 pre-operatively to 66 post-operatively, then gradually increased to 75 (24 months). Most domains exhibited changes over time, with initial declines, but eventually surpassing pre-operative levels after 2-year follow-up. Neuromuscular/Syndromic patients had lower scores, but showed similar improvements over time compared with other etiologies. Multiple regression showed lower Parental Burden domain score (- 14 points) in patients with UPRORs, although no significant reductions were found in total score, or in other domains. CONCLUSION: HRQoL decreases immediately following SDS surgery but quickly recovers and exceeds pre-operative levels at 2-year follow-up in all domains. Neuromuscular/Syndromic patients have lower initial scores, but progress similarly over time. UPRORs do not influence EOSQ-24 scores, except for a negative impact on the Parental Burden domain in the short term. LEVEL OF EVIDENCE: III.

Morphological Changes of the Intervertebral Disc During Growth.

STUDY DESIGN: Cross-sectional. OBJECTIVE: To describe morphological changes of the annulus fibrosus (AF) and nucleus pulposus (NP) in children during growth using magnetic resonance imaging (MRI). SUMMARY OF BACKGROUND DATA: Little is known of intervertebral disc (IVD) maturation as opposed to degeneration, such as changes in relative AF/NP proportions and orientation during growth. Studies suggest the IVD plays a role in the etiology of pediatric spinal deformities. Therefore, understanding the morphological development of the AF and NP during growth is key. METHODS: An existing database of children aged 0-18 that had magnetic resonance imaging (MRI) for indications unrelated to the spine were analyzed. The AF/NP were segmented semi-automatically from T1-L5. The parameters: mean IVD height, cross-sectional area, slenderness (height/width ratio), volume (ratio) and relative position of the centroid of the NP within the IVD in three directions (x,y,z) were extracted, and compared between age, sex and spinal level. RESULTS: IVD height increased modestly and predominantly in the low-thoracic and lumbar spine during the first 5-10 years of life. Cross-sectional area and thus volume increased steadily at all levels throughout growth. IVD slenderness decreased sharply the first years of life and remains relatively stable throughout the remainder of growth. IVDs were smaller and more slender in females, especially in the mid-thoracic spine at early adolescence. In the upper- and mid-thoracic spine the NP comprises 10-12% of total IVD volume during growth, this percentage increases in the low-thoracic and lumbar spine towards 20-25%. In the anterior-posterior direction, the position of the nucleus increasingly shifts with age, possibly in line with the developing sagittal profile of the spine. CONCLUSION: This study describes the development of thoracic and lumbar IVDs during growth and may be used as a reference for future studies on the IVD its role in the etiology of disc related disorders.

The three-dimensional coupling mechanism in scoliosis and its consequences for correction.

INTRODUCTION: In idiopathic scoliosis, the anterior spinal column has rotated away from the midline and has become longer through unloading and expansion of the intervertebral discs. Theoretically, extension of the spine in the sagittal plane should provide room for this longer anterior spinal column, allowing it to swing back towards the midline in the coronal and axial plane, thus reducing both the Cobb angle and the apical vertebral rotation. METHODS: In this prospective experimental study, ten patients with primary thoracic adolescent idiopathic scoliosis (AIS) underwent MRI (BoneMRI and cVISTA sequences) in supine as well as in an extended position by placing a broad bolster, supporting both hemi-thoraces, under the scoliotic apex. Differences in T4-T12 kyphosis angle, coronal Cobb angle, vertebral rotation, as well as shape of the intervertebral disc and shape and position of the nucleus pulposus, were analysed and compared between the two positions. RESULTS: Extension reduced T4-T12 thoracic kyphosis by 10° (p < 0.001), the coronal Cobb angle decreased by 9° (p < 0.001) and vertebral rotation by 4° (p = 0.036). The coronal wedge shape of the disc significantly normalized and the wedged and lateralized nucleus pulposus partially reduced to a more symmetrical position. CONCLUSION: Simple extension of the scoliotic spine leads to a reduction of the deformity in the coronal and axial plane. The shape of the disc normalizes and the eccentric nucleus pulposus partially moves back to the midline.

Comment on Burgos et al. 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. J. Clin. Med. 2023, 12, 2408.

With great interest, we read the recently published paper "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" by Burgos et al. [...].

Surgical treatment of neuromuscular Early Onset Scoliosis with a bilateral posterior one-way rod compared to the Spring Distraction System: study protocol for a limited-efficacy Randomized Controlled Trial (BiPOWR).

BACKGROUND: Early Onset Scoliosis (EOS) is a progressive spinal deformity in children, and a potentially life-threatening disease. "Growth-friendly" surgical techniques aim to control the deformity, while allowing the spine and trunk to maintain growth. Current "growth-friendly" systems such as the traditional growing rod (TGR) and magnetically controlled growing rod (MCGR) have limitations that reduce their efficacy and cost-effectiveness. Recently, two "growth-friendly" systems have been developed that mitigate many of these limitations, the Spring Distraction System (SDS) and the One Way Self-Expanding Rod (OWSER). The purpose of the multicenter BiPOWR trial is to investigate, describe and compare the 1-year limited-efficacy and -safety of both strategies in the treatment of neuromuscular EOS. METHODS: After informed consent, 28 neuromuscular EOS patients will be randomized to receive either the SDS or the OWSER. Patients and caregivers will be blinded to allocation until after surgery. Primary outcomes will be maintenance of coronal curve correction and the occurrence of serious adverse events. In addition, spinal growth, implant lengthening, and perioperative findings are recorded systematically. At each follow-up moment, the Early Onset Scoliosis Questionnaire (EOSQ-24) will be used to assess health-related quality of life. All outcomes will be compared between groups. DISCUSSION: The BiPOWR trial is the first randomized controlled trial that compares two specific "growth-friendly" implants in a specified EOS population. It will determine the 1-year limited-efficacy and safety of the SDS and OWSER implants. TRIAL REGISTRATION: Clinicaltrials.gov: NCT04021784 (13-06-2019). CCMO registry: NL64018.041.17 (06-05-2019).

Three-dimensional correction of scoliosis by a double spring reduction system as a dynamic internal brace: a pre-clinical study in Göttingen minipigs.

BACKGROUND CONTEXT: Adolescent idiopathic scoliosis (AIS) is a major skeletal deformity that is characterized by a combination of apical rotation, lateral bending and apical lordosis. To provide full 3D correction, all these deformations should be addressed. We developed the Double Spring Reduction (DSR) system, a (growth-friendly) concept that continuously corrects the deformity through two different elements: A posterior convex Torsional Spring Implant (TSI) that provides a derotational torque at the apex, and a concave Spring Distraction System (SDS), which provides posterior, concave distraction to restore thoracic kyphosis. PURPOSE: To determine whether the DSR components are able to correct an induced idiopathic-like scoliosis and to compare correction realized by the TSI alone to correction enforced by the complete DSR implant. STUDY DESIGN/SETTING: Preclinical randomized animal cohort study. PATIENT SAMPLE: Twelve growing Göttingen minipigs. OUTCOME MEASURES: Coronal Cobb angle, T10-L3 lordosis/kyphosis, apical axial rotation, relative anterior lengthening. METHODS: All mini-pigs received the TSI with a contralateral tether to induce an idiopathic-like scoliosis with apical rotation (mean Cobb: 20.4°; mean axial apical rotation: 13.1°, mean lordosis: 4.9°). After induction, the animals were divided into two groups: One group (N=6) was corrected by TSI only (TSI only-group), another group (N=6) was corrected by a combination of TSI and SDS (DSR-group). 3D spinal morphology on CT was compared between groups over time. After 2 months of correction, animals were euthanized. RESULTS: Both intervention groups showed excellent apical derotation (TSI only-group: 15.0° to 5.4°; DSR-group: 11.2° to 3.5°). The TSI only-group showed coronal Cobb improvement from 22.5° to 6.0°, while the DSR-group overcorrected the 18.3° Cobb to -9.2°. Lordosis was converted to kyphosis in both groups (TSI only-group: -4.6° to 4.3°; DSR-group: -5.2° to 25.0°) which was significantly larger in the DSR-group (p<.001). CONCLUSIONS: The TSI alone realized strong apical derotation and moderate correction in the coronal and sagittal plane. The addition of distraction on the posterior concavity resulted in more coronal correction and reversal of induced lordosis into physiological kyphosis. CLINICAL SIGNIFICANCE: This study shows that dynamic spring forces could be a viable method to guide the spine towards healthy alignment, without fusing it or inhibiting its growth.

Convex-concave and anterior-posterior spinal length discrepancies in adolescent idiopathic scoliosis with major right thoracic curves versus matched controls.

PURPOSE: The apical deformation in adolescent idiopathic scoliosis (AIS) is a combination of rotation, coronal deviation and passive anterior lengthening of the spine. In AIS surgery, posterior-concave lengthening or anterior-convex shortening can be part of the corrective maneuver, as determined by the individual surgeon's technique. The magnitude of convex-concave and anterior-posterior length discrepancies, and how this needs to be modified to restore optimal spinal harmony, remains unknown. METHODS: CT-scans of 80 pre-operative AIS patients with right convex primary thoracic curves were sex- and age-matched to 80 healthy controls. The spinal length parameters of the main thoracic curves were compared to corresponding levels in controls. Vertebral body endplates and posterior elements were semi-automatically segmented to determine the length of the concave and convex side of the anterior column and along the posterior pedicle screw entry points while taking the 3D-orientation of each individual vertebra into account. RESULTS: The main thoracic curves showed anterior lengthening with a mean anterior-posterior length discrepancy of + 3 ± 6%, compared to a kyphosis of - 6 ± 3% in controls (p < 0.01). In AIS, the convex side was 20 ± 7% longer than concave (0 ± 1% in controls; p < 0.01). The anterior and posterior concavity were 7 and 22 mm shorter, respectively, while the anterior and posterior convexity were 21 and 8 mm longer compared to the controls. CONCLUSIONS: In thoracic AIS, the concave shortening is more excessive than the convex lengthening. To restore spinal harmony, the posterior concavity should be elongated while allowing for some shortening of the posterior convexity.

Assessment of Posterolateral Lumbar Fusion: A Systematic Review of Imaging-Based Fusion Criteria.

BACKGROUND: Noninvasive assessment of osseous fusion after spinal fusion surgery is essential for timely diagnosis of patients with symptomatic pseudarthrosis and for evaluation of the performance of spinal fusion procedures. There is, however, no consensus on the definition and assessment of successful posterolateral fusion (PLF) of the lumbar spine. This systematic review aimed to (1) summarize the criteria used for imaging-based fusion assessment after instrumented PLF and (2) evaluate their diagnostic accuracy and reliability. METHODS: First, a search of the literature was conducted in November 2018 to identify reproducible criteria for imaging-based fusion assessment after primary instrumented PLF between T10 and S1 in adult patients, and to determine their frequency of use. A second search in July 2021 was directed at primary studies on the diagnostic accuracy (with surgical exploration as the reference) and/or reliability (interobserver and intraobserver agreement) of these criteria. Article selection and data extraction were performed by at least 2 reviewers independently. The methodological quality of validation studies was assessed with the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2) and QAREL (Quality Appraisal of Reliability Studies). RESULTS: Of the 187 articles included from the first search, 47% used a classification system and 63% used ≥1 descriptive criterion related to osseous bridging (104 articles), absence of motion (78 articles), and/or absence of static signs of nonunion (39 articles). A great variation in terminology, cutoff values, and assessed anatomical locations was observed. While the use of computed tomography (CT) increased over time, radiographs remained predominant. The second search yielded 11 articles with considerable variation in outcomes and quality concerns. Agreement between imaging-based assessment and surgical exploration with regard to demonstration of fusion ranged between 55% and 80%, while reliability ranged from poor to excellent. CONCLUSIONS: None of the available criteria for noninvasive assessment of fusion status after instrumented PLF were demonstrated to have both sufficient accuracy and reliability. Further elaboration and validation of a well-defined systematic CT-based assessment method that allows grading of the intertransverse and interfacet fusion mass at each side of each fusion level and includes signs of nonunion is recommended. LEVEL OF EVIDENCE: Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Perioperative Management of an Adolescent Fontan Patient with Narrowing of the Aortopulmonary Space for Posterior Scoliosis Surgery.

Congenital cardiac patients who received neonatal reconstructive aortic arch surgery are at risk of aortopulmonary space narrowing with compression of the left pulmonary artery and left main bronchus (LMB) later in life. We discuss a challenging adolescent single ventricle patient who presented for surgical treatment of a non-idiopathic thoracic scoliosis (posterior spinal fusion) with severe stenosis of the LMB and left pulmonary artery due to a narrow aortopulmonary space. Careful preoperative imaging, evaluation, and decision making resulted in successful surgical treatment and uneventful perioperative course.

The Spring Distraction System for Growth-Friendly Surgical Treatment of Early Onset Scoliosis: A Preliminary Report on Clinical Results and Safety after Design Iterations in a Prospective Clinical Trial.

Background: The Spring Distraction System (SDS) is a dynamic growth-friendly implant to treat early onset scoliosis (EOS). Previous SDS studies showed promising results in terms of curve correction and complication profile. Nevertheless, complications did occur, which led to modifications in the implant design. The main iterations were a larger rod diameter and a more sagittal stable sliding mechanism. The purpose of this study was to investigate the performance of these iterations. Methods: All patients treated with the modified SDS and >1 year follow-up were included. Radiographic outcomes, severe adverse events (SAEs), unplanned returns to the operating room (UPRORs) and health-related quality of life (HRQoL) were investigated. Results: Seventeen EOS patients (three congenital, four idiopathic, nine neuromuscular, one syndromic) were included. Mean age at surgery was 9.5 ± 2.5 years. Similar to the first generation SDS, about 50% initial correction was achieved and maintained, and spinal growth was near physiological. Most importantly, SAEs and UPRORs were diminished and favorable with 0.10/patient/year. In addition, HRQoL increased during the first year postoperatively, indicating the implant was well accepted. Conclusion: These preliminary results indicate that the iterations of the SDS are effective in terms of reducing SAEs and UPRORs and increasing HRQoL in patients with EOS.

An In Vitro Model to Test the Influence of Immune Cell Secretome on Mesenchymal Stromal Cell Osteogenic Differentiation.

Immune cells and their soluble factors have an important role in the bone healing process. Modulation of the immune response, therefore, offers a potential strategy to enhance bone formation. To investigate the influence of the immune system on osteogenesis, we developed and applied an in vitro model that incorporates both innate and adaptive immune cells. Human peripheral blood mononuclear cells (PBMCs) were isolated and cultured for 24 h and subsequently stimulated with immune-modulatory agents; C-class CpG oligodeoxynucleotide (CpG ODN C), polyinosinic acid-polycytidylic acid [Poly(I:C)], and lipopolysaccharide (LPS); all pathogen recognition receptor agonists, that target Toll-like receptors (TLRs) 9, 3, and 4, respectively. The conditioned medium (CM) obtained from PBMCs after 24 h was used to investigate its effects on the metabolic activity and osteogenic differentiation capacity of human bone marrow-derived mesenchymal stromal cells (MSCs). Conditioned media from unstimulated PBMCs did not affect the metabolic activity and osteogenic differentiation capacity of MSCs. The CM from CpG ODN C and LPS-stimulated PBMCs increased alkaline phosphatase activity (ALP) of MSCs by approximately threefold as compared with the unstimulated control, whereas Poly(I:C) CM did not enhance ALP activity of MSCs. Moreover, direct stimulation of MSCs with the immune-modulatory stimuli did not result in increased ALP. These results demonstrate that soluble factors present in CM from PBMCs stimulated with immune-modulatory factors enhance osteogenesis of MSCs. This in vitro model can serve as a tool in screening immune-modulatory stimulants from a broad variety of immune cells for (indirect) effects on osteogenesis and also to identify soluble factors from multiple immune cell types that may modulate bone healing.

Ultrasound Shear Wave Elastography of the Intervertebral Disc and Idiopathic Scoliosis: A Systematic Review.

Ultrasound shear wave elastography is a radiation-free and low-cost technique for evaluating the mechanical properties of different tissues. This study systematically reviewed all relevant literature on shear wave elastography of the intervertebral disc. The purpose was twofold: first, to determine the validity of the elastography method, that is, the correlation between elastographically measured shear wave speed and disc mechanical properties, and inter-/intra-operator reliability; and second, to explore if disc elastography is potentially useful in identifying children at risk for idiopathic scoliosis. This systematic review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. A comprehensive search was performed in PubMed and Embase, and study quality was assessed using the AXIS (Appraisal Tool for Cross-sectional Studies) critical appraisal instrument. Seven articles were included. Three animal ex vivo studies reported moderate-to-good correlations between shear wave speed and disc mechanical properties (r = 0.45-0.81). Three studies reported high intra-operator repeatability (intra-class correlation coefficient [ICC] 0.94-0.99) and inter-operator reproducibility (ICC 0.97-0.98). Four clinical studies measured shear wave speed in asymptomatic children. Two studies reported significantly higher shear wave speeds in scoliosis patients compared with healthy controls, measured in discs both inside and outside the scoliotic curve. In conclusion, shear wave elastography appears reliable in assessing intervertebral disc mechanical characteristics. Despite its promising capabilities to distinguish patients with asymptomatic from those with pathological discs, the exact correlation between disc mechanical properties and shear wave speed remains unclear.

Comment on Grivas et al. Morphology, Development and Deformation of the Spine in Mild and Moderate Scoliosis: Are Changes in the Spine Primary or Secondary? J. Clin. Med. 2021, 10, 5901.

With great interest, we have read the article entitled "Morphology, Development and Deformation of the Spine in Mild and Moderate Scoliosis: Are Changes in the Spine Pri-mary or Secondary [...].