An estimated 10 million Americans have osteoporosis and another 44 million have low bone mass. The primary concern for patients with this disease is the increased risk of fracture. The most common site of osteoporotic fracture is the vertebral column, accounting for 700,000 fractures annually. Given the fragility of osteoporotic vertebrae, trauma is not necessarily a factor in these fractures; often, everyday postural stresses are sufficient to induce a fracture. These fractures can substantially reduce patient quality of life. Current therapies attempt to control this disease on the cellular level; however, existing treatment regimes fail to address methods for preventing fractures based on patient motion and instruction.
The Bone Safety Evaluation (BSE) is a clinical technique that qualitatively and quantitatively evaluates a patient's risk of fracture. The BSE consists of a Safe Functional Motion (SFM) subtest, which analyzes ten everyday activities for spinal compression forces, balance and coordination, and strength and flexibility. The goal of this research was to develop a quantitative patient-specific score of fracture risk during the BSE activities.
A Functional Risk for Fracture Index (FRFI) was defined as the ratio of the compressive force on the spine associated with a specific activity (Fact) to the theoretical failure force sustainable by the vertebral body (Fmax). The calculations made were specific to L3, which is assumed to experience the highest degree of flexion, and is most prone to fracture.
A biomechanical analysis of the spinal forces during bending was used as the basis for the calculation of Fact (Duan, Seeman et al. 2001). The force calculation method developed by these authors was applied to the postural configurations associated with ten typical activities of daily living. The analysis by Duan et al was expanded to more accurately estimate the location of the center of mass of the trunk, to compensate for spinal deformities and different body morphologies for each patient. Specifically, spinal deformities such as lordosis or kyphosis were taken into account through the measurement of the angular orientation of spinal segments during erect posture. The mass distribution of the upper body was refined by adapting information on body type (endomorph, mesomorph and ectomorph). Also, the relative positions of the upper body segments during the different activities and external weight added during lifting tasks were incorporated into the calculation of location of the center of mass during different activities for each patient. Thus this calculation of compressive force on L3 (Fact) was patient-specific and task-specific.
The theoretical maximum force sustainable by a vertebral body (Fmax) was estimated from dual-energy x-ray absorptiometry (DXA) bone mineral density (BMD) scores. Regression equations were calculated based on graphical results of the maximum force sustained by a vertebral body as a function of BMD (Ebbesen, Thomsen et al. 1999).
An FRFI (Fact/Fmax) greater than or equal to one represents an activity with high fracture risk. Once a patient's fracture risk for specific activities is assessed, the patient can be instructed on which activities to avoid and alternative motions that reduce spinal compression forces. Future refinement of the FRFI will utilize motion analysis to determine more accurate vertebral body flexion angles during each of the BSE activities, allowing the compressive force (Fact) to be more specific to how each patient completes each activity. Additional information on the effects of activities involving trunk rotation and dynamic motion on the spinal compression forces will be investigated. More accurate methods of estimating Fmax for each patient will also be explored.
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Faculty Member's Name: Chris Recknor, MD
I have no relationships to disclose.
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