Multifidus dysfunction and restorative neurostimulation: a scoping review

OBJECTIVE

Chronic low back pain (CLBP) is multifactorial in nature, with recent research highlighting the role of multifidus dysfunction in a subset of nonspecific CLBP. This review aimed to provide a foundational reference that elucidates the pathophysiological cascade of multifidus dysfunction, how it contrasts with other CLBP etiologies and the role of restorative neurostimulation.

METHODS

A scoping review of the literature.

RESULTS

In total, 194 articles were included, and findings were presented to highlight emerging principles related to multifidus dysfunction and restorative neurostimulation. Multifidus dysfunction is diagnosed by a history of mechanical, axial, nociceptive CLBP and exam demonstrating functional lumbar instability, which differs from other structural etiologies. Diagnostic images may be used to grade multifidus atrophy and assess other structural pathologies. While various treatments exist for CLBP, restorative neurostimulation distinguishes itself from traditional neurostimulation in a way that treats a different etiology, targets a different anatomical site, and has a distinctive mechanism of action.

CONCLUSIONS

Multifidus dysfunction has been proposed to result from loss of neuromuscular control, which may manifest clinically as muscle inhibition resulting in altered movement patterns. Over time, this cycle may result in potential atrophy, degeneration and CLBP. Restorative neurostimulation, a novel implantable neurostimulator system, stimulates the efferent lumbar medial branch nerve to elicit repetitive multifidus contractions. This intervention aims to interrupt the cycle of dysfunction and normalize multifidus activity incrementally, potentially restoring neuromuscular control. Restorative neurostimulation has been shown to reduce pain and disability in CLBP, improve quality of life and reduce health care expenditures.

Ultrasound Imaging Analysis of the Lumbar Multifidus Muscle Echo Intensity: Intra-Rater and Inter-Rater Reliability of a Novice and an Experienced Rater

Background and Objectives: Ultrasound echo intensity (EI) of the lumbar multifidus muscle (LMM) could offer valuable insights regarding muscle quality in people with low back pain (LBP). However, whether the rater’s experience noticeably influences the reliability and precision of LMM EI measurements has not been established. The aims of this study were to investigate the intra-rater and inter-rater reliability of LMM EI measurements, and to compare the reliability and SEM between a novice and an experienced rater. Materials and Methods: Twenty athletes (10 females, 10 males) with a history of LBP were included in this study. Transverse ultrasound images of LMM were taken at L5 in prone. LMM EI measurements were obtained bilaterally by tracing the maximum ROI representing the LMM cross-sectional area (CSA), avoiding the inclusion of bone or surrounding fascia. All measurements were performed by two novice raters and an experienced researcher. Each measurement was acquired by each rater three times for each side on three different images, and the average was used in the analyses. Raters were blinded to each other’s measurements and the participant’s clinical information. Intra-class correlation coefficients (ICCs) were obtained to assess the intra-rater and inter-rater reliability. Results: The intra-rater ICC values for the LMM measurements for the experienced rater were excellent (ICC all > 0.997). The inter-rater reliability ICC values showed moderate to excellent reliability (0.614 to 0.994) and agreement between the novice raters and the experienced rater, except for Novice 1 for the right LMM, which revealed lower ICCs and a wider 95% CI. Intra-rater and inter-rater reliability results were similar when separately looking at the right and left side of the muscle and participant gender. Conclusions: Our findings support the clinical use of ultrasound imaging for the assessment of LMM EI in individuals with LBP.

Relationship between straight leg-raising test measurements and area of fat infiltration in multifidus muscles in patients with lumbar disc hernation

BACKGROUND

A few studies have noted that paraspinal muscle training is important to reduce pain for patients with lumbar disc herniation (LDH). However, little is known about the exact signs for necessary training of lumbar multifidus muscles (LMM).

OBJECTIVE

The study aimed to analyze the relationship between the straight leg-raising test (SLR) and the area of fat infiltration in LMM for patients with LDH.

METHOD

One hundred and fourteen LDH patients were involved in this study. Clinical data were collected from a medical record system. On the MRI images, the cross-sectional areas (CSA) of bilateral fat infiltration in LMM were measured by picture archiving and communication system (PACS).

RESULT

For 61 patients with inclusive LDH, the positive side of SLR was positively correlated with the side of the larger total CSA of fat infiltration in LMM of L2-S1 (r= 0.75, p⁢ï⁢¼⁢ 0.01), and the CSA of fat infiltration on the side of SLR with a positive result was significantly larger than that on the side of SLR with a negative result only at L3-4 and L4-5 levels (p⁢ï⁢¼⁢ 0.01).

CONCLUSION

SLR may be used as an important sign for dysfunction of LMM and can identify the more severe side.

Ultrasonography of multifidus muscle morphology and function in ice hockey players with and without low back pain

OBJECTIVES

To examine the relationship between lumbar multifidus (LM) morphology, function, echo-intensity (EI) and body composition among a group of university level ice hockey players with and without low back pain (LBP).

DESIGN

Cross-sectional study.

SETTING

University Research Centre.

PARTICIPANTS

Thirty-two hockey players (18 females, 14 males) participated in this study.

MAIN OUTCOME MEASURES

Resting LM cross-sectional area (CSA) was assessed bilaterally at the L5 level in prone and standing using ultrasound imaging. The LM thickness at rest and during contraction was evaluated in addition to LM EI. Body composition measures were acquired using dual-energy X-ray absorptiometry (DEXA) and LBP history was acquired using a self-reported questionnaire.

RESULTS

LM muscle CSA was significantly associated with body composition measurements. LM EI was strongly associated with total % body fat and significantly greater in females. Resting LM muscle CSA and thickness (prone) was significantly smaller in players with LBP 4-weeks prior. LM side-to-side asymmetry (standing) was also significantly greater in players with LBP 3-months prior.

CONCLUSION

The results provide new insights with regards to LM morphology and activation in ice hockey players and revealed specific deficits in LM morphology in athletes with LBP. LM morphology was strongly associated with body composition measurements.

Stabilization of the lumbar spine by spinal muscle forces producing compressive follower loads: 3-dimensional computational study

Axial compressive loads whose direction changes along the spinal curvature (so called compressive follower loads (CFLs)) was postulated as a normal physiological load in the lumbar spine in the literature. Computational analyses were conducted in this study using finite element and optimization models of the spinal system incorporating 244 fascicles of back muscles. It was feasible to find optimum solutions for spinal muscle forces generating CFLs in the lumbar spine in 3-D postures of neutral standing, flexion 40°, extension 10°, axial rotation 10°, or lateral bending 30°. FE analyses demonstrated that the lumbar spine can be in a stable condition not under all CFL generating muscle forces but under those producing CFLs along a curve parallel to the spinal curvature located in the vicinity of the base spinal curve constructed by connecting the geometrical centers of the vertebral bodies. It was also possible to estimate the stable range of the relative location of such CFL curve to the base spinal curve. These results suggest that the lumbar spine in various 3-D postures can be stabilized by spinal muscles that generate CFLs in the spine, which at least in part supports the hypothesis of CFLs as a physiological load in the lumbar spine. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3004-3012, 2018.

Association between paraspinal muscle morphology, clinical symptoms and functional status in patients with lumbar spinal stenosis

PURPOSE

Lumbar spinal stenosis (LSS) is a disabling condition associated with narrowing of the spinal canal or vertebral foramina. Paraspinal muscle atrophy and fatty infiltration have been reported in patients with chronic LBP and disc herniation. However, very few imaging studies have examined paraspinal muscle morphology and composition in patients with LSS. The purpose of this study was to investigate the association of paraspinal muscle size, composition and asymmetry with functional status in patients with LSS.

METHODS

Thirty-six patients diagnosed with LSS at L4-L5 with neurogenic claudication were included. Paraspinal muscle measurements were obtained from axial T2-weighted MR images, bilaterally, at the level of the superior and inferior vertebral endplates of L5. Muscle measurements of interest included: total cross-sectional area (CSA), functional CSA (FCSA), the ratio of FCSA to CSA (FCSA/CSA) as an indicator of muscle composition, and relative % asymmetry in muscle CSA. The association between muscle parameters and other patient characteristics with function as indicated from Oswestry Disability Index (ODI) scores and pain interference status was investigated.

RESULTS

Greater multifidus muscle fatty infiltration (e.g., lower FCSA/CSA) and lower psoas relative CSA were associated with lower function (higher ODI and pain interference scores) in univariable and multivariable analyses. There was no association between the different muscle parameters and stenosis severity or back or leg pain duration or severity.

CONCLUSIONS

Our findings suggest an association of multifidus muscle fatty infiltration and psoas muscle size with functional status in patients diagnosed with LSS. Future prospective studies are needed to evaluate whether such muscle parameters are associated with prognosis and functional recovery following surgical treatment.

The lumbar paraspinal muscle morphometry of fast bowlers in cricket

OBJECTIVE

To describe the functional cross-sectional area (FCSA) of the lumbar paraspinal muscles of professional fast bowlers in cricket and to investigate the nature of any muscle asymmetry.

DESIGN

Descriptive cross-sectional between-groups study.

SETTING

The England and Wales Cricket Board.

PARTICIPANTS

Forty-six asymptomatic professional fast bowlers and 17 athletic controls.

MAIN OUTCOME MEASUREMENTS

The magnetic resonance imaging of functional cross-sectional area (FCSA) of the lumbar paraspinal muscles, and the prevalence of asymmetry (greater than 10% difference in the FCSA between the dominant and nondominant side muscles).

RESULTS

A relatively high percentage of fast bowlers had asymmetrically larger dominant side quadratus lumborum FCSAs at L1 (47%), L3 (41%), and L4 (47%). The nondominant side psoas FCSA was larger in fast bowlers at L5, and the dominant side multifidus FCSA was larger in both the fast bowlers at L3 to S1 and in the control subjects at L4 and L5.

CONCLUSIONS

There was a higher prevalence of lumbar muscle asymmetry in the fast bowler group. Paraspinal muscle asymmetry was most prevalent in the quadratus lumborum of fast bowlers, and it was also evident in the lumbar multifidus in both groups of subjects. In both muscle groups, this was consistent with hypertrophy of the dominant side muscle. This study may be used to inform prospective studies of risk factors for low back injury in athletic males and enhance the development of more accurate models of stress production in the lumbar spine during fast bowling and other asymmetrical sports.

Differentiating temporal electromyographic waveforms between those with chronic low back pain and healthy controls

OBJECTIVES

Temporal activation patterns from abdominal and lumbar muscles were compared between healthy control subjects and those with chronic low back pain.

STUDY DESIGN

A cross-sectional comparative study.

BACKGROUND

Synergist and antagonist coactivity has been considered an important neuromuscular control strategy to maintain spinal stability. Differences in onset times and amplitudes have been reported from trunk muscle EMG recordings between healthy subjects and those with low back pain;however, evaluating temporal EMG waveforms should demonstrate whether differences exist in the ability of those with and those without low back pain to respond to changing perturbations.

METHODS

The Karhunen-Loève expansion was applied to the ensemble-average EMG profiles recorded from four abdominal and three trunk extensor muscle sites while subjects performed a leg-lifting task aimed at challenging lumbar spine stability. The principal patterns were derived and the weighting coefficients for each pattern were the main dependent variables in a series of two-factor (group and muscle) mixed ANOVA models.

RESULTS

Three principal patterns explained 96% of the variance in the temporal EMG profiles. The ANOVAs revealed statistically significant group and muscle main effects (P<0.05) for the principal pattern and significant group by muscle interactions (P<0.05) for patterns two and three. Post hoc analysis showed that patterns were not different among all muscle sites for the healthy controls, but differences were significant for the low back pain group.

CONCLUSIONS

The healthy group coactivated all seven sites with the same temporal pattern of activation. The low back pain group used different activation patterns indicative of a lack of synergistic coactivitation among the muscle sites examined.

RELEVANCE

These results provide a foundation for developing a diagnostic classifier of neuromuscular impairment associated with low back pain, that could be used to evaluate the effectiveness of therapeutic interventions to improve muscle coactivation.