Amanda L. Lorbergs

Imaging-Based Methods for Non-invasive Assessment of Bone Properties Influenced by Mechanical Loading

PURPOSE To describe the most common in vivo imaging-based research tools used to assess bone properties that are influenced by mechanical loading associated with exercise, habitual physical activity, or disease states. Bone is a complex metabolically active tissue that adapts to changes in mechanical loading by altering the amount and spatial organization of mineral. METHOD Using a narrative review design, the authors provide an overview of bone biology and biomechanics to emphasize the importance of bone size scale, porosity, and degree of mineralization when interpreting measures acquired using quantitative ultrasound (QUS), dual-energy X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI), and finite element analysis (FEA). For each imaging modality, basic imaging principles, typical outcome measures associated with changes in mechanical loading, and salient features for physiotherapists are described. MAIN RESULTS While each imaging modality has strengths and limitations, currently CT-based methods are best suited for determining the effects of mechanical loading on bone properties-particularly in the peripheral skeleton. CONCLUSIONS Regardless of the imaging technology used, the physiotherapist must carefully consider the assumptions of the imaging-based method, the clinical context, the nature of the change in mechanical loading, and the expected time course for change in bone properties. Purpose: To describe the most common in vivo imaging-based research tools used to assess bone properties that are influenced by mechanical loading associated with exercise, habitual physical activity, or disease states. Bone is a complex metabolically active tissue that adapts to changes in mechanical loading by altering the amount and spatial organization of mineral. Method: Using a narrative review design, the authors provide an overview of bone biology and biomechanics to emphasize the importance of bone size scale, porosity, and degree of mineralization when interpreting measures acquired using quantitative ultrasound (QUS), dual-energy X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI), and finite element analysis (FEA). For each imaging modality, basic imaging principles, typical outcome measures associated with changes in mechanical loading, and salient features for physiotherapists are described. Main Results: While each imaging modality has strengths and limitations, currently CT-based methods are best suited for determining the effects of mechanical loading on bone properties—particularly in the peripheral skeleton. Conclusions: Regardless of the imaging technology used, the physiotherapist must carefully consider the assumptions of the imaging-based method, the clinical context, the nature of the change in mechanical loading, and the expected time course for change in bone properties.

Heritability of Thoracic Spine Curvature and Genetic Correlations With Other Spine Traits: The Framingham Study

Hyperkyphosis is a common spinal disorder in older adults, characterized by excessive forward curvature of the thoracic spine and adverse health outcomes. The etiology of hyperkyphosis has not been firmly established, but may be related to changes that occur with aging in the vertebrae, discs, joints, and muscles, which function as a unit to support the spine. Determining the contribution of genetics to thoracic spine curvature and the degree of genetic sharing among co‐occurring measures of spine health may provide insight into the etiology of hyperkyphosis. The purpose of our study was to estimate heritability of thoracic spine curvature using T4–T12 kyphosis (Cobb) angle and genetic correlations between thoracic spine curvature and vertebral fracture, intervertebral disc height narrowing, facet joint osteoarthritis (OA), lumbar spine volumetric bone mineral density (vBMD), and paraspinal muscle area and density, which were all assessed from computed tomography (CT) images. Participants included 2063 women and men in the second and third generation offspring of the original cohort of the Framingham Study. Heritability of kyphosis angle, adjusted for age, sex, and weight, was 54% (95% confidence interval [CI], 43% to 64%). We found moderate genetic correlations between kyphosis angle and paraspinal muscle area ( ρˆG, –0.46; 95% CI, –0.67 to –0.26), vertebral fracture ( ρˆG, 0.39; 95% CI, 0.18 to 0.61), vBMD ( ρˆG, –0.23; 95% CI, –0.41 to –0.04), and paraspinal muscle density ( ρˆG, –0.22; 95% CI, –0.48 to 0.03). Genetic correlations between kyphosis angle and disc height narrowing ( ρˆG, 0.17; 95% CI, –0.05 to 0.38) and facet joint OA ( ρˆG, 0.05; 95% CI, –0.15 to 0.24) were low. Thoracic spine curvature may be heritable and share genetic factors with other age‐related spine traits including trunk muscle size, vertebral fracture, and bone mineral density.

Severity of Kyphosis and Decline in Lung Function: The Framingham Study

Background Hyperkyphosis reduces the amount of space in the chest, mobility of the rib cage, and expansion of the lungs. Decline in pulmonary function may be greater in persons with more severe kyphosis; however, no prospective studies have assessed this association. We conducted a longitudinal study to quantify the impact of kyphosis severity on decline in pulmonary function over 16 years in women and men. Methods Participants included a convenience sample of 193 women and 82 men in the Framingham Study original cohort (mean age: 63 years; range: 50-79 years), who had measurements of kyphosis angle from lateral spine radiographs obtained in 1972-1976 and forced expiratory volume in 1 second (FEV1) from spirometry taken four times over 16 (±1.87) years from 1972 through 1988. Results Kyphosis severity was associated with greater decline in FEV1 in women but not in men. Adjusted mean change in FEV1 over 16 years was -162, -245, and -261mL (trend, p = .02) with increasing tertile of kyphosis angle in women and -372, -297, and -257mL (trend, p = .20) in men, respectively. Conclusions This longitudinal study found that kyphosis severity increased subsequent decline in pulmonary function in women but not in men. Reasons for an association between kyphosis and pulmonary function in women but in not men may be due, at least in part, to the small number of men in our study. Nevertheless, our findings suggest that preventing or slowing kyphosis progression may reduce the burden of pulmonary decline in older adults.

Thoracic Kyphosis and Physical Function: The Framingham Study

To evaluate the association between thoracic kyphosis and physical function.

The International Classification of Functioning, Disability and Health (ICF) Core Sets: Application to a postmenopausal woman with rheumatoid arthritis and osteoporosis of the spine

The International Classification of Functioning, Disability and Health (ICF) framework facilitates systematic assessment of functioning across four components. ICF Core Sets are proposed to be beneficial for clinicians in multidisciplinary care settings because they provide a common language for communication. A clinical vignette of a postmenopausal woman with rheumatoid arthritis (RA) and a non-traumatic vertebral fracture is presented to discuss how the ICF Core Sets for RA and osteoporosis (OP) can be helpful in structuring clinical decisions. To demonstrate how condition-specific ICF Core Sets can be used to evaluate and treat women with two comorbidities, each component of the ICF Core Sets is compared across conditions and integrated into clinical decision-making. Topics covered include: exercise tolerance, urinary continence, bone mass, fear of falling, and environmental factors. The benefits of thorough communication with the client and a common language across healthcare disciplines are highlighted as the potential benefits of the ICF framework; however, limitations to uptake of the ICF in clinical practice are also addressed.

A longitudinal study of disc height narrowing and facet joint osteoarthritis at the thoracic and lumbar spine, evaluated by computed tomography: the Framingham Study

BACKGROUND CONTEXT Prevalence and progression of disc height narrowing (DHN) and facet joint osteoarthritis (FJOA) in the thoracic and lumbar regions in non-clinical populations are not well established. PURPOSE The present study aimed to use computed tomography (CT) images to determine the prevalence and progression of DHN and FJOA according to age, sex, and spinal region. STUDY DESIGN This is a 6-year longitudinal study. SAMPLE A total of 1,195 members of the Framingham Study (mean baseline age 61±9 years) were included in the study. OUTCOME MEASURES We compared the prevalence and progression (new or worsening) of moderate-to-severe DHN and FJOA by age, sex, and spinal region. METHODS A musculoskeletal radiologist evaluated DHN and FJOA from T4/T5 to L4/L5 on baseline and follow-up CT images using a semi-quantitative scale: 0=normal, 1=mild, 2=moderate, and 3=severe. RESULTS One-third or more of women and men ages 40-59 years at baseline had imaged-based evidence of prevalent DHN, more than half had prevalent FJOA, and DHN and FJOA prevalence increased approximately two- to fourfold in those age 60-69 and 70-89 years at baseline, respectively (p<.01). Progression of DHN and FJOA occurred more frequently at the lumbar than at the thoracic spine and more in women than in men (DHN: odds ratio [OR]=1.42, 95% confidence interval [CI]=1.07, 1.88; FJOA: OR=1.70, CI=1.33, 2.17). CONCLUSIONS Prevalence and progression of moderate-to-severe DHN and FJOA are common in non-clinical populations of older adults. The high frequency of spinal degeneration observed on CTs in this community-based study may contribute to challenges in interpreting the clinical significance of imaging evidence of DHN and FJOA. Future studies investigating the association of CT-based spinal degenerative features with pain and functional impairments in population-based samples are needed to help determine the clinical significance of imaged-based findings of DHN and FJOA.

A Longitudinal Study of Trunk Muscle Properties and Severity of Thoracic Kyphosis in Women and Men: The Framingham Study

BACKGROUND Cross-sectional studies suggest that trunk muscle morphology in the lumbar spine is an important determinant of kyphosis severity in older adults. The contribution of age-related changes in muscle morphology in the thoracic and lumbar spine to progression of kyphosis is not known. Our objective was to determine cross-sectional and longitudinal associations of thoracic and lumbar muscle size and density with kyphosis. METHODS Participants were 1,087 women and men (mean age: 61 years) of the Framingham Heart Study who underwent baseline and follow-up quantitative computed tomography (QCT) scanning 6 years apart. We used QCT scans to measure trunk muscle cross-sectional area (CSA, cm2) and density (HU) at the thoracic and lumbar spine and Cobb angle (degrees) from T4 to T12. Linear regression models estimated the association between muscle morphology and kyphosis. RESULTS At baseline, smaller muscle CSA and lower density of thoracic (but not lumbar) spine muscles were associated with a larger (worse) Cobb angle in women and men. For example, each standard deviation decrease in baseline thoracic paraspinal muscle CSA was associated with a larger baseline Cobb angle in women (3.7 degrees, 95% CI: 2.9, 4.5) and men (2.5 degrees, 95% CI: 1.6, 3.3). Longitudinal analyses showed that loss of muscle CSA and density at the thoracic and lumbar spine was not associated with progression of kyphosis. CONCLUSIONS Our findings suggest that kyphosis severity is related to smaller and lower density trunk muscles at the thoracic spine. Future studies are needed to determine how strengthening mid-back musculature alters muscle properties and contributes to preventing kyphosis progression.