Assessment of fatty infiltration of the multifidus muscle in patients with adolescent idiopathic scoliosis through evaluation by magnetic resonance imaging compared with histological analysis: a diagnostic accuracy study

Associations between paraspinal muscle characteristics and spinal curvature in conservatively treated adolescent idiopathic scoliosis: a systematic review

BACKGROUND CONTEXT

Children with adolescent idiopathic scoliosis (AIS) may show asymmetrical paraspinal muscle characteristics.

PURPOSE

To summarize the evidence regarding: (1) the associations between various paraspinal muscle characteristics and spinal curvature; (2) whether paraspinal muscle properties significantly differed between children with and without AIS; and (3) whether baseline paraspinal muscle characteristics predicted curve progression.

STUDY DESIGN/SETTING

Systematic literature review.

METHODS

Five databases (CINAHL, Academic Search Premier, MEDLINE, Scopus, and PubMed) were searched from inception to May 2022. This protocol was registered in the PROSPERO database of systematic reviews CRD 42020171263. The Critical appraisal skills program, the Appraisal Tool for Cross-Sectional Studies and Quality In Prognosis Studies tool were used to evaluate the risk of bias of the included studies. The strength of evidence of each identified association was determined by the Grading of Recommendations Assessment, Development, and Evaluation System (GRADE).

RESULTS

Of 1,530 identified citations, four cohort, 17 cross-sectional, and 23 case-control studies including 31 with low, nine with moderate and four with high risk of bias were included. Low to very low-strength evidence supported that the convex side of the curve had more type I muscle fibers, higher muscle volume and paraspinal muscle activity, while the concavity had more intramuscular fatty infiltration. Very low-strength evidence substantiated greater side-to-side surface electromyography signals during left trunk bending in prone lying, standing, and standing with perturbation between people with and without AIS. Also, low to very low-strength evidence supported that a larger side-to-side surface electromyography ratio at the lower end vertebra predicted curve progression.

CONCLUSIONS

Our review highlights that paraspinal muscles on the concavity of the curve demonstrate consistent changes (ie, altered muscle-related gene expression, muscle atrophy, increased fatty infiltration, reduced type I fibers, and reduced muscle activity), which may be the cause or consequence.

Quantifying Muscle Size Asymmetry in Adolescent Idiopathic Scoliosis Using Three-dimensional Magnetic Resonance Imaging

STUDY DESIGN

This is a case-control study of prospectively collected data.

OBJECTIVE

To quantify paraspinal muscle size asymmetry in adolescent idiopathic scoliosis (AIS) and determine if this asymmetry is (i) greater than observed in adolescent controls with symmetrical spines; and (ii) positively associated with skeletal maturity using Risser grade, scoliosis severity using the Cobb angle, and chronological age in years.

SUMMARY OF BACKGROUND DATA

AIS is a three-dimensional deformity of the spine which occurs in 2.5% to 3.7% of the Australian population. There is some evidence of asymmetry in paraspinal muscle activation and morphology in AIS. Asymmetric paraspinal muscle forces may facilitate asymmetric vertebral growth during adolescence.

METHODS

An asymmetry index [Ln(concave/convex volume)] of deep and superficial paraspinal muscle volumes, at the level of the major curve apex (Thoracic 8-9 th vertebral level) and lower-end vertebrae ( LEV , Thoracic 10-12 th vertebral level), was determined from three-dimensional Magnetic Resonance Imaging of 25 adolescents with AIS (all right thoracic curves), and 22 healthy controls (convex=left); all female, 10 to 16 years.

RESULTS

Asymmetry index of deep paraspinal muscle volumes was greater in AIS (0.16±0.20) than healthy spine controls (-0.06±0.13) at the level of the apex ( P <0.01, linear mixed-effects analysis) but not LEV ( P >0.05). Asymmetry index was positively correlated with Risser grade ( r =0.50, P <0.05) and scoliosis Cobb angle ( r =0.45, P <0.05), but not age ( r =0.34, P >0.05). There was no difference in the asymmetry index of superficial paraspinal muscle volumes between AIS and controls ( P >0.05).

CONCLUSIONS

The asymmetry of deep apical paraspinal muscle volume in AIS at the scoliosis apex is greater than that observed at equivalent vertebral levels in controls and may play a role in the pathogenesis of AIS.

Aerobic Exercise Training Under Normobaric Hypoxic Conditions to Improve Glucose and Lipid Metabolism in Overweight and Obese Individuals: A Systematic Review and Meta-Analysis

Guo, Hai, Linjie Cheng, Dilihumaier Duolikun, and Qiaoling Yao. Aerobic exercise training under normobaric hypoxic conditions to improve glucose and lipid metabolism in overweight and obese individuals: a systematic review and meta-analysis. High Alt Med Biol. 24:312-320, 2023. Background: Obesity is a critical public health issue around the world, reaching epidemic proportions in some countries. However, only a few studies have examined the effects of hypoxic training on metabolic parameters in an obese population. This systematic review and meta-analysis aimed to determine the effects of aerobic exercise training under normobaric hypoxic conditions versus normoxic training in improving glucose and lipid metabolism in obese individuals. Methods: A systematic search of PubMed, EMBASE, Web of Science, and Wan Fang databases (up to August 2021) was performed to identify randomized controlled trials (RCTs) of overweight or obese human subjects eligible for inclusion. Main study endpoints were changes in body mass index (BMI), waist/hip (W/H) ratio, leptin, blood glucose and insulin levels, as well as blood lipids between hypoxic and normoxic conditioning. Results: Fourteen RCTs with a total of 413 subjects qualified for inclusion. Pooled analyses revealed that BMI (d = 0.38), W/H ratio (d = 0), blood glucose (d = 0.01), and triglyceride (d = -2.27) were not significantly different between aerobic exercise training under hypoxic and normoxic conditions. However, significant differences were found in heart rate at rest (d = -4.50) between aerobic exercise training under hypoxic versus normoxic conditions. Conclusions: In conclusion, no significant benefits were noted in aerobic exercise training under hypoxic conditions over normoxic conditions in overweight or obese individuals. However, the maximum training heart rate mm was significantly higher under hypoxic conditions than under normoxic conditions. Future studies with larger samples controlling for exercise-related parameters, and addressing the potential modifying effects of level of hypoxia, sex, or age on the role of hypoxic exercise training are warranted. PROSPERO registration number: CRD42020221680.

The association between morphological characteristics of paraspinal muscle and spinal disorders

BACKGROUND

Spinal disorders affect millions of people worldwide, and can cause significant disability and pain. The paraspinal muscles, located on either side of the spinal column, play a crucial role in the movement, support, and stabilization of the spine. Many spinal disorders can affect paraspinal muscles, as evidenced by changes in their morphology, including hypertrophy, atrophy, and degeneration.

OBJECTIVES

The objectives of this review were to examine the current literature on the relationship between the paraspinal muscles and spinal disorders, summarize the methods used in previous studies, and identify areas for future research.

METHODS

We reviewed studies on the morphological characteristics of the paravertebral muscle and discussed their relationship with spinal disorders, as well as the current limitations and future research directions.

RESULTS

The paraspinal muscles play a critical role in spinal disorders and are important targets for the treatment and prevention of spinal disorders. Clinicians should consider the role of the paraspinal muscles in the development and progression of spinal disorders and incorporate assessments of the paraspinal muscle function in clinical practice.

CONCLUSION

The findings of this review highlight the need for further research to better understand the relationship between the paraspinal muscles and spinal disorders, and to develop effective interventions to improve spinal health and reduce the burden of spinal disorders.

Proteomic Comparison of Paraspinal Muscle Imbalance Between Idiopathic Scoliosis and Congenital Scoliosis

OBJECTIVE

This study aims to compare the proteomic profiles of paraspinal muscle imbalance between idiopathic scoliosis (IS) and congenital scoliosis (CS).

METHODS

Bilateral paraspinal muscles of 5 pairs of matched IS and CS patients were collected. Proteome patterns of paraspinal muscles were established. Differentially expressed proteins (DEPs) in paraspinal muscles between the convexity and the concavity were screened out. DEPs shared by both IS and CS and IS-specific DEPs were identified. Bioinformatic analyses of DEPs were performed.

RESULTS

Among 105 DEPs identified in IS, 30 displayed predominant expression on the convexity, whereas other 75 exhibited predominant expression on the concavity. DEPs in IS were mainly enriched in calcium ion binding and DNA binding in gene ontology (GO) term and glycolysis/gluconeogenesis and purine metabolism in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Among 48 DEPs identified in CS, 25 were predominantly expressed on the convexity and 23 on the concavity. DEPs in CS were mainly enriched in receptor activity and immune response in GO term and glycolysis/gluconeogenesis and cellular senescence in KEGG pathway. Comparison of DEPs between IS and CS identified only 8 proteins shared by both types of scoliosis. Among the 97 IS-specific DEPs, 28 were predominantly expressed on the convexity and 69 on the concavity. IS-specific genes were enriched in calcium ion binding and protein glycosylation in GO term and glycolysis/gluconeogenesis and hypertrophic cardiomyopathy in KEGG pathway.

CONCLUSION

IS and CS exhibit proteomic imbalance in bilateral paraspinal muscles but share few similarities. Paraspinal muscle imbalance in IS might not be the consequence of spinal deformities.

Characteristics of the paravertebral muscle in adult degenerative scoliosis with PI-LL match or mismatch and risk factors for PI-LL mismatch

Objective

Pelvic incidence (PI) minus the lumbar lordosis (LL) angle (PI-LL) correlates with function and disability. It is associated with paravertebral muscle (PVM) degeneration and is a valuable tool for surgical planning of adult degenerative scoliosis (ADS). This study aims to explore the characteristics of PVM in ADS with PI-LL match or mismatch and to identify the risk factors for PI-LL mismatch.

Methods

A total of 67 patients with ADS were divided into PI-LL match and mismatch groups. The visual analog scale (VAS), symptom duration, and Oswestry disability index (ODI) were used to assess patients’ clinical symptoms and quality of life. The percentage of fat infiltration area (FIA%) of the multifidus muscle at the L1-S1 disc level was measured by using MRI with Image-J software. Sagittal vertical axis, LL, pelvic tilt (PT), PI, sacral slope, and the asymmetric and average degeneration degree of the multifidus were recorded. Logistic regression analysis was done to identify the risk factors for PI-LL mismatch.

Results

In the PI-LL match and mismatch groups, the average FIA% of the multifidus on the convex side was less than that on the concave side (P &lt; 0.05). There was no statistical difference of asymmetric degeneration degree of the multifidus between the two groups (P &gt; 0.05). In the PI-LL mismatch group, the average degeneration degree of the multifidus, VAS, symptom duration, and ODI were significantly higher than that in the PI-LL match group, respectively (32.22 ± 6.98 vs. 26.28 ± 6.23 (%), 4.33 ± 1.60 vs. 3.52 ± 1.46, 10.81 ± 4.83 vs. 6.58 ± 4.23 (month), 21.06 ± 12.58 vs. 12.97 ± 6.49, P &lt; 0.05). The average degeneration degree of the multifidus muscle was positively correlated with the VAS, symptom duration, and ODI, respectively (r = 0.515, 0.614, and 0.548, P &lt; 0.05). Sagittal plane balance, LL, PT, and the average degeneration degree of the multifidus were the risk factors for PI-LL mismatch (OR: 15.447, 95% CI: 1.274–187.269; OR: 0.001, 95% CI: 0.000–0.099; OR: 107.540, 95% CI: 5.195–2,225.975; OR: 52.531, 95% CI: 1.797–1,535.551, P &lt; 0.05).

Conclusion

The PVM on the concave side was larger than that on the convex side in ADS irrespective of whether PI-LL matched or not. PI-LL mismatch could aggravate this abnormal change, which is an important cause of pain and disability in ADS. Sagittal plane imbalance, decreased LL, higher PT, and larger average degeneration degree of the multifidus were independent risk factors for PI-LL mismatch.

The use of MRI in the study of patients with idiopathic scoliosis: a systematic review of the literature

Objective. To analyze the frequency of hidden neuraxial pathology in idiopathic scoliosis (IS), to substantiate the need for MRI in IS and to identify promising areas for the use of MRI in the examination of patients with IS.Material and Methods. The literature review was carried out using the PubMed and Google Scholar databases. Of the 780 papers on the research topic, 65 were selected after removing duplicates and checking for inclusion/exclusion criteria. As a result, 49 original studies were included in the analysis. Level of evidence – II.Results. According to modern literature, the main direction of using MRI in idiopathic scoliosis is the search for predictors of latent pathology of the spinal cord and craniovertebral junction. The frequency of neuraxial pathology in idiopathic scoliosis is 8 % for adolescent IS and 16 % for early IS. The main predictors of neuraxial pathology are male sex, early age of deformity onset, left-sided thoracic curve and thoracic hyperkyphosis. MRI in IS may be a useful addition to radiological diagnostic methods to identify risk factors and to study degenerative changes in the spine.Conclusion. MRI of the spine should be performed in the early stages of IS to detect latent spinal cord tethering. In type I Chiari anomalies, there is a possibility that early neurosurgery can prevent the development of scoliosis. The main signs of latent neuraxial pathology in IS are early progression of spinal deformity, left-sided thoracic curve, male gender and thoracic kyphosis over 40° according to Cobb.MRI can be used as an effective non-invasive tool in research aimed at identifying risk factors for IS, including helping to track early degeneration of intervertebral discs.

Comparison of multifidus degeneration between scoliosis and lumbar disc herniation

Objective

To assess and compare the pathological and radiological outcomes of multifidus degeneration in scoliosis and lumbar disc herniation patients.

Methods

We performed a retrospective review on 24 patients with scoliosis and 26 patients with lumbar disc herniation (LDH) in the Third Hospital of Hebei Medical University from January 2017 to March2021. The patients were divided into scoliosis group and LDH group according to the treatment. The MRI fatty infiltration rate (FIR) of multifidus and strength of back muscle were calculated to evaluate muscle condition. Multifidus biopsy samples were obtained during surgery in the affected side at L4 or L5 segment in LDH group and on the concavity side of apical vertebrae in scoliosis group. The biopsy fatty infiltration degree (FID) and FIR in two groups, the FIR of affected and unaffected side in LDH group, and the FIR of concavity and convexity side in scoliosis group were compared. The correlation between concavity-convexity FIR difference and cobb angle in scoliosis group, back muscle strength and FIR in LDH group, FID and FIR in both groups was calculated respectively.

Results

The FIR was higher in scoliosis group than in LDH group, higher in concavity side than convexity side in scoliosis group (both P < 0.05). The FID was higher in scoliosis group than in LDH group (P < 0.05). No significant difference was found between affected and unaffected side in LDH group (P > 0.05). There was a positive correlation between concavity-convexity FIR difference and cobb angle, FIR and FID (both P < 0.01). There was a negative correlation between back muscle strength and FIR (P < 0.01). The biopsy staining results showed that both two groups were found the existence of rimmed vacuoles, nuclear aggregation, and abnormal enzyme activity, indicating that the scoliosis and LDH may be associated with myogenic diseases.

Conclusion

The scoliosis patients showed more serious fatty infiltration than LDH patients and rare pathological findings were found in both diseases.

Biological effect of dysregulated LBX1 on adolescent idiopathic scoliosis through modulating muscle carbohydrate metabolism

BACKGROUND CONTEXT

Abnormal energy metabolism such as lower body weight and body mass index (BMI) and less fat mass is widely reported in patients with adolescent idiopathic scoliosis (AIS) and has been implicated in deformity development. However, the underlying mechanism is largely unclear. LBX1 is one of the promising AIS predisposing genes validated by multicenter studies.

PURPOSE

This study aimed to identify differentially expressed proteins (DEPs) relating to energy metabolism in AIS by using proteomic and metabolic analysis and to explore if the expression of these DEPs is associated with clinical parameters and modulated by LBX1.

STUDY DESIGN

This is a cross-sectional study using clinical data and biological samples followed by basic study using a cellular model.

PATIENT SAMPLE

Plasma samples were collected from Chinese girls with nonprogressive and progressive AIS (N=7 and 8, respectively) and age-matched healthy girls (N=50). Paraspinal muscle tissues were collected intraoperatively from concave and convex side of the apex of the major spinal curve in AIS (N=24) and either side from nonscoliosis patients (N=14).

OUTCOME MEASURES

Radiological Cobb angle and basic anthropometric data of recruited subjects were measured. The DEPs and metabolites were compared in plasma using proteomics and metabolomics technique. The relative expression of selected genes was measured in muscles.

METHODS

Plasma samples from AIS were collected at first clinical visit and were further divided into nonprogressive or progressive groups according to Cobb angle changes in 6-year follow-up. Age-matched healthy girls were recruited as control. High-performance liquid chromatography-mass spectrometry based proteomic analysis was carried out in three groups to identify DEPs and their annotated metabolic pathways. An independent cohort was used for validation by gas chromatography-mass spectrometry based metabolomic analysis. Paraspinal muscles were subjected to quantitative polymerase chain reaction (qPCR) followed by correlation analysis. Human skeletal muscle myoblast (HSMM) was used as the cellular model.

RESULTS

The likelihood of aberrant galactose metabolism and glycolysis was found to be associated with AIS curve progression as evidenced by the thirteen DEPs and seven related metabolites according to proteomic and metabolomic analysis. Some of the DEPs showed significantly altered expression in AIS concave and convex sides paraspinal muscles compared with those in nonscoliosis control. Four DEPs were found significantly and negatively correlated with LBX1 in AIS convex side paraspinal muscles. Overexpressing LBX1 in HSMM cells led to increased expression of three DEPs and decreased expression of three DEPs, respectively.

CONCLUSIONS

This is the first integrated proteomic and metabolomic analysis on AIS. Our findings show dysregulated galactose metabolism and glycolysis pathways in progressive group of AIS, suggesting the presence of abnormal energy metabolism at early stage of this disease, and their association with higher risk of progressing into more severe curvature. Evidence from ex vivo study with human muscle biopsies and in vitro study with human myoblast cells propose the possible effect of LBX1 on these two pathways in skeletal muscles. The present study provides new evidence of LBX1 function in AIS via modulating effect on the expression of energy metabolism related genes. This study might provide new insights into etiopathogenesis and development of novel treatment strategy targeting on abnormal body weight and BMI in patients with AIS. Additionally, the plasma proteomic and metabolomic studies suggested new candidates as biomarkers for establishing predictive model for AIS onset/progression.

RELIABILITY OF THE GOUTALLIER CLASSIFICATION SYSTEM IN THE EVALUATION OF THE MULTIFIDUS MUSCLE

ABSTRACT Introduction: The paravertebral musculature is essential for the biomechanics and stability of the spine, and its involvement in the pathophysiology of spinal diseases has been demonstrated. Qualitative evaluation of muscle degeneration is usually performed by analyzing the fat infiltration rate proposed by the Goutallier classification system. Objective: The objective of this study is to analyze the intra- and interobserver agreement of the Goutallier Classification for the evaluation of fatty degeneration of the multifidus muscle, using magnetic resonance imaging exams. Methods: The study included 68 patients, all diagnosed with symptomatic disc hernia and indicated for surgery. Preoperative magnetic resonance images were used for the analyses. The images were initially evaluated by two orthopedists and two medical students, and then re-evaluated after two weeks. Intra- and inter-observer reliability analysis was performed using the Fleiss Kappa test and the Landis and Koch criteria. All the analyses were performed using the R statistical environment (R Development Core Team, version 3.3.1, 2016) and the significance level was set at 5%. Results: The percentages of intra- and inter-observer agreement were 86.76% and 61.03%, respectively. The intraobserver agreement was near perfect and the interobserver agreement was moderate. Conclusion: The Goutallier Classification System showed moderate interobserver and intraobserver agreement, being a relevant tool for the evaluation of paravertebral musculature fat replacement. Level of evidence II; Prospective study for diagnostic purposes.

Paraspinal muscle morphology and composition in adolescent idiopathic scoliosis: A histological analysis

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is a condition resulting in spinal deformity and tissue adaptation of the paraspinal muscles. Although prior studies have demonstrated asymmetries in fiber type and other energetic features of muscle on the concave side of the curve, muscle morphology, architecture, and composition have not been evaluated. Therefore, the purpose of this study was to compare differences in paraspinal muscle microarchitecture and composition between concave and convex sides of a scoliotic curve in individuals with AIS.

METHODS

Paraspinal muscle biopsies were obtained at the apex of the scoliotic curve in 29 individuals with AIS undergoing surgical deformity correction. Histological assays were performed to quantify fiber size, evidence of muscle degeneration and regeneration, and tissue composition (proportion of muscle, collagen, and fat). Differences between contralateral muscle samples were compared using two-tailed paired Student's t tests, and relationships between clinical characteristics (age and curve severity) and muscle characteristics were investigated using Pearson correlations.

RESULTS

Muscle fibers were significantly larger on the convex side of the curve apex (P = .001), but were lower than literature-based norms for healthy paraspinal muscle. There were no differences in amount of degeneration/regeneration (P = .490) or the proportion of muscle and collagen (P > .350) between the concave and convex sides, but high levels of collagen were observed. There was a trend toward higher fat content on the concave side (P = .074). Larger fiber size asymmetries were associated with greater age (r = .43, P = .046), and trended toward an association with greater curve severity (r = .40, P = .069).

CONCLUSIONS

This study demonstrates that although muscle fibers are larger on the convex side of the scoliotic curve in AIS, muscles on both sides are atrophic compared to non-scoliotic individuals, and demonstrate levels of collagen similar to severe degenerative spinal pathologies. These findings provide insight into biological maladaptations occurring in paraspinal muscle in the presence of AIS.

The influence of 3D curve severity on paraspinal muscle fatty infiltration in patients with adolescent idiopathic scoliosis

PURPOSE

In a sex-inclusive cohort of patients with adolescent idiopathic scoliosis (AIS): (1) assess the relationship between 3D curve severity, curve flexibility, and paraspinal muscle fatty infiltration, and (2) describe three-dimensional (3D) fatty infiltration of the paraspinal muscles.

METHODS

Fat signal fraction of the paravertebral muscles was measured in pre-operative magnetic resonance images (MRIs) of males and females with AIS at the apex, ± 1, and ± 2 levels from the apex of the curve (n = 62). In a subset of patients with biplanar erect radiographic imaging (n = 35), 3D measures of deformity (axial rotation of the apical vertebrae, thoracic kyphosis, and coronal Cobb angle) were measured.

RESULTS

Contrary to previous studies, no relationship between coronal Cobb angle and fatty infiltration was found. However, axial apical rotation and sagittal Cobb angle were found to be significant predictors of paravertebral fatty infiltration (R² = 0.196-0.222). Curve concavity, female sex, and proximity to the curve apex were found to be the strongest predictors of fatty infiltration. Greater fatty infiltration of the paravertebral muscles was found on the concave side of the curve (15-24% vs. 11-13%), with increasing fatty infiltration toward the apex of the curve. Fatty infiltration was protected on the convex side of the curve, with no differences in the amount of fatty infiltration across levels.

CONCLUSION

These findings highlight that coronal curve severity and flexibility are not the primary influencing factors for the degree of paraspinal fatty infiltration in patients with AIS. This may have implications for nonsurgical rehabilitation strategies such as bracing and physical therapy.

LEVEL OF EVIDENCE

II.

Research Progress on the Mechanism of Lumbarmultifidus Injury and Degeneration

This review summarizes recent research progress in the clinical features, image manifestations, and pathological mechanism of multifidus injury. After a brief introduction to the fiber classification, innervation, blood supply, and multifidus function, some factors of multifidus injury, consisting of denervation, intraoperative incision selection and traction, and lumbar degenerative disease are overviewed. In addition, the clinical index of multifidus injury including myoglobin, creatine kinase, IL-6, C-reactive protein, the cross-sectional area of multifidus, the degree of fat infiltration, and intraoperative biopsy are summarized. Furthermore, we recommend that patients with chronic low back pain should take the long-term exercise of lumbodorsal muscles. Finally, some remaining issues, including external fixation and the imaging quantitative evaluation criteria of multifidus, need to be further explored in the future.

Fiber Type-Specific Morphological and Cellular Changes of Paraspinal Muscles in Patients with Severe Adolescent Idiopathic Scoliosis

Background

Paraspinal muscle (PSM) has been suggested to have a role in adolescent idiopathic scoliosis (AIS). Few studies have investigated the fiber type-specific changes of PSM in detail.

Material/Methods

Bilateral multifidus muscles were harvested from the apical vertebra level (T7–T10) of 12 AIS patients and 6 control individuals. Immunohistological staining was performed to evaluate the muscle fiber type composition, fiber type-specific cross-sectional area (CSA), myonuclei density, and the total and activated satellite cell (SC) density. The correlations between these characteristics and curve initiation/severity were analyzed.

Results

In comparison with the PSM in convexity and the control group, PSM in concavity showed a significant reduction of CSA (concavity, 2601.1±574.1 μm²; convexity, 3732.1±545.1 μm²; control, 3426.5±248.4 μm²), myonuclei density (concavity, 2.0±0.3 myonuclei/fiber; convexity, 2.5±0.4 myonuclei/fiber; control, 2.2±0.2 myonuclei/fiber), and activated SC density (concavity, 0.7±0.4 cells/100 fibers; convexity, 1.5±0.7 cells/100 fibers; control, 1.2±0.3 cells/100 fibers) for fiber type I. The Cobb angle was positively correlated with the bilateral ratio of CSA (convexity/concavity) for both fiber types. The apical vertebral translation was positively correlated with bilateral difference of myonuclei density (type I), total SC density (types I and II), and activated SC density (type I).

Conclusions

The fiber type-specific pathological changes on the concave side seemed to be more severe. Some fiber type-specific characteristics (CSA, myonuclei density, total/activated SC density) were closely associated with curve severity. More attention should be paid to PSM physiotherapy treatment on the concave side.

Muscular Contribution to Adolescent Idiopathic Scoliosis from the Perspective of Stem Cell-Based Regenerative Medicine

Adolescent idiopathic scoliosis (AIS) is a relatively frequent disease within a range 0.5%-5.0% of population, with higher frequency in females. While a resultant spinal deformity is usually medically benign condition, it produces far going psychosocial consequences, which warrant attention. The etiology of AIS is unknown and current therapeutic approaches are symptomatic only, and frequently inconvenient or invasive. Muscular contribution to AIS is widely recognized, although it did not translate to clinical routine as yet. Muscle asymmetry has been documented by pathological examinations as well as systemic muscle disorders frequently leading to scoliosis. It has been also reported numerous genetic, metabolic and radiological alterations in patients with AIS, which are linked to muscular and neuromuscular aspects. Therefore, muscles might be considered an attractive and still insufficiently exploited therapeutic target for AIS. Stem cell-based regenerative medicine is rapidly gaining momentum based on the tremendous progress in understanding of developmental biology. It comes also with a toolbox of various stem cells such as satellite cells or mesenchymal stem cells, which could be transplanted; also, the knowledge acquired in research on regenerative medicine can be applied to manipulation of endogenous stem cells to obtain desired therapeutic goals. Importantly, paravertebral muscles are located relatively superficially; therefore, they can be an easy target for minimally invasive approaches to treatment of AIS. It comes in pair with a fast progress in image guidance, which allows for precise delivery of therapeutic agents, including stem cells to various organs such as brain, muscles, and others. Summing up, it seems that there is a link between AIS, muscles, and stem cells, which might be worth of further investigations with a long-term goal of setting foundations for eventual bench-to-bedside translation.

Rotator Cuff Fibro-Adipogenic Progenitors Demonstrate Highest Concentration, Proliferative Capacity, and Adipogenic Potential Across Muscle Groups

Fatty infiltration (FI) of rotator cuff (RC) muscles is common in patients with RC tears. Studies have demonstrated that fibro-adipogenic progenitors (FAPs), a population of resident muscle stem cells, are the main contributors of FI, which adversely affects muscle quality and RC repair success. Although FI is common in RC injuries, it is not frequently reported after other musculotendinous injuries. Additionally, studies have shown the development of different pathology patterns across muscle groups suggestive of intrinsic differences in cellular composition and behavior. This study evaluates FAP distribution and differentiation properties across anatomic locations in mice. Muscles from seven different anatomic locations were harvested from PDGFRα-eGFP FAP reporter mice. FAPs were quantified using histology and FACS sorting with BD Aria II with CD31^- /CD45^- /Integrinα7^- /Sca-1⁺ and PDGFRα reporter signal (n = 3 per muscle). The cells were analyzed for adipogenesis using immunocytochemistry and for proliferation properties with Brdu-Ki67 staining. In a separate group of mice, RC and tibialis anterior muscles received glycerol injection and were harvested after 2 weeks for FI quantification (n = 4). One-way analysis of variance was used for statistical comparisons among groups, with significance at p < 0.05. FAPs from the RC, masseter, and paraspinal muscles were more numerous and demonstrated greater proliferative capacity and adipogenic potency than those from the tibialis anterior and gastrocnemius. The RC demonstrated significantly greater levels of FI than the tibialis anterior after glycerol-injection injury. Clinical Significance: This study suggests differences in FAP distribution and differentiation characteristics may account for the propensity to develop FI in RC tears as compared with other musculotendinous injuries. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1113-1121, 2020.