Transversospinalis Muscles Research Articles

Changes in cross-sectional areas of posterior extensor muscles in thoracic spine: a 10-year longitudinal MRI study

Age-related changes in the posterior extensor muscles of the cervical and lumbar spine have been reported in some studies; however, longitudinal changes in the thoracic spine of healthy subjects are rarely reported. Therefore, this study aimed to evaluate changes in the cross-sectional areas (CSAs) of posterior extensor muscles in the thoracic spine over 10 years and identify related factors. The subjects of this study were 85 volunteers (mean age: 44.7 ± 11.5) and the average follow-up period was about 10 years. The CSAs of the transversospinalis muscles, erector spinae muscles, and total CSAs of the extensor muscles from T1/2 to T11/12 were measured on magnetic resonance imaging. The extent of muscle fat infiltration was assessed by the signal intensity (luminance) of the extensor muscles’ total cross-section compared to a section of pure muscle. We applied a Poisson regression model, which is included in the generalized linear model, and first examined the univariate (crude) association between each relevant factor (age, sex, body mass index, lifestyle, back pain, neck pain, neck stiffness, and intervertebral disc degeneration) and CSA changes. Then, we constructed a multivariate model, which included age, sex, and related factors in the univariate analysis. The mean CSAs of the transversospinalis muscles, erector spinae muscles, and total CSAs of the extensor muscles significantly increased over 10 years. Exercise habit was associated with increased CSAs of the erector spinae muscles and the total area of the extensor muscles. The cross-section mean luminance significantly increased from baseline, indicating a significant increase of fat infiltration in the posterior extensor muscles. Progression of disc degeneration was inversely associated with increased fat infiltration in the total extensor muscles.

Whole‐Body MRI in Limb Girdle Muscular Dystrophy Type R1/2A: Correlation With Clinical Scores

The most common limb girdle muscular dystrophy (LGMD) worldwide is LGMD type R1 (LGMDR1). The aim of this study was to correlate the magnetic resonance imaging (MRI) findings with functional scores and to describe the whole-body MRI (WBMRI) pattern in a LGMDR1 Brazilian cohort. LGMDR1 patients under follow-up in three centers were referred for the study. Clinical data were collected and a functional evaluation was performed, consisting of Gardner-Medwin and Walton (GMW) and Brooke scales. All patients underwent a WBMRI study (1.5T) with axial T1 and STIR images. Fifty-one muscles were semiquantitatively assessed regarding fatty infiltration and muscle edema. The study group consisted of 18 patients. The highest fatty infiltration scores involved the serratus anterior, biceps femoris long head, adductor magnus and lumbar erector spinae. There was a latero-medial and caudo-cranial descending gradient of involvement of the paravertebral muscles, with erector spinae being significantly more affected than the transversospinalis muscles (p<0.05). A striped appearance that has been dubbed the "pseudocollagen sign" was present in 72% of the patients. There was a positive correlation between the MRI score and GMW (Rho:0.83) and Brooke (Rho:0.53) scores. WBMRI in LGMDR1 allows a global patient evaluation including involvement of the paraspinal muscles, usually an underestimated feature in the clinical and imaging study of myopathies. Knowledge of the WBMRI pattern of LGMDR1 involvement can be useful in the diagnostic approach and in future studies to identify the best target muscles to serve as outcome measures in clinical trials.

Factors of Postural Asymmetry (FPA) At The Pre- and Subclinical Stages of the Develop-ment of 3D Deformity of the Vertebral Complex

In the pathogenesis of typical scoliosis, as a three-dimensional deformation, the process of formation of its horizontal component is of particular interest. From the point of view of the functional anatomy of the vertebral complex, appearance of this component is directly related to the work of the transverso-spinal muscles. Thus, their contraction on the left side results in a rotational displacement of the vertebral bodies to the right, and the same phenomenon on the right causes a left-sided rotation of the main bone elements of the supporting column of the spine. It has already been shown that longterm asymmetric contraction of these muscles is a key at the subclinical stage of the transition of a healthy spine to the “scoliotic” status [1-3]. The method of blood serum bioassay (BT SC) has confirmed our assumption that among the participants in the pathogenesis of progressive scoliosis there are so-called neuropeptide factors of postural asymmetry (FPA), which have an ability to lateralize the activity of motor neurons in the spinal cord. These were natural regulators - oxytocin and arginine-8-vasopressin, and this ability appears in a case of a multiple increase in their concentration. Determination of their quantitative characteristics using ELISA showed high correlations between the levels of these factors and the process of spinal column deformation at the pre-and subclinical stages of scoliosis development.

The Impact of Cervical Spinal Muscle Degeneration on Cervical Sagittal Balance and Spinal Degenerative Disorders.

This is a retrospective analysis of kinematic magnetic resonance images (kMRI). To assess the association of cervical paraspinal muscle with cervical sagittal balance and degenerative spinal disorders. Although the effects of spinal disorders and cervical imbalance on patient's symptoms have been well described, the relationship of the cervical muscle quality and volume to cervical imbalance or spinal disorders is not well established. In total, 100 kMRI taken in a neutral weight-bearing position were analyzed. The adjusted cross-sectional area ratio (aCSA ratio: the value of muscle CSA divided by the vertebral CSA) and fat infiltration ratio of the transversospinalis muscles at C4 and C7 vertebral levels were measured using axial slice of kMRI. The correlation with cervical balance parameters [Oc-C2 angle, C2-C7 angle, C7-T1 angle, C7 slope, T1 slope, cranial tilt, cervical tilt, thoracic inlet angle (TIA), and neck tilt] and cervical degenerative disorders (disk degeneration, Modic change, and spondylolisthesis) were evaluated. The aCSA ratio at C4 correlated with C2-C7 angle (r=0.267), C7 slope (r=0.207), T1 slope (r=0.221), disk degeneration at C3-4, C4-5, C5-6 (r=-0.234, -0.313, -0.262) and spondylolisthesis at C3 (anterior: r=-0.206, posterior: r=-0.249). The aCSA ratio at C7 correlated with disk degeneration at C3-4, C4-5, C5-6, C6-7 (r=-0.209, -0.294, -0.239, -0.209). The fat infiltration ratio at C4 correlated with TIA (r=0.306) and neck tilt (r=0.353), likewise the ratio at C7 correlated with TIA (r=0.270) and neck tilt (r=0.405). All correlations above were statistically significant with P<0.05. The paraspinal muscle volume showed significant relationship with the cervical balance parameters and disk degeneration. While, paraspinal muscle quality related to the thoracic inlet parameters. Our findings can be an important step to develop the knowledge of the association between cervical muscle and cervical degenerative disorders, as well as the sagittal balance of the cervical spine. Level III.

Small C7–T1 lordotic angle and muscle degeneration at C7 level were independent radiological characteristics of patients with cervical imbalance: a propensity score-matched analysis

Background contextCervical sagittal vertical axis (cSVA) of ≥40 mm is recognized as the key factor of poor health-related quality of life, poor surgical outcomes, and correction loss after surgery for cervical deformity. However, little is known about the radiological characteristics of patients with cSVA≥40 mm. PurposeThe purpose of this study was to identify the radiological characteristics of patients with cervical imbalance. DesignRetrospective analysis of weight-bearing cervical magnetic resonance (MR) images. Patient sampleConsecutive 1,500 MR images of symptomatic patients in weight-bearing position. Outcome measuresCervical sagittal vertical axis, cervical alignment, cervical balance parameters (T1 slope, Co–C2 angle, C2–C7 angle, C7–T1 angle, neck tilt, and thoracic inlet angle), disc degeneration (Pfirmann and Suzuki classification), end plate degeneration (Modic change), spondylolisthesis (antero- and retrolisthesis), anteroposterior (AP) diameter of dural sac, cross-sectional area (CSA), and fat infiltration ratio of the transversospinalis muscles at C4 and C7 levels. MethodsPatients were divided into two groups: cSVA≥40 mm and cSVA<40 mm. Gender, age, and cervical alignment were analyzed. Subsequently, matched imbalance (cSVA≥40 mm) and control (<40 mm) groups were created using the propensity score to adjust for age, gender, and cervical alignment. Cervicothoracic angular parameters, disc degeneration, Modic change, spondylolisthesis, and degeneration of the transversospinalis muscles at C4 and C7 were compared. Variables with p<.05 were included in the multinomial logistic regression model to identify factors that relate to the cervical balance grouping. ResultsThe incidence of patients with cervical imbalance was 2.5% (37 patients). Those patients had a higher incidence of kyphosis, were older, and there were more male patients. In the matched imbalance group, the T1 slope was greater (p=.028), C7–T1 lordotic angle was smaller (p<.001), the number of anterolisthesis was greater (p=.012), and the fat infiltration ratio at C4 and C7 was higher (p=.023, 0.030) compared with the control. Logistic regression analysis showed that the C7–T1 angle (adjusted odds ratio [aOR]=0.592, p=.001) and fat infiltration ratio at C7 level (aOR=1.178, p=.030) were significant independent variables. ConclusionsSmaller C7–T1 lordotic angle and severe muscle degeneration at C7 level were independent characteristics of patients with cervical imbalance.

Epaxial Musculature in Armadillos, Sloths, and Opossums: Functional Significance and Implications for the Evolution of Back Muscles in the Xenarthra

To investigate the evolution of xenarthran epaxial muscles, fresh specimens of the North American Common long-nosed armadillo Dasypus novemcinctus and of a marsupial, the Virginia opossum Didelphis virginiana, were dissected. Data from one fixed specimen of a two-toed sloth Choloepus didactylus were also used for comparison, because it is a xenarthran exhibiting a highly derived locomotor mode. The opossum was used to represent a more generalized mammalian condition. Each of the three mammalian epaxial muscle groups, the iliocostalis, longissimus dorsi, and transversospinalis, was removed and its mass was determined. All data were corrected for body mass and length. Unpaired, one-tailed t-tests showed the average mass of the iliocostalis and transversospinalis of Dasypus to be significantly larger than the mass of the same muscles in Didelphis, whereas the average mass of the longissimus dorsi was not statistically different between the two species. In agreement with pronounced lateral bending and de-emphasized dorso-ventral flexion and extension, Choloepus also had a relatively large iliocostalis and small longissimus. Our limited data suggest that this condition was inherited from non-arboreal and probably digging early xenarthrans. We believe the relatively larger iliocostalis and transversospinalis muscles in Dasypus can be attributed to the need to provide vertical stabilization of the trunk and resist lateral reaction forces generated by digging. Thus, for Xenarthra it represents a synapomorphy linked to adaptations for fossoriality.

Acute electromyographic responses of deep thoracic paraspinal muscles to spinal manual therapy interventions. An experimental, randomized cross-over study

This single group, randomized, cross-over study explored whether manual therapy alters motor tone of deep thoracic back muscles by examining resting electromyographic activity (EMG) after 2 types of manual therapy and a sham control intervention. Twenty-two participants with thoracic spinal pain (15 females, 7 males, mean age 28.1 ± 6.4 years) had dual fine-wire, intramuscular electrodes inserted into deep transversospinalis muscles at a thoracic level where tissues appeared abnormal to palpation (AbP) and at 2 sites above and below normal and non-tender to palpation (NT). A surface electrode was on the contralateral paraspinal mass at the level of AbP. EMG signals were recorded for resting prone, two 3-s free neck extension efforts, two 3-s resisted maximal voluntary isometric contractions (MVIC), and resting prone before the intervention. Randomized spinal manipulation, counterstrain, or sham manipulation was delivered and EMG re-measured. Participants returned 1 and 2 weeks later for the remaining 2 treatments. Reductions in resting EMG followed counterstrain in AbP (median decrease 3.3%, P = 0.01) and NT sites (median decrease 1.0%, P = 0.05) and for the surface electrode site (median decrease 2.0%, P = 0.009). Reduction in EMG following counterstrain during free neck extension was found for the surface electrode site (median decrease 2.7%, P < 0.01). Spinal manipulation produced no change in EMG, whereas counterstrain technique produced small significant reductions in paraspinal muscle activity during prone resting and free neck extension conditions. The clinical relevance of these changes is unclear.

Development of the Epaxial Muscles in the Human Embryo

BackgroundThe appearance of the true muscles of the back is dominated by three muscle columns, but a division into a lateral sacrospinal compartment with longissimus (medial) and iliocostal (lateral) divisions, and a medial compartment with transversospinal muscles is presently more often used. Although back muscles are defined by their embryological origin and innervation pattern, no detailed study on their development is available.MethodsHuman embryos (5–10 weeks development) were studied, using Amira® and Cinema4D® remodeling software for visualization.ResultsAt Carnegie Stage (CS)15, the epaxial portions of the myotomes became identifiable laterally to the developing vertebrae. At CS16, these portions fused to form a longitudinal muscle column, which became innervated by the dorsal branch of the spinal nerve. At CS17, the longitudinal muscle mass segregated into medial and lateral columns (completed at CS18). At CS18, the medial column segregated again into intermediate and medial columns (completed at CS20). Between CS20 and CS23, the cervical portions of the three columns segregated again form lateral to medial resulting ventrolaterally in rod‐like continuations of the caudal portions of the columns and dorsomedially in spade‐like portions. The lateral and intermediate columns did not separate in the lower lumbar and sacral region. The observed topography identifies the iliocostalis and splenius as belonging to the lateral column, the longissimus to the intermediate column, and the multifidus and (semi‐)spinalis to the medial column. The medial group acquired its transverso‐spinal course during closure of the vertebral arches in the early fetal period.ConclusionEpaxial muscle growth is characterized by cranio‐caudal and latero‐medial gradients in development. Our ontogenetic approach shows that all back muscles can be classified as components of the erector spinae.Support or Funding InformationNFP (Netherlands Fellowship Programmes)

Electromyographic responses of deep thoracic transversospinalis muscles to osteopathic manipulative interventions

BackgroundSpinal manipulative procedures have been claimed to alter resting electromyographic activity (EMG) of paraspinal muscles, but the evidence is inconsistent. This study examined the effect of two osteopathic techniques, high-velocity low-amplitude (HVLA) thrust and counterstrain (CS), on resting EMG of the deep thoracic paraspinal muscles in regions that appear abnormal to palpation. MethodsThis randomized controlled crossover study was conducted using 3 treatments, HVLA, CS, and sham laser control, with a 1-week washout between. Dual fine-wire, intramuscular electrodes were inserted into the deep transversospinalis muscles at a thoracic level where the tissues appeared abnormal and tender to palpation (AbP), and at two normal sites superior and inferior to the AbP. Surface electrodes were placed over the erector spinae muscles adjacent to the AbP site. During the following conditions, pre- and post-treatment EMG signals were recorded while subjects were prone: 1. Resting before and after other conditions (baseline); 2. Two 3-s free neck extension tasks (EXT, a sub-maximal functional task); 3. Two 3-s resisted maximal voluntary isometric contractions (MVIC).Two second periods from each condition were processed and the mean amplitude (uV) was normalized to the highest pre-treatment MVIC reading. EMG scores for normal sites were averaged (NTav). Wilcoxon signed ranks tests were used to test whether the normalized baseline scores changed from pre- to post-treatment. Friedman tests were used to determine whether the change in muscle activity from pre- to post-treatment differed between treatments. ResultsTwenty-two participants were recruited [15 females and 7 males, mean age of 28.1-years (SD = 6.4), mean BMI of 23.8 kg.m−2 (SD = 6.4)]. Mean current pain intensity was 3.2 out of 10 (SD = 1.1). A significant reduction in baseline EMG was found following the CS treatment in the AbP (median decrease 3.3%; p = 0.01, d = 0.33), NTav (median decrease 1.0%; p = 0.05, d = 0.024), and surface (median decrease 2.0%; p = 0.009, d = 0.29) sites. A significant reduction in surface EMG following CS treatment during EXT was also found (median decrease 2.7%; p = 0.003, d = 0.20). EMG activity from other sites and following other treatments was not significantly changed. There was a significant between-group difference in baseline activity for the surface site (p = 0.02, d = 0.58); the change for the CS treatment (median decrease 2.0%) was larger than the change for the HVLA treatment (median increase 0.6%). There were no other significant differences between the treatments. ConclusionsCS appeared to produce small significant reductions in paraspinal muscle activity during resting and free neck extension conditions, whereas the other treatments produced no change. However, given the very small reductions produced, clinical relevance of these changes is unclear.

Fetal development of deep back muscles in the human thoracic region with a focus on transversospinalis muscles and the medial branch of the spinal nerve posterior ramus

Fetal development of human deep back muscles has not yet been fully described, possibly because of the difficulty in identifying muscle bundle directions in horizontal sections. Here, we prepared near-frontal sections along the thoracic back skin (eight fetuses) as well as horizontal sections (six fetuses) from 14 mid-term fetuses at 9-15 weeks of gestation. In the deep side of the trapezius and rhomboideus muscles, the CD34-positive thoracolumbar fascia was evident even at 9 weeks. Desmin-reactivity was strong and homogeneous in the superficial muscle fibers in contrast to the spotty expression in the deep fibers. Thus, in back muscles, formation of the myotendinous junction may start from the superficial muscles and advance to the deep muscles. The fact that developing intramuscular tendons were desmin-negative suggested little possibility of a secondary change from the muscle fibers to tendons. We found no prospective spinalis muscle or its tendinous connections with other muscles. Instead, abundant CD68-positive macrophages along the spinous process at 15 weeks suggested a change in muscle attachment, an event that may result in a later formation of the spinalis muscle. S100-positive intramuscular nerves exhibited downward courses from the multifidus longus muscle in the original segment to the rotatores brevis muscles in the inferiorly adjacent level. The medial cutaneous nerve had already reached the thoracolumbar fascia at 9 weeks, but by 15 weeks the nerve could not penetrate the trapezius muscle. Finally, we propose a folded myotomal model of the primitive transversospinalis muscle that seems to explain a fact that the roofing tile-like configuration of nerve twigs in the semispinalis muscle is reversed in the multifidus and rotatores muscles.

Morphology of the Lumbar Transversospinal Muscles Examined in a Mouse Bearing a Muscle Fiber‐Specific Nuclear Marker

Although the morphology of human lumbar transversospinal (TSP) muscles has been studied, little is known about the structure of these muscles in the mouse (Mus musculus). Such information is relevant given mice are often used as a "normal" phenotype for studies modeling human development. This study describes the gross morphology, muscle fiber arrangement, and innervation pattern of the mouse lumbar TSP muscles. A unique feature of the study is the use of a transgenic mouse line bearing a muscle-specific nuclear marker that allows clear delineation of muscle fiber and connective tissue boundaries. The lumbar TSP muscles of five mice were examined bilaterally; at each spinal level muscles attached to the caudal edge of the spinous process and passed caudally as a single complex unit. Fibers progressively terminated over the four vertebral segments caudad, with multiple points of muscle fiber attachment on each vertebra. Motor endplates, defined with acetylcholinesterase histochemistry, were consistently located half way along each muscle fiber, regardless of length, with all muscle fibers arranged in-parallel rather than in-series. These results provide information relevant to interpretation of developmental and functional studies involving this muscle group in the mouse and show mouse lumbar TSP muscles are different in form to descriptions of equivalent muscles in humans and horses.

Resting Electromyographic Activity of Deep Thoracic Transversospinalis Muscles Identified as Abnormal With Palpation

In the 1940s, osteopathic researchers suggested that paraspinal tissue abnormality was associated with spontaneous muscle activity, but few studies have since re-examined these reports. To determine whether abnormal motor activity plays a role in deep paraspinal tissues that appear abnormal to palpation. Using an observational study design, the PVG of participants with thoracic pain were palpated by two examiners for consensus on the most marked level of tissue abnormality. Dual fine-wire, intramuscular electrodes were inserted into the deep transversospinalis (multifidus, rotatores) muscles at the abnormal level and at two normal sites (above and below the abnormal level). Surface electrodes were placed over the erector spinae muscles adjacent to each intramuscular electrode site. Electromyography signals were recorded during initial prone resting, three maximal voluntary isometric contractions (MVIC), and a second prone resting. The area under the curve for a 2-second period was analyzed for each condition, and values were normalized and reported as a percentage of MVIC. Data were analyzed using a 2-factor repeated-measures analysis of variance. Twenty-five participants with mean (SD) thoracic pain of 3.3 (1.9) on a 0 to 10 visual analog pain scale completed the study protocol. There were no statistically significant differences in normalized resting activity between the three intramuscular sites (P=.25) or between the three surface sites (P=.33). Substantial variability in normalized resting activity at each of the three intramuscular sites was evident (mean [SD] percent of MVIC: abnormal 7.83 [8.76]; normal 9.47 [8.45], 6.65 [7.39]). No statistically significant differences existed in the intramuscular EMG values between the two resting baseline periods (P=.10). The lack of statistically significant differences between EMG activity at the abnormal and normal paraspinal sites suggests that factors other than muscle activity are responsible for the apparent abnormality of these tissues to palpation. Investigation of these regions for increased tissue fluid and inflammatory mediators is recommended.

Localization of Acupuncture Points BL25 and BL26 Using Computed Tomography

The aim of this study was to provide a metric description of acupuncture points BL25 and BL26, to investigate their relation to individual anatomical landmarks and structures, and to identify anatomical structures that are involved in needle manipulation during de qi. Fifty-eight (58) white patients with low-back pain received 107 needlings that were documented using computed tomography (CT). For each patient, the body-mass index (BMI) and the interscapular distance were measured. Using the CT scan, the following parameters were assessed: thickness of the soft tissue layer, distance of the puncture site and the needle tip to the vertebral line, distance of the needle tip to the body surface and the intermuscular space, and the needle depth in muscle tissue. The mean distance from the puncture site to the vertebral line was 3.5 +/- 0.5 cm for BL25 and 3.4 +/- 0.4 cm for BL26. The distance of the needle tip to the vertebral line was similar (3.4 +/- 0.5 cm for BL25 and 3.2 +/- 0.4 cm for BL26). The mean distance of the needle tip to the body surface was 4.1 +/- 0.9 cm at BL25 and 3.9 +/- 0.8 cm at BL26. The majority of the needle tips were located in the intermuscular region between the erector spinae and the transversospinal muscles. There was a significant correlation between the interscapular distance and the thickness of the soft tissue layer with the BMI at both acupuncture points. Nearly all parameters correlated with the BMI. At BL26, correlations between the distance of needle to the vertebral line and the BMI were not statistically significant but the scatter plots indicate a positive dependency. The results of this study show an association between de qi and needle location within the intermuscular septa. BL25 and BL26 are located as clusters in and around the intermuscular region of the erector spinae and the transversospinal muscles, with a distance to the vertebral line of 3.49 +/- 0.58 cm and 3.32 +/- 0.53 cm, respectively. Using proportional methods is relevant for the success of acupuncture therapy.

Morphology of the paravertebral muscles in adolescent idiopathic scoliosis.

Histochemical studies of paravertebral muscles in idiopathic scoliosis have shown a consistently higher proportion of type I fibers on the convex side. In this study of the transversospinal muscles in moderate idiopathic scoliosis, we could demonstrate a lower type II B/II A fiber ratio on the convex side, along with an increased proportion of type I fibers. The capillary count was also higher on the convex side, especially around the type I fibers. The few pathologic changes found were predominately seen in the gravest cases of scoliosis. It is concluded that the fiber type distribution, capillary count, and metabolic enzyme activity on the convex side resembles that seen after endurance training. This suggests a secondary adaptive origin of these changes.

Vertebral Muscles of the Back and Tail of the Albino Rat (&lt;i&gt;Rattus norvegicus albinu&lt;/i&gt;&lt;i&gt;s&lt;/i&gt;); pp. 1–23

The dorsal and ventral vertebral muscles of the back and the tail of the albino Norway rat are described and discussed. These muscles were analyzed because they are undoubtably used during the sexual posturing, lordosis, of the female rat, as well as participating in a variety of other behaviors. The muscles are described by region (thoracic-lumbar or sacrocaudal), and the classifications of Vallois are followed where possible. Of the epaxial (dorsal) muscles, the three longitudinal systems of muscles, the transversospinalis, the longissimus, and the iliocostalis systems, can be identified in the albino rat. Muscles of the transversospinalis system are fused in the lumbar region, distinct and specialized in the thoracic region, and form the tail muscle extensor caudae medialis caudally. The iliocostalis system of the lumbar region is fused with one component of the lumbar longissimus system to form lateral longissimus. Anteriorly, iliocostalis thoracis and cervicis represent the iliocostalis system. The lumbar longissimus system is represented by the longissimus component of lateral longissimus, medial longissimus, and a short-fiber component. Longissimus dorsi is the anterior continuation of the longissimus portion of the lateral longissimus. The short-fiber component also continues into the thoracic region, where it becomes difficult to separate out from longissimus dorsi. Medial longissimus represents the excursion into the lumbar region of the long, tendinous, tailbase-tail muscle, longissimus caudae; the caudal portion of this muscle is extensor caudae lateralis. The remaining dorsal muscle described is the tail muscle, abductor caudae dorsalis. The hyposomal (ventral) muscles described are quadratus lumborum and the intertransversarii, present in the lumbar region; the muslces iliococcygeus, pubococcygeus and coccygeus which arise from the medial face of the pelvis and insert onto the proximal tail; the long, tendinous, tail muscles, flexor caudae brevis and longus; and the ventral and lateral set of segmental tail muscles. The innervation of the lumbar transversospinalis muscles by the medial branches and of lateral longissimus by the lateral branches of the dorsal rami of the spinal nerves was traced and confirmed by electrical stimulation of the nerve branches. The innervation of medial longissimus is also described. Additionally, movements of the vertebral column produced by direct unilateral or bilateral muscle stimulation were observed for a number of the muscles.

Vertebral Muscles of the Back and Tail of the Albino Rat (&lt;i&gt;Rattus norvegicus albinu&lt;/i&gt;&lt;i&gt;s&lt;/i&gt;); pp. 24–47

The dorsal and ventral vertebral muscles of the back and tail of the albino Norway rat are described and discussed. These muscles were analyzed because they are undoubtably used during the sexual posturing, lordosis, of the female rat, as well as participating in a variety of other behaviors.The muscles are described by region (thoracic-lumbar or sacrocaudal), and the classifications of <i>Vallois </i>are followed where possible. Of the epaxial (dorsal) muscles, the three longitudinal systems of muscles, the transversospinalis, the longissimus, and the iliocostalis systems, can be identified in the albino rat. Muscles of the transversospinalis system are fused in the lumbar region, distinct and specialized in the thoracic region, and form the tail muscle extensor caudae medialis caudally. The iliocostalis system of the lumbar region is fused with one component of the lumbar longissimus system to form lateral longissimus. Anteriorly, iliocostalis thoracis and cervicis represent the iliocostalis system. The lumbar longissimus system is represented by the longissimus component of lateral longissimus, medial longissimus, and a short-fiber component. Longissimus dorsi is the anterior continuation of the longissimus portion of the lateral longissimus. The short-fiber component also continues into the thoracic region, where it becomes difficult to separate out from longissimus dorsi. Medial longissimus represents the excursion into the lumbar region of the long, tendinous, tailbase-tail muscle, longissimus caudae; the caudal portion of this muscle is extensor caudae lateralis. The remaining dorsal muscle described is the tail muscle, abductor caudae dorsalis.The hyposomal (ventral) muscles described are quadratus lumborum and the intertransversarii, present in the lumbar region; the muscles iliococcygeus, pubococ-cygeus and coccygeus which arise from the medial face of the pelvis and insert onto the proximal tail; the long, tendinous, tail muscles, flexor caudae brevisi and longus; and the ventral and lateral set of segmental tail muscles.The innervation of the lumbar transversospinalis muscles by the medial branches and of lateral longissimus by the lateral branches of the dorsal rami of the spinal nerves was traced and confirmed by electrical stimulation of the nerve branches. The innervation of medial longissimus is also described. Additionally, movements of the vertebral column produced by direct unilateral or bilateral muscle stimulation were observed for a number of the muscles.

Localization of lumbar epaxial motoneurons in the rat

In the rat, lateral longissimus and the lumbar transverso-spinalis muscles are lumbar trunk muscles, and participate in the lordosis reflex (female sexual posturing). Medial longissimus, the remaining major lumbar epaxial muscle, is a muscle of the proximal tail-tailbase. To allow an analysis of the motor control of lordosis, motoneurons for these muscles must be localized. Horseradish peroxidase (HRP) was injected into lumbar epaxial muscles of female rats. Following injection into medial longissimus, labeled cells were found posterior to the lumbar enlargement, ventrolaterally in the ventral horn. Following injections into lateral longissimus or into lumbar transverso-spinalis muscles, most labeled cells were found on the medial side of the ventral horn, extending through and anterior to the lumbar enlargement. Injections into lumbar transverso-spinalis muscles at more posterior levels led to more posterior locations of labeled cells. The distributions of the labeled cells agree with previous observations on innervation of the muscles. Additionally, the spinal cord was scanned for sites at which microstimulation produced visible twitches of medial longissimus or transverso-spinalis muscles. Locations of low threshold twitch sites were consistent with conclusions based on the HRP findings.

Electromyography of deep back muscles in man.

AbstractThe deep layers of the transversospinal back muscles were studied in 25 healthy human subjects. Bipolar fine wire electrodes were inserted bilaterally at the level of the sixth thoracic and the third lumbar spinous processes. Activity was registered simultaneously in sitting and standing, and during movements while in these positions. It was shown that the same muscle group displayed different patterns of activity in the thoracic compared to the lumbar level. Variations in the pattern of activity during forward flexion, extension and axial rotation suggest that the transversospinal muscles adjust the motion between individual vertebrae. The experimental evidence confirms the anatomical hypothesis that the multifidi are stabilizers rather than prime movers of the whole vertebral column.