An evaluation of the muscle-bone unit theory among individuals with chronic spinal cord injury

Abstract

Study design: Cross-sectional observation. Objectives: To explore the association between muscle size and function, and indices of bone strength among a sample of adults with chronic spinal cord injury (SCI). Setting: Ontario, Canada. Methods: Sixty-five participants (n¼47 men) with chronic SCI (C1-T12 American Spinal Injury Association Impairment Scale (AIS) A-D) were recruited, mean ± s.d. age 49.4 ± 12.8 years and years post-injury 14.3 ± 10.7. Muscle cross-sectional area (CSA) and indices of bone strength at the distal tibia and tibia shaft were measured by peripheral quantitative computed tomography. Muscle CSA was multiplied by tibia length to obtain muscle-bending moment (MBM), a surrogate of torque. Plantar flexor components of the lower-extremity motor scores (pf-LEMS) were used as clinical measures of muscle function. Pearson's correlations (r) were used to determine the strength of relationships. Results: Correlations were found between MBM and indices of bone strength at the distal tibia and tibia shaft (r¼0.44-0.56), as well as between pf-LEMS and indices of bone strength at the distal tibia and tibia shaft (r¼0.37-0.71). pf-LEMS had a stronger association with bone variables at the distal tibia compared with MBM (r¼0.6 vs r¼0.4). All relationships between muscle and bone remained significant when controlling for the duration of injury.Conclusion: It appears that lower limb muscle size and function are more strongly correlated with bone strength indices at the distal tibia than at the tibia shaft among individuals with SCI. The relationships between muscle and bone are clinically important, as muscle CSA and strength (motor scores) are potentially amenable to rehabilitation intervention(s).

Effect of whole-body vibration on lower-limb EMG activity in subjects with and without spinal cord injury

“…6 Our results therefore suggest that the clinical application of WBV to prevent or treat musculoskeletal degradation after SCI warrants further investigation.…”

“…5 The muscle-bone theory suggests that declines in muscle and bone mass could be closely linked. 6 Therefore, rehabilitation interventions that can counteract muscle atrophy may also have significant clinical implications for limiting osteoporosis. Current rehabilitation interventions including functional electrical stimulation (FES) cycle ergometry, body-weight-supported treadmill training, and passive standing have failed to demonstrate substantial sustained increases in lower extremity muscle and bone mass among patients with chronic SCI.…”

Muscle Density and Bone Quality of the Distal Lower Extremity Among Individuals with Chronic Spinal Cord Injury

“…Secondary analyses using baseline data from this cohort study have been previously published. 3,13,41,51 Independent samples t tests were performed to compare bone quality and muscle outcomes in participants with chronic SCI grouped by sex (men vs women) and AIS classification (AIS A/B vs AIS C/D). Pearson's correlations were performed to determine the strength of the associations between muscle density and indices of bone quality.…”

“…13,40 However, neither study measured muscle density (a surrogate of fatty infiltration when evaluating the functional muscle-bone unit). Fatty infiltration of muscle is common after SCI 1,16,37 and may affect muscle function or the muscle-bone unit, but the association between muscle density and bone quality indices at the tibia in individuals with chronic SCI is unclear.…”

“…8,14,31,32 Decreases in muscle CSA Muscle Density and Bone Quality of the Distal Lower Extremity Among Individuals with Chronic Spinal Cord Injury S pinal cord injury (SCI) is associated with sublesional muscle atrophy, [1][2][3] changes in muscle fiber type, 4,5 reductions in hip and knee region bone mineral density (BMD), [6][7][8] and increased central and regional adiposity after injury. 9,10 Adverse changes in muscle and bone health in individuals with SCI contribute to an increased risk of osteoporosis, [11][12][13] fragility fractures, 14 and endocrine-metabolic disease (eg, diabetes, dyslipidemia, heart disease). [15][16][17] Crosssectional studies have shown a higher prevalence of lower extremity fragility fractures among individuals with SCI ranging from 1% to 34%.…”