Determinants of paraspinal muscle cross-sectional area in male monozygotic twins

Radiologic Features of T10 Paravertebral Muscle Sarcopenia: Prognostic Factors in COVID-19

Background

Sarcopenia, defined as a small cross-sectional area (CSA) in computed tomography (CT) measurements of skeletal muscles, serves as a disease severity marker in various clinical scenarios, including pulmonary conditions and critical illness. Another parameter of sarcopenia, the level of myosteatosis, reflected by the tissue's radiodensity, in the thoracic skeletal muscles group, has been linked to disease progression in coronavirus disease 2019 (COVID-19) patients. We hypothesize that CT-derived measurements of the skeletal muscle density (SMD) and the CSA of thoracic skeletal muscles can predict outcomes in COVID-19 pneumonia.

Methods

We retrospectively reviewed the CT scans of 84 patients with COVID-19 pneumonia admitted to two of Greece's largest academic teaching hospitals between April 2020 and February 2021. CSA and SMD at the level of the T10 vertebra were measured using computational imaging methods. The patient population was stratified according to survival status and CT severity score (CT-SS). Correlations were drawn between the radiologic features of sarcopenia, CT severity subgroups, serum inflammatory markers, and adverse events, e.g., death and intubation.

Results

Thoracic muscles' CSA measurements correlate with CT-SS and prominent inflammatory markers, such as white blood cell (WBC), C-reactive protein (CRP), fibrinogen, and D-dimers. Moreover, according to linear regression analysis, CSA seems to predict CT-SS variation significantly (β = -0.266, P = 0.018). CSA proved to differ significantly across survivors (P = 0.027) but not between CT severity categories and intubation subgroups. The AUC (area under the curve) of the receiver operating characteristic (ROC) curve for the predictive value of thoracic muscles' CSA in mortality is 0.774 (95% confidence interval (CI): 0.66 - 0.83, P < 0.000). The optimal cut-off value (Youden index = 0.57) for mortality prognosis, with a sensitivity of 66.7% and a specificity of 88.9%, is 15.55. Thoracic muscles' SMD analyses did not reveal any significant correlations.

Conclusions

Easy to obtain and accurately calculated, radiologic features can provide a reliable alternative to laboratory methods for predicting survival in COVID-19. Thoracic muscles' CSA measurement in the level of the T10 vertebra, an acclaimed prognostic imaging assessment that relates directly to CT-SS and inflammatory markers in COVID-19 pneumonia, is a fairly specific tool for survival prognosis.

Evaluation of the degeneration of the multifidus and erector spinae muscles in patients with low back pain and healthy individuals

BACKGROUND

Although several studies have been conducted to determine the cause of low back pain (LBP), a sufficient correlation has not been found between research findings and symptoms. Therefore there seems to be a need for studies to explain the relationship between pain and morphological changes in the paraspinal muscles of patients with LBP through comparisons with healthy control subjects.

OBJECTIVE

The aim of this study was to examine degeneration in the lumbar musculus multifidus (LMF) and lumbar musculus erector spinae (LES) muscles in patients with chronic LBP with non-radiculopathy lumbar disc herniation (LDH), patients with mechanical LBP, and healthy individuals.

METHODS

The study included 35 patients with mechanical LBP, 38 patients with non-radiculopathy LDH, and a control group of 36 healthy participants. In all patients and the control group, evaluations were made on axial magnetic resonance imaging slices at L3-S1 level of the LMF and LES cross-sectional areas (CSA), total CSA (TCSA = LMF+LES), fat infiltrations and asymmetries.

RESULTS

The mean CSA values of the right and left LMF and LES showed significant differences between the groups (p< 0.001, p= 0.002, p= 0.002, p= 0.010, respectively). Fat infiltrations showed a difference between the right-left LMF and left LES groups (p= 0.007, p< 0.001, p= 0.026, respectively). Asymmetry was not observed between the CSA and TCSA of the right and left sides.

CONCLUSION

A correlation was found between fat infiltration in the LMF and mechanical LBP and LDH. However, no significant correlation was determined between LBP and the CSA and TCSA of the LMF and LES. This was thought to be due to an incorrect result of CSA and TCSA in the evaluation of muscle mass. Therefore, for a more accurate evaluation of muscle mass, it can be considered necessary to measure muscle atrophy associated with fat infiltration or functional CSA.

Alteration in the Cross-sectional Area (CSA) Ratio of the Paraspinal Muscles following Vertebral Insufficiency Fractures

Background  Vertebral insufficiency fractures in the elderly are associated with increased morbidity and mortality. Early diagnosis is essential to direct patient-specific rehabilitation. Aims  We hypothesize that in patients with vertebral insufficiency fractures, there is atrophy of the psoas and paraspinal muscles with alteration in the cross-sectional area (CSA) of the muscles. Materials and Methods  Magnetic resonance imaging (MRI) studies for 100 consecutive patients, older than 60 years presenting with lower back pain, were included in the study. For each MRI study, the CSA of the psoas and paraspinal muscles (multifidus) at the level of L4/5-disc space was measured to calculate the cross-sectional area ratio (CSAR) by two readers. One reader repeated the measurements after an interval of 2 weeks. We divided the patients ( n  = 100) into various groups based on the number of vertebral fractures. Results  In total, 77 patients with vertebral body fractures (48 with one, 16 with two and 13 with more than two fractures) were identified with a mean age of 73 (range 60-92) years. The ratio of multifidus CSA to psoas CSA was calculated with mean values of each group (1-4) as 2.56, 1.89, 2.09 and 2.16, respectively. There was statistically significance difference of the CSAR between the cohorts ( p -value = 0.0115). Conclusion  Vertebral insufficiency fractures in the elderly are associated not only with atrophy of psoas and the multifidus group of muscles as evident by the CSA values, but they also affect the CSAR depending on the number of fractures. This finding may help to direct targeted patient-specific physiotherapy rehabilitation and interventions to prevent further such fractures.

Investigation of the relationship between the clinical evaluation results of lumbar region muscles with cross-sectional area and fat infiltration

BACKGROUND

The relationship between the endurance of the lumbar paraspinal muscles and morphological changes needs to be clarified. In this context, the importance can be revealed of increasing the endurance level of the paraspinal muscles in the prevention and treatment of low back diseases.

OBJECTIVE

The aim of this study was to examine the relationship between the clinical evaluation results of the cross-sectional area (CSA) and fat infiltration of the lumbar deep paraspinal muscles.

METHODS

The study included 37 patients with mechanical low back pain (mechanical), 41 patients with lumbar hernia without root compression (discopathy) and 36 healthy individuals as a control group. The functional status of the lumbar deep paraspinal muscles was evaluated clinically with muscle endurance tests. The fat infiltration and CSA of the muscles were evaluated on axial MRI sections at the L3-S1 level.

RESULTS

The mean values of the prone bridge, Biering-Sorenson, and trunk flexion tests were seen to be highest in the control group and lowest in the discopathy group (p< 0.001). In all tests, the longest test period was obtained at < 10% fat infiltration and the shortest at > 50% fat infiltration. It was observed that as the amount of fat infiltration of the muscles increased, the test times were shortened. There was no significant relationship between the endurance level and the CSA of the groups.

CONCLUSION

The study results demonstrated that the endurance of the paraspinal muscles is associated with the fat infiltration of the muscles. In patients with chronic low back pain, information about muscle morphology and degeneration can be obtained with simple endurance tests without the need for further measurements. On clinical examination, a weak endurance level of the paraspinal muscles indicates the presence of a low back problem and an increase in the amount of fat infiltration.

Assessing Fatty Infiltration of Paraspinal Muscles in Patients With Lumbar Spinal Stenosis: Goutallier Classification and Quantitative MRI Measurements

Objective: Fatty infiltration of paraspinal muscle is associated with spinal disorders. It can be assessed qualitatively (i.e., Goutallier classification) and quantitatively using image processing software. The aims of this study were to compare paraspinal muscle fatty infiltration as assessed using the Goutallier classification vs. quantitative magnetic resonance images (MRI) measurements and to investigate the association between anthropometric parameters and paraspinal muscle morphology and fatty infiltration in patients with symptomatic lumbar spinal stenosis (LSS).

Methods: Patients affected by symptomatic LSS scheduled for surgery with available MRI of the lumbar spine were included in this retrospective cross-sectional study. Fatty infiltration at each lumbar level was rated qualitatively according to the Goutallier classification and quantified based on the cross-sectional area (CSA) of the paraspinal muscle, of its lean fraction (LeanCSA), and the ratio between LeanCSA and CSA and the CSA relative to the CSA of vertebral body (RCSA). Considering the muscle as a single unit, overall fatty infiltration according to Goutallier, overall CSA, LeanCSA, LeanCSA/CSA, and RCSA were computed as averages (aGoutallier, aCSA, aLeanCSA, aLeanCSA/aCSA, and aRCSA). Associations among parameters were assessed using Spearman's respective Pearson's correlation coefficients.

Results: Eighteen patients, with a mean age of 71.3 years, were included. aGoutallier correlated strongly with aLeanCSA and aLeanCSA/aCSA (R = −0.673 and R = −0.754, both P < 0.001). There was a very strong correlation between values of the left and right sides for CSA (R = 0.956, P < 0.001), LeanCSA (R = 0.900, P < 0.001), and LeanCSA/CSA (R = 0.827, P < 0.001) at all levels. Among all anthropometric measurements, paraspinal muscle CSA correlated the most with height (left: R = 0.737, P < 0.001; right: R = 0.700, P < 0.001), while there was a moderate correlation between vertebral body CSA and paraspinal muscle CSA (left: R = 0.448, P < 0.001; right: R = 0.454, P < 0.001). Paraspinal muscle CSA correlated moderately with body mass index (BMI; left: R = 0.423, P < 0.001; right: R = 0.436, P < 0.001), and there was no significant correlation between aLeanCSA or aLeanCSA/CSA and BMI.

Conclusions: The Goutallier classification is a reliable yet efficient tool for assessing fatty infiltration of paraspinal muscles in patients with symptomatic LSS. We suggest taking body height as a reference for normalization in future studies assessing paraspinal muscle atrophy and fatty infiltration.

Age-related degeneration of lumbar muscle morphology in healthy younger versus older men

AIM

The aim of this study was to evaluate age-related changes in lumbar paravertebral muscle (LPM) morphology in healthy younger and older adult men.

METHODS

T2-weighted axial MRI of the lumbar spine were obtained for 12 healthy older (67.3 ± 6.0 years) and younger (24.7 ± 3.1 years) men. Normalised muscle volume (NMV) and muscle fat infiltrate (MFI) were determined bilaterally for the psoas (PS), quadratus lumborum (QL), erector spinae (ES) and multifidus (MF). MANOVA was used to compare NMV and MFI between age groups. Follow-up ANOVA compared NMV and MFI for each muscle between age groups, with physical activity (PA) as a covariate. Stepwise regression was used to explore the association between muscle morphology.

RESULTS

NMV of the ES and QL were significantly lower in the older group (OG) (p = 0.040 and p < 0.001, respectively). MFI across all muscles was significantly greater in the OG (p < 0.001). PA did not moderate the relationship between aging and muscle degeneration. Non-dominant handgrip strength was associated with NMV (p = 0.003).

CONCLUSIONS

Age-related atrophy is muscle specific in the lumbar spine; changes in lumbar musculature is independent of PA, handgrip strength may reflect morphological changes in the postural muscles with age. This study supports establishing effective targeted exercise interventions in the lumbar musculature.

Cross-sectional area of the paraspinal muscles and its association with muscle strength among fighter pilots: a 5-year follow-up

Background

A small cross sectional area (CSA) of the paraspinal muscles may be related to low back pain among military aviators but previous studies have mainly concentrated on spinal disc degeneration. Therefore, the primary aim of the study was to investigate the changes in muscle CSA and composition of the psoas and paraspinal muscles during a 5-year follow up among Finnish Air Force (FINAF) fighter pilots.

Methods

Study population consisted of 26 volunteered FINAF male fighter pilots (age: 20.6 (±0.6) at the baseline). The magnetic resonance imaging (MRI) examinations were collected at baseline and after 5 years of follow-up. CSA and composition of the paraspinal and psoas muscles were obtained at the levels of 3–4 and 4–5 lumbar spine. Maximal isometric strength tests were only performed on one occasion at baseline.

Results

The follow-up comparisons indicated that the mean CSA of the paraspinal muscles increased (p < 0.01) by 8% at L3–4 level and 7% at L4–5 level during the 5-year period. There was no change in muscle composition during the follow-up period. The paraspinal and psoas muscles’ CSA was positively related to overall maximal isometric strength at the baseline. However, there was no association between LBP and muscle composition or CSA.

Conclusions

The paraspinal muscles’ CSA increased among FINAF fighter pilots during the first 5 years of service. This might be explained by physically demanding work and regular physical activity. However, no associations between muscle composition or CSA and low back pain (LBP) experienced were observed after the five-year follow-up.

The association between back muscle characteristics and pressure pain sensitivity in low back pain patients

BACKGROUND AND AIMS

Some low back pain (LBP) patients recover after every pain episode whereas others develop chronicity. Research indicates that the amount of atrophy and fat infiltration differs between patients with LBP. Also enhanced pain sensitivity is present only in a subgroup of LBP patients. The relationship between pain sensitivity and muscular deformations in LBP, is however unexplored. This study examined the association between pressure pain sensitivity and the structural characteristics of the lumbar muscles in three different groups of non-specific LBP patients.

METHODS

This cross-sectional study examined the total cross-sectional area (CSA), fat CSA, muscle CSA and muscle fat index (MFI) of the lumbar multifidus (MF) and erector spinae (ES) at level L4 by magnetic resonance imaging in 54 patients with non-specific LBP (23 recurrent LBP, 15 non-continuous chronic LBP and 16 continuous chronic LBP). Pressure pain thresholds were measured at four locations (lower back, neck, hand and leg) by a manual pressure algometer and combined into one "pain sensitivity" variable. As a primary outcome measure, the association between pain sensitivity and muscle structure characteristics was investigated by multiple independent general linear regression models. Secondly, the influence of body mass index (BMI) and age on muscle characteristics was examined.

RESULTS

A positive association was found between pain sensitivity and the total CSA of the MF (p=0.006) and ES (p=0.001), and the muscle CSA of the MF (p=0.003) and ES (p=0.001), irrespective of the LBP group. No association was found between pain sensitivity and fat CSA or MFI (p>0.01). Furthermore, a positive association was found between BMI and the fat CSA of the MF (p=0.004) and ES (p=0.006), and the MFI of the MF (p<0.01) and ES (p=0.003). Finally, a positive association was found between age with the fat CSA of the MF (p=0.008) but not with the fat CSA of the ES (p>0.01), nor the MFI of the MF (p>0.01) and ES (p>0.01).

CONCLUSIONS

A higher pain sensitivity is associated with a smaller total and muscle CSA in the lumbar MF and ES, and vice versa, but results are independent from the LBP subgroup. On the other hand, the amount of fat infiltration in the lumbar muscles is not associated with pain sensitivity. Instead, a higher BMI is associated with more lumbar fat infiltration. Finally, older patients with LBP are associated with higher fat infiltration in the MF but not in the ES muscle.

IMPLICATIONS

These results imply that reconditioning muscular tissues might possibly decrease the pain sensitivity of LBP patients. Vice versa, therapy focusing on enhancement of pain sensitivity might also positively influence the CSA and that way contribute to the recovery of LBP. Furthermore, the amount of lumbar muscle fat seems not susceptible to pain sensitivity or vice versa, but instead a decrease in BMI might decrease the fat infiltration in the lumbar muscles and therefore improve the muscle structure quality in LBP. These hypothesis apply for all non-specific LBP patients, despite the type of LBP.

Fat Replacement of Paraspinal Muscles with Aging in Healthy Adults

PURPOSE

The aims of this study were to investigate the age-related changes in fatty replacement and cross-sectional area (CSA) of cervical, thoracic, and lumbar paraspinal muscles versus leg muscles in healthy adults and to test for association between muscle fat fraction and lifestyle factors.

METHODS

Fifty-three healthy adults (24-76 yr) were included. Dixon magnetic resonance imaging technique was used to determine CSA and to quantify the fat fraction of paraspinal and leg muscles. Muscle CSA and fat fractions were tested for association with age and muscle strength. The fat fractions were also tested for association with sex, body mass index (BMI), physical activity, and lower back pain.

RESULTS

Both paraspinal and leg fat fractions correlated directly with age (P < 0.0001). At all ages, fat fraction was higher in paraspinal than leg muscles. The age-related increase in fat fraction was higher in paraspinal muscles than leg muscles (P < 0.0001). The CSA of the muscles did not correlate with age. Knee extension strength correlated with fat fraction (P < 0.05), and the muscle strength of hip muscles, thigh muscles, and anterior calf muscles correlated with CSA (P < 0.05). Sex was associated with lumbar paraspinal fat fraction (P < 0.05) and BMI with thigh fat fraction (P < 0.001). There was no association between fat fraction and physical activity or lower back pain.

CONCLUSION

The paraspinal muscles were more susceptible to age-related changes than leg muscles. Further, men had significantly lower fat fractions in lumbar paraspinal muscles, and BMI was positively associated with thigh, but not paraspinal, fat fraction.

Maintenance of the paraspinal muscles may protect against radiographic knee osteoarthritis

Background

Knee osteoarthritis (OA) is an increasing health problem worldwide. So far, only obesity and quadriceps weakness are identified as modifiable risk factors for knee OA. Core muscle strengthening is becoming increasingly popular among older adults because of its ability to enhance the activities of daily living during old age. This study investigated the associations of the size and quality of the abdominal trunk muscles with radiographic knee osteoarthritis (RKOA).

Methods

From 2012 to 2016, data were collected from 146 males and 135 females (age 63.9±13.4 years, BMI 23.2±3.8 kg/m²) at annual musculoskeletal examinations, including knee radiographs and body composition analyses, by dual-energy X-ray absorptiometry. Cross-sectional areas of abdominal trunk muscles were measured using a single-slice computed tomography scan image obtained at the level of the umbilicus.

Results

The prevalence of RKOA was 21.2% in males and 28.1% in females. Compared to subjects without RKOA, subjects with RKOA were ~6 years older and had smaller paraspinal muscle (38.4±8.7 vs 33.1±10.1 cm², p<0.01 in males; 24.1±7.1 vs 20.7±7.5 cm², p<0.05 in females). In contrast, there was no decrease in appendicular or total lean mass, and only in females, BMI and total fat mass (FM) were higher in subjects with RKOA (21.5±3.5 vs 24.5±4.4 kg/m², 16.7±7.0 vs 20.5±7.7 kg, respectively, both p<0.01). After adjusting for age and sex, smaller cross-sectional area/lower attenuation value of the paraspinal muscles was associated with RKOA (both p<0.05), while greater appendicular or total lean mass as well as greater FM was associated with RKOA. The size and quality of the paraspinal muscles were not associated with knee pain or habitual exercise.

Conclusion

Small, poor-quality paraspinal muscles may be linked to a higher risk of RKOA, but appendicular or total lean mass was not a good predictor of RKOA.

Contribution of Lumbar Spine Pathology and Age to Paraspinal Muscle Size and Fatty Infiltration

STUDY DESIGN

Retrospective chart analysis of 199 individuals aged 18 to 80 years scheduled for lumbar spine surgery.

OBJECTIVE

The purpose of this study was to quantify changes in muscle cross-sectional area (CSA) and fat signal fraction (FSF) with age in men and women with lumbar spine pathology and compare them to published normative data.

SUMMARY OF BACKGROUND DATA

Pathological changes in lumbar paraspinal muscle are often confounded by age-related decline in muscle size (CSA) and quality (fatty infiltration). Individuals with pathology have been shown to have decreased CSA and fatty infiltration of both the multifidus and erector spinae muscles, but the magnitude of these changes in the context of normal aging is unknown.

METHODS

Individuals aged 18 to 80 years who were scheduled for lumbar surgery for diagnoses associated with lumbar spine pain or pathology were included. Muscle CSA and FSF of the multifidus and erector spinae were measured from preoperative T2-weighted magnetic resonance images at the L4 level. Univariate and multiple linear regression analyses were performed for each outcome using age and sex as predictor variables. Statistical comparisons of univariate regression parameters (slope and intercept) to published normative data were also performed.

RESULTS

There was no change in CSA with age in either sex (P > 0.05), but women had lower CSAs than men in both muscles (P < 0.0001). There was an increase in FSF with age in erector spinae and multifidus muscles in both sexes (P < 0.0001). Multifidus FSF values were higher in women with lumbar spine pathology than published values for healthy controls (P = 0.03), and slopes tended to be steeper with pathology for both muscles in women (P < 0.08) but not in men (P > 0.31).

CONCLUSION

Lumbar muscle fat content, but not CSA, changes with age in individuals with pathology. In women, this increase is more profound than age-related increases in healthy individuals.

LEVEL OF EVIDENCE

3.

Paraspinal muscle morphology and composition: a 15-yr longitudinal magnetic resonance imaging study

PURPOSE

The purposes of this study were to define the natural progression of age-related changes of the lumbar paraspinal muscles during adulthood and to investigate the influence of lifestyle and individual factors (e.g., physical activity levels at work and leisure, body mass index, and low back pain [LBP]).

METHODS

This population-based longitudinal study included a sample of 99 adult male twins. Data were collected through a structured interview, physical examination, and magnetic resonance imaging. Measurements of the lumbar multifidus and erector spinae muscles were obtained from T2-weighted axial images at L3-L4 and L5-S1 at baseline and 15-yr follow-up. Muscle cross-sectional area (CSA), functional CSA (FCSA) (fat-free mass), and FCSA/CSA (composition) as well as CSA and FCSA asymmetry and FCSA/CSA side-to-side differences were measured.

RESULTS

Subjects' mean ± SD age was 47.3 ± 7.4 yr at baseline and 62.3 ± 8.0 yr at follow-up. During the 15-yr period, both muscles exhibited a decrease in CSA and FCSA and an increase in fatty infiltration and side-to-side differences in size and composition at both spinal levels. Both muscles displayed greater changes at L5-S1 than L3-L4. Age and BMI were found to be significantly associated with the degree of paraspinal muscle changes over time. However, there was no association between the change in paraspinal muscle size, composition, or asymmetry with the level of physical demands at work or leisure or LBP history.

CONCLUSIONS

The present longitudinal study suggests that over adulthood, the multifidus and erector spinae undergo similar morphological changes. Moreover, our findings suggest that the long-term progression of lumbar paraspinal muscle changes evaluated through magnetic resonance imaging are not associated with the range of physical demand levels as were typical of Finnish men or LBP history.

Do variations in paraspinal muscle morphology and composition predict low back pain in men?

This longitudinal study aimed to clarify the longstanding controversy over whether variations in paraspinal muscle morphology (e.g., size, composition and asymmetry) are predictors of low back pain (LBP). A sample of 99 Finnish men were included in this population-based longitudinal study. Data were collected through a structured interview, physical examination and magnetic resonance imaging (MRI). Baseline measurements of the lumbar multifidus and erector spinae muscles were obtained from T2-weighted axial images at L3-L4 and L5-S1, and interview data were obtained at baseline, 1- and 15-year follow-ups. Few of the paraspinal muscle parameters investigated were predictors of change in LBP frequency, intensity or sciatica at 1- and 15-year follow-ups in the population-based sample, and findings were not consistent across muscles and spinal levels. However, greater multifidus and erector spinae fatty infiltration at L5-S1 was associated with a higher risk of having continued, frequent, persistent LBP at 1-year follow-up. None of the relationships observed was confounded by body mass index or the amount of physical activity at work or leisure. This longitudinal study provided evidence that variations in paraspinal muscle morphology on MRI have a limited, if not uncertain, role in the short- and long-term predictions of LBP in men.

Factors associated with paraspinal muscle asymmetry in size and composition in a general population sample of men

BACKGROUND

Paraspinal muscle asymmetry in cross-sectional area (CSA) and composition have been associated with low back pain and pathology. However, substantial multifidus muscle asymmetry also has been reported in men who were asymptomatic, and little is known about other factors influencing asymmetry.

OBJECTIVE

The goal of this study was to identify behavioral, environmental, and constitutional factors associated with paraspinal muscle asymmetry.

DESIGN

A cross-sectional study of 202 adult male twins was conducted.

METHODS

Data were collected through a structured interview, physical examination, and magnetic resonance imaging. Measurements of multifidus and erector spinae muscle CSA and the ratio of fat-free CSA to total CSA were obtained from T2-weighted axial images at L3-L4 and L5-S1.

RESULTS

In multivariable analyses, greater asymmetry in multifidus CSA at L3-L4 was associated with lower occupational physical demands and less disk height narrowing. Handedness was the only factor associated with multifidus muscle CSA asymmetry at L5-S1. For the erector spinae muscle, greater age, handedness, and disk height narrowing were associated with CSA asymmetry at L3-L4, and sports activity, handedness, disk height narrowing, and familial aggregation were associated with CSA asymmetry at L5-S1. In multivariable analyses of asymmetry in muscle composition, familial aggregation explained 7% to 20% of the variance in multifidus and erector spinae muscle side-to-side differences at both levels measured. In addition, handedness and pain severity entered the model for erector spinae muscle asymmetry at L5-S1, and disability, handedness, and disk height narrowing entered the model for multifidus muscle asymmetry at L5-S1.

LIMITATIONS

Reliance on participants' recall for low back pain history, occupation, and physical activity levels was a limitation of this study.

CONCLUSIONS

Few of the factors investigated were associated with paraspinal muscle asymmetry, and associations were inconsistent and modest, explaining little of the variance in paraspinal muscle asymmetry.

The reliability of paraspinal muscles composition measurements using routine spine MRI and their association with back function

This study examines the reliability of quantitative and qualitative muscle composition measurements of paraspinal muscle cross-sectional areas (CSAs) from routine lumbar spine magnetic resonance images and their association with maximal isokinetic lifting performance. The extent of paraspinal muscle composition reflects back function is currently not known. Measurements were repeated 4-8 weeks apart and different measurements of related constructs were compared. Participants were a population-based sample of 169 males, 35-67 years old, without considering the presence or absence of a history of low back pain or related problems in the selection of subjects. The quantitative and qualitative muscle composition measurements for axial magnetic resonance (MR) images of paraspinal muscles at the L3-L4 lumbar spine level, isokinetic lifting force and work, and body fat percentage were the main outcome measures. Results showed that the reproducibility of different paraspinal muscle composition measurements at the L3-L4 level was excellent for CSAs (ICC=0.95-0.99) and quantitative muscle composition measurements using cerebrospinal fluid adjusted signal intensity (ICC=0.96-0.99), and moderate for qualitative muscle composition ratings (Kappa=0.54-0.76). The correlations of the quantitative and qualitative muscle composition measurements with isokinetic lifting force and work were generally low (r=0.02-0.41), and favoured the qualitative assessments. In conclusion, quantitative and qualitative muscle composition measurements of paraspinal muscles are highly reproducible tissue measures, have low associations with body fat and isokinetic lifting performance, and show that paraspinal muscle morphology using routine spine magnetic resonance imaging (MRI) is poorly related to back function.

Genetic and environmental contributions to back pain in old age: a study of 2,108 danish twins aged 70 and older

STUDY DESIGN

Self-reported 1-month prevalence of back pain in older twins assessed at intake in a population-based longitudinal survey.

OBJECTIVES

To determine the relative contribution of genetic and environmental factors to back pain in old age.

SUMMARY OF BACKGROUND DATA

To date, genetic contributions to back pain in old age have not been assessed, to the authors' best knowledge.

METHODS

Interview data given at entry into a nationwide cohort-sequential population-based survey of Danish twins aged 70 years and older in 1995, 1997, 1999, and 2001 form the basis of this analysis. Analysis of twin similarity was estimated using probandwise concordance rates, odds ratios, and tetrachoric correlations for back pain. Heritability (proportion of the population variance attributable to genetic variation) was estimated by bivariate probit estimation and adjusted for known significant environmental factors. Odds ratios for known environmental effects were estimated after controlling for age, sex, and genetic effects.

RESULTS

Modest and nonsignificant differences between monozygotic and dizygotic twin pairs were found for probandwise concordance rates, odds ratios, and tet-rachoric correlations for both men and women. In the bivariate probit estimation, a current or previous diagnosis of osteoporosis, degenerative joint disease, or lumbar disc prolapse was found to significantly affect the risk of back pain. Additive genetic effects explained approximately one fourth of the liability to report back pain in men and none of the occurrence in women. Individual environmental effects were found to explain roughly 75% of the occurrence of back pain in men and 100% in women.

CONCLUSIONS

Additive genetic effects are modest contributors to back pain in older men but not in women. A current or previous medical diagnosis of osteoporosis, degenerative joint disease, or lumbar disc prolapse is-strongly associated with back pain, also when genetic factors are controlled for. Because of inherent methodologic issues, this estimate of the genetic influence on back pain in old age is probably conservative.

The effect of comprehensive group training on cross-sectional area, density, and strength of paraspinal muscles in patients sick-listed for subacute low back pain

The effect of exercise on back muscle cross-sectional area (CSA), density, and strength was evaluated in patients sick-listed for subacute low back pain. Twenty-four patients were randomized into an exercise (n = 11) or a control (n = 13) group. Patients in the exercise group followed a biweekly exercise protocol for 15 weeks. Control patients received usual care. Muscle CSA and density were measured by computed tomography before and after intervention. Isokinetic test of back extensors was conducted simultaneously. Results showed a tendency to increased muscle CSA and density in patients in the exercise group, a significant decrease in muscle CSA at L4-L5 in control group patients, and a significant difference in change between groups in muscle CSA at L4-L5. Back extension strength increased in patients in the exercise group, but the improvement was not significant compared with control group patients. In conclusion, there was a tendency for reversal of muscle atrophy after exercise.

Hand grip strength: a phenotype suitable for identifying genetic variants affecting mid- and late-life physical functioning

Physical functioning late in life has been shown to be affected by genetic factors. Only a few genetic variants have been suggested to be associated with physical functioning, and this only in selected populations (e.g., young healthy males and elite athletes). Declining physical functioning late in life is a major problem in terms of prevalence, morbidity, functional limitations, and quality of life. It is therefore of interest to find a phenotype reflecting physical functioning which has a relatively high heritability and which can be measured in large samples. Hand grip strength is known to be associated with muscular functioning in other muscle groups and with activities of daily living (ADL) functioning, and it predicts incident disability. We studied 1,757 Danish twin pairs aged 45-96 years, and found that this phenotype has a heritability of 52% (95% confidence interval (CI), 48-55%). A powerful design to detect genes associated with a phenotype is obtained using the extreme discordant and concordant sib pairs, of whom 28 and 77 dizygotic twin pairs, respectively, were found in this study. Hence grip strength is a suitable phenotype for identifying genetic variants of importance to mid- and late-life physical functioning.