Development of Quantitative Instrumentation for Cone of Economy Analysis: Bridging Radiographic and Clinical Measures

Background context: Postural misalignment and compromised balance are major contributors to fall risk in the elderly, leading to significant physical injuries, reduced quality of life (QOL), and increased healthcare burdens. Evaluating postural stability is critical for fall prevention. The cone of economy (CoE) concept explores the range of motion of the center of mass and head required to maintain a stable upright posture, yet its measurement remains challenging due to the limitations of existing methods.

Purpose: This study introduces a novel apparatus for real-time measurement of both external and internal CoEs, offering a cost-effective alternative to expensive and complex traditional methods that require extensive data processing.

Study design/setting: The study employed a controlled experimental design to develop and validate the proposed CoE measurement apparatus in a laboratory setting using a sample of healthy young adults.

Methods: The proposed apparatus used two spherical measuring units to independently track pelvic and T1 vertebra motion, employing dual rotational magnetic encoders and a linear displacement sensor for precise 3D motion contour capture.

Results: Validation experiments confirmed the system's reliability, achieving an average measurement error below 1.5 mm. The CoE is not an idealized cone but has an irregular conical shape, influenced by physiological factors (height and weight). The average range of sway (RoS) for external CoE at T1 was 42.7 (coronal), 47.6 (sagittal), and 12.5 cm (vertical), whereas that at the pelvic position was 14.3, 13.4, and 8 cm, respectively. The average RoS for internal CoE were smaller: 10.4 (coronal), 6.9 (sagittal), and 2 cm (vertical) at T1 and 8.2, 5.8, and 2.2 cm, respectively, at the pelvic position. The external CoE exhibited a larger RoS at the body's front, reflecting the foot's role in balancing forward shifts of gravity.

Conclusions: Preliminary findings highlight a stronger correlation between external CoE and height than internal CoE, establishing a foundation for CoE research with implications for fall prevention and balance assessment.

Clinical significance: This study introduces a reliable, cost-effective apparatus for real-time cone of economy (CoE) measurement, offering dynamic insights into postural stability, fall risk, and personalized balance assessment in clinical settings.