Trabecular bone microarchitecture is deteriorated in men with spinal cord injury

The Efficacy of Body-Weight Supported Treadmill Training and Neurotrophin-Releasing Scaffold in Minimizing Bone Loss Following Spinal Cord Injury

Spinal cord injury (SCI) can lead to significant bone loss below the level of the lesion increasing the risk of fracture and increased morbidity. Body-weight-supported treadmill training (BWSTT) and transplantation strategies using neurotrophins have been shown to improve motor function after SCI. While rehabilitation training including BWSTT has also been effective in reducing bone loss post-SCI, the effects of transplantation therapies in bone restoration are not fully understood. Furthermore, the effects of a combinational treatment strategy on bone post-SCI also remain unknown. The aim of this study was to determine the effect of a combination therapy including transplantation of scaffold-releasing neurotrophins and BWSTT on the forelimb and hindlimb bones of a T9-T10 contused SCI animals. Humerus and tibia bones were harvested for Micro-CT scanning and a three-point bending test from four animal groups, namely injury, BWSTT (injury with BWSTT), scaffold (injury with scaffold-releasing neurotrophins), and combinational (injury treated with scaffold-releasing neurotrophins and BWSTT). BWSTT and combinational groups reported higher biomechanical properties in the tibial bone (below injury level) and lower biomechanical properties in the humerus bone (above injury level) when compared to the injury and scaffold groups. Studied structural parameters, including the cortical thickness and bone volume/tissue volume (BV/TV) were also higher in the tibia and lower in the humerus bones of BWSTT and combinational groups when compared to the injury and scaffold groups. While no significant differences were observed, this study is the first to report the effects of a combinational treatment strategy on bone loss in contused SCI animals and can help guide future interventions.

Exercise prescription for persons with spinal cord injury: a review of physiological considerations and evidence-based guidelines

Persons with spinal cord injury (SCI) experience gains in fitness, physical and mental health from regular participation in exercise and physical activity. Due to changes in physiological function of the cardiovascular, nervous, and muscular systems, general population physical activity guidelines and traditional exercise prescription methods are not appropriate for the SCI population. Exercise guidelines specific to persons with SCI recommend progressive training beginning at 20 min of moderate to vigorous intensity aerobic exercise twice per week transitioning to 30 min three times per week, with strength training of the major muscle groups two times per week. These population-specific guidelines were designed considering the substantial barriers to physical activity for persons with SCI and can be used to frame an individual exercise prescription. Rating of perceived exertion (i.e., perceptually regulated exercise) is a practical way to indicate moderate to vigorous intensity exercise in community settings. Adapted exercise modes include arm cycle ergometry, hybrid arm-leg cycling, and recumbent elliptical equipment. Body weight-supported treadmill training and other rehabilitation modalities may improve some aspects of health and fitness for people with SCI if completed at sufficient intensity. Disability-specific community programs offer beneficial opportunities for persons with SCI to experience quality exercise opportunities but are not universally available.

Employment of Neuromuscular Electrical Stimulation to Examine Muscle and Bone Qualities after Spinal Cord Injury

(1) Background: Resource intensive imaging tools have been employed to examine muscle and bone qualities after spinal cord injury (SCI). We tested the hypothesis that surface neuromuscular electrical stimulation (NMES) amplitude can be used to examine knee extensor muscle quality, distal femur and proximal tibia bone mineral density (BMD) in persons with SCI. (2) Methods: Seventeen persons (2 women) with chronic SCI participated in three weeks of NMES-resistance training twice weekly of 4 sets of 10 repetitions. Participants were classified according to the current amplitude (>100 mA) and the number of repetitions (>70 reps) of leg extension into greater (n = 8; 1 woman; group A) and lower (n = 9; 1 woman; group B) musculoskeletal qualities. Magnetic resonance imaging, dual energy x-ray absorptiometry, isometric peak torque, Modified Ashworth and Penn spasm frequency scales were conducted. (3) Results: In between group comparisons, current amplitude was lower (38−46%) in group A. Whole (27−32%; p = 0.02), absolute (26−33%, p = 0.02) thigh muscle and absolute knee extensor muscle cross-sectional areas (22−33%, p = 0.04) were greater in group A. Right distal femur (24%; p = 0.08) and proximal tibia (29%; p = 0.03) BMDs were lower in group B, and peak isometric torque (p < 0.01), extensor spasticity scorers (p = 0.04) and muscle spasm scores (p = 0.002) were significantly higher in group A. Regression models revealed that amplitude of current, repetitions and body weight can accurately predict musculoskeletal qualities in persons with SCI. (4) Conclusions: Surface NMES amplitude and repetitions of leg extension differentiated between SCI survivors with greater versus lower musculoskeletal qualities. The study may shed the light on the interplay between muscle and bone in persons with SCI.

Osteopenia in a Mouse Model of Spinal Cord Injury: Effects of Age, Sex and Motor Function

Simple Summary

In the first two years following spinal cord injury, people lose up to 50% of bone below the injury. This injury-induced bone loss significantly affects rehabilitation and leaves people vulnerable to fractures and post-fracture complications, including lung and urinary tract infections, blood clots in the veins, and depression. Unfortunately, little is known about the factors driving this bone loss. In fact, even though we know that injury, age, and sex independently increase bone loss, there have been no studies looking at the cumulative effects of these variables. People with spinal injury are aging, and the age at which injuries occur is increasing. It is essential to know whether these factors together will further compromise bone. To examine this, we assessed bone loss in young and old, male and female mice after spinal injury. As expected, we found that aging alone decreased motor activity and bone volume. Spinal injury also reduced bone volume, but it did not worsen the effects of age. Instead, injury effects appeared related to reduced rearing activity. The data suggest that although partial weight-bearing does not reduce bone loss after spinal cord injury, therapies that put full weight on the legs may be clinically effective.

Abstract

After spinal cord injury (SCI), 80% of individuals are diagnosed with osteopenia or osteoporosis. The dramatic loss of bone after SCI increases the potential for fractures 100-fold, with post-fracture complications occurring in 54% of cases. With the age of new SCI injuries increasing, we hypothesized that a SCI-induced reduction in weight bearing could further exacerbate age-induced bone loss. To test this, young (2–3 months) and old (20–30 months) male and female mice were given a moderate spinal contusion injury (T9–T10), and recovery was assessed for 28 days (BMS, rearing counts, distance traveled). Tibial trabecular bone volume was measured after 28 days with ex vivo microCT. While BMS scores did not differ across groups, older subjects travelled less in the open field and there was a decrease in rearing with age and SCI. As expected, aging decreased trabecular bone volume and cortical thickness in both old male and female mice. SCI alone also reduced trabecular bone volume in young mice, but did not have an additional effect beyond the age-dependent decrease in trabecular and cortical bone volume seen in both sexes. Interestingly, both rearing and total activity correlated with decreased bone volume. These data underscore the importance of load and use on bone mass. While partial weight-bearing does not stabilize/reverse bone loss in humans, our data suggest that therapies that simulate complete loading may be effective after SCI.

Effects of Different Types of Mechanical Loading on Trabecular Bone Microarchitecture in Rats

Mechanical loading is generally considered to have a positive impact on the skeleton; however, not all types of mechanical loading have the same beneficial effect. Many researchers have investigated which types of mechanical loading are more effective for improving bone mass and strength. Among the various mechanical loads, high-impact loading, such as jumping, appears to be more beneficial for bones than low-impact loadings such as walking, running, or swimming. Therefore, the different forms of mechanical loading exerted by running, swimming, and jumping exercises may have different effects on bone adaptations. However, little is known about the relationships between the types of mechanical loading and their effects on trabecular bone structure. The purpose of this article is to review the recent reports on the effects of treadmill running, jumping, and swimming on the trabecular bone microarchitecture in small animals. The effects of loading on trabecular bone architecture appear to differ among these different exercises, as several reports have shown that jumping increases the trabecular bone mass by thickening the trabeculae, whereas treadmill running and swimming add to the trabecular bone mass by increasing the trabecular number, rather than the thickness. This suggests that different types of exercise promote gains in trabecular bone mass through different architectural patterns in small animals.

Measuring tibial hemodynamics and metabolism at rest and after exercise using near-infrared spectroscopy

The bone vascular system is important, yet evaluation of bone hemodynamics is difficult and expensive. This study evaluated the utility and reliability of near-infrared spectroscopy (NIRS), a portable and relatively inexpensive device, in measuring tibial hemodynamics and metabolic rate. Eleven participants were tested twice using post-occlusive reactive hyperemia technique with the NIRS probes placed on the tibia and the medial gastrocnemius (MG) muscle. Measurements were made at rest and after 2 levels of plantarflexion exercise. The difference between oxygenated and deoxygenated hemoglobin signal could be reliably measured with small coefficients of variation (CV; range 5.7-9.8%) and high intraclass correlation coefficients (ICC; range 0.73-0.91). Deoxygenated hemoglobin rate of change, a potential marker for bone metabolism, also showed good reliability (CV range 7.5-9.8%, ICC range 0.90-0.93). The tibia was characterized with a much slower metabolic rate compared with MG (p < 0.001). While exercise significantly increased MG metabolic rate in a dose-dependent manner (all p < 0.05), no changes were observed for the tibia after exercise compared with rest (all p > 0.05). NIRS is a suitable tool for monitoring hemodynamics and metabolism in the tibia. However, the local muscle exercise protocol utilized in the current study did not influence bone hemodynamics or metabolic rate. Novelty: NIRS can be used to monitor tibial hemodynamics and metabolism with good reliability. Short-duration local muscle exercise increased metabolic rate in muscle but not in bone. High level of loading and exercise volume may be needed to elicit measurable metabolic changes in bone.

Heterogeneity in microstructural deterioration following spinal cord injury

BACKGROUND

Modelling and remodelling adapt bone morphology to accommodate strains commonly encountered during loading. If strains exceed a threshold threatening fracture, modelling-based bone formation increases bone volume reducing these strains. If unloading reduces strains below a threshold that inhibits resorption, increased remodelling-based bone resorption reduces bone volume restoring strains, but at the price of compromised bone volume and microstructure. As weight-bearing regions are adapted to greater strains, we hypothesized that microstructural deterioration will be more severe than at regions commonly adapted to low strains following spinal cord injury.

METHODS

We quantified distal tibial, fibula and radius volumetric bone mineral density (vBMD) using high-resolution peripheral quantitative computed tomography in 31 men, mean age 43.5 years (range 23.5-75.0), 12 with tetraplegia and 19 with paraplegia of 0.7 to 18.6 years duration, and 102 healthy age- and sex-matched controls. Differences in morphology relative to controls were expressed as standardized deviation (SD) scores (mean ± SD). Standardized between-region differences in vBMD were expressed as SDs (95% confidence intervals, CI).

RESULTS

Relative to controls, men with tetraplegia had deficits in total vBMD of -1.72 ± 1.38 SD at the distal tibia (p < 0.001) and - 0.68 ± 0.69 SD at distal fibula (p = 0.041), but not at the distal radius, despite paralysis. Deficits in men with paraplegia were -2.14 ± 1.50 SD (p < 0.001) at the distal tibia and -0.83 ± 0.98 SD (p = 0.005) at the distal fibula while distal radial total vBMD was 0.23 ± 1.02 (p = 0.371), not significantly increased, despite upper limb mobility. Comparing regions, in men with tetraplegia, distal tibial total vBMD was 1.04 SD (95%CI 0.07, 2.01) lower than at the distal fibula (p = 0.037) and 1.51 SD (95%CI 0.45, 2.57) lower than at the distal radius (p = 0.007); the latter two sites did not differ from each other. Results were similar in men with paraplegia, but total vBMD at the distal fibula was 1.06 SD (95%CI 0.35, 1.77) lower than at the distal radius (p = 0.004).

CONCLUSION

Microarchitectural deterioration following spinal cord injury is heterogeneous, perhaps partly because strain thresholds regulating the cellular activity of mechano-transduction are region specific.

Stiffness and Strength Predictions From Finite Element Models of the Knee are Associated with Lower-Limb Fractures After Spinal Cord Injury

Spinal cord injury (SCI) is associated with bone fragility and fractures around the knee. The purpose of this investigation was to validate a computed tomography (CT) based finite element (FE) model of the proximal tibia and distal femur under biaxial loading, and to retrospectively quantify the relationship between model predictions and fracture incidence. Twenty-six cadaveric tibiae and femora (n = 13 each) were loaded to 300 N of compression, then internally rotated until failure. FE predictions of torsional stiffness (K) and strength (T_ult) explained 74% (n = 26) and 93% (n = 7) of the variation in experimental measurements, respectively. Univariate analysis and logistic regression were subsequently used to determine if FE predictions and radiographic measurements from CT and dual energy X-ray absorptiometry (DXA) were associated with prevalent lower-limb fracture in 50 individuals with SCI (n = 14 fractures). FE and CT measures, but not DXA, were lower in individuals with fracture. FE predictions of T_ult at the tibia demonstrated the highest odds ratio (4.98; p = 0.006) and receiver operating characteristic (0.84; p = 0.008) but did not significantly outperform other metrics. In conclusion, CT-based FE model predictions were associated with prevalent fracture risk after SCI; this technique could be a powerful tool in future clinical research.

Zoledronic Acid Attenuates Early Bone Loss at Forearm in Patients with Acute Spinal Cord Injury

STUDY DESIGN

Randomized controlled trial.

OBJECTIVES

To study the magnitude of bone loss at forearm in persons with acute spinal cord injury (SCI) & the effect of early administration of Zoledronic acid on its' prevention.

SETTINGS

Sawai Man Singh Medical College, Jaipur, India.

METHODS

Sixty patients with acute SCI were randomized either to receive standard medical and nursing care or Zoledronic acid infusion in combination with standard medical and nursing care. Areal bone mineral density (aBMD) was measured at the forearm (radius + ulna) once patients were medically stable using Dual Energy X-Ray Absorptiometry (DXA) at baseline and at 3, 6 and 12 months.

RESULTS

Significant differences in aBMD was found between the control & Zoledronic acid group at 1/3 forearm (- 0.064; 95% CI - 0.092 to - 0.036, p = 0.001), mid forearm (- 0.059; 95% CI - 0.084 to - 0.034, p = 0.001), UD forearm (- 0.048; 95% CI - 0.097 to 0.001, p = 0.016) and total forearm (- 0.048; 95% CI - 0.088 to - 0.008, p = 0.021) at 1 year in the paraplegic patients with SCI. Similar significant difference was also observed at 1/3 forearm (- 0.046; 95% CI - 0.073 to - 0.019, p = 0.002), mid forearm (- 0.063; 95% CI - 0.088 to - 0.037, p < 0.0001), UD forearm (- 0.084; 95% CI - 0.101 to - 0.067, p < 0.0001) and total forearm (- 0.115; 95% CI - 0.132 to - 0.097, p < 0.0001) respectively at 1 year in the quadriplegic patients with SCI. Significant differences in aBMD between the groups at 6 months post infusion was also observed at these sites in quadriplegic patients. [1/3 forearm - 0.022; 95% CI - 0.039 to - 0.005; p = 0.015, Mid forearm - 0.023; 95% CI - 0.042 to - 0.004; p = 0.019, UD forearm - 0.041; 95% CI - 0.055 to - 0.027; p < 0.0001 and Total forearm - 0.049; 95%CI - 0.062 to - 0.036; p < 0.0001]. Bone loss was reduced in the Zoledronic acid treated group compared to the standard treatment group in both paraplegic and quadriplegic patients.

CONCLUSION

Single dose of 5mg intravenous Zoledronic acid is an effective treatment in preventing bone loss at the forearm for 12 months following acute spinal cord injury.

Trabecular Bone Score at the Distal Femur and Proximal Tibia in Individuals With Spinal Cord Injury

Rapid declines in bone mineral density (BMD) at the knee after spinal cord injury (SCI) are associated with an increased risk of fracture. Evaluation of bone quality using the trabecular bone score (TBS) may provide a complimentary measure to BMD assessment to examine bone health and fracture risk after SCI. The purpose of this study was to assess bone mineral density (BMD) and trabecular bone score (TBS) at the knee in individuals with and without SCI. Nine individuals with complete SCI (mean time since SCI 2.9 ± 3.8 yr) and 9 non-SCI controls received dual-energy X-ray absorptiometry scans of the right knee using the lumbar spine protocol. BMD and TBS were quantified at epiphyseal, metaphyseal, diaphyseal, and total bone regions of the distal femur and proximal tibia. Individuals with SCI illustrated significantly lower total BMD at the distal femur (23%; p = 0.029) and proximal tibia (19%; p = 0.02) when compared with non-SCI controls. Despite these marked differences in BMD from both locations, significant differences in total TBS were observed at the distal femur only (6%; p = 0.023). The observed differences in total BMD and TBS could be attributed to reductions in epiphyseal rather than metaphyseal or diaphysis measurements. The relationship between TBS and duration of SCI was well explained by a logarithmic trend at the distal femoral epiphysis (r² = 0.54, p = 0.025). The logarithmic trend would predict that after 3 yr of SCI, TBS would be approximately 6% lower than the non-SCI controls. Further evaluation is needed to determine if TBS measures at the knee provide important information about bone quality that is not captured by traditional BMD.

Progressive Sublesional Bone Loss Extends into the Second Decade After Spinal Cord Injury

OBJECTIVE

The rate of areal bone mineral density (aBMD) loss at the knee (distal femur (DF) and proximal tibia ) and hip (femoral neck (FN) and total hip (TH)) was determined in persons with traumatic spinal cord injury (SCI) who were stratified into subgroups based on time since injury (TSI).

DESIGN

Cross-sectional retrospective review.

SETTING

Department of Veterans Affairs Medical Center and Private Rehabilitation Hospital.

PARTICIPANTS

Data on 105 individuals with SCI (TSI ≤12 months, n = 19; TSI 1-5 years, n = 35; 6-10 years, n = 19; TSI 11-20 years, n = 16; TSI >20 years, n = 15) and 17 able-bodied reference (AB_ref) controls.

INTERVENTIONS

NA Main Outcome Measures: The knee and hip aBMD values were obtained by dual energy X-ray absorptiometry (GE Lunar iDXA) using standard clinical software for the proximal femur employed in conjunction with proprietary research orthopedic knee software applications. Young-normal (T-score) and age-matched (Z-scores) standardized scores for the FN and TH were obtained using the combined GE Lunar/National Health and Nutrition Examination Survey (NHANES III) combined reference database.

RESULTS

When groups were stratified and compared as epochs of TSI, significantly lower mean aBMD and reference scores were observed as TSI increased, despite similar mean ages of participants among the majority of TSI epoch subgroups. Loss in aBMD occurred at the distal femur (DF), proximal tibia (PT), FN, and TH with 46%, 49%, 32%, and 43% of the variance in loss, respectively, described by the exponential decay curves with a time to steady state (t_ss) occurring at 14.6, 11.3, 14, and 6.2 years, respectively, after SCI.

CONCLUSIONS

Sublesional bone loss after SCI was marked and occurred as an inverse function of TSI. For aBMD at the hip and knee, t_ss extended into the second decade after SCI.

Characterization of trabecular bone microstructure in premenopausal women with distal radius fractures

Individual trabecular segmentation was utilized to identify differences in trabecular bone structure in premenopausal women with wrist fractures and non-fracture controls. Fracture subjects had reduced trabecular plate volume, number, thickness, and connectivity. Identifying altered trabecular microarchitecture in young women offers opportunities for counseling and lifestyle modifications to reduce fracture risk.

INTRODUCTION

Premenopausal women with distal radius fractures (DRF) have worse trabecular bone microarchitecture than non-fracture controls (CONT), yet the characteristics of their trabecular bone structure are unknown.

METHODS

Premenopausal women with DRF (n = 40) and CONT (n = 80) were recruited. Primary outcome variables included trabecular structure at the distal radius and tibia, assessed by volumetric decomposition of individual trabecular plates and rods from high-resolution peripheral quantitative CT images. Trabecular morphology included plate and rod number, volume, thickness, and connectivity. Areal bone mineral density (aBMD) of the femoral neck (FN aBMD), and ultradistal radius (UDR aBMD) were measured by DXA.

RESULTS

Trabecular morphology differed between DRF and CONT at the radius and tibia (OR per SD decline 1.58-2.7). At the radius, associations remained significant when adjusting for age and FN aBMD (ORs = 1.76-3.26) and age and UDR aBMD (ORs = 1.72-3.97). Plate volume fraction, number and axially aligned trabeculae remained associated with DRF after adjustment for trabecular density (ORs = 2.55-2.85). Area under the curve (AUC) for discriminating DRF was 0.74 for the proportion of axially aligned trabeculae, compared with 0.60 for FN aBMD, 0.65 for UDR aBMD, and 0.69 for trabecular density. Plate number, plate-plate junction, and axial bone volume fraction remained associated with DRF at the tibia (ORs = 2.14-2.77) after adjusting for age, FN aBMD, or UDR aBMD. AUC_P.P.Junc.D was 0.72 versus 0.61 for FNaBMD, 0.66 for UDRaBMD, and 0.70 for trabecular density.

CONCLUSION

Premenopausal women with DRF have lower trabecular plate volume, number, thickness, and connectivity than CONT. Identification of young women with altered microarchitecture offers opportunities for lifestyle modifications to reduce fracture risk.

Bone loss at the distal femur and proximal tibia in persons with spinal cord injury: imaging approaches, risk of fracture, and potential treatment options

Persons with spinal cord injury (SCI) undergo immediate unloading of the skeleton and, as a result, have severe bone loss below the level of lesion associated with increased risk of long-bone fractures. The pattern of bone loss in individuals with SCI differs from other forms of secondary osteoporosis because the skeleton above the level of lesion remains unaffected, while marked bone loss occurs in the regions of neurological impairment. Striking demineralization of the trabecular epiphyses of the distal femur (supracondylar) and proximal tibia occurs, with the knee region being highly vulnerable to fracture because many accidents occur while sitting in a wheelchair, making the knee region the first point of contact to any applied force. To quantify bone mineral density (BMD) at the knee, dual energy x-ray absorptiometry (DXA) and/or computed tomography (CT) bone densitometry are routinely employed in the clinical and research settings. A detailed review of imaging methods to acquire and quantify BMD at the distal femur and proximal tibia has not been performed to date but, if available, would serve as a reference for clinicians and researchers. This article will discuss the risk of fracture at the knee in persons with SCI, imaging methods to acquire and quantify BMD at the distal femur and proximal tibia, and treatment options available for prophylaxis against or reversal of osteoporosis in individuals with SCI.

Mice with sclerostin gene deletion are resistant to the severe sublesional bone loss induced by spinal cord injury

Bone loss after spinal cord injury (SCI) is rapid, severe, and refractory to interventions studied to date. Mice with sclerostin gene deletion are resistant to the severe sublesional bone loss induced by SCI, further indicating pharmacological inhibition of sclerostin may represent a promising novel approach to this challenging medical problem.

INTRODUCTION

The bone loss secondary to spinal cord injury (SCI) is associated with several unique pathological features, including the permanent immobilization, neurological dysfunction, and systemic hormonal alternations. It remains unclear how these complex pathophysiological changes are linked to molecular alterations that influence bone metabolism in SCI. Sclerostin is a key negative regulator of bone formation and bone mass. We hypothesized that sclerostin could function as a major mediator of bone loss following SCI.

METHODS

To test this hypothesis, 10-week-old female sclerostin knockout (SOST KO) and wild type (WT) mice underwent complete spinal cord transection or laminectomy (Sham).

RESULTS

At 8 weeks after SCI, substantial loss of bone mineral density was observed at the distal femur and proximal tibia in WT mice but not in SOST KO mice. By μCT, trabecular bone volume of the distal femur was markedly decreased by 64 % in WT mice after SCI. In striking contrast, there was no significant reduction of bone volume in SOST KO/SCI mice compared with SOST KO/sham. Histomorphometric analysis of trabecular bone revealed that the significant reduction in bone formation rate following SCI was observed in WT mice but not in SOST KO mice. Moreover, SCI did not alter osteoblastogenesis of marrow stromal cells in SOST KO mice.

CONCLUSION

Our findings demonstrate that SOST KO mice were protected from the major sublesional bone loss that invariably follows SCI. The evidence indicates that sclerostin is an important mediator of the marked sublesional bone loss after SCI, and that pharmacological inhibition of sclerostin may represent a promising novel approach to this challenging clinical problem.

Substance P Promotes the Proliferation, but Inhibits Differentiation and Mineralization of Osteoblasts from Rats with Spinal Cord Injury via RANKL/OPG System

Spinal cord injury (SCI) causes a significant amount of bone loss, which results in osteoporosis (OP). The neuropeptide substance P (SP) and SP receptors may play important roles in the pathogenesis of OP after SCI. To identify the roles of SP in the bone marrow mesenchymal stem cell derived osteoblasts (BMSC-OB) in SCI rats, we investigated the expression of neurokinin-1 receptors (NK1R) in BMSC-OB and the effects of SP on bone formation by development of BMSC-OB cultures. Sixty young male Sprague-Dawley rats were randomized into two groups: SHAM and SCI. The expression of NK1R protein in BMSC-OB was observed using immunohistochemistry and Western blot analysis. The dose- and time-dependent effects of SP on the proliferation, differentiation and mineralization of BMSC-OB and the expression of osteoblastic markers by in vitro experiments. The expression of NK1R in BMSC-OB was observed on plasma membranes and in cytoplasm. One week after osteogenic differentiation, the expression of NK1R was significantly increased after SCI at mRNA and protein levels. However, this difference was gradually attenuated at 2 or 3 weeks later. SP have the function to enhance cell proliferation, inhibite cell differentiation and mineralization at a proper concentration and incubation time, and this effect would be inhibited by adding SP or NK1R antagonist. The expression of RANKL/OPG was significantly increased in tibiae after SCI. Similarly, the RANKL/OPG expression in SCI rats was significantly increased when treating with 10-8 M SP. SP plays a very important role in the pathogenesis of OP after SCI. The direct effect of SP may lead to increased bone resorption through the RANKL/OPG axis after SCI. In addition, high expression of SP also results in the suppression of osteogenesis in SCI rats. Then, the balance between bone resorption and bone formation was broken and finally osteoporosis occurred.

Musculoskeletal Effects of 2 Functional Electrical Stimulation Cycling Paradigms Conducted at Different Cadences for People With Spinal Cord Injury: A Pilot Study

OBJECTIVE

To compare the musculoskeletal effects of low cadence cycling with functional electrical stimulation (FES) with high cadence FES cycling for people with spinal cord injury (SCI).

DESIGN

Randomized pre-post design.

SETTING

Outpatient rehabilitation clinic.

PARTICIPANTS

Participants (N=17; 14 men, 3 women; age range, 22-67y) with C4-T6 motor complete chronic SCI were randomized to low cadence cycling (n=9) or high cadence cycling (n=8).

INTERVENTIONS

Low cadence cycling at 20 revolutions per minute (RPM) and high cadence cycling at 50 RPM 3 times per week for 6 months. Cycling torque (resistance per pedal rotation) increased if targeted cycling cadence was maintained.

MAIN OUTCOME MEASURES

Dual-energy x-ray absorptiometry was used to assess distal femur areal bone mineral density, magnetic resonance imaging was used to assess to assess trabecular bone microarchitecture and cortical bone macroarchitecture and thigh muscle volume, and biochemical markers were used to assess bone turnover. It was hypothesized that subjects using low cadence cycling would cycle with greater torque and therefore show greater musculoskeletal improvements than subjects using high cadence cycling.

RESULTS

A total of 15 participants completed the study. Low cadence cycling obtained a maximal average torque of 2.9±2.8Nm, and high cadence cycling obtained a maximal average torque of 0.8±0.2Nm. Low cadence cycling showed greater decreases in bone-specific alkaline phosphatase, indicating less bone formation (15.5% decrease for low cadence cycling, 10.7% increase for high cadence cycling). N-telopeptide decreased 34% following low cadence cycling, indicating decreased resorption. Both groups increased muscle volume (low cadence cycling by 19%, high cadence cycling by 10%). Low cadence cycling resulted in a nonsignificant 7% increase in apparent trabecular number (P=.08) and 6% decrease in apparent trabecular separation (P=.08) in the distal femur, whereas high cadence cycling resulted in a nonsignificant (P>.3) 2% decrease and 3% increase, respectively.

CONCLUSIONS

This study suggests that the greater torque achieved with low cadence cycling may result in improved bone health because of decreased bone turnover and improved trabecular bone microarchitecture. Longer-term outcome studies are warranted to identify the effect on fracture risk.

Cycling with Functional Electrical Stimulation Before and After a Distal Femur Fracture in a Man with Paraplegia

CASE PRESENTATION

A man with chronic paraplegia sustained a distal femur fracture following an unrelated fall while enrolled in a study examining musculoskeletal changes after 6 months of cycling with functional electrical stimulation (FES). After healing, he restarted and completed the study.

MANAGEMENT AND OUTCOME

Study measures included areal bone mineral density, trabecular bone microarchitecture, cortical bone macroarchitecture, serum bone formation/resorption markers, and muscle volume. The patient made small gains in bone- and muscle-related measures. Bone markers had not returned to baseline prior to restarting cycling, which may have impacted results.

DISCUSSION

This case shows that cycling with FES may be safely resumed after distal femur fracture.

Measurement of Bone: Diagnosis of SCI-Induced Osteoporosis and Fracture Risk Prediction

BACKGROUND

Spinal cord injury (SCI) is associated with a rapid loss of bone mass, resulting in severe osteoporosis and a 5- to 23-fold increase in fracture risk. Despite the seriousness of fractures in SCI, there are multiple barriers to osteoporosis diagnosis and wide variations in treatment practices for SCI-induced osteoporosis.

METHODS

We review the biological and structural changes that are known to occur in bone after SCI in the context of promoting future research to prevent or reduce risk of fracture in this population. We also review the most commonly used methods for assessing bone after SCI and discuss the strengths, limitations, and clinical applications of each method.

CONCLUSIONS

Although dual-energy x-ray absorptiometry assessments of bone mineral density may be used clinically to detect changes in bone after SCI, 3-dimensional methods such as quantitative CT analysis are recommended for research applications and are explained in detail.

Neuromuscular Electrical Stimulation-Induced Resistance Training After SCI: A Review of the Dudley Protocol

BACKGROUND

Neuromuscular electrical stimulation (NMES), often referred to as functional electrical stimulation (FES), has been used to activate paralyzed skeletal muscle in people with spinal cord injury (SCI). The goal of NMES has been to reverse some of the dramatic losses in skeletal muscle mass, to stimulate functional improvements in people with incomplete paralysis, and to produce some of the health benefits associated with exercise.

OBJECTIVE

The purpose of this brief review is to describe a quantifiable resistance training form of NMES developed by Gary A. Dudley.

METHODS

People with motor complete SCI were first tested to confirm that an NMES-induced muscle contraction of the quadriceps muscle could be achieved. The contraction stimulus consisted of biphasic pulses at 35 Hz performed with increasing current up to what was needed to produce full knee extension. Four sets of 10 knee extensions were elicited, if possible. Training occurred biweekly for 3 to 6 months, with ankle weights being increased up to an added weight of 9.1 kg if the 40 repetitions could be performed successfully for 2 sessions.

RESULTS

Many participants have performed this protocol without adverse events, and all participants showed progression in the number of repetitions and/or the amount of weight lifted. Large increases in muscle mass occur, averaging 30% to 40%. Additional physiological adaptations to stimulated muscle have also been reported.

CONCLUSIONS

These results demonstrate that the affected skeletal muscle after SCI responds robustly to progressive resistance training many years after injury. Future work with NMES should determine whether gains in lean mass translate to improved health, function, and quality of life.

A Predictive Model of Vertebral Trabecular Anisotropy From Ex Vivo Micro-CT

Spine-related disorders are amongst the most frequently encountered problems in clinical medicine. For several applications such as 1) to improve the assessment of the strength of the spine, as well as 2) to optimize the personalization of spinal interventions, image-based biomechanical modeling of the vertebrae is expected to play an important predictive role. However, this requires the construction of computational models that are subject-specific and comprehensive. In particular, they need to incorporate information about the vertebral anisotropic micro-architecture, which plays a central role in the biomechanical function of the vertebrae. In practice, however, accurate personalization of the vertebral trabeculae has proven to be difficult as its imaging in vivo is currently infeasible. Consequently, this paper presents a statistical approach for accurate prediction of the vertebral fabric tensors based on a training sample of ex vivo micro-CT images. To the best of our knowledge, this is the first predictive model proposed and validated for vertebral datasets. The method combines features selection and partial least squares regression in order to derive optimal latent variables for the prediction of the fabric tensors based on the more easily extracted shape and density information. Detailed validation with 20 ex vivo T12 vertebrae demonstrates the accuracy and consistency of the approach for the personalization of trabecular anisotropy.

Underdevelopment of trabecular bone microarchitecture in the distal femur of nonambulatory children with cerebral palsy becomes more pronounced with distance from the growth plate

SUMMARY

We found that the underdeveloped trabecular bone microarchitecture in the distal femur of children with cerebral palsy (CP) who are unable to ambulate independently becomes more pronounced with increased distance from the growth plate. This suggests that the degree of underdevelopment in trabecular bone in children with CP is greater than previously understood.

INTRODUCTION

Children with CP who are unable to ambulate independently have severely underdeveloped trabecular bone microarchitecture in the distal femur. The aim of the study was to determine if the level of underdevelopment in trabecular bone microarchitecture is consistent across the distal femur in children with CP.

METHODS

Children with quadriplegic CP and typically developing children were studied (n=12/group, 5-14 years). Apparent bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th), and trabecular separation (appTb.Sp) were estimated in each of 20 magnetic resonance images collected above the growth plate in the distal femur.

RESULTS

For the total region, appBV/TV, appTb.N, and appTb.Th were lower (30, 21, and 12%, respectively) and appTb.Sp was higher (52%) (all p≤0.001) in children with CP than in controls. Distance from the growth plate was inversely related to appBV/TV and appTb.N and was positively related to appTb.Sp at the same distance in children with CP and controls (all p<0.01). However, the relationships were stronger (r2=0.87 to 0.92 versus 0.36 to 0.65) and the slopes were steeper in children with CP (all p<0.01). Furthermore, the steepness of the slopes in children with CP was positively related to appBV/TV, appTb.N, appTb.Th, and appTb.Sp for the total region (r2=0.37 to 0.75, p<0.05).

CONCLUSIONS

The underdeveloped trabecular bone microarchitecture in the metaphysis of the distal femur in children with CP becomes more pronounced with greater distance from the growth plate. This pattern is most profound in children with the least developed trabecular bone microarchitecture.

Reduction in proximal femoral strength in patients with acute spinal cord injury

Bone loss after spinal cord injury (SCI) is associated with an increased risk of fracture resulting from minor trauma. Proximal femoral fractures account for approximately 10% to 20% of the fractures in this population and are among the most serious of injuries. Our purpose was to quantify changes to proximal femoral strength in patients with acute SCI. Thirteen subjects received dual-energy X-ray absorptiometry (DXA) and clinical computed tomography (CT) scans at serial time points during acute SCI separated by a mean of 3.5 months (range 2.6 to 4.8 months). Areal bone mineral density (aBMD) at the proximal femur was quantified from DXA, and proximal femoral strength was predicted using CT-based finite element (FE) modeling in a sideways fall configuration. During the acute period of SCI, femoral neck and total proximal femur aBMD decreased by 2.0 ± 1.1%/month (p < 0.001) and 2.2 ± 0.7%/month (p < 0.001), respectively. The observed reductions in aBMD were associated with a 6.9 ± 2.0%/month (p < 0.001) reduction in femoral strength. Thus, changes in femoral strength were some 3 times greater than the observed changes in aBMD (p < 0.001). It was interesting to note that in just 3.5 months of acute SCI, reductions in strength for some patients were on the order of that predicted for lifetime declines owing to aging. Therefore, it is important that therapeutic interventions are implemented soon after SCI in an effort to halt bone loss and decrease fracture risk. In addition, clinicians utilizing DXA to monitor bone health after SCI should be aware of the potential discrepancy between changes in aBMD and strength.

Potential regenerative rehabilitation technology: implications of mechanical stimuli to tissue health

BACKGROUND

Mechanical loads induced through muscle contraction, vibration, or compressive forces are thought to modulate tissue plasticity. With the emergence of regenerative medicine, there is a need to understand the optimal mechanical environment (vibration, load, or muscle force) that promotes cellular health. To our knowledge no mechanical system has been proposed to deliver these isolated mechanical stimuli in human tissue. We present the design, performance, and utilization of a new technology that may be used to study localized mechanical stimuli on human tissues. A servo-controlled vibration and limb loading system were developed and integrated into a single instrument to deliver vibration, compression, or muscle contractile loads to a single limb (tibia) in humans. The accuracy, repeatability, transmissibility, and safety of the mechanical delivery system were evaluated on eight individuals with spinal cord injury (SCI).

FINDINGS

The limb loading system was linear, repeatable, and accurate to less than 5, 1, and 1 percent of full scale, respectively, and transmissibility was excellent. The between session tests on individuals with spinal cord injury (SCI) showed high intra-class correlations (>0.9).

CONCLUSIONS

All tests supported that therapeutic loads can be delivered to a lower limb (tibia) in a safe, accurate, and measureable manner. Future collaborations between engineers and cellular physiologists will be important as research programs strive to determine the optimal mechanical environment for developing cells and tissues in humans.

Bone Mineral Density and Biochemical Markers of Bone Turnover during the First Year of Injury in Patients with Spinal Cord Injury

Background

Spinal cord injury (SCI) is associated with bone mass loss that can be complicated by fractures, which result in further disabilities for patients. After a SCI, the body starts losing large amounts of calcium and other minerals in the urine (demineralisation). This study aimed to assess the changes in bone mineral density (BMD) during the 1st year of acute SCI in patients with neurological deficit.

Methods

A total of 95 patients with acute SCI and neurological deficit were evaluated in this prospective study. Haematological investigations such as evaluation of serum calcium, serum phosphate, serum creatinine, and serum alkaline phosphatase (ALP) were carried out. Urinary investigations such as 24-hour urinary creatinine level and excretion of calcium and phosphate in the urine were measured. BMD was measured using dual-energy X-ray absorptiometry scan with Hologic QDR 2000 scanner (Explorer). All of the aforementioned parameters were measured again at 3, 6, and 12 months.

Results

Serum ALP at 1-year follow up was significantly raised (p < 0.05). The BMD at 1-year follow up had statistically significant lower values than the initial BMD at the hip (p < 0.05), proximal tibia (p < 0.00l), and distal tibial epiphysis (p < 0.001). The BMD in motor-complete SCI patients [American Spinal Injury Association (ASIA) grades A and B] had significant lower values than motor-incomplete SCI patients (ASIA C and D) at the hip (p < 0.05) and proximal tibial epiphysis (p < 0.05).

Conclusion

There was a marked decrease in BMD in metaphyseal sites than below the neurological deficit level with maximum decrease at the proximal tibia during the 1st year of SCI. Although the markers of osteoblastic activity did not show much change, the decrease in BMD was influenced by the neurological recovery after SCI.

The influence of disuse on bone microstructure and mechanics assessed by HR-pQCT

Numerous clinical cohorts are exposed to reduced skeletal loading and associated bone loss, including surgical patients, stroke and spinal cord injury victims, and women on bed rest during pregnancy. In this context, understanding disuse-related bone loss is critical to developing interventions to prevent fractures and the associated morbidity, mortality, and cost to the health care system. The aim of this pilot study was to use high-resolution peripheral QCT (HR-pQCT) to examine changes in trabecular and cortical microstructure and biomechanics during a period of non weight bearing (WB) and during recovery following return to normal WB. Surgical patients requiring a 6-week non WB period (n=12, 34.8±7.7 yrs) were scanned at the affected and contralateral tibia prior to surgery, after the 6-week non WB period, and 6 and 13 weeks after returning to full WB. At the affected ultradistal tibia, integral vBMD (including both trabecular and cortical compartments) decreased with respect to baseline (-1.2%), trabecular number increased (+5.6%), while trabecular thickness (-5.4%), separation (-4.6%), and heterogeneity (-7.2%) decreased (all p<0.05). Six weeks after return to full WB, trabecular structure measures reverted to baseline levels. In contrast, integral vBMD continued to decrease after 6 (-2.0%, p<0.05) and 13 weeks (-2.5%, p=0.07) of full WB. At the affected distal site, the disuse period resulted in increased porosity (+16.1%, p<0.005), which remained elevated after 6 weeks (+16.8%, p<0.01) and after 13 weeks (+16.2%, p<0.05). A novel topological analysis applied to the distal tibia cortex demonstrated increased number of canals with surface topology ("slabs" +21.7%, p<0.01) and curve topology ("tubes" +15.0%, p<0.05) as well as increased number of canal junctions (+21.4%, p<0.05) following the disuse period. Porosity increased uniformly through increases in both pore size and number. Finite element analysis at the ultradistal tibia showed decreased stiffness and failure load (-2.8% and -2.4%, p<0.01) following non WB. These biomechanical predictions remained depressed following 6 and 13 weeks of full WB. Finite element analysis at the distal site followed similar trends. Our results suggest that detectable microstructural and biomechanical degradation occurs--particularly within the cortical compartment--as a result of non WB and persists following return to normal loading. A better understanding of these microstructural changes and their short- and long-term influence on biomechanics may have clinical relevance in the context of disuse-related fracture prevention.

The mechanical consequence of actual bone loss and simulated bone recovery in acute spinal cord injury

INTRODUCTION

Spinal cord injury (SCI) is characterized by rapid bone loss and an increased risk of fragility fracture around regions of the knee. Our purpose was to quantify changes in torsional stiffness K and strength Tult at the proximal tibia due to actual bone loss and simulated bone recovery in acute SCI.

METHODS

Computed tomography scans were acquired on ten subjects with acute SCI at serial time points separated by a mean of 3.9months (range 3.0 to 4.8months). Reductions in bone mineral were quantified and a validated subject-specific finite element modeling procedure was used to predict changes in K and Tult. The modeling procedure was subsequently used to examine the effect of simulated hypothetical treatments, in which bone mineral of the proximal tibiae were restored to baseline levels, while all other parameters were held constant.

RESULTS

During the acute period of SCI, subjects lost 8.3±4.9% (p<0.001) of their bone mineral density (BMD). Reductions in K (-9.9±6.5%; p=0.002) were similar in magnitude to reductions in BMD, however reductions in Tult (-15.8±13.8%; p=0.005) were some 2 times greater than the reductions in BMD. Owing to structural changes in geometry and mineral distribution, Tult was not necessarily recovered when bone mineral was restored to baseline, but was dependent upon the degree of bone loss prior to hypothetical treatments (r≥0.719; p≤0.019).

CONCLUSIONS

Therapeutic interventions to halt or attenuate bone loss associated with SCI should be implemented soon after injury in an attempt to preserve mechanical integrity and prevent fracture.

Longitudinal study of body composition in spinal cord injury patients

BACKGROUND

Bone mass loss and muscle atrophy are the frequent complications occurring after spinal cord injury (SCI). The potential risks involved with these changes in the body composition have implications for the health of the SCI individual. Thus, there is a need to quantitate and monitor body composition changes accurately in an individual with SCI. Very few longitudinal studies have been reported in the literature to assess body composition and most include relatively small number of patients. The present prospective study aimed to evaluate the body composition changes longitudinally by DEXA in patients with acute SCI.

MATERIALS AND METHODS

Ninety five patients with acute SCI with neurological deficits were evaluated for bone mineral content (BMC), body composition [lean body mass (LBM) and fat mass] by dual-energy X-ray absorptiometry during the first year of SCI.

RESULTS

There was a significant decrease in BMC (P < 0.05) and LBM (P < 0.05) and increase in total body fat mass (TBFM) and percentage fat at infra-lesional sites. The average decrease was 14.5% in BMC in lower extremities, 20.5% loss of LBM in legs and 15.1% loss of LBM in trunk, and increase of 0.2% in fat mass in legs and 17.3% increased fat in the lower limbs at 1 year. The tetraplegic patients had significant decrease in arm BMC (P < 0.001), arm LBM (P < 0.01) and fat percentage (P < 0.01) compared to paraplegics. Patients with complete motor injury had higher values of TBFM and fat percentage, but comparable values of BMC and LBM to patients with incomplete motor injury.

CONCLUSIONS

Our findings suggest that there is a marked decrease in BMC and LBM with increase in adiposity during the first year of SCI. Although these changes depend on the level and initial severity of lesions, they are also influenced by the neurological recovery after SCI.

The pattern of trabecular bone microarchitecture in the distal femur of typically developing children and its effect on processing of magnetic resonance images

INTRODUCTION

Magnetic resonance imaging (MRI) is used to assess trabecular bone microarchitecture in humans; however, image processing can be labor intensive and time consuming. One aim of this study was to determine the pattern of trabecular bone microarchitecture in the distal femur of typically developing children. A second aim was to determine the proportion and location of magnetic resonance images that need to be processed to yield representative estimates of trabecular bone microarchitecture.

MATERIALS AND METHODS

Twenty-six high resolution magnetic resonance images were collected immediately above the growth plate in the distal femur of 6-12year-old typically developing children (n=40). Measures of trabecular bone microarchitecture [i.e., apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th) and trabecular separation (appTb.Sp)] in the lateral aspect of the distal femur were determined using the twenty most central images (20IM). The average values for appBV/TV, appTb.N, appTb.Th and appTb.Sp from 20IM were compared to the average values from 10 images (10IM), 5 images (5IM) and 3 images (3IM) equally dispersed throughout the total image set and one image (1IM) from the center of the total image set using linear regression analysis. The resulting mathematical models were cross-validated using the leave-one-out technique.

RESULTS

Distance from the growth plate was strongly and inversely related to appBV/TV (r(2)=0.68, p<0.001) and appTb.N (r(2)=0.92, p<0.001) and was strongly and positively related to appTb.Sp (r(2)=0.86, p<0.001). The relationship between distance from the growth plate and appTb.Th was not linear (r(2)=0.06, p=0.28), but instead it was quadratic and statistically significant (r(2)=0.54, p<0.001). Trabecular bone microarchitecture estimates from 10IM, 5IM, 3IM and 1IM were not different from estimates from 20IM (p>0.05). However, there was a progressive decrease in the strength of the relationships as a smaller proportion of images were used to predict estimates from 20IM (r(2)=0.98 to 0.99 using 10IM, 0.94 to 0.96 using 5IM, 0.87 to 0.90 using 3IM and 0.66 to 0.72 using 1IM; all p<0.001). Using the resulting mathematical models and the leave-one-out cross-validation analysis, measures of trabecular bone microarchitecture estimated from the 10IM and 5IM partial image sets agreed extremely well with estimates from 20IM.

CONCLUSIONS

The findings indicate that partial magnetic resonance image sets can be used to provide reasonable estimates of trabecular bone microarchitecture status in the distal femur of typically developing children. However, because the relative amount of trabecular bone in the distal femur decreases with distance from the growth plate due to a decrease in trabecular number, careful positioning of the region of interest and sampling from throughout the region of interest is necessary.

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.

Prevalence and associated factors of T-score discordance between different sites in Iranian patients with spinal cord injury

OBJECTIVES

The present study was conducted to determine the prevalence of T-score discordance and its risk factors in a group of patients with spinal cord injury in a university teaching hospital in the Iranian capital of Tehran.

METHODS

This cross-sectional study was conducted on paraplegic men undergoing bone density testing in an outpatient clinic at a hospital in the Iranian capital, Tehran, between March 2011 and 2012. A questionnaire on demographic and anthropometric characteristics, including age, height, weight, engagement in physical activity and personal smoking habits, was filled out for each subject. All the subjects underwent bone mineral density measurement and blood samples were sent for laboratory testing.

RESULTS

Major T-score discordance between two sites was noted in 54 (41.22%) patients. Multivariate logistic regression revealed that every unit increase in serum calcium levels, as the only factor influencing T-score discordance, was associated with a 2.49-fold increased risk in T-score discordance in the area. As for the spine and radius, BMI was the only influencing factor as every unit increase in BMI was associated with a 14% lower risk for T-score discordance in these regions. Body mass index was the only factor, based on the multivariate model, affecting the risk of developing T-score discordance between two sites.

CONCLUSION

Our study revealed the high prevalence of T-score discordance in patients with spinal cord injury. Physicians should therefore be encouraged to perform BMD at three sites when visiting patients with such injuries.

Femoral bone marrow adiposity and cortical bone cross-sectional areas in men with motor complete spinal cord injury

OBJECTIVES

To (1) quantify yellow and red bone marrow (BM) and cortical bone cross-sectional areas (CSAs) of the femur in persons with motor complete spinal cord injury (SCI) compared with healthy able-bodied control subjects and (2) determine the relationships between yellow and red BM, cortical CSAs, and thigh composition and measurements from dual-energy x-ray absorptiometry in men with complete SCI.

DESIGN

Cross-sectional.

SETTINGS

Clinical hospital and academic settings.

METHODS

Eight persons with motor complete SCI and 6 age-matched healthy control subjects underwent magnetic resonance imaging of both thighs to measure BM adiposity (BMA) and cortical CSA followed by whole-body dual-energy x-ray absorptiometry to measure bone mineral density and body composition for the SCI group.

RESULTS

Cortical bone CSA adjusted to total subperiosteal bone CSA was 1.5-2 times lower in men with SCI compared with able-bodied control subjects across the femoral length (P =.003). Yellow BMA CSA was 2-3 times greater in men with SCI compared with able-bodied control subjects (P < .0001). Opposite relationships were found between the yellow BMA CSA and cortical bone CSAs in men with SCI (negative association) and able-bodied control subjects (positive association). Yellow BMA was negatively associated with bone mineral density and bone mineral content and with skeletal muscle CSA and fat-free mass (P <.05) in men with SCI. Finally, yellow BMA was positively related to thigh subcutaneous adipose tissue.

CONCLUSIONS

After SCI, cortical bone CSA becomes thinner and is associated with greater accumulation of yellow BMA. Yellow BMA is associated with changes in bone CSA and bone mass, as well as increased fat mass, after SCI.

Torsional stiffness and strength of the proximal tibia are better predicted by finite element models than DXA or QCT

Individuals with spinal cord injury experience a rapid loss of bone mineral below the neurological lesion. The clinical consequence of this bone loss is a high rate of fracture around regions of the knee. The ability to predict the mechanical competence of bones at this location may serve as an important clinical tool to assess fracture risk in the spinal cord injury population. The purpose of this study was to develop, and statistically compare, non-invasive methods to predict torsional stiffness (K) and strength (Tult) of the proximal tibia. Twenty-two human tibiae were assigned to either a "training set" or a "test set" (11 specimens each) and mechanically loaded to failure. The training set was used to develop subject-specific finite element (FE) models, and statistical models based on dual energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT), to predict K and Tult; the test set was used for cross-validation. Mechanical testing produced clinically relevant spiral fractures in all specimens. All methods were accurate and reliable predictors of K (cross-validation r(2)≥0.91; error≤13%), however FE models explained an additional 15% of the variance in measured Tult and illustrated 12-16% less error than DXA and QCT models. Given the strong correlations between measured and FE predicted K (cross-validation r(2)=0.95; error=10%) and Tult (cross-validation r(2)=0.91; error=9%), we believe the FE modeling procedure has reached a level of accuracy necessary to answer clinically relevant questions.

Premenopausal women with a distal radial fracture have deteriorated trabecular bone density and morphology compared with controls without a fracture

BACKGROUND

Measurement of bone mineral density by dual x-ray absorptiometry combined with clinical risk factors is currently the gold standard in diagnosing osteoporosis. Advanced imaging has shown that older patients with fragility fractures have poor bone microarchitecture, often independent of low bone mineral density. We hypothesized that premenopausal women with a fracture of the distal end of the radius have similar bone mineral density but altered bone microarchitecture compared with control subjects without a fracture.

METHODS

Forty premenopausal women with a recent distal radial fracture were prospectively recruited and matched with eighty control subjects without a fracture. Primary outcome variables included trabecular and cortical microarchitecture at the distal end of the radius and tibia by high-resolution peripheral quantitative computed tomography. Bone mineral density at the wrist, hip, and lumbar spine was also measured by dual x-ray absorptiometry.

RESULTS

The fracture and control groups did not differ with regard to age, race, or body mass index. Bone mineral density was similar at the femoral neck, lumbar spine, and distal one-third of the radius, but tended to be lower in the fracture group at the hip and ultradistal part of the radius (p = 0.06). Trabecular microarchitecture was deteriorated in the fracture group compared with the control group at both the distal end of the radius and distal end of the tibia. At the distal end of the radius, the fracture group had lower total density and lower trabecular density, number, and thickness compared with the control group (-6% to -14%; p < 0.05 for all). At the distal end of the tibia, total density, trabecular density, trabecular thickness, and cortical thickness were lower in the fracture group than in the control group (-7% to -14%; p < 0.01). Conditional logistic regression showed that trabecular density, thickness, separation, and distribution of trabecular separation remained significantly associated with fracture after adjustment for age and ultradistal radial bone mineral density (adjusted odds ratios [OR]: 2.01 to 2.98; p < 0.05). At the tibia, total density, trabecular density, thickness, cortical area, and cortical thickness remained significantly associated with fracture after adjustment for age and femoral neck bone mineral density (adjusted OR:1.62 to 2.40; p < 0.05).

CONCLUSIONS

Despite similar bone mineral density values by dual x-ray absorptiometry, premenopausal women with a distal radial fracture have significantly poorer bone microarchitecture at the distal end of the radius and tibia compared with control subjects without a fracture. Early identification of women with poor bone health offers opportunities for interventions aimed at preventing further deterioration and reducing fracture risk.

Measuring apparent trabecular density and bone structure using peripheral quantitative computed tomography at the tibia: precision in participants with and without spinal cord injury

The objective of the study was to investigate the precision of standard outcomes obtained using peripheral quantitative computed tomography as well as apparent trabecular structure measures in adults with and without spinal cord injury (SCI). Twelve individuals with SCI, mean (standard deviation [SD]) 20 (13)yrs postinjury and mean (SD) age 44 (9)yrs, and 21 individuals without SCI (mean [SD] age: 27 [5]yrs) participated. Repeat scans of tibia epiphysis (4%) and shaft (66%) were performed using a Stratec XCT-2000 (Stratec Medizintechnik, Pforzheim, Germany). Bone mineral density and geometry variables (e.g., cortical thickness, bone area, polar moment of inertia) were derived with manufacturer's software. The following apparent trabecular structure variables were determined using custom software: average trabecular thickness (TrTh) (mm), trabecular spacing (TrSp) (mm), and trabecular number (TrN) (1/mm); average hole size (HA) and maximum hole size (HM) (mm(2)); connectivity index (CI); cortical thickness (CTh) (mm); bone volume to total volume (BVTV) ratio. Root mean square standard deviation and root mean square coefficient of variation (RMSCV; root mean square coefficient of variation percent [RMSCV%]) were calculated. The RMSCV% for all standard bone mineral density and geometry variables was ≤2% except for total area (4% site), where precision was 3.8%. RMSCV% for bone structure variables were as follows: CTh 5.1, TrTh 1.7, TrN 1.9, TrSp 2.6, HA 9.5, HM 20.1, CI 5.1, and BVTV 1.4. Precision for bone density and geometry was excellent across a range of bone mineral densities. RMSCVs for some apparent trabecular structure variables were comparable to that of standard variables. The RMSCV for others may necessitate larger studies to detect between-group differences.

Micro-finite element analysis applied to high-resolution MRI reveals improved bone mechanical competence in the distal femur of female pre-professional dancers

Micro-finite element analysis applied to high-resolution (0.234-mm length scale) MRI reveals greater whole and cancellous bone stiffness, but not greater cortical bone stiffness, in the distal femur of female dancers compared to controls. Greater whole bone stiffness appears to be mediated by cancellous, rather than cortical bone adaptation.

INTRODUCTION

The purpose of this study was to compare bone mechanical competence (stiffness) in the distal femur of female dancers compared to healthy, relatively inactive female controls.

METHODS

This study had institutional review board approval. We recruited nine female modern dancers (25.7±5.8 years, 1.63±0.06 m, 57.1±4.6 kg) and ten relatively inactive, healthy female controls matched for age, height, and weight (32.1±4.8 years, 1.6±0.04 m, 55.8±5.9 kg). We scanned the distal femur using a 7-T MRI scanner and a three-dimensional fast low-angle shot sequence (TR/TE=31 ms/5.1 ms, 0.234 mm×0.234 mm×1 mm, 80 slices). We applied micro-finite element analysis to 10-mm-thick volumes of interest at the distal femoral diaphysis, metaphysis, and epiphysis to compute stiffness and cross-sectional area of whole, cortical, and cancellous bone, as well as cortical thickness. We applied two-tailed t-tests and ANCOVA to compare groups.

RESULTS

Dancers demonstrated greater whole and cancellous bone stiffness and cross-sectional area at all locations (p<0.05). Cortical bone stiffness, cross-sectional area, and thickness did not differ between groups (>0.08). At all locations, the percent of intact whole bone stiffness for cortical bone alone was lower in dancers (p<0.05). Adjustment for cancellous bone cross-sectional area eliminated significant differences in whole bone stiffness between groups (p>0.07), but adjustment for cortical bone cross-sectional area did not (p<0.03).

CONCLUSIONS

Modern dancers have greater whole and cancellous bone stiffness in the distal femur compared to controls. Elevated whole bone stiffness in dancers may be mediated via cancellous, rather than cortical bone adaptation.

Jump exercise during hindlimb unloading protect against the deterioration of trabecular bone microarchitecture in growing young rats

Three-dimensional femoral trabecular architecture was investigated in tail-suspended young growing rats and the effects of jump exercise during the period of tail-suspension were also examined. Eight-week-old male Wistar rats (n = 24) were randomly assigned to three body weight-matched groups: a tail suspended group (SUS, n = 8); a sedentary control group (CON, n = 8) and rats primed with jump exercise during the period of tail suspension (JUM, n = 8). The jump exercise protocol consisted of 30 jumps/day, five days/week with a 40 cm jump height. After 3 weeks of jump exercise, bone mineral density (BMD) of the entire right femur was measured using dual energy X-ray absorptiometry. Three-dimensional trabecular bone architecture at the distal femoral metaphysis was evaluated using microcomputed tomography (micro-CT). Tail suspension caused a decrease in femoral BMD (-5%, p < 0.001) and trabecular bone architectural deterioration. Deterioration in the trabecular network during hindlimb unloading was mostly attributed to the reduction of trabecular number (-32%, p < 0.001) in the distal femoral metaphysis. Jump exercise during the tail suspension period increased trabecular thickness (14%, p < 0.001) and the reduction of trabecular number was suppressed. The present data indicate that jump exercise applied during hindlimb unloading could be able to inhibit bone loss and trabecular bone architectural deterioration caused by tail suspension.

Spinal cord injury-induced osteoporosis: pathogenesis and emerging therapies

Spinal cord injury causes rapid, severe osteoporosis with increased fracture risk. Mechanical unloading after paralysis results in increased osteocyte expression of sclerostin, suppressed bone formation, and indirect stimulation of bone resorption. At this time, there are no clinical guidelines to prevent bone loss after SCI, and fractures are common. More research is required to define the pathophysiology and epidemiology of SCI-induced osteoporosis. This review summarizes emerging therapeutics including anti-sclerostin antibodies, mechanical loading of the lower extremity with electrical stimulation, and mechanical stimulation via vibration therapy.

Comparison of cortical bone measurements between pQCT and HR-pQCT

The primary purpose of this study was to determine the accuracy of tibial cortical thickness measurements derived from peripheral quantitative computed tomography (pQCT) with analysis based on the circular ring model, using high-resolution peripheral quantitative computed tomography (HR-pQCT) (isotopic voxel size of 82 μm) as a gold standard. The secondary objective was to evaluate whether the accuracy of the pQCT-based estimates of cortical thickness (CTh), cortical area (CoA), cortical density (CDen), and total area (TotA) improve with alterations of voxel size from the standard 0.5-0.2mm. Fifteen dry tibia specimens were immersed in saline in a sealed cylinder and scanned 22.5mm from the distal tibia plateau using pQCT and HR-pQCT. pQCT yielded higher values for CTh and CDen and lower values for CoA. The differences between imaging techniques increased as the average CTh increased. No systematic bias was observed for CDen, CoA, and TotA. Similar differences were found between pQCT with voxel size 0.2mm and HR-pQCT. Significant correlations were observed for CTh (R=0.97, p ≤ 0.0001), CDen (R=0.99, p ≤ 0.0001), CoA (R=0.98, p ≤ 0.0001), and TotA (R=1.0, p ≤ 0.0001) when pQCT- and HR-pQCT-derived values were compared irrespective of which voxel size was used. Measurement variability between the imaging techniques was evident. Future studies aimed at examining cortical structure with pQCT should note that there are differences between the 2 techniques.

Zoledronic acid improves bone mineral density in pediatric spinal cord injury

Spinal cord injury (SCI) is associated with rapid and sustained bone loss and increase risk of fracture. Disuse is the primary cause for bone loss, although neural and hormonal changes may also contribute via different mechanisms. Bisphosphonates are used widely to treat osteoporosis in adults and are used increasingly for primary and secondary osteoporosis in children. Current data are insufficient to recommend routine use of bisphosphonates for fracture prevention in adult patients post-SCI and there are no available data in pediatric SCI. We report a 12-year-old boy with non-traumatic SCI who was treated with six monthly zoledronic acid (0.05 mg/kg/dose) for 18 months. The patient (AA) was diagnosed with transverse myelitis at 8.1 years of age, resulting in ventilator-dependent incomplete C3 tetraplegia. Following a fragility fracture to the surgical neck of the right humerus at 9.5 years of age, he was started on zoledronic acid. Bone turnover decreased and bone densitometry data (dual-energy X-ray absorptiometry [DXA] and peripheral quantitative computed tomography [pQCT]) showed improvement in metaphyseal and diaphyseal bone mineral content (BMC), volumetric bone mineral density (vBMD), and size, after 18 months of treatment. In the growing skeleton post-SCI, zoledronic acid potentially increases vertebral and long-bone strength by preserving trabecular bone (increased BMC and vBMD) and increasing cortical vBMD and cross-sectional area (CSA).

Mechanical regulation of signaling pathways in bone

A wide range of cell types depend on mechanically induced signals to enable appropriate physiological responses. The skeleton is particularly dependent on mechanical information to guide the resident cell population towards adaptation, maintenance and repair. Research at the organ, tissue, cell and molecular levels has improved our understanding of how the skeleton can recognize the functional environment, and how these challenges are translated into cellular information that can site-specifically alter phenotype. This review first considers those cells within the skeleton that are responsive to mechanical signals, including osteoblasts, osteoclasts, osteocytes and osteoprogenitors. This is discussed in light of a range of experimental approaches that can vary parameters such as strain, fluid shear stress, and pressure. The identity of mechanoreceptor candidates is approached, with consideration of integrins, pericellular tethers, focal adhesions, ion channels, cadherins, connexins, and the plasma membrane including caveolar and non-caveolar lipid rafts and their influence on integral signaling protein interactions. Several mechanically regulated intracellular signaling cascades are detailed including activation of kinases (Akt, MAPK, FAK), β-catenin, GTPases, and calcium signaling events. While the interaction of bone cells with their mechanical environment is complex, an understanding of mechanical regulation of bone signaling is crucial to understanding bone physiology, the etiology of diseases such as osteoporosis, and to the development of interventions to improve bone strength.

A biomechanical analysis of exercise in standing, supine, and seated positions: Implications for individuals with spinal cord injury

CONTEXT/OBJECTIVE

The distal femur is the primary fracture site in patients with osteoporosis after spinal cord injury (SCI).

OBJECTIVE

To mathematically compare the compression and shear forces at the distal femur during quadriceps stimulation in the standing, supine, and seated positions. A force analysis across these positions may be a consideration for people with SCI during neuromuscular electrical stimulation of the quadriceps.

DESIGN

A biomechanical model.

SETTING

Research laboratory.

OUTCOME MEASURES

Compression and shear forces from the standing, supine, and seated biomechanical models at the distal femur during constant loads generated by the quadriceps muscles.

RESULTS

The standing model estimated the highest compressive force at 240% body weight and the lowest shear force of 24% body weight at the distal femur compared with the supine and seated models. The supine model yielded a compressive force of 191% body weight with a shear force of 62% body weight at the distal femur. The seated model yielded the lowest compressive force of 139% body weight and the highest shear force of 215% body weight.

CONCLUSIONS

When inducing a range of forces in the quadriceps muscles, the seated position yields the highest shear forces and lowest compressive forces when compared with the supine and standing positions. Standing with isometric contractions generates the highest compressive loads and lowest shear forces. Early active resistive standing may provide the most effective means to prevent bone loss after SCI.

Bone loss following spinal cord injury in a rat model

The current study was undertaken to follow the time course of bone loss in the proximal tibia of rats over several weeks following thoracic contusion spinal cord injury (SCI) of varying severity. It was hypothesized that bone loss would be more pronounced in the more severely injured animals, and that hindlimb weight bearing would help prevent bone loss. Twenty-six female Sprague-Dawley rats (200-225 g, 6-7 weeks old) received standard thoracic (T9) injuries at energies of 6.25, 12.5, 25, or 50 g-cm. The rats were scored weekly for hindlimb function during locomotion. At 0, 2 or 3, and 8 weeks, high-resolution micro-CT images of each right tibia were obtained. Mechanical indentation testing was done to measure the compressive strength of the cancellous bone structure. The 6.25 g-cm group showed near normal locomotion, the 12.5 and 25 g-cm groups showed the ability to frequently or occasionally generate weight-supported plantar steps, respectively, and the 50 g-cm group showed only movement without weight-supported plantar stepping. The 6.25, 12.5 and 25 g-cm groups remained at the same level of bone volume fraction (cancBV/TV=0.24±0.07), while the 50 g-cm group experienced severe bone loss (67%), resulting in significantly lower (p<0.05) bone volume fraction (cancBV/TV=0.11±0.05) at 8 weeks. Proximal tibia cancellous bone strength was reduced by approximately 50% in these severely injured rats. Instead of a linear proportionality between injury severity and bone loss, there appears to be a distinct functional threshold, marked by occasional weight-supported stepping, above which bone loss does not occur.

The changing field of rehabilitation: optimizing spontaneous regeneration and functional recovery

For neurorehabilitation of patients with spinal cord injury (SCI), the traditional emphasis on social adaptation is being expanded to include strategies that promote plasticity and regeneration in the central nervous system. Such strategies are needed to optimize recovery of neurological function. For example, the known dependence of most cellular processes on physical activity has led to the novel concept that activity is important in neural repair. This hypothesis has given rise to activity-based restoration therapies (ABRT), which aim to optimize neural activity in the damaged spinal cord, particularly below the injury level. Here, we review the basic science and clinical evidence supporting the lifelong use of ABRT for recovery from spinal cord injury. We define and describe ABRT, and discuss its components, its clinical applications, its relationship to medical management of spinal cord injury, and the potential influences of medications on recovery. We also discuss the health benefits of ABRT under physiological and pathological conditions. We stress that lifelong ABRT is required to optimize return of function and to allow patients to benefit from any "cures" that will be discovered.

Differential effects of jump versus running exercise on trabecular architecture during remobilization after suspension-induced osteopenia in growing rats

High-impact exercise is considered to be very beneficial for bones. We investigated the ability of jump exercise to restore bone mass and structure after the deterioration induced by tail suspension in growing rats and made comparisons with treadmill running exercise. Five-week-old male Wistar rats (n = 28) were randomly assigned to four body weight-matched groups: a spontaneous recovery group after tail suspension (n = 7), a jump exercise group after tail suspension (n = 7), a treadmill running group after tail suspension (n = 7), and age-matched controls without tail suspension or exercise (n = 7). Treadmill running was performed at 25 m/min, 1 h/day, 5 days/wk. The jump exercise protocol consisted of 10 jumps/day, 5 days/wk, with a jump height of 40 cm. Bone mineral density (BMD) of the total right femur was measured by dual-energy X-ray absorptiometry. Three-dimensional trabecular bone architecture at the distal femoral metaphysis was evaluated using microcomputed tomography. After 5 wk of free remobilization, right femoral BMD, right hindlimb muscle weight, and body weight returned to age-matched control levels, but trabeculae remained thinner and less connected. Although both jump and running exercises during the remobilization period increased trabecular bone mass, jump exercise increased trabecular thickness, whereas running exercise increased trabecular number. These results indicate that restoration of trabecular bone architecture induced by jump exercise during remobilization is predominantly attributable to increased trabecular thickness, whereas running adds trabecular bone mass through increasing trabecular number, and suggest that jumping and running exercises have different mechanisms of action on structural characteristics of trabecular bone.

Bone remodeling and calcium homeostasis in patients with spinal cord injury: a review

Patients with spinal cord injury exhibit early and acute bone loss with the major functional consequence being a high incidence of pathological fractures. The bone status of these patients is generally investigated by dual-energy x-ray absorptiometry, but this technique does not reveal the pathophysiological mechanism underlying the bone loss. Bone cell activity can be indirectly evaluated by noninvasive techniques, including measurement of specific biochemical markers of bone formation (such as osteocalcin or bone-alkaline phosphatase) and resorption (such as procollagen type I N- or C-terminal propeptide). The bone loss in spinal cord injury is clearly due to an uncoupling of bone remodeling in favor of bone resorption, which starts just after the injury and peaks at about 1 to 4 months. Beyond 6 months, bone resorption activity decreases progressively but remains elevated for many years after injury. Conversely, bone formation is less affected. Antiresorptive treatment induces an early and acute reduction in bone resorption markers. Level of injury and health-related complications do not seem to be implicated in the intensity of bone resorption. During the acute phase, the hypercalcemic status is associated with the suppression of parathyroid hormone and vitamin D metabolites. The high sensitivity of these markers after treatment suggests that they can be used for monitoring treatment efficacy and patient compliance. The concomitant use of bone markers and dual-energy x-ray absorptiometry may improve the physician's ability to detect patients at risk of severe bone loss and subsequent fractures.

Sex differences in trabecular bone microarchitecture are not detected in pre and early pubertal children using magnetic resonance imaging

INTRODUCTION

Sex differences in trabecular bone microarchitecture have been reported in adults and adolescents, but studies in children are lacking. The primary aim of this study was to determine if there are sex differences in magnetic resonance imaging (MRI)-based measures of trabecular bone microarchitecture at the distal femur of children.

MATERIALS AND METHODS

Pre and early pubertal boys (n=23) and girls (n=20) between the 5th and 95th percentiles for height, body mass and BMI were studied. Apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th), trabecular separation (appTb.Sp) and a composite measure of trabecular bone microarchitecture (TBMcom) were assessed at the lateral aspect of the distal femur using MRI. Areal bone mineral density (aBMD), bone mineral content (BMC) and bone area were assessed at the distal femur using dual-energy X-ray absorptiometry (DXA). Tanner staging was used to assess pubertal development. Physical activity was assessed using an accelerometry-based activity monitor. Calcium intake was assessed using diet records.

RESULTS

There were no sex differences in age, height, femur length, body mass, physical activity or calcium intake (all P>0.05). There were no sex differences in any MRI-based measure of trabecular bone microarchitecture. Consistent with the MRI-based measures, there were no differences in aBMD, BMC or bone area from DXA at the distal femur (P>0.05). appBV/TV, appTb.N, appTb.Th, appTb.Sp and TBMcom were also moderately to strongly related to aBMD (r=0.73, 0.63, 0.51, -0.74 and 0.61, respectively, p<0.001) and BMC (r=0.84, 0.63, 0.66, -0.80 and 0.77, respectively, P<0.001).

CONCLUSIONS

The findings suggest that there are no differences in measures of trabecular bone microarchitecture at the distal femur of pre and early pubertal boys and girls who are similar in size, physical activity and calcium intake. Future studies with larger sample sizes that cover all pubertal stages are needed to determine if sex differences in trabecular bone microarchitecture emerge at the distal femur and other weight bearing bone sites.