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

Spinal Cord Injury Associated Disease of the Skeleton, an Unresolved Problem with Need for Multimodal Interventions

Spinal cord injury is associated with skeletal unloading, sedentary behavior, decreases in skeletal muscle mass, and exercise intolerance, which results in rapid and severe bone loss. To date, monotherapy with physical interventions such as weight-bearing in standing frames, computer-controlled electrically stimulated cycling and ambulation exercise, and low-intensity vibration are unsuccessful in maintaining bone density after SCI. Strategies to maintain bone density with commonly used osteoporosis medications also fail to provide a significant clinical benefit, potentially due to a unique pathology of bone deterioration in SCI. In this review, the available data is discussed on evaluating and monitoring bone loss, fracture, and physical and pharmacological therapeutic approaches to SCI-associated disease of the skeleton. The treatment of SCI-associated disease of the skeleton, the implications for clinical management, and areas of need are considered for future investigation.

Effectiveness of FES-supported leg exercise for promotion of paralysed lower limb muscle and bone health-a systematic review

Leg exercises through standing, cycling and walking with/without FES may be used to preserve lower limb muscle and bone health in persons with physical disability due to SCI. This study sought to examine the effectiveness of leg exercises on bone mineral density and muscle cross-sectional area based on their clinical efficacy in persons with SCI. Several literature databases were searched for potential eligible studies from the earliest return date to January 2022. The primary outcome targeted was the change in muscle mass/volume and bone mineral density as measured by CT, MRI and similar devices. Relevant studies indicated that persons with SCI that undertook FES- and frame-supported leg exercise exhibited better improvement in muscle and bone health preservation in comparison to those who were confined to frame-assisted leg exercise only. However, this observation is only valid for exercise initiated early (i.e., within 3 months after injury) and for ≥30 min/day for ≥ thrice a week and for up to 24 months or as long as desired and/or tolerable. Consequently, apart from the positive psychological effects on the users, leg exercise may reduce fracture rate and its effectiveness may be improved if augmented with FES.

Exploring changes in bone mass in individuals with a chronic spinal cord injury

People experience rapid bone loss shortly after a spinal cord injury (SCI), but the long-term bone changes are yet to be confirmed. This study showed that trabecular bone may have reached a steady state, whereas cortical bone continued to decline in people with a chronic SCI (mean time post injury: 15.5 ± 10 years).

INTRODUCTION

(1) To explore changes in bone [primary measure: trabecular volumetric bone mineral density (vBMD); secondary measures: cortical vBMD, cortical thickness, cortical cross-sectional area (CSA), and polar moment of inertia] over 2 years in individuals with a chronic spinal cord injury (SCI). (2) To explore whether muscle density changes were potential correlates of the observed bone changes.

METHODS

This study is a secondary data analysis of a prospective, observational study involving 70 people with a chronic SCI (≥ 2 years post injury). The study included 4 strata of participants with diverse impairments: (1) Paraplegia (T1-T12) motor complete American Spinal Injury Association Impairment Scale (AIS) A/B (n = 23), (2) Paraplegia motor incomplete AIS C/D (n = 11), (3) Tetraplegia (C2-C8) AIS A/B (n = 22), and (4) Tetraplegia AIS C/D (n = 14). Peripheral quantitative computed tomography scans were taken at the 4% (distal tibia), 38% (diaphyseal tibia), and 66% (muscle cross-sectional area) tibia sites by measuring from the distal to proximal tibia starting at the inferior border of the medial malleolus. The tibia sites were assessed annually over a span of 2 years. Comparisons were made using a paired-samples t test and simple linear regression was used to adjust for sex, time post injury, and bisphosphonate use.

RESULTS

We observed no changes in trabecular vBMD at the 4% tibia site, but there was a statistically significant decline in cortical vBMD, cortical thickness, and CSA at the 38% tibia site. Changes in muscle density were not associated with the decreases observed in cortical bone.

CONCLUSION

Our findings suggest that individuals with chronic SCI (mean duration of injury: 15.5 ± 10 years) may have reached a plateau in bone loss with respect to trabecular bone, but cortical bone loss can continue well into the chronic stages.

Neurogenic Obesity and Skeletal Pathology in Spinal Cord Injury

Spinal cord injury (SCI) results in dramatic changes in body composition, with lean mass decreasing and fat mass increasing in specific regions that have important cardiometabolic implications. Accordingly, the recent Consortium for Spinal Cord Medicine (CSCM) released clinical practice guidelines for cardiometabolic disease (CMD) in SCI recommending the use of compartmental modeling of body composition to determine obesity in adults with SCI. This recommendation is guided by the fact that fat depots impact metabolic health differently, and in SCI adiposity increases around the viscera, skeletal muscle, and bone marrow. The contribution of skeletal muscle atrophy to decreased lean mass is self-evident, but the profound loss of bone is often less appreciated due to methodological considerations. General-population protocols for dual-energy x-ray absorptiometry (DXA) disregard assessment of the sites of greatest bone loss in SCI, but the International Society for Clinical Densitometry (ISCD) recently released an official position on the use of DXA to diagnose skeletal pathology in SCI. In this review, we discuss the recent guidelines regarding the evaluation and monitoring of obesity and bone loss in SCI. Then we consider the possible interactions of obesity and bone, including emerging evidence suggesting the possible influence of metabolic, autonomic, and endocrine function on bone health in SCI.

Prevention and management of osteoporosis and osteoporotic fractures in persons with a spinal cord injury or disorder: A systematic scoping review

Objectives: The primary objective was to review the literature regarding methodologies to assess fracture risk, to prevent and treat osteoporosis and to manage osteoporotic fractures in SCI/D.Study Design: Scoping review.Settings/Participants: Human adult subjects with a SCI/D.Outcome measures: Strategies to identify persons with SCI/D at risk for osteoporotic fractures, nonpharmacological and pharmacological therapies for osteoporosis and management of appendicular fractures.Results: 226 articles were included in the scoping review. Risk of osteoporotic fractures in SCI is predicted by a combination of DXA-defined low BMD plus clinical and demographic characteristics. Screening for secondary causes of osteoporosis, in particular hyperparathyroidism, hyperthyroidism, vitamin D insufficiency and hypogonadism, should be considered. Current antiresorptive therapies for treatment of osteoporosis have limited efficacy. Use of surgery to treat fractures has increased and outcomes are good and comparable to conservative treatment in most cases. A common adverse event following fracture was delayed healing.Conclusions: Most of the research in this area is limited by small sample sizes, weak study designs, and significant variation in populations studied. Future research needs to address cohort definition and study design issues.

Peripheral Quantitative Computed Tomography: Review of Evidence and Recommendations for Image Acquisition, Analysis, and Reporting, Among Individuals With Neurological Impairment

In 2015, the International Society for Clinical Densitometry (ISCD) position statement regarding peripheral quantitative computed tomography (pQCT) did not recommend routine use of pQCT, in clinical settings until consistency in image acquisition and analysis protocols are reached, normative studies conducted, and treatment thresholds identified. To date, the lack of consensus-derived recommendations regarding pQCT implementation remains a barrier to implementation of pQCT technology. Thus, based on description of available evidence and literature synthesis, this review recommends the most appropriate pQCT acquisition and analysis protocols for clinical care and research purposes, and recommends specific measures for diagnosis of osteoporosis, assigning fracture risk, and monitoring osteoporosis treatment effectiveness, among patients with neurological impairment. A systematic literature search of MEDLINE, EMBASE^©, CINAHL, and PubMed for available pQCT studies assessing bone health was carried out from inception to August 8th, 2017. The search was limited to individuals with neurological impairment (spinal cord injury, stroke, and multiple sclerosis) as these groups have rapid and severe regional declines in bone mass. Of 923 references, we identified 69 that met review inclusion criteria. The majority of studies (n = 60) used the Stratec XCT 2000/3000 pQCT scanners as reflected in our evaluation of acquisition and analysis protocols. Overall congruence with the ISCD Official Positions was poor. Only 11% (n = 6) studies met quality reporting criteria for image acquisition and 32% (n = 19) reported their data analysis in a format suitable for reproduction. Therefore, based on current literature synthesis, ISCD position statement standards and the authors' expertise, we propose acquisition and analysis protocols at the radius, tibia, and femur sites using Stratec XCT 2000/3000 pQCT scanners among patients with neurological impairment for clinical and research purposes in order to drive practice change, develop normative datasets and complete future meta-analysis to inform fracture risk and treatment efficacy evaluation.

MRI measures of fat infiltration in the lower extremities following motor incomplete spinal cord injury: reliability and potential implications for muscle activation

Muscle fat infiltration (MFI) is an expected consequence of incomplete spinal cord injury (iSCI). The MFI magnitude may have clinical value in determining functional recovery. However, there is a lack of understanding of how MFI relates to the volitional muscle activity in people with motor incomplete spinal cord injury (iSCI). Five iSCI and 5 uninjured age-matched control subjects participated in the study. In this preliminary study, we established the reliability of MFI quantification of select lower extremity muscles across different raters. Secondly, we assessed the magnitude and distribution of MFI in the lower legs of iSCI and uninjured control participants. Thirdly, we explored the relationship between MFI in the plantar flexor muscles and the ability to volitionally activate these muscles. High levels of inter-rater reliability were observed. The iSCI group had significantly elevated and a vastly different MFI distribution in the lower leg muscles compared to healthy controls. MFI was negatively correlated with volitional activation in iSCI. Our preliminary results sanction the importance of lower extremity MFI quantification as a potential measure in determining the functional outcomes in iSCI, and the subsequent pathological sequelae.

Exercise, muscle, and the applied load-bone strength balance

A fracture occurs when the applied load is greater than the bone can withstand. Clinical practice guidelines for the management of osteoporosis include recommendations for exercise; one of the few therapies where the proposed anti-fracture mechanisms that include effects on both bone strength and applied loads, where applied loads can come in the form of a fall, externally applied loads, body weight, or muscle forces. The aim of this review is to provide an overview of the clinical evidence pertaining to the potential efficacy of exercise for preventing fractures in older adults, including its direct effects on outcomes along the causal pathway to fractures (e.g., falls, posture, bone strength) and the indirect effects on muscle or the muscle-bone relationship. The evidence is examined as it pertains to application in clinical practice. Considerations for future research are discussed, such as the need for trials in individuals with low bone mass or students that evaluate whether changes in muscle mediate changes in bone. Future trials should also consider adequacy of calorie or protein intake, the confounding effect of exercise-induced weight loss, or the most appropriate therapeutic goal (e.g., strength, weight bearing, or hypertrophy) and outcome measures (e.g., fracture, disability, cost-effectiveness).

Measuring muscle and bone in individuals with neurologic impairment; lessons learned about participant selection and pQCT scan acquisition and analysis

Peripheral quantitative computed tomography (pQCT) can be used to examine bone strength outcomes and muscle size and fatty infiltration. Our research team and others have used it to examine bone loss after spinal cord injury (SCI). However, the high prevalence of restricted lower extremity range of motion, spasticity, edema, excessive muscle atrophy, or severe osteoporosis necessitates changes to standard protocols for screening, positioning during scan acquisition, and analysis methods. This manuscript outlines the challenges that we experienced using pQCT in individuals with SCI, and provides solutions, ones that may also be applicable when using pQCT in individuals with other chronic conditions or in older adults. Suggestions for participant screening, positioning individuals for scanning while in a wheelchair, scan site selection, need for attendant assistance, and considerations in the presence of secondary complications, such as contracture, spasticity, and paralysis, are presented. In the presence of very low bone mineral density or severe muscle atrophy, the default analysis modes provided by the manufacturer may not provide valid estimates of bone or muscle indices; we propose alternates. We have used watershed segmentation methods to determine muscle size and density based on lower precision error compared to threshold-based edge-detection segmentation, particularly for adults with SCI, where more fatty infiltration was present. By presenting our "lessons learned," we hope to reduce the learning curve for researchers using pQCT in the future.

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

BACKGROUND

Understanding the related fates of muscle density and bone quality after chronic spinal cord injury (SCI) is an important initial step in determining endocrine-metabolic risk.

OBJECTIVE

To examine the associations between muscle density and indices of bone quality at the distal lower extremity of adults with chronic SCI.

METHODS

A secondary data analysis was conducted in 70 adults with chronic SCI (C2-T12; American Spinal Injury Association Impairment Scale [AIS] A-D; ≥2 years post injury). Muscle density and cross-sectional area (CSA) and bone quality indices (trabecular bone mineral density [TbBMD] at the distal tibia [4% site] and cortical thickness [CtTh], cortical area [CtAr], cortical BMD [CtBMD], and polar moment of inertia [PMI] at the tibial shaft [66% site]) were measured using peripheral quantitative computed tomography. Calf lower extremity motor score (cLEMS) was used as a clinical measure of muscle function. Multivariable linear regression analyses were performed to determine the strength of the muscle-bone associations after adjusting for confounding variables (sex, impairment severity [AIS A/B vs AIS C/D], duration of injury, and wheelchair use).

RESULTS

Muscle density was positively associated with TbBMD (b = 0.85 [0.04, 1.66]), CtTh (b = 0.02 [0.001, 0.034]), and CtBMD (b = 1.70 [0.71, 2.69]) (P < .05). Muscle CSA was most strongly associated with CtAr (b = 2.50 [0.12, 4.88]) and PMI (b = 731.8 [161.7, 1301.9]) (P < .05), whereas cLEMS was most strongly associated with TbBMD (b = 7.69 [4.63, 10.76]) (P < .001).

CONCLUSIONS

Muscle density and function were most strongly associated with TbBMD at the distal tibia in adults with chronic SCI, whereas muscle size was most strongly associated with bone size and geometry at the tibial shaft.

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

OBJECTIVE

Traumatic spinal cord injury (SCI) results in substantial reductions in lower extremity muscle mass and bone mineral density below the level of the lesion. Whole-body vibration (WBV) has been proposed as a means of counteracting or treating musculoskeletal degradation after chronic motor complete SCI. To ascertain how WBV might be used to augment muscle and bone mass, we investigated whether WBV could evoke lower extremity electromyography (EMG) activity in able-bodied individuals and individuals with SCI, and which vibration parameters produced the largest magnitude of effect.

METHODS

Ten male subjects participated in the study, six able-bodied and four with chronic SCI. Two different manufacturers' vibration platforms (WAVE(®) and Juvent™) were evaluated. The effects of vibration amplitude (0.2, 0.6 or 1.2 mm), vibration frequency (25, 35, or 45 Hz), and subject posture (knee angle of 140°, 160°, or 180°) on lower extremity EMG activation were determined (not all combinations of parameters were possible on both platforms). A novel signal processing technique was proposed to estimate the power of the EMG waveform while minimizing interference and artifacts from the plate vibration.

RESULTS

WBV can elicit EMG activity among subjects with chronic SCI, if appropriate vibration parameters are employed. The amplitude of vibration had the greatest influence on EMG activation, while the frequency of vibration had lesser but statistically significant impact on the measured lower extremity EMG activity.

CONCLUSION

These findings suggest that WBV with appropriate parameters may constitute a promising intervention to treat musculoskeletal degradation after chronic SCI.

Exploring the determinants of fracture risk among individuals with spinal cord injury

In this cross-sectional study, we found that areal bone mineral density (aBMD) at the knee and specific tibia bone geometry variables are associated with fragility fractures in men and women with chronic spinal cord injury (SCI).

INTRODUCTION

Low aBMD of the hip and knee regions have been associated with fractures among individuals with chronic motor complete SCI; however, it is unclear whether these variables can be used to identify those at risk of fracture. In this cross-sectional study, we examined whether BMD and geometry measures are associated with lower extremity fragility fractures in individuals with chronic SCI.

METHODS

Adults with chronic [duration of injury ≥ 2 years] traumatic SCI (C1-L1 American Spinal Cord Injury Association Impairment Scale A-D) reported post injury lower extremity fragility fractures. Dual-energy X-ray absorptiometry (DXA) was used to measure aBMD of the hip, distal femur, and proximal tibia regions, while bone geometry at the tibia was assessed using peripheral quantitative computed tomography (pQCT). Logistic regression and univariate analyses were used to identify whether clinical characteristics or bone geometry variables were associated with fractures.

RESULTS

Seventy individuals with SCI [mean age (standard deviation [SD]), 48.8 (11.5); 20 females] reported 19 fragility fractures. Individuals without fractures had significantly greater aBMD of the hip and knee regions and indices of bone geometry. Every SD decrease in aBMD of the distal femur and proximal tibia, trabecular volumetric bone mineral density, and polar moment of inertia was associated with fracture prevalence after adjusting for motor complete injury (odds ratio ranged from 3.2 to 6.1).

CONCLUSION

Low knee aBMD and suboptimal bone geometry are significantly associated with fractures. Prospective studies are necessary to confirm the bone parameters reported to predict fracture risk in individuals with low bone mass and chronic SCI.

Vascular elasticity and grip strength are associated with bone health of the hemiparetic radius in people with chronic stroke: implications for rehabilitation

BACKGROUND

People with stroke often have increased bone loss and fracture rate. Increasing evidence has demonstrated a link between cardiovascular health and bone loss in other patient populations.

OBJECTIVE

The study objectives were: (1) to compare the bone density and geometry of the radius diaphysis on the left and right sides in people with chronic stroke and people who were matched for age (control participants) and (2) to examine the relationship between the bone strength index at the hemiparetic radius diaphysis and vascular health in people with chronic stroke.

DESIGN

This was a case-control study.

METHODS

The radius diaphysis on both sides was scanned with peripheral quantitative computed tomography in 65 participants with chronic stroke and 34 control participants. Large-artery and small-artery elasticity indexes were evaluated with a cardiovascular profiling system.

RESULTS

The paretic radius diaphysis had significantly lower values for cortical bone mineral density, cortical thickness, cortical area, and the bone strength index but a larger marrow cavity area than the nonparetic radius diaphysis in participants with chronic stroke, whereas no bone measurement showed a significant side-to-side difference in control participants. Multiple regression analyses showed that the large-artery elasticity index and grip strength remained significantly associated with the bone strength index at the hemiparetic radius diaphysis after controlling for age, sex, time since stroke diagnosis, body mass index, and physical activity (R(2)=.790).

LIMITATIONS

This study was cross-sectional and could not establish causality. The radius diaphysis is not the most common site of fracture after stroke.

CONCLUSIONS

Both the integrity of the vasculature and muscle strength were significantly associated with the bone strength index at the hemiparetic radius diaphysis in participants with chronic stroke. The results may be useful in guiding rehabilitative programs for enhancing bone health in the paretic arm after stroke.

Relative impact of neuromuscular and cardiovascular factors on bone strength index of the hemiparetic distal radius epiphysis among individuals with chronic stroke

The objective of this study was to examine the associations of neuromuscular and cardiovascular impairments with the bone strength index of the hemiparetic distal radius epiphysis in chronic stroke survivors. The results showed that grip strength is the most predominant predictor of the bone strength index.

INTRODUCTION

The purpose of the study was to examine the associations of neuromuscular and cardiovascular impairments with the bone strength index of the hemiparetic distal radius epiphysis in chronic stroke survivors.

METHODS

Sixty-five chronic stroke survivors and 34 healthy control subjects underwent scanning of the distal radius epiphyseal site on both sides using peripheral quantitative computed tomography to measure trabecular volumetric bone mineral density (vBMD) (mg/cm(3)), total vBMD (mg/cm(3)), total area (mm(2)), and compressive bone strength index (cBSI) (g(2)/cm(4)). Various indicators of neuromuscular (grip strength, spasticity) and cardiovascular function (vascular elasticity, oxygen consumption during 6-min walk test) were evaluated.

RESULTS

Analysis of variance revealed a significant main effect of side (p < 0.001) and group × side interaction (p < 0.05) for total BMC, total vBMD, trabecular vBMD, and cBSI (p < 0.05), with the stroke group showing greater side-to-side difference in these variables. However, no significant side-to-side difference in total area was detected in either group (p > 0.05). Sex-specific analysis yielded similar results. Multiple regression analyses revealed that the cBSI of the hemiparetic distal radius epiphysis had a stronger association with neuromuscular factors than cardiovascular factors. Overall, grip strength was the strongest determinant of the cBSI of the hemiparetic distal radius epiphysis (p < 0.01).

CONCLUSIONS

Muscle weakness is the most predominant determinant of cBSI in the hemiparetic distal radius epiphysis among chronic stroke patients. Future studies should investigate the efficacy of different muscle-strengthening strategies in enhancing bone strength of this skeletal site in the chronic stroke population.