Increased Fibrogenic Gene Expression in Multifidus Muscles of Patients With Chronic Versus Acute Lumbar Spine Pathology

Increased water content in multifidus muscles of young adults with chronic nonspecific low back pain detected by dual-energy CT and MRI

OBJECTIVES

To demonstrate the feasibility of better diagnosing young adults with chronic nonspecific low back pain (CNLBP) by measuring water content in paraspinal muscles using water-muscle decomposition technique in dual-energy CT (DECT) and T2-mapping in MRI.

METHODS

This prospective cross-sectional study included 110 young individuals (56 with CNLBP at age of 25.7 ± 2.0 years and 54 of asymptomatic at age of 25.1 ± 1.9 years) who underwent both MRI and DECT on the spine. T2 values on T2 mapping in MRI and water density (WD) value on water(muscle) images in DECT were generated at the L1-L4 levels for erector spinae muscle and L2-L5 for multifidus muscle. Pain duration time, Oswestry Disability Index (ODI), Visual Analogue Scale (VAS) were recorded for CNLBP patients. Difference of T2 value and WD between the two patient groups, and correlations between T2 value and WD, and T2 value and WD with clinical indicators were analyzed.

RESULTS

Compared with asymptomatic participants, the mean WD of multifidus muscle at L4-L5 and mean T2 values of multifidus muscle at L5 were significantly higher in CNLBP patients (all P < 0.05). T2 values had moderate to strong positive correlations (r = 0.34-0.60, all P < 0.05) with DECT WD in CNLBP patients and healthy volunteers. There was a weak correlation between VAS and WD in L5-level multifidus muscle (r = 0.29, P < 0.05).

CONCLUSIONS

The T2 values in MRI and WD in DECT are higher in multifidus muscles of lower vertebra levels for young CNLBP patients, and there exists positive correlation between WD and T2 values, providing useful information for diagnosing CNLBP.

Targeted multifidus muscle activation reduces fibrosis of multifidus muscle following intervertebral disc injury

PURPOSE

Aerobic exercise produces beneficial outcomes in patients with low back pain and partially attenuates the fibrotic changes to the multifidus in a model of intervertebral disc (IVD) degeneration. More targeted exercise might be required to fully attenuate these fibrotic alterations. This study aimed to investigate whether activation of the multifidus induced by neurostimulation could reduce fibrosis of the multifidus in a model of IVD degeneration in sheep.

METHODS

IVD degeneration was induced in 18 merino sheep via a partial thickness unilateral annulus fibrosus lesion to the L1/2 and L3/4 IVDs. All sheep received an implantable neurostimulation device that provides stimulation of the L2 medial branch of the dorsal ramus. Three months after surgery, the animals were assigned to Injury or Activated groups. Activated animals received neurostimulation and the Injury group received no stimulation. Six months after surgery, the multifidus was harvested at L2 and L4. Van Gieson's, Sirius Red and immunofluorescence staining for Collagen-I and -III and quantitative PCR was used to examine fibrosis. Muscle harvested from a previous study without IVD injury was used as a control.

RESULTS

Neurostimulation of the multifidus attenuated IVD degeneration dependent increases in the connective tissue, including Collagen-I but not Collagen-III, compared to the Injury group at L4. No measures of the multifidus muscle at L2, which received no stimulation, differed between the Injury and Activated groups.

CONCLUSIONS

These data reveal that targeted activation of the multifidus muscle attenuates IVD degeneration dependent fibrotic alterations to the multifidus.

Multifidus lesions: A possible pathological component in patients with low back pain after posterior lumbar surgery

There are few histological studies on multifidus after lumbar surgery, and it is not clear whether multifidus changes affect the clinical outcome after lumbar surgery. The aim of this study was to investigate the relationship between multifidus changes and clinical outcomes after lumbar surgery. Patients underwent internal fixation removal after lumbar posterior surgery were enrolled. Patients were divided into a low back pain (LBP) group (n = 15) and a non-low back pain (non-LBP) group (n = 10).The Oswestry disability index (ODI) and visual analog scale (VAS) were completed. 18 patients with lumbar fracture surgery were included as the control group. Multifidus morphological changes were observed by hematoxylin and eosin and Masson staining. The expression of TGF-β1 was observed by immunohistochemistry, immunofluorescence and Western blot. The cross-sectional area (CSA) of the multifidus in the non-LBP group and the control group were greater than those in the LBP group. TGF-β1 expression and gray value ratio in the non-LBP group and the control group were lower than those in the LBP group. The multifidus CSA and TGF-β1 expression in multifidus were strongly correlated with ODI and VAS. Patients with LBP after posterior lumbar surgery suffered from atrophy and fibrosis lesions in the multifidus, and the degree of multifidus lesions was closely related to dysfunction and pain, which might be one of the causes of LBP after posterior lumbar surgery.

Paraspinal muscles in individuals undergoing surgery for lumbar spine pathology lack a myogenic response to an acute bout of resistance exercise

Background

Lumbar spine pathology (LSP) is a common source of low back or leg pain, and paraspinal muscle in these patients demonstrates fatty and fibrotic infiltration, and cellular degeneration that do not reverse with exercise-based rehabilitation. However, it is unclear of this lack of response is due to insufficient exercise stimulus, or an inability to mount a growth response. The purpose of this study was to compare paraspinal muscle gene expression between individuals with LSP who do and do not undergo an acute bout of resistance exercise.

Methods

Paraspinal muscle biopsies were obtained from 64 individuals with LSP undergoing spinal surgery. Eight participants performed an acute bout of machine-based lumbar extension resistance exercise preoperatively. Gene expression for 42 genes associated with adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic pathways was measured, and differential expression between exercised and non-exercised groups was evaluated for (a) the full cohort, and (b) an age, gender, acuity, and etiology matched sub-cohort. Principal components analyses were used to identify gene expression clustering across clinical phenotypes.

Results

The exercised cohort demonstrated upregulation of inflammatory gene IL1B, inhibition of extracellular matrix components (increased MMP3&9, decreased TIMP1&3, COL1A1) and metabolic/adipogenic genes (FABP4, PPARD, WNT10B), and downregulation of myogenic (MYOD, ANKRD2B) and atrophic (FOXO3) genes compared to the non-exercised cohort, with similar patterns in the matched sub-analysis. There were no clinical phenotypes significantly associated with gene expression profiles.

Conclusion

An acute bout of moderate-high intensity resistance exercise did not result in upregulation of myogenic genes in individuals with LSP. The response was characterized by mixed metabolic and fibrotic gene expression, upregulation of inflammation, and downregulation of myogenesis.

Transcriptional time course after rotator cuff repair in 6 month old female rabbits

Introduction: Rotator cuff tears are prevalent in the population above the age of 60. The disease progression leads to muscle atrophy, fibrosis, and fatty infiltration, which is not improved upon with surgical repair, highlighting the need to better understand the underlying biology impairing more favorable outcomes. Methods: In this study, we collected supraspinatus muscle tissue from 6 month old female rabbits who had undergone unilateral tenotomy for 8 weeks at 1, 2, 4, or 8 weeks post-repair (n = 4/group). RNA sequencing and enrichment analyses were performed to identify a transcriptional timeline of rotator cuff muscle adaptations and related morphological sequelae. Results: There were differentially expressed (DE) genes at 1 (819 up/210 down), 2 (776/120), and 4 (63/27) weeks post-repair, with none at 8 week post-repair. Of the time points with DE genes, there were 1092 unique DE genes and 442 shared genes, highlighting that there are changing processes in the muscle at each time point. Broadly, 1-week post-repair differentially expressed genes were significantly enriched in pathways of metabolism and energetic activity, binding, and regulation. Many were also significantly enriched at 2 weeks, with the addition of NIF/NF-kappaB signaling, transcription in response to hypoxia, and mRNA stability alongside many additional pathways. There was also a shift in transcriptional activity at 4 weeks post-repair with significantly enriched pathways for lipids, hormones, apoptosis, and cytokine activity, despite an overall decrease in the number of differentially expressed genes. At 8 weeks post-repair there were no DE genes when compared to control. These transcriptional profiles were correlated with the histological findings of increased fat, degeneration, and fibrosis. Specifically, correlated gene sets were enriched for fatty acid metabolism, TGF-B-related, and other pathways. Discussion: This study identifies the timeline of transcriptional changes in muscle after RC repair, which by itself, does not induce a growth/regenerative response as desired. Instead, it is predominately related to metabolism/energetics changes at 1 week post-repair, unclear or asynchronous transcriptional diversity at 2 weeks post-repair, increased adipogenesis at 4 weeks post-repair, and a low transcriptional steady state or a dysregulated stress response at 8 weeks post-repair.

Paraspinal muscle gene expression across different aetiologies in individuals undergoing surgery for lumbar spine pathology

PURPOSE

The purpose of this study was to understand potential baseline transcriptional expression differences in paraspinal skeletal muscle from patients with different underlying lumbar pathologies by comparing multifidus gene expression profiles across individuals with either disc herniation, facet arthropathy, or degenerative spondylolisthesis.

METHODS

Multifidus biopsies were obtained from patients (n = 44) undergoing lumbar surgery for either disc herniation, facet arthropathy, or degenerative spondylolisthesis. Diagnostic categories were based on magnetic resonance images, radiology reports, and intraoperative reports. Gene expression for 42 genes was analysed using qPCR. A one-way analysis of variance was performed for each gene to determine differences in expression across diagnostic groups. Corrections for multiple comparisons across genes (Benjamini-Hochberg) and for between-group post hoc comparisons (Sidak) were applied.

RESULTS

Adipogenic gene (ADIPOQ) expression was higher in the disc herniation group when compared to the facet arthropathy group (p = 0.032). Adipogenic gene (PPARD) expression was higher in the degenerative spondylolisthesis group when compared to the disc herniation group (p = 0.013), although absolute gene expression levels for all groups was low. Fibrogenic gene (COL3A1) had significantly higher expression in the disc herniation group and facet arthropathy group when compared to the degenerative spondylolisthesis group (p < 0.001 and p = 0.038, respectively). When adjusted for multiple comparisons, only COL3A1 remained significant (p = 0.012).

CONCLUSION

Individuals with disc herniation and facet arthropathy demonstrate higher COL3A1 gene expression compared to those with degenerative spondylolisthesis. Future research is required to further understand the biological relevance of these transcriptional differences.

Cervical Paraspinal Muscle Fatty Infiltration is Directly Related to Extension Reserve in Patients With Cervical Spine Pathology

STUDY DESIGN/SETTING

Retrospective review of a prospectively collected database.

OBJECTIVE

The objective of this study was to determine the relationship between paracervical muscle area, density, and fat infiltration and cervical alignment among patients presenting with cervical spine pathology.

BACKGROUND CONTEXT

The impact of cervical spine alignment on clinical outcomes has been extensively studied, but little is known about the association between spinal alignment and cervical paraspinal musculature.

METHODS

We examined computed tomography scans and radiographs for patients presenting with cervical spine pathology. The posterior paracervical muscle area, density, and fat infiltration was calculated on axial slices at C2, C4, C6, and T1. We measured radiographic parameters including cervical sagittal vertical axis, cervical lordosis, T1 slope (T1S), range of motion of the cervical spine. We performed Pearson correlation tests to determine if there were significant relationships between muscle measurements and alignment parameters.

RESULTS

The study included 51 patients. The paracervical muscle area was higher for males at C2 ( P =0.005), C4 ( P =0.001), and T1 ( P =0.002). There was a positive correlation between age and fat infiltration at C2, C4, C6, and T1 (all P <0.05). The cervical sagittal vertical axis positively correlated with muscle cross-sectional area at C2 ( P =0.013) and C4 ( P =0.013). Overall cervical range of motion directly correlated with muscle density at C2 ( r =0.48, P =0.003), C4 ( r =0.41, P =0.01), and C6 ( r =0.53. P <0.001) and indirectly correlated with fat infiltration at C2 ( r =-0.40, P =0.02), C4 ( r =-0.32, P =0.04), and C6 ( r =-0.35, P =0.02). Muscle density correlated directly with reserve of extension at C2 ( r =0.57, P =0.009), C4 ( r =0.48, P =0.037), and C6 ( r =0.47, P =0.033). Reserve of extension indirectly correlated with fat infiltration at C2 ( r =0.65, P =0.006), C4 ( r =0.47, P =0.037), and C6 ( r =0.48, P =0.029).

CONCLUSIONS

We have identified specific changes in paracervical muscle that are associated with a patient's ability to extend their cervical spine.

The relationship between the degeneration and asymmetry of the lumbar multifidus and erector spinae muscles in patients with lumbar disc herniation with and without root compression

BACKGROUND

The determination of muscle pathologies in lumbar disc herniation (LDH) and other conditions with low back pain is important for understanding low back problems and determining appropriate treatment methods. In patients with lumbar disc herniation with radiculopathy, elucidating the effect of root compression on the severity of muscle degeneration may predict the importance of alleviating root compression. For this purpose, magnetic resonance imaging (MRI) was used to compare the degeneration and asymmetries of the lumbar musculus multifidus (MF) and lumbar musculus erector spinae (ES) muscles in patients with lumbar discopathy without root compression (radiculopathy) and in patients with lumbar discopathy with root compression (radiculopathy).

METHODS

The patients were examined in two groups: 56 patients with lumbar discopathy and no radiculopathy (Non-rad group) and 51 patients with lumbar discopathy and radiculopathy (Rad group). On axial MRI sections passing through the centre of the disc at the L3-S1 level, the asymmetry, cross-sectional area (CSA), fat infiltration, and total CSA (TCSA = MF + ES) of the MF and ES muscles were measured and compared.

RESULTS

No difference was seen between the groups with respect to the CSA values of the right and left MF and left ES, but a significant difference was found in the right ES CSA (p = 0.021). The CSA and TCSA of the MF and ES showed no asymmetry according to group. Severe fat infiltration of > 50% in the right and left MF and left ES was found in the Rad group at a higher rate than in the Non-rad group. Fat infiltration was significantly positively correlated with age, body mass index, and the duration of pain (p < 0.001, p < 0.001, p = 0.004, respectively).

CONCLUSIONS

The study results showed a correlation between LDH and paraspinal muscle degeneration, while no correlation was found with asymmetry. Severe (> 50%) fat infiltration is associated with root compression, and the severity of fat filtration increases in the presence of root compression. The development of more severe degeneration due to denervation associated with root compression plays a role in the emergence of this situation. Therefore, in patients with lumbar disc herniation with radiculopathy, it can be foreseen that to stop and correct severe fat infiltration and muscle degeneration, first, nerve root compression should be corrected with appropriate medical treatment methods, and in patients in whom there is no response, the pressure should be alleviated with appropriate surgical methods.

Spatial distribution of fat infiltration within the paraspinal muscles: implications for chronic low back pain

PURPOSE

Fat infiltration (FI) of the paraspinal muscles (PSMs) measured using MRI is an aspect of muscle quality and is considered to be worse in chronic low back pain (cLBP) patients. However, there is not a clear association between paraspinal muscle FI and cLBP, leaving the clinical importance of paraspinal muscle composition unestablished. The spatial distribution of FI in the PSMs may inform mechanistic understanding of non-specific cLBP as it relates to degenerative intervertebral disc (IVD) pathology. We hypothesized that paraspinal muscle fat-mapping would reveal distinct FI distribution patterns in relation to cLBP symptoms and proximity to symptomatic IVD degeneration.

METHODS

From advanced-sequence water-fat MRI of 40 axial cLBP patients and 21 controls, we examined the spatial distribution of paraspinal muscle FI in relation to the center of rotation at the L4L5 disc. Using statistical parametric mapping, we compared FI patterns for multifidus (MF), erector spinae (ES), and psoas between patients and controls, and to the presence and severity of adjacent degenerative IVD pathology.

RESULTS

The spatial distribution of PSMs FI differs between PSMs and according to symptoms and the adjacent degenerative IVD pathology. Furthermore, the region of MF closest to the disc center of rotation appears most susceptible to FI in the presence of symptomatic IVD degeneration.

CONCLUSION

Our study identified spatial distribution patterns of FI in the PSMs as a potential diagnostic biomarker that may also provide granular mechanistic insights into spine biomechanics related to cLBP, as well as advancing the use of prior summary measures limited to overall muscle FI.

Spatial transcriptomics tools allow for regional exploration of heterogeneous muscle pathology in the pre-clinical rabbit model of rotator cuff tear

Background

Conditions affecting skeletal muscle, such as chronic rotator cuff tears, low back pain, dystrophies, and many others, often share changes in muscle phenotype: intramuscular adipose and fibrotic tissue increase while contractile tissue is lost. The underlying changes in cell populations and cell ratios observed with these phenotypic changes complicate the interpretation of tissue-level transcriptional data. Novel single-cell transcriptomics has limited capacity to address this problem because muscle fibers are too long to be engulfed in single-cell droplets and single nuclei transcriptomics are complicated by muscle fibers’ multinucleation. Therefore, the goal of this project was to evaluate the potential and challenges of a spatial transcriptomics technology to add dimensionality to transcriptional data in an attempt to better understand regional cellular activity in heterogeneous skeletal muscle tissue.

Methods

The 3′ Visium spatial transcriptomics technology was applied to muscle tissue of a rabbit model of rotator cuff tear. Healthy control and tissue collected at 2 and 16 weeks after tenotomy was utilized and freshly snap frozen tissue was compared with tissue stored for over 6 years to evaluate whether this technology is retrospectively useful in previously acquired tissues. Transcriptional information was overlayed with standard hematoxylin and eosin (H&E) stains of the exact same histological sections.

Results

Sequencing saturation and number of genes detected was not affected by sample storage duration. Unbiased clustering matched the underlying tissue type-based on H&E assessment. Connective-tissue-rich areas presented with lower unique molecular identifier counts are compared with muscle fibers even though tissue permeabilization was standardized across the section. A qualitative analysis of resulting datasets revealed heterogeneous fiber degeneration–regeneration after tenotomy based on (neonatal) myosin heavy chain 8 detection and associated differentially expressed gene analysis.

Conclusions

This protocol can be used in skeletal muscle to explore spatial transcriptional patterns and confidently relate them to the underlying histology, even for tissues that have been stored for up to 6 years. Using this protocol, there is potential for novel transcriptional pathway discovery in longitudinal studies since the transcriptional information is unbiased by muscle composition and cell type changes.

Paraspinal Muscle Health is Related to Fibrogenic, Adipogenic, and Myogenic Gene Expression in Patients with Lumbar Spine Pathology

BACKGROUND

Lumbar spine pathology is a common feature of lower back and/or lower extremity pain and is associated with observable degenerative changes in the lumbar paraspinal muscles that are associated with poor clinical prognosis. Despite the commonly observed phenotype of muscle degeneration in this patient population, its underlying molecular mechanisms are not well understood. The aim of this study was to investigate the relationships between groups of genes within the atrophic, myogenic, fibrogenic, adipogenic, and inflammatory pathways and multifidus muscle health in individuals undergoing surgery for lumbar spine pathology.

METHODS

Multifidus muscle biopsies were obtained from patients (n = 59) undergoing surgery for lumbar spine pathology to analyze 42 genes from relevant adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic gene pathways using quantitative polymerase chain reaction. Multifidus muscle morphology was examined preoperatively in these patients at the level and side of biopsy using T2-weighted magnetic resonance imaging to determine whole muscle compartment area, lean muscle area, fat cross-sectional areas, and proportion of fat within the muscle compartment. These measures were used to investigate the relationships between gene expression patterns and muscle size and quality.

RESULTS

Relationships between gene expression and imaging revealed significant associations between decreased expression of adipogenic/metabolic gene (PPARD), increased expression of fibrogenic gene (COL3A1), and lower fat fraction on MRI (r = -0.346, p = 0.018, and r = 0.386, p = 0.047 respectively). Decreased expression of myogenic gene (mTOR) was related to greater lean muscle cross-sectional area (r = 0.388, p = 0.045).

CONCLUSION

Fibrogenic and adipogenic/metabolic genes were related to pre-operative muscle quality, and myogenic genes were related to pre-operative muscle size. These findings provide insight into molecular pathways associated with muscle health in the presence of lumbar spine pathology, establishing a foundation for future research that addresses how these changes impact outcomes in this patient population.

Identification of differentially expressed genes in mouse paraspinal muscle in response to microgravity

Lower back pain (LBP) is the primary reason leading to dyskinesia in patients, which can be experienced by people of all ages. Increasing evidence have revealed that paraspinal muscle (PSM) degeneration (PSMD) is a causative contributor to LBP. Current research revealed that fatty infiltration, tissue fibrosis, and muscle atrophy are the characteristic pathological alterations of PSMD, and muscle atrophy is associated with abnormally elevated oxidative stress, reactive oxygen species (ROS) and inflammation. Interestingly, microgravity can induce PSMD and LBP. However, studies on the molecular mechanism of microgravity in the induction of PSMD are strongly limited. This study identified 23 differentially expressed genes (DEGs) in the PSM (longissimus dorsi) of mice which were flown aboard the Bion M1 biosatellite in microgravity by bioinformatics analysis. Then, we performed protein-protein interaction, Gene Ontology function, and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis for the DEGs. We found that Il6ra, Tnfaip2, Myo5a, Sesn1, Lcn2, Lrg1, and Pik3r1 were inflammatory genes; Fbox32, Cdkn1a, Sesn1, and Mafb were associated with muscle atrophy; Cdkn1a, Sesn1, Lcn2, and Net1 were associated with ROS; and Sesn1 and Net1 were linked to oxidative stress. Furthermore, Lcn2, Fbxo32, Cdkn1a, Pik3r1, Sesn1, Net1, Il6ra, Myo5a, Lrg1, and Pfkfb3 were remarkably upregulated, whereas Tnfaip2 and Mafb were remarkably downregulated in PSMD, suggesting that they might play a significant role in regulating the occurrence and development of PSMD. These findings provide theoretical basis and therapeutic targets for the treatment of PSMD.

An assessment of morphological and pathological changes in paravertebral muscle degeneration using imaging and histological analysis: a cross-sectional study

Background

The high signal of paravertebral muscle (PVM) on T2-weighted image (T2WI) is usually considered to be fatty degeneration. However, it is difficult to distinguish inflammatory edema from fatty degeneration on T2WI. The purpose of this study was to identify different types of PVM high signal in patients with low back pain (LBP) through magnetic resonance imaging (MRI) and histology.

Methods

Seventy patients with LBP underwent MRI. The signal change of multifidus both on T2WI and fat suppression image (FSI) was quantified by Image J. Furthermore, 25 of the 70 patients underwent surgery for degenerative lumbar disease and their multifidus were obtained during the operation. Histological analysis of the samples was performed by HE staining.

Result

Three types of PVM signal changes were identified from the MRI. Type 1 (n = 36) indicated fatty degeneration characterized by a high signal on T2WI and low signal on FSI. High signal on both T2WI and FSI, signifying type 2 meant inflammatory edema (n = 9). Type 3 (n = 25) showed high signal on T2WI and partial signal suppression on FSI, which meant a combination of fatty degeneration and inflammatory edema. Histological results were consistent with MRI. Among the 25 patients who underwent surgery, type 1 (n = 14) showed adipocytes infiltration, type 2 (n = 3) showed inflammatory cells infiltration and type 3 (n = 8) showed adipocytes and inflammatory cells infiltration.

Conclusion

From our results, there are three types of pathological changes in patients with PVM degeneration, which may help to decide on targeted treatments for LBP.

Paraspinal muscle pathophysiology associated with low back pain and spine degenerative disorders

Low back pain disorders affect more than 80% of adults in their lifetime and are the leading cause of global disability. The muscles attaching to the spine (ie, paraspinal muscles) are critical for proper spine health and play a crucial role in the functioning of the spine and whole body; however, reports of muscle dysfunction and insufficiency in chronic LBP (CLBP) patients are common. This article presents a review of the current understanding of the relationship between paraspinal muscle pathophysiology and spine-related disorders. Human literature demonstrates a clear association between altered muscle structure/function, most notably fatty infiltration and fibrosis, and low back pain disorders; other associations, including muscle cell atrophy and fiber type changes, are less clear. Animal literature then provides some mechanistic insight into the complex relationships, including initiating factors and time courses, between the spine and spine muscles under pathological conditions. It is apparent that spine pathology can directly lead to changes in the paraspinal muscle structure, function, and biology. It also appears that changes to the muscle structure and function can directly lead to changes in the spine (eg, deformity); however, this relationship is less well studied. Future work must focus on providing insight into possible mechanisms that regulate spine and paraspinal muscle health, as well as probing how muscle degeneration/dysfunction might be an initiating factor in the progression of spine pathology.

Does the Interaction between Local and Systemic Inflammation Provide a Link from Psychology and Lifestyle to Tissue Health in Musculoskeletal Conditions?

Musculoskeletal conditions are known to involve biological, psychological, social and, often, lifestyle elements. However, these domains are generally considered in isolation from each other. This siloed approach is unlikely to be adequate to understand the complexity of these conditions and likely explains a major component of the disappointing effects of treatment. This paper presents a hypothesis that aims to provide a foundation to understand the interaction and integration between these domains. We propose a hypothesis that provides a plausible link between psychology and lifestyle factors with tissue level effects (such as connective tissue dysregulation/accumulation) in musculoskeletal conditions that is founded on understanding the molecular basis for interaction between systemic and local inflammation. The hypothesis provides plausible and testable links between mind and body, for which empirical evidence can be found for many aspects. We present this hypothesis from the perspective of connective tissue biology and pathology (fibrosis), the role of inflammation locally (tissue level), and how this inflammation is shaped by systemic inflammation through bidirectional pathways, and various psychological and lifestyle factors via their influence on systemic inflammation. This hypothesis provides a foundation for new consideration of the development and refinement of personalized multidimensional treatments for individuals with musculoskeletal conditions.

Paraspinal Muscle Contractile Function is Impaired in the ENT1-deficient Mouse Model of Progressive Spine Pathology

STUDY DESIGN

Basic science study of the relationship between spine pathology and the contractile ability of the surrounding muscles.

OBJECTIVE

The aim of this study was to investigate single muscle fiber contractile function in a model of progressive spine mineralization (ENT1-/- mice).

SUMMARY OF BACKGROUND DATA

Altered muscle structure and function have been associated with various spine pathologies; however, studies to date have provided limited insight into the fundamental ability of spine muscles to actively contract and generate force, and how this may change in response to spine pathology.

METHODS

Experiments were performed on two groups (ENT1-/- [KO] and ENT1+/+ [WT]) of mice at 8 months of age (n = 12 mice/group). Single muscle fibers were isolated from lumbar multifidus and erector spinae, as well as tibialis anterior (a non-spine-related control) and tested to determine their active contractile characteristics.

RESULTS

The multifidus demonstrated decreases in specific force (type IIax fibers: 36% decrease; type IIb fibers: 29% decrease), active modulus (type IIax: 35% decrease; type IIb: 30% decrease), and unloaded shortening velocity (Vo) (type IIax: 31% decrease) in the ENT1-/- group when compared to WT controls. The erector spinae specific force was reduced in the ENT1-/- mice when compared to WT (type IIax: 29% decrease), but active modulus and Vo were unchanged. There were no differences in any of the active contractile properties of the lower limb TA muscle, validating that impairments observed in the spine muscles were specific to the underlying spine pathology and not the global loss of ENT1.

CONCLUSION

These results provide the first direct evidence of cellular level impairments in the active contractile force generating properties of spine muscles in response to chronic spine pathology.Level of Evidence: N/A.

A Novel Magnetic Resonance Imaging-based Lumbar Muscle Grade to Predict Health-related Quality of Life Scores Among Patients Requiring Surgery

STUDY DESIGN

Retrospective cross-sectional cohort.

OBJECTIVE

The aim of this sudy was to determine whether muscle health measurements are associated with health-related quality of life scores (HRQOLs) for patients with lumbar spine pathology.

SUMMARY OF BACKGROUND DATA

Poor muscle health has been implicated as a source of pain/dysfunction for patients with lumbar spine pathology. Our aim was to quantify the relationship using muscle health measurements and HRQOLs.

METHODS

Three hundred and eight patients were included (mean age 57.7 ± standard deviation 18.2 years' old). We randomly selected patients into a derivation cohort (200) and validation cohort (108) to create our muscle health grade. We measured muscle health by the lumbar indentation value (LIV), goutallier classification (GC), and ratio of paralumbar muscle cross-sectional area over body mass index (PL-CSA/BMI). A muscle health grade was derived based on whether a measurement showed a statistically significant impact on visual analog scale back and leg pain (VAS-leg and VAS-leg), Oswestry Disability Index (ODI), short-form 12 physical health score (SF-12 PHS), short-form 12 mental health score (SF-12 MHS) and Patient-reported Outcomes Measurement Information System (PROMIS). A variety of statistical tools were used to determine whether there was a relationship between a measurement and HRQOLs.

RESULTS

In the derivation cohort, a muscle health grade was created based on the GC and PL-CSA/BMI ratio. For patients with a GC ≤2, one point was given. For patients with a PL-CSA/BMI ≥130, one point was given. Patients with 2 points were graded as "A" and 0 or 1 point were graded "B." Within the validation cohort of patients, there was a statistically significant higher PROMIS (mean 34.5 ± standard deviation 12.6 vs. 27.6 ± 14.0, P = 0.002), ODI (38.8 ± 18.3 vs. 45.8 ± 18.1, P = 0.05) and SF-12 PHS (34.7 ± 11.3 vs. 29.1 ± 6.3, P = 0.002) for patients with a good muscle health grade of "A."

CONCLUSION

This study offers an objective measurement of muscle health that correlates with HRQOLs for patients with lumbar spine pathology.Level of Evidence: 3.

Regional differences between superficial and deep lumbar multifidus in patients with chronic lumbar spine pathology

BACKGROUND

Due to its unique arrangement, the deep and superficial fibers of the multifidus may have differential roles for maintaining spine stabilization and lumbar posture; the superficial multifidus is responsible for lumbar extension and the deep multifidus for intersegmental stability. In patients with chronic lumbar spine pathology, muscle activation patterns have been shown to be attenuated or delayed in the deep, but not superficial, multifidus. This has been interpreted as pain differentially influencing the deep region. However, it is unclear if degenerative changes affecting the composition and function of the multifidus differs between the superficial and deep regions, an alternative explanation for these electrophysiological changes. Therefore, the goal of this study was to investigate macrostructural and microstructural differences between the superficial and deep regions of the multifidus muscle in patients with lumbar spine pathology.

METHODS

In 16 patients undergoing lumbar spinal surgery for degenerative conditions, multifidus biopsies were acquired at two distinct locations: 1) the most superficial portion of muscle adjacent to the spinous process and 2) approximately 1 cm lateral to the spinous process and deeper at the spinolaminar border of the affected vertebral level. Structural features related to muscle function were histologically compared between these superficial and deep regions, including tissue composition, fat fraction, fiber cross sectional area, fiber type, regeneration, degeneration, vascularity and inflammation.

RESULTS

No significant differences in fat signal fraction, muscle area, fiber cross sectional area, muscle regeneration, muscle degeneration, or vascularization were found between the superficial and deep regions of the multifidus. Total collagen content between the two regions was the same. However, the superficial region of the multifidus was found to have less loose and more dense collagen than the deep region.

CONCLUSIONS

The results of our study did not support that the deep region of the multifidus is more degenerated in patients with lumbar spine pathology, as gross degenerative changes in muscle microstructure and macrostructure were the same in the superficial and deep regions of the multifidus. In these patients, the multifidus is not protected in order to maintain mobility and structural stability of the spine.

Trunk stiffness decreases and trunk damping increases with experimental low back pain

Movement adaptations to low back pain (LBP) are believed to protect the painful area. Increased trunk stiffness and decreased trunk damping have been shown in people with recurrent LBP. However, no study has examined these properties using external force perturbations to the trunk during acute LBP when protective adaptations might be expected to have most relevance. Adaptations to an acute painful stimulus via unilateral injection of hypertonic saline into the right longissimus muscle were assessed using a trunk force perturbation paradigm and a mass-spring-damper model to describe effective trunk dynamical properties. Equal weights (15% body weight) were connected to the front and back of the trunk via a cable. Either one was dropped at random to perturb the trunk. Effective trunk dynamical properties were estimated in fourteen males (mean (standard deviation) age 25 (6) years) assuming that trunk movement can be modelled as a second order linear system. Effective trunk dynamical properties were compared before, during and after the experimentally induced painful period. Estimates of effective trunk stiffness (K) decreased and damping (B) increased during pain compared to both before ([mean contrast, 95% CI] K: -403 [-651 to -155] Nm^-1, B: 28 [9-50] Nms^-1) and after (K: -324 [-58 to -591] Nm^-1, B: 20 [4-33] Nms^-1) the experimentally induced painful period. We interpret our results to show that, when challenged by a step force perturbation, a healthy system adapts to noxious input by controlling trunk velocity rather than trunk displacement, in contrast to observations during remission from recurrent clinical LBP.

Confirming the geography of fatty infiltration in the deep cervical extensor muscles in whiplash recovery

Previous preliminary work mapped the distribution of neck muscle fat infiltration (MFI) in the deep cervical extensor muscles (multifidus and semispinalis cervicis) in a small cohort of participants with chronic whiplash associated disorders (WAD), recovered, and healthy controls. While MFI was reported to be concentrated in the medial portion of the muscles in all participants, the magnitude was significantly greater in those with chronic WAD. This study aims to confirm these results in a prospective fashion with a larger cohort and compare the findings across a population of patients with varying levels of WAD-related disability one-year following the motor vehicle collision. Sixty-one participants enrolled in a longitudinal study: Recovered (n = 25), Mild (n = 26) and Severe WAD (n = 10) were studied using Fat/Water magnetic resonance imaging, 12-months post injury. Bilateral measures of MFI in four quartiles (Q1–Q4; medial to lateral) at cervical levels C4 through C7 were included. A linear mixed model was performed, controlling for covariates (age, sex, body mass index), examining interaction effects, and comparing MFI distribution between groups. The recovered group had significantly less MFI in Q1 compared to the two symptomatic groups. Group differences were not found in the more lateral quartiles. Results at 12 months are consistent with the preliminary study, indicating that MFI is spatially concentrated in the medial portions of the deep cervical extensors regardless of WAD recovery, but the magnitude of MFI in the medial portions of the muscles is significantly larger in those with severe chronic WAD.

Intervertebral disc herniation effects on multifidus muscle composition and resident stem cell populations

BACKGROUND

Paraspinal muscles are crucial for vertebral stabilization and movement. These muscles are prone to develop fatty infiltration (FI), fibrosis, and atrophy in many spine conditions. Fibro-adipogenic progenitors (FAPs), a resident muscle stem cell population, are the main contributors of muscle fibrosis and FI. FAPs are involved in a complex interplay with satellite cells (SCs), the primary myogenic progenitor cells within muscle. Little is known about the stem cell composition of the multifidus. The aim of this study is to examine FAPs and SCs in the multifidus in disc herniation patients. Multifidus muscle samples were collected from 10 patients undergoing decompressive spine surgery for lumbar disc herniation. Hamstring muscle was collected from four patients undergoing hamstring autograft ACL reconstruction as an appendicular control. Multifidus tissue was analyzed for FI and fibrosis using Oil-Red-O and Masson's trichrome staining. FAPs and SCs were visualized using immunostaining and quantified with fluorescence-activated cell sorting (FACS) sorting. Gene expression of these cells from the multifidus were analyzed with reverse transcription-polymerase chain reaction and compared to those from hamstring muscle. FI and fibrosis accounted for 14.2%± 7.4% and 14.8%±4.2% of multifidus muscle, respectively. The multifidus contained more FAPs (11.7%±1.9% vs 1.4%±0.2%; P<.001) and more SCs (3.4%±1.6% vs 0.08%±0.02%; P=.002) than the hamstring. FAPs had greater α Smooth Muscle Actin (αSMA) and adipogenic gene expression than FAPs from the hamstring. SCs from the multifidus displayed upregulated expression of stem, proliferation, and differentiation genes.

CONCLUSION

The multifidus in patients with disc herniation contains large percentages of FAPs and SCs with different gene expression profiles compared to those in the hamstring. These results may help explain the tendency for the multifidus to atrophy and form FI and fibrosis as well as elucidate potential approaches for mitigating these degenerative changes by leveraging these muscle stem cell populations.