Change in bone density, geometry and bone strength index of the radius and tibia in chronic stroke survivors

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Change in bone density, geometry and bone strength index of the radius and tibia in chronic stroke survivors

 

Author: Yang, Zhen Hui
Title: Change in bone density, geometry and bone strength index of the radius and tibia in chronic stroke survivors
Degree: M.Phil.
Year: 2012
Subject: Cerebrovascular disease -- Patients -- Rehabilitation.
Bone densitometry.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Rehabilitation Sciences
Pages: xxii, 245 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2522650
URI: http://theses.lib.polyu.edu.hk/handle/200/6568
Abstract: Background and purpose: A common complication following stroke is secondary bone loss in the upper and lower extremities, which can contribute to an increased risk of fragility fractures. Various stroke impairments, such as muscle weakness, spasticity, impaired cardiovascular health, and chronic disuse, may have a negative impact on bone health status in the hemiparetic extremities of patients after stroke. This study aimed to investigate (1) changes in forearm and hip bone mineral density (aBMD) using dual-energy X-ray absorptiometry (DXA), and volumetric BMD, bone strength indices of the radial and tibial epiphysis and diaphysis using peripheral quantitative computed tomography (pQCT) in patients after chronic stroke during a one-year follow-up period; and (2) the association of the changes in the key bone parameters with various stroke impairments measured at baseline. Methods: A total of 28 patients after chronic stroke (post-stroke duration of one year or more) and 27 healthy individuals participated in the study. DXA was used to evaluate the aBMD (in g/cm²) of the forearm and proximal femur on both sides. pQCT was used to evaluate the volumetric BMD (vBMD, in mg/cm³) and bone geometry of the radial and tibial epiphysis and diaphysis. Based on the pQCT-derived densitometric and geometric parameters obtained, a bone strength index was computed for each skeletal site. Each subject was also evaluated for grip strength (hand-held dynamometry), knee-extensor strength (hand-held dynamometry), spasticity (Modified Ashworth Scale), motor function (Fugl-Meyer Motor Assessment and Chedoke McMaster Stroke Assessment), and disuse (Motor Activity Log) of the paretic extremities. Cardiovascular health was measured by large artery elasticity index (C₁), and small artery elasticity index (C₂). The oxygen consumption rate (VO₂) during the Six-Minute-Walk Test was also measured. Each subject underwent the above assessment at the time of enrolment in this study, and again one year later.
Results: The results showed that in the stroke group, the DXA-derived aBMD values measured at the paretic forearm and proximal femur underwent significant decline (p<0.025) during the follow-up period, while the non-paretic side and healthy control subjects showed no remarkable changes in the same variables (p>0.05). pQCT-derived data revealed that the distal radial epiphysis on the paretic side showed a significant reduction in total vBMD (p=0.008) and bone strength index (p=0.014), whereas the non-paretic side revealed no significant change over time (p>0.05). In the radial diaphysis, the paretic side sustained a significant reduction in cortical bone mass (p=0.001), cortical area (p=0.001), and cortical thickness (p<0.001), while the non-paretic side demonstrated no significant change (p>0.05). In the distal tibial epiphysis, the stroke group sustained a significant reduction in total vBMD, trabecular vBMD and bone strength index on both sides, with the paretic side showing a greater amount of change (p<0.01). In the tibial diaphysis, the one-year reduction in cortical BMC on the paretic side was also more prominent than that on the non-paretic side. In contrast, the changes in pQCT parameters in the measured skeletal sites among the control subjects were largely non-significant. Pearson’s correlation analysis showed that in the upper limb, higher BMI at baseline was significantly related to less decline in bone strength index of the radius diaphysis on the paretic side (r=0.473, p=0.035). In the lower limb, better knee-extensor muscle strength (r=0.444, p=0.050) and longer six-minute-walk distance (r=0.471, p=0.036) measured in the initial assessment showed a significant correlation with less reduction of bone strength index measured at the tibial diaphysis on the paretic side. Conclusions: This study suggests that the hemiparetic radius, hip and tibia sustained unfavorable changes over time in the chronic stage of recovery. The magnitude of these changes, however, was less when compared with that previously reported in patients with acute and sub-acute stroke, indicating that the rate of bone changes is decelerating when the chronic stage is reached. Better recovery in certain neuromuscular (e.g., muscle strength) and cardiovascular (e.g., endurance) outcomes are related to more favorable bone outcomes in patients after chronic stroke. Strategies to modify these factors may be important in improving bone health in this group but will need further investigations.

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