Comparative histochemical composition of muscle fibres in a pre- and a postvertebral muscle of the cervical spine

Extreme Tolerance of Extraocular Muscles to Diseases and Aging: Why and How?

The extraocular muscles (EOMs) possess unique characteristics that set them apart from other skeletal muscles. These muscles, responsible for eye movements, exhibit remarkable resistance to various muscular dystrophies and aging, presenting a significant contrast to the vulnerability of skeletal muscles to these conditions. In this review, we delve into the cellular and molecular underpinnings of the distinct properties of EOMs. We explore their structural complexity, highlighting differences in fiber types, innervation patterns, and developmental origins. Notably, EOM fibers express a diverse array of myosin heavy-chain isoforms, retaining embryonic forms into adulthood. Moreover, their motor innervation is characterized by a high ratio of nerve fibers to muscle fibers and the presence of unique neuromuscular junctions. These features contribute to the specialized functions of EOMs, including rapid and precise eye movements. Understanding the mechanisms behind the resilience of EOMs to disease and aging may offer insights into potential therapeutic strategies for treating muscular dystrophies and myopathies affecting other skeletal muscles.

Effect of long-term cervical extensor exercise program on functional disability, pain intensity, range of motion, cervical muscle mass, and cervical curvature in young adult population with chronic non-specific neck pain: a randomized controlled trial

BACKGROUND

The prevalence of chronic non-specific neck pain (CNNP) is on the rise among the young adult population. We herein aimed to compare the effects of long-term specific cervical extensor training and stretching exercises on improving this chronic disorder in young adults.

METHODS

In this prospective, randomized, controlled study, 70 participants aged 18-35 years with CNNP and cervical lordosis loss were included. The participants were assigned to undergo either specific cervical extensor training (observation group) or perform usual stretching exercises (control group). The exercise duration was set at 12 months, with 9 months at the clinic and 3 months at home. The outcome assessments included changes in the neck disability index, visual analog scale from baseline, cervical range of motion (CROM), cross-sectional areas (CSAs) of cervical extensors, and cervical curvature from baseline. The outcome measures were compared between groups at 3, 6, and 12 months of follow-up.

RESULTS

All 70 participants underwent randomization, and no significant differences in demographics and baseline data were found between the two groups. The observation group showed a greater improvement in neck disability index and visual analog scale scores at the 12-month follow-up than the control group. Additionally, a more substantial increase in CROM and CSAs of cervical extensors was observed in the observation group at the 6-month and 12-month follow-ups (P < 0.05). Although more participants in the observation group achieved cervical lordosis at the 12-month follow-up, the difference was marginally nonsignificant (9% in the control group vs. 28% in the observation group, P = 0.075).

CONCLUSIONS

In young adults with CNNP, long-term specific cervical extensor training was associated with a more significant clinically meaningful improvement in disability, pain, and CROM than stretching exercises. The increased CSAs of cervical extensors may potentially contribute to the restoration of cervical lordosis. Trial registration The study is registered at the Chinese domestic clinical trial (ChiCTR2000040009) at Chictr.org. The date of registration: November 18, 2020.

Effects of spinal stabilization exercises delivered using telerehabilitation on outcomes in patients with chronic neck pain: a randomized controlled trial

BACKGROUND

When spinal stabilization exercises (SSE) are performed regularly, may provide benefits on outcome measures in chronic nonspecific neck pain (CNNP) patients. The pandemic has made it difficult for CNNP patients to access regular physiotherapy-exercise services. This study aims to compare telerehabilitation (TR) with face-to-face rehabilitation in CNNP.

METHODS

Neck Functional Capacity Evaluation Test (NFCET) results were the primary outcomes. Pain intensity (PI), disability, awareness, neck muscles architecture, andexercise satisfaction were the secondary outcomes. Patients were randomized into the TR group (TRG) (n = 15) and the control group (CG) (n = 16). Patients performed SSE 3 days a week, for 8 weeks. The TRG was instructed remotely while the CG was instructed in the clinic.

RESULTS

After 8 weeks in both groups, NFCET values and neck awareness increased (p < 0.05), PI and disability decreased (p < 0.05).      Muscle architecture improved in both groups (p < 0.05), except for the Right Sternocleidomastoideus in both groups and the Right Upper-Trapezius in TRG (p > 0.05). There was no difference between the groups for all variables and exercise satisfaction(p > 0.05).

CONCLUSION

SSE for CNNP, whether supervised by therapists in the clinic or by telerehabilitation, was equally effective.

THE CLINICAL TRIAL NUMBER

NCT04691024.

Electromyographic Activity of Sternocleidomastoid Muscle in Individuals With Neck Pain and Healthy Volunteers: A Reliability and Between-Group Differences Examination

OBJECTIVES

The purpose of this study was to evaluate the electromyographic activity of the sternocleidomastoid muscle during the performance of the craniocervical flexion test (CCFT) in individuals with neck pain and healthy volunteers, assess the reliability of this method, and examine possible between-population differences.

METHODS

Electromyographic activity of the sternocleidomastoid muscles of 22 individuals with neck pain and 22 healthy participants was recorded during the 55 stages of the CCFT. Pain (visual analog scale) and disability (Neck Disability Index) levels and pain duration were recorded for the participants with neck pain. Reliability of electromyography was evaluated with the intraclass correlation coefficient, standard error of measurement, and minimum detectable change.

RESULTS

Within-day reliability indices of electromyographic activity were very good to excellent (intraclass correlation coefficients, 0.86-0.98; standard error of measurement, 1.8%-7.6%; minimum detectable change, 5.0%-21.1%). For the head-lift normalization method, 2-way analysis of variance revealed significant between-group differences (P < .02); however, these were not clinically significant when reliability test-retest error was considered. Differences between contraction levels were significant (P < .001); however, the group by contraction level interaction factor was nonsignificant. Therefore, the between-groups electromyographic increases noted with increasing contraction levels were similar. No correlation was identified between participants' electromyography data and pain or disability.

CONCLUSION

In participants with moderate pain, disability, and pain duration, no clear alterations in electromyographic activity of the sternocleidomastoid could be detected with the CCFT. Reliability of the test used was very good.

Microscopic changes in the spinal extensor musculature in people with chronic spinal pain: a systematic review

BACKGROUND CONTEXT

Chronic spinal pain is one the most common musculoskeletal disorders. Previous studies have observed microscopic structural changes in the spinal extensor muscles in people with chronic spinal pain. This systematic review synthesizes and analyzes all the existing evidence of muscle microscopic changes in people with chronic spinal pain.

PURPOSE

To assess the microscopy of spinal extensor muscles including the fiber type composition, the area occupied by fiber types, fiber size/cross sectional area (CSA), and narrow diameter (ND) in people with and without chronic spinal pain. Further, to compare these outcome measures across different regions of the spine in people with chronic neck, thoracic and low back pain.

STUDY DESIGN

Systematic review with meta-analysis.

METHODS

MEDLINE (Ovid Interface), Embase, PubMed, CINAHL Plus, and Web of Science were searched from inception to October 2020. Key journals, conference proceedings, grey literature and hand searching of reference lists from eligible studies were also searched. Two independent reviewers were involved in the selection process. Only studies examining the muscle microscopy of the spinal extensor muscles (erector spinae [ES] and/or multifidus [MF]) between people with and without chronic spinal pain were selected. The risk of bias from the studies was assessed using modified Newcastle Ottawa Scale and the level of evidence was established using the GRADE approach. Data were synthesized based on homogeneity on the methodology and outcome measures of the studies for ES and MF muscles and only four studies were eligible for analysis.

RESULTS

All the five studies included were related to chronic low back pain (CLBP). Meta-analysis (inverse variance method for random effect to calculate mean difference and 95% CI) was performed for the ES fiber type composition by numbers for both type I and type II fibers (I²=43% and 0% respectively indicating homogeneity of studies) and showed no difference between the people with and without CLBP with an overall effect estimate Z= 1.49 (p=.14) and Z=1.06 (p=.29) respectively. Meta-analysis was performed for ES fiber CSA for both type I and type II fibers (I²=0 for both) and showed no difference between people with and without CLBP with an overall effect estimate Z=0.08 (p=.43) and Z=0.75 (p=.45) respectively. Analysis was not performed for ES area occupied by fiber types and ND due to heterogeneity of studies and lack of evidence respectively. Similarly, meta-analysis was not performed for MF fiber type composition by numbers due to heterogeneity of studies. MF analysis for area occupied by fiber type, fiber CSA and ND did not yield sufficient evidence.

CONCLUSIONS

For the ES muscle, there was no difference in fiber type composition and fiber CSA between people with and without CLBP and no conclusions could be drawn for ND for the ES. For the MF, no conclusions could be drawn for any of the muscle microscopy outcome measures. Overall, the quality of evidence is very low and there is very low evidence that there are no differences in microscopic muscle features between people with and without CLBP.

Increased Stiffness of the Superficial Cervical Extensor Muscles in Patients With Cervicogenic Headache: A Study Using Shear Wave Elastography

Background

Cervicogenic headache (CEH) is a secondary headache caused by lesions of the cervical spine and surrounding soft tissues. Cervical muscle dysfunction may be related to the onset of CEH. However, whether cervical muscle stiffness changes in patients with CEH has not been well studied. The purpose of this study was to explore changes in superficial cervical extensor muscle stiffness in patients with CEH using shear wave elastography (SWE).

Methods

In this study, 19 patients with CEH and 20 healthy controls were recruited. Superficial cervical extensor muscle stiffness was obtained from SWE, and the SuperLinear SL10-2 MHz linear array probe in the musculoskeletal muscle mode was chosen as the transducer. Regions of interest in the trapezius (TRAP), splenius capitis (SPL), semispinalis capitis (SCap), and semispinalis cervicis (SCer) were manually segmented. Correlations between superficial cervical extensor muscle stiffness and visual analog scale (VAS) scores, age, and body mass index (BMI) were analyzed using Pearson's correlation. Receiver operating characteristic (ROC) curve was used to investigate the diagnostic ability of superficial cervical extensor stiffness for CEH.

Results

Superficial cervical extensor muscle stiffness on the headache side of patients with CEH was higher than that on the non-headache side and in healthy controls (p < 0.05). Increased stiffness was also observed in SCer on the non-headache side of patients with CEH compared to healthy controls (p < 0.01). In patients with CEH, SCer stiffness was positively correlated with VAS scores (r = 0.481, p = 0.037), but no correlation was found between other muscles and VAS scores (p > 0.05). The areas under the curve of TRAP, SPL, SCap, and SCer in diagnosing CEH were 0.766, 0.759, 0.964, and 1.000, respectively.

Conclusions

Increased stiffness was observed in the superficial cervical extensor muscles on the headache side of patients with CEH. SCer stiffness was correlated with headache intensity in patients with CEH and may provide clues for the diagnosis of CEH.

Deep and superficial cervical muscles respond differently to unstable motor skill tasks

Biomechanical modelling and physiological studies suggest that various spinal muscle layers differ in their contribution to spine movement and stiffness. This study aimed to investigate the activation of deep and superficial muscles in stable and unstable task conditions. Nine healthy participants performed a task of controlling a metal ball on a plate fixed to the head in seated position. In unstable tasks, visual feedback was provided by mirrors to move the ball to the centre of the plate by small head movements and maintain the position for 3 s. Task difficulty was adjusted in a stepwise progression of difficulty using five surfaces with materials of decreasing resistance. In the stable condition, the ball was fixed to the plate's centre. EMG was recorded with surface (sternocleidomastoid, anterior scalenes, upper trapezius) and fine-wire electrodes (rectus capitis posterior major, obliquus inferior, multifidus, semispinalis cervicis, splenius capitis). The outcome variable was root mean square (RMS) EMG during the part of the task when the ball was maintained in the centre position. Results revealed greater cervical muscle activity in the unstable than stable conditions (p < 0.001, η_p² = 0.746). Control of deep and superficial cervical muscles differed (p = 0.003, η_p² = 0.354). Deep cervical muscle activity was greater with unstable tasks, but did not differ with task difficulty. In contrast, superficial cervical muscle activity increased in a stepwise manner with increasing challenge. These results support the notion that the central nervous system uses different strategies for control of deep versus superficial muscle layers of the cervical spine in association with instability.

Exercise Effects on Neck Function Among F-15E Aircrew

BACKGROUND: Neck pain (NP) is common among high performance aircrew, yet evidence remains insufficient to guide examination, treatment, and prevention. The purpose of this randomized pilot study was to collect baseline data for neck function for F-15E aircrew and determine efficacy and feasibility of two separate exercise protocols in measuring short-term outcomes of subjective and objective neck function in order to inform future study design. METHODS: Randomized to either progressive (PRO) or general (GEN) exercise groups were 41 F-15E aircrew. Data collection occurred at baseline, 3 wk, and 3 mo. RESULTS: At baseline, 39% of the subjects reported current NP, 79.5% reported a history of NP attributed to flying, 12.8% reported being removed from flying duties due to NP, and 10% reported receiving medical care for NP. PRO and GEN group randomization showed similar baseline assessment data. Blinding was successful and exercise logs showed 31.6% compliance with prescribed exercise regimens. There were small but statistically significant increases in neck range of motion in both groups over the course of the study. Aircrew with current NP had significantly higher F-15E flight hours. DISCUSSION: This study supports the high prevalence of NP in aircrew, yet low frequency of seeking care for NP. Future studies to assess NP prevention and treatment in aircrew require an integrated approach that includes operational exercise policy and long-term data collection in flying units with dedicated resources for assessment and analysis. Lee MS, Briggs R, Scheirer V, Kearby G, Young BA. Exercise effects on neck function among F-15E aircrew. Aerosp Med Hum Perform. 2021; 92(10):815824.

Sexual dimorphism of the posterior cervical spine muscle attachments

Cervical spinal injury and neck pain are common disorders with wide physical implications. Neck pain and disability are reported to occur in females more often than in males, and chronic or persistent neck pain after whiplash is twice as common in females. Female athletes also sustain a higher percentage of concussions compared to male athletes. Still, while sexual differences in clinical presentation and outcome are well-established, the underlying etiology for the disparity remains less clear. It is well-established that the origin and insertion landmarks of posterior neck muscles are highly variable, but we do not know if these interindividual differences are associated with sex. Expanding our knowledge on sexual dimorphism in the anatomy of the cervical muscles is essential to our understanding of the possible biomechanical differences between the sexes and hence improves our understanding as to why females suffer from cervical pain more than males. It is also of paramount importance for accurate planning of posterior cervical spine surgery, which cuts through the posterior cervical musculature. Therefore, our main objective is to characterize the anatomy of posterior neck musculature and to explore possible sexual differences in the location of their attachment points. Meticulous posterior neck dissection was performed on 35 cadavers, 19 females, and 16 males. In each specimen, 8 muscle groups were examined bilaterally at 45 osseous anatomical landmarks. Muscles and their attachment sites were evaluated manually then photographed and recorded using Microscribe Digitizer technology built into 3D models. A comparison of attachment landmarks between males and females for each muscle was conducted. Out of the eight muscles that were measured, only two muscles demonstrated significant sex-related anatomical differences-Spinotranversales (splenius capitis and cervicis) and Multifidus. Male Spinotransversales muscle has more attachment points than female. It showed more cranial insertion points in the upper cervical attachments (superior nuchal line, C1 posterior tubercle, and mastoid process) and more caudal insertion points in the spinous processes and transverse processes of the lower cervical and upper thoracic vertebrae. Thus, the male subjects in this study exhibited a greater coverage of the posterior neck both cranially and caudally. Female Multifidus has more attachment points on the spinous processes and articular processes at middle and lower cervical vertebrae and at the transverse processes of the upper thoracic vertebrae. All remaining muscles exhibited no sexual differences. Our findings highlight, for the first time, a sexual dimorphism in attachment points of posterior cervical musculature. It reinforces the notion that the female neck is not a scaled version of the male neck. These differences in muscle attachment could partially explain differences in muscle torque production and range of motion and thus biomechanical differences in cervical spine stabilization between sexes. It sheds a much-needed light on the reason for higher whiplash rates, concussion, and chronic cervical pain among females. Surgeons should take these sexual morphological differences into consideration when deliberating the best surgical approach for posterior cervical surgery.

Preoperative paraspinal neck muscle characteristics predict early onset adjacent segment degeneration in anterior cervical fusion patients: A machine-learning modeling analysis

Early onset adjacent segment degeneration (ASD) can be found within six months after anterior cervical discectomy and fusion (ACDF). Deficits in deep paraspinal neck muscles may be related to early onset ASD. This study aimed to determine whether the morphometry of preoperative deep neck muscles (multifidus and semispinalis cervicis) predicted early onset ASD in patients with ACDF. Thirty-two cases of early onset ASD after a two-level ACDF and 30 matched non-ASD cases were identified from a large-scale cohort. The preoperative total cross-sectional area (CSA) of bilateral deep neck muscles and the lean muscle CSAs from C3 to C7 levels were measured manually on T2-weighted magnetic resonance imaging. Paraspinal muscle CSA asymmetry at each level was calculated. A support vector machine (SVM) algorithm was used to identify demographic, radiographic, and/or muscle parameters that predicted proximal/distal ASD development. No significant between-group differences in demographic or preoperative radiographic data were noted (mean age: 52.4 ± 10.9 years). ACDFs comprised C3 to C5 (n = 9), C4 to C6 (n = 20), and C5 to C7 (n = 32) cases. Eighteen, eight, and six patients had proximal, distal, or both ASD, respectively. The SVM model achieved high accuracy (96.7%) and an area under the curve (AUC = 0.97) for predicting early onset ASD. Asymmetry of fat at C5 (coefficient: 0.06), and standardized measures of C7 lean (coefficient: 0.05) and total CSA measures (coefficient: 0.05) were the strongest predictors of early onset ASD. This is the first study to show that preoperative deep neck muscle CSA, composition, and asymmetry at C5 to C7 independently predicted postoperative early onset ASD in patients with ACDF. Paraspinal muscle assessments are recommended to identify high-risk patients for personalized intervention.

Muscle Fibre Architecture of Thoracic and Lumbar Longissimus Dorsi Muscle in the Horse

Simple Summary

As the longissimus dorsi muscle is the largest muscle in the equine back, it has great influence on the stability of the spine and facilitates proper locomotion. In general, muscle function is determined by its specific intramuscular architecture. However, only limited three-dimensional metrical data are available for the inner organisation of the equine longissimus dorsi muscle. The thoracic and lumbar longissimus muscles of five formalin-fixed cadaveric horse backs of different ages and body types were dissected layerwise from cranial to caudal. Three-dimensional coordinates along individual muscle fibre bundles were digitised from the origin to the insertion and 3D models were created using imaging software and computed tomography. The muscle was divided into functional compartments and morphometric parameters (muscle fascicle length, pennation angles, muscle volume and the physiological cross-sectional area (PCSA)) were determined. Fascicle length showed the highest values in the thoracic region and decreased from cranial to caudal, while in most caudal compartments, fascicle length was less than 50% of the fascicle length in thoracic compartments. The pennation angles differ between compartments. In the cranial compartment, fascicles almost run parallel to the horizontal plane (mean angle 0°), while in the caudal compartment, the angles increase up to a mean angle of 38°. In the sagittal plane, the pennation angles varied from parallel (0°) in cranial compartments to 0–22° in the caudal compartments. The muscle volume ranged from 1350 cm³ to 4700 cm³ and PCSA from 219 cm² to 700 cm². This study lays the anatomical basis for a biomechanical model to simulate muscle function.

Abstract

As the longissimus dorsi muscle is the largest muscle in the equine back, it has great influence on the stability of the spine and facilitates proper locomotion. The longissimus muscle provides support to the saddle and rider and thereby influences performance in the horse. Muscular dysfunction has been associated with back disorders and decline of performance. In general, muscle function is determined by its specific intramuscular architecture. However, only limited three-dimensional metrical data are available for the inner organisation of the equine longissimus dorsi muscle. Therefore, we aimed at investigating the inner architecure of the equine longissimus. The thoracic and lumbar longissimus muscles of five formalin-fixed cadaveric horse backs of different ages and body types were dissected layerwise from cranial to caudal. Three-dimensional coordinates along individual muscle fibre bundles were recorded using a digitisation tool (MicroScribe^®), to capture their origin, insertion and general orientation. Together with skeletal data from computed tomography (CT) scans, 3D models were created using imaging software (Amira). For further analysis, the muscle was divided into functional compartments during preparation and morphometric parameters, such as the muscle fascicle length, pennation angles to the sagittal and horizontal planes, muscle volume and the physiological cross-sectional area (PCSA), were determined. Fascicle length showed the highest values in the thoracic region and decreased from cranial to caudal, with the cranial lumbar compartment showing about 75% of cranial fascicle length, while in most caudal compartments, fascicle length was less than 50% of the fascicle length in thoracic compartments. The pennation angles to the horizontal plane show that there are differences between compartments. In most cranial compartments, fascicles almost run parallel to the horizontal plane (mean angle 0°), while in the caudal compartment, the angles increase up to a mean angle of 38°. Pennation angles to the sagittal plane varied not only between compartments but also within compartments. While in the thoracic compartments, the fascicles run nearly parallel to the spine, in the caudal compartments, the mean angles range from 0–22°. The muscle volume ranged from 1350 cm³ to 4700 cm³ depending on body size. The PCSA ranged from 219 cm² to 700 cm² depending on the muscle volume and mean fascicle length. In addition to predictable individual differences in size parameters, there are obvious systemic differences within the muscle architecture along the longissimus muscle which may affect its contraction behaviour. The obtained muscle data lay the anatomical basis for a specific biomechanical model of the longissimus muscle, to simulate muscle function under varying conditions and in comparison to other species.

Muscle endurance and cervical electromyographic activity during submaximal efforts in women with and without migraine

BACKGROUND

Despite previous reports supporting cervical muscle weakness and altered motor control in migraine, the endurance under standardized submaximal loads has not been investigated. Therefore, this study aimed to assess the endurance and muscle activity of the cervical musculature during submaximal isometric contractions in women with migraine and those without headache.

METHODS

Cervical muscle endurance tests were performed for flexors and extensors at 25%, 50%, and 75% of the output force during maximal isometric contraction using the Multi-Cervical Rehabilitation Unit with customized biofeedback. Initial values and relative rates of changes in root mean square and median frequency were calculated using cervical muscle superficial electromyography.

FINDINGS

Women with chronic migraine presented significantly shorter flexor endurance time in all load tests than controls (25%, P = .001, 50%, P = .005; 75%, P = .013), while episodic migraine only differed from controls at 75% (P = .018). The frequency of neck pain and/or pain referred to the head after the endurance test was up 12% in the control group, 40% in the episodic migraine group and 68% of the chronic migraine group. Few differences between groups were observed in the electromyographic variables and none of them was related to a worse performance in the endurance tests.

INTERPRETATION

Cervical flexor endurance was reduced in women with chronic migraine when independent of the load, whereas it was reduced to 75% of the maximal force in those with episodic migraine. No difference in the electromyographic variables could be related to this reduced flexor endurance. Also, no differences were detected in extensors endurance.

Ultrasound shear wave elastography measurement of the deep posterior cervical muscles: Reliability and ability to differentiate between muscle contraction states

The deep posterior cervical muscles (DPCM), specifically the semispinalis cervicis and cervical multifidus, are often impaired in patients with neck disorders and have been assessed by several imaging techniques. Prior ultrasound shear wave elastography (SWE) imaging and reliability assessments of the DPCM were performed utilizing similar positioning as assessments for the more superficial cervical extensors. Our objectives were to describe an SWE imaging technique for the DPCM, establish intra-rater reliability of DPCM SWE, and compare DPCM shear modulus during rest and submaximal contraction in both prone and seated positions in individuals without spinal pain. In sixteen participants, the DPCM was located using B-mode ultrasound, then muscle shear modulus was assessed via SWE at both rest and with contraction against a 2-kg resistance applied at the C2 spinous process. Within-day intra-rater reliability was moderate to good (ICC = 0.70-0.88). The DPCM were stiffer during contraction than at rest in the prone position (p = 0.002), and at rest in sitting versus at rest in prone (p = 0.003). Further research is needed to assess DPCM-specific SWE in symptomatic individuals and compare DPCM shear modulus to electromyography across contraction intensities.

Sustained Isometric Wrist Flexion and Extension Maximal Voluntary Contractions Similarly Impair Hand-Tracking Accuracy in Young Adults Using a Wrist Robot

Due to their stabilizing role, the wrist extensor muscles demonstrate an earlier onset of performance fatigability and may impair movement accuracy more than the wrist flexors. However, minimal fatigue research has been conducted at the wrist. Thus, the purpose of this study was to examine how sustained isometric contractions of the wrist extensors/flexors influence hand-tracking accuracy. While gripping the handle of a three-degrees-of-freedom wrist manipulandum, 12 male participants tracked a 2:3 Lissajous curve (±32° wrist flexion/extension; ±18° radial/ulnar deviation). A blue, circular target moved about the trajectory and participants tracked the target with a yellow circle (corresponding to the handle's position). Five baseline tracking trials were performed prior to the fatiguing task. Participants then exerted either maximal wrist extension or flexion force (performed on separate days) against a force transducer until they were unable to maintain 25% of their pre-fatigue maximal voluntary contraction (MVC). Participants then performed 7 tracking trials from immediately post-fatigue to 10 min after. Performance fatigability was assessed using various metrics to account for errors in position-tracking, error tendencies, and movement smoothness. While there were no differences in tracking error between flexion/extension sessions, tracking error significantly increased immediately post-fatigue (Baseline: 1.40 ± 0.54°, Post-fatigue: 2.02 ± 0.51°, P < 0.05). However, error rapidly recovered, with no differences in error from baseline after 1-min post-fatigue. These findings demonstrate that sustained isometric extension/flexion contractions similarly impair tracking accuracy of the hand. This work serves as an important step to future research into workplace health and preventing injuries of the distal upper-limb.

Do longus capitis and colli really stabilise the cervical spine? A study of their fascicular anatomy and peak force capabilities

BACKGROUND

Longus capitis and colli are proposed to play a role in stabilising the cervical spine, targeted in clinical and research practice with cranio-cervical flexion. However, it is not clear if these muscles are anatomically or biomechanically suited to a stabilising role.

OBJECTIVES

To describe the fascicular morphology of the longus capitis and colli, and estimate their peak force generating capabilities across the individual cervical motion segments.

STUDY DESIGN

Biomechanical force modelling based on anatomical data.

METHODS

Three-part design including cadaveric dissection (n = 7), in vivo MRI muscle volume calculation from serial slices in young healthy volunteers (n = 6), and biomechanical modelling of the peak force generating capacities based on computed tomography scans of the head and neck.

RESULTS

Longus capitis and colli are small muscles spanning multiple cervical motion segments. Bilateral peak flexion torque estimates were higher in the upper cervical spine (0.5 Nm), and unlikely to affect motion below the level of C5 (<0.2 Nm). Peak shear estimates were negligible (<20 N), while peak compression estimates were small (<80 N).

CONCLUSIONS

These data highlight the complex anatomy and small force capacity of longus capitis and colli, and have implications for their function. In particular, the small peak compression forces indicate that these muscles have a limited capacity to contribute to cervical stability via traditional mechanisms. This implies that the mechanism(s) by which cranio-cervical flexion exercises produce clinical benefits is worth exploring further.

Relationship between neck acceleration and muscle activation in people with chronic neck pain: Implications for functional disability

BACKGROUND

Previous study has found that people with chronic neck pain moved with a consistently compromised acceleration/deceleration at their cervical and thoracic spines. This study examined the strength of the association between the electromyographic activities and the acceleration/deceleration of the cervical and thoracic spine, and its correlation with the functional disabilities in individuals with neck pain.

METHODS

Time history of the cervical and thoracic acceleration/deceleration and EMG activity was acquired in thirty-four subjects with chronic neck pain and thirty-four age- and gender-matched asymptomatic subjects during active neck movements. The strength of the association between the electromyographic activity of spinal muscles and the cervical and thoracic acceleration/deceleration was determined using cross-correlation method. Relationship between the strength of this association and the severity of the functional disabilities in neck pain group was examined using correlation analysis.

FINDINGS

The strength of the association between cervical and thoracic acceleration/deceleration and electromyographic activities was significantly lower in neck pain group. Significant negative correlations were found between the functional disability level and the strength of this defined association in the symptomatic group.

INTERPRETATION

The compromised capability of the spinal muscles to produce acceleration/deceleration in the neck pain group may imply an impaired electromechanical coupling of these spinal muscles when performing neck movements. Significant negative correlation of the degree of functional disabilities suggests that the present approach can be used as an objective and specific evaluation of the dynamic performance of the spinal muscles and its relationship with the functional disabilities in neck pain subjects.

Reliability of ultrasonography measurement for the longus colli according to inward probe pressure

[Purpose] To investigate the intra- and inter-rater reliability of the cross-sectional area (CSA) and muscle thickness (MT) of the longus colli according to the inward pressure of an ultrasonography (US) probe (0.5 and 1 kg). [Subjects] Thirteen subjects (11 males and 2 females; age, 23.1 ± 2.9 years) were recruited via convenience sampling of university students. [Methods] Real-time US measurements of the CSA and MT of the longus colli were recorded. Repeated US measurements using a standard protocol were performed on the same day 1 hour apart to assess intra- and inter-rater reliability. Intra-class correlation coefficients (ICC; 2, 1) were used to determine the intra- and inter-rater reliability of the CSA and MT measurements. [Results] This study demonstrated that the US measurements (0.5 and 1 kg) of the CSA and MT of the longus colli give reliable and consistent results. [Conclusion] Based on these results, a consistent inward pressure of the probe is needed to ensure precise US measurement of the longus colli muscle.

Morphological changes in the cervical muscles of women with chronic whiplash can be modified with exercise-A pilot study

INTRODUCTION

In this preliminary study we determined whether MRI markers of cervical muscle degeneration [elevated muscle fatty infiltration (MFI), cross-sectional area (CSA), and reduced relative muscle CSA (rmCSA)] could be modified with exercise in patients with chronic whiplash.

METHODS

Five women with chronic whiplash undertook 10 weeks of neck exercise. MRI measures of the cervical multifidus (posterior) and longus capitus/colli (anterior) muscles, neck muscle strength, and self-reported neck disability were recorded at baseline and at completion of the exercise program.

RESULTS

Overall significant increases in CSA and rmCSA were observed for both muscles, but significant reductions in MFI were only evident in the cervical multifidus muscle. These changes coincided with increased muscle strength and reduced neck disability.

CONCLUSIONS

MRI markers of muscle morphology in individuals with chronic whiplash appear to be modifiable with exercise.

MRI-determined lumbar muscle morphometry in man and sheep: potential biomechanical implications for ovine model to human spine translation

The sheep is a commonly used animal model for human lumbar spine surgery, but only in vitro investigations comparing the human and ovine spine exist. Spinal musculature has previously not been compared between man and sheep. This additional knowledge could further indicate to what extent these species are biomechanically similar. Therefore, the purpose of the study was to investigate spinal muscle morphometric properties using magnetic resonance imaging (MRI) in different age groups of healthy human participants and sheep in vivo. Healthy human participants (n = 24) and sheep (n = 17) of different age groups underwent T1-weighted MRI of the lumbar spine. Regions of interest of the muscles erector spinae (ES), multifidus (M) and psoas (PS) were identified. The ratio of flexor to extensor volume, ratio of M to ES volume, and muscle fat relative to an area of intermuscular fat were calculated. Sheep M to ES ratio was significantly smaller than in the human participants (sheep 0.16 ± 0.02; human 0.37 ± 0.05; P < 0.001), although flexor to extensor ratio was not significantly different between species (human 0.39 ± 0.08; sheep 0.43 ± 0.05; P = 0.06). Age did not influence any muscle ratio outcome. Sheep had significantly greater extensor muscle fat compared with the human participants (M left human 40.64%, sheep 53.81%; M right human 39.17%, sheep 51.33%; ES left human 40.86%, sheep 51.29%; ES right human 35.93%, sheep 44.38%; all median values; all P < 0.001), although PS did not show any significant between-species differences (PS left human 36.89%, sheep 33.67%; PS right human 32.78%, sheep 30.09%; P < 0.05). The apparent differences in the size and shape of sheep and human lumbar spine muscles may indicate dissimilar biomechanical and functional demands, which is an important consideration when translating to human surgical models.

Cross-species comparison of anticipatory and stimulus-driven neck muscle activity well before saccadic gaze shifts in humans and nonhuman primates

Recent studies have described a phenomenon wherein the onset of a peripheral visual stimulus elicits short-latency (<100 ms) stimulus-locked recruitment (SLR) of neck muscles in nonhuman primates (NHPs), well before any saccadic gaze shift. The SLR is thought to arise from visual responses within the intermediate layers of the superior colliculus (SCi), hence neck muscle recordings may reflect presaccadic activity within the SCi, even in humans. We obtained bilateral intramuscular recordings from splenius capitis (SPL, an ipsilateral head-turning muscle) from 28 human subjects performing leftward or rightward visually guided eye-head gaze shifts. Evidence of an SLR was obtained in 16/55 (29%) of samples; we also observed examples where the SLR was present only unilaterally. We compared these human results with those recorded from a sample of eight NHPs from which recordings of both SPL and deeper suboccipital muscles were available. Using the same criteria, evidence of an SLR was obtained in 8/14 (57%) of SPL recordings, but in 26/29 (90%) of recordings from suboccipital muscles. Thus, both species-specific and muscle-specific factors contribute to the low SLR prevalence in human SPL. Regardless of the presence of the SLR, neck muscle activity in both human SPL and in NHPs became predictive of the reaction time of the ensuing saccade gaze shift ∼70 ms after target appearance; such pregaze recruitment likely reflects developing SCi activity, even if the tectoreticulospinal pathway does not reliably relay visually related activity to SPL in humans.

Neck muscle fatigue alters the cervical flexion relaxation ratio in sub-clinical neck pain patients

BACKGROUND

The cervical flexion relaxation ratio is lower in neck pain patients compared to healthy controls. Fatigue modulates the onset and offset angles of the silent period in both the lumbar and cervical spine in healthy individuals; however, this response has not been studied with neck pain patients. The purpose of this study was to determine if cervical extensor fatigue would alter the parameters of the cervical flexion relaxation more in a neck pain group than a healthy control group.

METHODS

Thirteen healthy and twelve neck pain patients participated. Cervical extensor activity was examined bilaterally and kinematics of the neck and head were collected. An isometric, repetitive neck extension task at 70% of maximum elicited fatigue. Participants performed 3 trials of maximal cervical flexion both pre and post fatigue.

FINDINGS

The healthy controls and neck pain groups fatigued after 56 (41) and 39 (31) repetitions, respectively. There was a significant interaction effect for the flexion relaxation ratio between the control and neck pain groups from pre to post fatigue trials (F1,96=22.67, P=0.0001), but not for onset and offset angles (F1, 96=0.017, P=0.897), although the onset and offset angles did decrease significantly for both groups following fatigue (F1,96=9.26, P=0.002).

INTERPRETATION

Individuals with mild to moderate neck pain have significant differences in their neuromuscular control relative to controls, experienced myoelectric fatigue with fewer repetitions in a shorter time, had a lower cervical flexion relaxation ratio at baseline and had an inability to decrease this ratio further in response to fatigue.

Fibre type composition of female longus capitis and longus colli muscles

Effective management of neck pain requires detailed knowledge of cervical muscle structure and function. Information on muscle fibre type assists in determining function; few data exist on the fibre type composition of many cervical muscles. The purpose of this study was to investigate the fibre type composition of longus capitis (LCa) and longus colli (LCo) to provide a better understanding of their function. Muscle sections were harvested unilaterally from LCa (C2-C7) and LCo (C3, C6, T1) in seven female cadavers (mean age 86 ± 9 years). Immunohistochemistry was used to identify type I and type II fibres, and stereology (random systematic sampling) used to determine fibre numbers. Data were assessed using descriptive statistics and one-way ANOVA (significance P < 0.05). Fifty-two sections were assessed (82,785 fibres; mean 1,592 ± 927 per section). LCa had a significantly greater proportion of type I fibres than LCo (64.3 % vs 55.7 %, P = 0.011). The percentage of fibre types varied significantly between individuals in LCa, but not LCo. No significant difference was found in the proportion of type I fibres between cervical levels for either LCa or LCo. LCa and LCo appear functionally different in elderly females, with LCa potentially having a more postural role (higher type I fibre proportion). Fibre types were homogenous throughout each muscle, indicating that contractile function is similar across the length of individual muscles. Further studies across a larger age-span and in males are required to determine whether results are representative of other populations.

Fiber types of the anterior and lateral cervical muscles in elderly males

PURPOSE

The anterior and lateral cervical muscles (ALCM) are generally considered to be postural, yet few studies have investigated ALCM fiber types to help clarify the function of these muscles. This study aimed to systematically investigate ALCM fiber types in cadavers.

METHODS

Anterior and lateral cervical muscles (four scalenus anterior, medius, posterior muscles; five longus colli, five longus capitis taken bilaterally from one cadaver) were removed from four male embalmed cadavers (mean age 87.25 years). Paraffin-embedded specimens were sectioned then stained immunohistochemically to identify type I and II skeletal muscle fibers. Proportional fiber type numbers and cross-sectional area (CSA) occupied by fiber types were determined using stereology (random systematic sampling). Results were analyzed using ANOVA (P < 0.05) and descriptive statistics.

RESULTS

Scalenus anterior had the greatest average number and CSA of type I fibers (71.9 and 83.7%, respectively); longus capitis had the lowest number (48.5%) and CSA (61.4%). All scalene muscles had significantly greater type I CSA than longus capitis and longus colli; scalenus anterior and medius had significantly greater type I numbers than longus capitis and longus colli. Some significant differences were observed between individual cadavers in longus colli for CSA, and longus capitis for number.

CONCLUSION

The ALCM do not share a common functional fiber type distribution, although similar fiber type distributions are shared by longus colli and longus capitis, and by the scalene muscles. Contrary to conventional descriptions, longus colli and longus capitis have type I fiber proportions indicative of postural as well as phasic muscle function.

Gross anatomy of the deep perivertebral musculature in horses

OBJECTIVE

To determine the gross morphology of the multifidus, longus colli, and longus thoracis muscles in the cervical and cranial thoracic portions of the equine vertebral column.

SAMPLE

15 horse cadavers.

PROCEDURES

The vertebral column was removed intact from the first cervical vertebra (C1) to the seventh thoracic vertebra (T7). After removing the superficial musculature, detailed anatomic dissections of the multifidus, longus colli, and longus thoracis muscles were performed.

RESULTS

The multifidus cervicis muscle consisted of 5 bundles/level arranged in lateral, medial, and deep layers from C2 caudally into the thoracic portion of the vertebral column. Fibers in each bundle attached cranially to a spinous process then diverged laterally, attaching caudally on the dorsolateral edge of the vertebral lamina and blending into the joint capsule of an articular process articulation after crossing 1 to 4 intervertebral joints. The longus colli muscle had ventral, medial, and deep layers with 5 bundles/level from C1 to C5 that attached cranially to the ventral surface of the vertebral body, diverged laterally and crossed 1 to 4 intervertebral joints, then attached onto a vertebral transverse process as far caudally as C6. The longus thoracis muscle consisted of a single, well-defined muscle belly from C6 to T5-T6, with intermediate muscular attachments onto the ventral aspects of the vertebral bodies, the intervertebral symphyses, and the craniomedial aspects of the costovertebral joint capsules.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that there were multiple, short bundles of the multifidus cervicis, multifidus thoracis, and longus colli muscles; this was consistent with a function of providing sagittal plane intersegmental vertebral column stability.

Muscle fibre type distribution of the thoracolumbar and hindlimb regions of horses: relating fibre type and functional role

BACKGROUND

Although the majority of equine muscles have a mixed fibre type distribution indicative of diverse functional roles, the predominance of a fibre type can indicate the primary function of a muscle. The deep epaxial musculature has an important role in core spinal stability in humans, reflected as a predominantly muscle fibre type (MFT) I or postural fibre type. The fibre type of the deep epaxial musculature has not been determined in horses. The objective of the study was to determine the MFT distribution in selected muscles of thoracolumbar and hindlimb region of horses. This included deep epaxial and hypaxial muscles that were hypothesised to have a postural stabilising role. A second objective was to examine differences in MFT distribution between horses bred for endurance (Arabian) and sprinting (Quarter horse). Muscle biopsy samples were obtained from selected thoracolumbar and hind limb muscles of 5 Quarter horses, 4 Arabians, and 2 Thoroughbreds. The myosin heavy chain distribution was determined by gel electrophoresis. Mann-Whitney rank test was used to compare the proportional MFT and differences between breeds.

RESULTS

Mm. sacrocaudalis dorsalis medialis and diaphragm had the highest proportion of MFT-I. The remaining deep epaxial muscles and the hypaxial muscle m. psoas minor had approximately equal MFT I and II proportions. Mm. psoas major, iliocostalis, longissimus dorsi and the hind limb muscles contained mostly MFT-IIX. The fibre type distribution was similar between Arabians and Quarter horses, although Quarter horses had more MFT-IIX fibres in psoas major (P = 0.02) while Arabians had more MFT-I fibres in m. longissimus dorsi (P = 0.03).

CONCLUSIONS

The fibre type distribution of the deep epaxial muscles, mm psoas minor and diaphragm varied from approximately equal MFT-I and II proportions to predominantly MFT-I suggesting a postural stabilising role possibly important in core spinal stability. In contrast the fibre type proportions of mm psoas major, iliocostalis, longissimus dorsi and the hind limb muscles were mainly MFT-II suggesting a locomotory role. Knowledge of fibre type distribution in such a clinically important area can direct diagnosis, prevention and treatment of muscular or neuromotor dysfunction.

Considerations in the physical rehabilitation of patients with whiplash-associated disorders

STUDY DESIGN

Review of research identifying physical impairments in the neuromuscular system in subjects with whiplash-associated disorders.

OBJECTIVE

Review the impairments in movement and neuromuscular function toward constructing research informed exercise programs.

SUMMARY OF BACKGROUND DATA

Pain and injury to the musculoskeletal system result in loss of motion and impaired neuromuscular function which impacts on functional activities, work and quality of life. Therapeutic exercise is a mainstay of rehabilitation, but the nature of the exercises prescribed are currently various and the effect sizes of current programs for patients with whiplash-associated disorders are modest at best.

METHODS

A review was undertaken of research investigating the changes in cervical motion and neuromuscular function to better inform exercise prescription and identify areas for future research. RESULTS.: Reduced range of movement as well as pathological movement patterns (reduced acceleration and velocity, reduced smoothness and irregular axes of neck movement) have been documented in subjects with whiplash-associated disorders. In relation to neuromuscular control, changes have been demonstrated in neck muscles' spatial and temporal relationships as well as in their strength and endurance. The presence or not and the extent of changes is highly variable between individuals and appears to have some relationship to pain intensity. It appears that there is a need for specificity in exercise prescription to address particular impairments rather than the use of generic programs. High pain intensity can modify effects of a therapeutic exercise program.

CONCLUSION

Pain and injury result in reorganization of the motor control strategies of neck muscles and movement. Further research is required to determine if outcomes after a whiplash injury can be improved by using research informed, individually prescribed exercise programs matched to the individual's presentation. Research into best methods of pain management is also required to facilitate physical rehabilitation.

Musculoskeletal modeling of the suboccipital spine: kinematics analysis, muscle lengths, and muscle moment arms during axial rotation and flexion extension

STUDY DESIGN

In vitro and modeling study of upper cervical spine (UCS) three-dimensional (3D) kinematics and muscle moment arm (MA) during axial rotation (AR) and flexion extension (FE).

OBJECTIVE

To create musculoskeletal models with movement simulation including helical axis (HA) and muscle features.

SUMMARY OF BACKGROUND DATA

Integration of various kinematics and muscle data into specific-specimen 3D anatomical models with graphical representation of HA and muscle orientation and MA is not reported for the UCS musculoskeletal system.

METHODS

Kinematics, anatomical, and computed tomographic imaging data were sampled in 10 anatomical specimens. Using technical markers and anatomical landmarks digitizing, spatial position of segments was computed for five discrete positions of AR and FE using a 3D digitizer. To obtain musculoskeletal model simulation, a registration method was used to combine collected data. Processing was performed using orientation vector and HA computation and suboccipital muscle features (i.e., length and MA) relative to motion angle.

RESULTS

Range of motion and coupling were in agreement with previous in vitro studies. HA (i.e., location and orientation) showed low variation at the occipitoaxial and atlantoaxial levels for FE and AR, respectively. The main orientation of the HA was vertical at C1-C2 during AR and horizontal at C0-C1 during FE. For muscles MA, absolute peak value (ranging from 20 to 40 mm) occurred at different poses depending on the analyzed muscle and motion. Poor magnitude was found for obliquus capitis inferior and rectus capitis posterior minor in FE and AR, respectively.

CONCLUSION

On the basis of previous methods, we developed a protocol to create UCS musculoskeletal modeling with motion simulation including HA and suboccipital muscles representation. In this study, simultaneous segmental movement displaying with HA and muscles features was shown to be feasible.

A magnetic resonance imaging investigation into the function of the deep cervical flexors during the performance of craniocervical flexion

OBJECTIVE

Evidence suggests that the deep cervical flexors (DCFs) are important for the control of the cervical spine. The craniocervical flexion (CCF) test is a clinical test developed for patients with neck pain disorders based on the action of the DCFs. Because these muscles are deeply situated, it is difficult to reach the DCFs with surface electromyography. Magnetic resonance imaging (MRI) can be used to measure these muscles in cross section. The objective of this study was (1) to determine the reliability of MRI for measuring cross-sectional area (CSA) of the longus colli (Lco) and longus capitis (Lca) and (2) to evaluate the changes in CSA during contraction.

METHODS

Thirty healthy subjects aged 29 +/- 9.3 years were imaged using MRI. The CSA of the Lco and Lca was evaluated at 4 different levels (C0-C1, C2-C3, C4-C5, and C6-C7) at rest and during CCF.

RESULTS

The intraclass correlation coefficients for the CSA of the Lco and Lca showed good to excellent reliability (0.73-0.92), except at the C4-C5 level. There was a significant increase in CSA of both Lco (F = 6.79, P = .015) and Lca (F = 19.20, P <or= .001) due to CCF, and this was at different levels. The highest increases in CSA occurred at the C0-C1 level for the Lca (11.1%) and at the C2-C3 level for the Lco (17.4%).

CONCLUSIONS

This study demonstrated that the action of CCF resulted in a contraction of the Lco and Lca at different levels. The results indicate that MRI is a promising technique to evaluate changes in CSA during contraction.

The effect of cell density on the maturation and contractile ability of muscle derived cells in a 3D tissue-engineered skeletal muscle model and determination of the cellular and mechanical stimuli required for the synthesis of a postural phenotype

The successful engineering of a truly biomimetic model of skeletal muscle could have a significant impact on a number of biomedical disciplines. Although a variety of techniques are currently being developed, there is, as of yet, no widely available and easily reproducible culture system for the synthesis of 3D artificial muscle tissues. In attempting to generate such a model it is essential to optimise any protocol in order to generate a tissue that best represents the in vivo environment. Since the maturation of muscle derived cells in culture is critically dependent on density, a major factor to be addressed in the development of these models is the ideal concentration at which to seed cells in order to generate an optimal response. In studying the effect of cell density on the performance of cells in an established 3D collagen based model of skeletal muscle, we demonstrate that an optimum density does exist in terms of peak force generation and myogenic gene expression data. Greater densities however, lead to the formation of a more physiologically relevant tissue with a phenotype characteristic of slow, postural muscle.

Fibre type composition of the human psoas major muscle with regard to the level of its origin

The aim of our study was to explore the fibre type composition of the human psoas major muscle at different levels of its origin, from the first lumbar to the fourth lumbar vertebra, and to compare the muscle fibre size and distribution of different fibre types between levels with respect to its complex postural and dynamic function. Muscle samples were collected from 15 young males (younger than 35 years). Serial transverse sections (5 microm) of the samples were cut by cryomicrotome. Type I, IIA and IIX muscle fibres were typed using myosin heavy chain identification. The serial sections were analysed using a light microscope with a magnitude of 100x. The differences between measurements were evaluated using a repeated-measures anova and Scheffé test for post-hoc analysis. Our study showed that the human psoas major muscle was composed of type I, IIA and IIX muscle fibres. It had a predominance of type IIA muscle fibres, whereas type I muscle fibres had the largest cross-sectional area. Type IIX muscle fibres were present as a far smaller percentage and had the smallest cross-sectional area. Moreover, the fibre type composition of the psoas major muscle was different between levels of its origin starting from the first lumbar to the fourth lumbar vertebra. We conclude that the fibre type composition of the psoas major muscle indicated its dynamic and postural functions, which supports the fact that it is the main flexor of the hip joint (dynamic function) and stabilizer of the lumbar spine, sacroiliac and hip joints (postural function). The cranial part of the psoas major muscle has a primarily postural role, whereas the caudal part of the muscle has a dynamic role.

Magnetic resonance imaging findings of fatty infiltrate in the cervical flexors in chronic whiplash

STUDY DESIGN

Retrospective investigation of muscle changes in patients suffering from chronic whiplash-associated disorders (WAD).

OBJECTIVES

To quantitatively compare the presence of muscle alterations (fatty infiltrate [MFI] and cross-sectional area [CSA]) in the anterior musculature of the cervical spine in a cohort of chronic whiplash patients (WAD II) and healthy control subjects across muscle and cervical segmental level.

SUMMARY OF BACKGROUND DATA

Magnetic resonance imaging can be regarded as the gold standard for muscle imaging. There is little knowledge about in vivo features of anterior neck muscles in patients suffering from chronic WAD and how muscle structure differs across the factors of muscle, vertebral level, age, self-reported pain and disability, body mass index, and duration of symptoms.

METHODS

Reliable magnetic resonance imaging measures for MFI and CSA were performed for the anterior cervical muscles bilaterally in 109 female subjects (78 WAD, 31 healthy control; 18-45 years, 3 months to 3 years postinjury). The measures were performed on all subjects for the longus capitis and colli and the sternocleidomastoid muscles.

RESULTS

The WAD subjects had significantly larger MFI and CSA for the anterior muscles compared to healthy control subjects (all P < 0.0001). In addition, the amount of MFI varied by both cervical level and muscle, with the longus capitis/colli having the largest amount of fatty infiltrates at the C2-C3 level (P < 0.0001). MFI was inversely related to age, self-reported pain/disability, and body mass index but directly proportional to duration of symptoms.

CONCLUSION

There is significantly greater MFI and CSA in the anterior neck muscles, especially in the deeper longus capitis/colli muscles, in subjects with chronic WAD when compared to healthy controls. Future studies are required to investigate the relationships between muscular morphometry and symptoms in patients suffering from acute and chronic WAD.

The clinical presentation of chronic whiplash and the relationship to findings of MRI fatty infiltrates in the cervical extensor musculature: a preliminary investigation

The objective was to determine whether any measurable changes in sensory responses, kinesthetic sense, cervical motion, and psychological features were related to established fatty infiltration values in the cervical extensor musculature in subjects with persistent whiplash. It is unknown if fatty infiltrate is related to any signs or symptoms. Data on motor function, Quantitative Sensory Testing, psychological and general well-being, and pain and disability were collected from 79 female subjects with chronic whiplash. Total fat values were created for all subjects by averaging the muscle fat indices by muscle, level, and side from our MRI dataset of all the cervical extensor muscles. Results of this study indicate the presence of altered physical, kinesthetic, sensory, and psychological features in this cohort of patients with chronic whiplash. Combined factors of sensory, physical, kinesthetic, and psychological features all contributed to a small extent in explaining the varying levels of fatty infiltrate, with cold pain thresholds having the most influence (r (2) = 0.28; P = 0.02). Identifying and relating quantifiable muscular alterations to clinical measures in the chronic state, underpin some clinical hypotheses for possible pathophysiological processes in this group with a chronic and recalcitrant whiplash disorder. Future research investigations aimed at accurate identification, sub-classification, prediction, and management of patients with acute and chronic whiplash is warranted and underway.

Strain and load thresholds for cervical muscle recruitment in response to quasi-static tensile stretch of the caprine C5-C6 facet joint capsule

The aim of this study was to investigate the response of cervical muscles to physiologic tensile stretch of cervical facet joint capsule (FJC) at a quasi-static displacement rate of 0.5mm/s. In vivo caprine left C5-C6 FJC preparations were subjected to an incremental tensile displacement paradigm. EMG activity was recorded during FJC stretch from the right trapezius (TR) and multifidus (MF) muscle groups at the C5 and C6 levels and bilaterally from the sternomastoid (SM) and longus colli (LC) muscle groups at the C5-C6 level. Onset of muscular activity was later analyzed using visual and computer-based methods. Capsule load and strain at the time of onset were recorded and compared between the muscle groups. Results indicated capsule load was a better indicator of the tensile stretch thresholds for muscular recruitment than capsule strain. MF responded at significantly smaller capsule loads than TR and LC, while TR and LC activation loads were not significantly different. SM did not respond to physiologic FJC stretch. Muscle group recruitment order reflected the muscles' fiber type compositions and functional roles in the spine. This study provides the first evidence that the cervical ligamento-muscular reflex pathways are activated via tensile FJC stretch and extend to superficial and deep musculature on the anterior and posterior aspects of the neck, ipsilateral and contralateral to the side of FJC stretch.

MRI analysis of muscle/fat index of the superficial and deep neck muscles in an asymptomatic cohort

All muscles of the neck have a role in motion and postural control of the cervical region. The aim of this study was to investigate the difference in muscle/fat index between (1) cervical flexors and extensors and (2) deep and superficial neck muscles. Twenty-six healthy subjects participated in the study. Magnetic resonance imaging (MRI) was used to quantify muscle fat indices in different cervical flexor and extensor muscles at the C4-C5 level. Overall, the ventral muscles had a significantly lower fat content compared with the dorsal muscles (P < or = 0.001). For the cervical extensors, significant differences between the muscle/fat index of the deep and superficial muscles were found (P < or = 0.001). For the cervical flexors, there were no significant differences between the different muscles. The higher fat content in the dorsal muscles can be explained by a discrepancy in function between the spine extensors and flexors, reflected in a different muscle fiber distribution. The rather small differences between superficial and deep neck muscles are in line with recent findings that have demonstrated that both muscles groups exhibit phasic activity during isometric muscles contractions and the presumption that there is no difference in fiber type distribution between superficial and deep neck muscles.

Viscoelastic finite element analysis of the cervical intervertebral discs in conjunction with a multi-body dynamic model of the human head and neck

This article presents the effects of the frontal and rear-end impact loadings on the cervical spine components by using a multi-body dynamic model of the head and neck, and a viscoelastic finite element (FE) model of the six cervical intervertebral discs. A three-dimensional multi-body model of the human head and neck is used to simulate 15 g frontal and 8.5 g rear-end impacts. The load history at each intervertebral joint from the predictions of the multi-body model is used as dynamic loading boundary conditions for the FE model of the intervertebral discs. The results from the multi-body model simulations, such as the intervertebral disc loadings in the form of compressive, tensile, and shear forces and moments, and from the FE analysis such as the von Mises stresses in the intervertebral discs are analysed. This study shows that the proposed approach that uses dynamic loading conditions from the multi-body model as input to the FE model has the potential to investigate the kinetics and the kinematics of the cervical spine and its components together with the biomechanical response of the intervertebral discs under the complex dynamic loading history.

Are cervical multifidus muscles active during whiplash and startle? An initial experimental study

BACKGROUND

The cervical multifidus muscles insert onto the lower cervical facet capsular ligaments and the cervical facet joints are the source of pain in some chronic whiplash patients. Reflex activation of the multifidus muscle during a whiplash exposure could potentially contribute to injuring the facet capsular ligament. Our goal was to determine the onset latency and activation amplitude of the cervical multifidus muscles to a simulated rear-end collision and a loud acoustic stimuli.

METHODS

Wire electromyographic (EMG) electrodes were inserted unilaterally into the cervical multifidus muscles of 9 subjects (6M, 3F) at the C4 and C6 levels. Seated subjects were then exposed to a forward acceleration (peak acceleration 1.55 g, speed change 1.8 km/h) and a loud acoustic tone (124 dB, 40 ms, 1 kHz).

RESULTS

Aside from one female, all subjects exhibited multifidus activity after both stimuli (8 subjects at C4, 6 subjects at C6). Neither onset latencies nor EMG amplitude varied with stimulus type or spine level (p > 0.13). Onset latencies and amplitudes varied widely, with EMG activity appearing within 160 ms of stimulus onset (for at least one of the two stimuli) in 7 subjects.

CONCLUSION

These data indicate that the multifidus muscles of some individuals are active early enough to potentially increase the collision-induced loading of the facet capsular ligaments.

Neural control of superficial and deep neck muscles in humans

Human neck muscles have a complex multi-layered architecture. The role and neural control of these neck muscles were examined in nine seated subjects performing three series of isometric neck muscle contractions: 50-N contractions in eight fixed horizontal directions, 25-N contractions, and 50-N contractions, both with a continuously changing horizontal force direction. Activity in the left sternocleidomastoid, trapezius, levator scapulae, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles was measured with wire electrodes inserted at the C(4)/C(5) level under ultrasound guidance. We hypothesized that deep and superficial neck muscles would function as postural and focal muscles, respectively, and would thus be controlled by different neural signals. To test these hypotheses, electromyographic (EMG) tuning curves and correlations in the temporal and frequency domains were computed. Three main results emerged from these analyses: EMG tuning curves from all muscles exhibited well-defined preferred directions of activation for the 50-N isometric forces, larger contractions (25 vs. 50 N) yielded more focused EMG tuning curves, and agonist neck muscles from all layers received a common neural drive in the range of 10-15 Hz. The current results demonstrate that all neck muscles can exhibit phasic activity during isometric neck muscle contractions. Similar oscillations in the EMG of neck muscles from different layers further suggest that neck motoneurons were activated by common neurons. The reticular formation appears a likely generator of the common drive to the neck motoneurons due to its widespread projections to different groups of neck motoneurons.