Evaluating stability of human spine in static tasks: a combined in vivo-computational study

Abstract

Various interpretations and parameters have been proposed to assess spinal stability such as antagonist muscle coactivity, trunk stiffness and spinal buckling load; however, the correlation between these parameters remains unknown. We evaluated spinal stability during different tasks while changing the external moment and load height and investigated likely relationships between different EMG- and model-based parameters (e.g., EMG coactivity ratio, trunk stiffness, force coactivity ratio) and stability margins. EMG and kinematics of 40 young healthy subjects were recorded during various quasi-static tasks. Muscle forces, trunk stiffness and stability margins were calculated by a nonlinear subject-specific EMG-assisted-optimization musculoskeletal model of the trunk. The load elevation and external moment increased muscle activities and trunk stiffness while all stability margins (i.e., buckling loads) decreased. The force coactivity ratio was strongly correlated with the hand-load stability margin (i.e., additional weight in hands to initiate instability; R² = 0.54) demonstrating the stabilizing role of abdominal muscles. The total trunk stiffness (Pearson’s r = 0.96) and the sum of EMGs of back muscles (Pearson’s r = 0.65) contributed the most to the T1 stability margin (i.e., additional required load at T1 for instability/buckling). Force coactivity ratio and trunk stiffness can be used as alternative spinal stability metrics.

Keywords:

• Spine biomechanics
• spinal stability
• musculoskeletal modeling
• finite element modeling

Acknowledgement

Ali Shahvarpour had a post doctoral scholarship from the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) of Quebec, Canada. The authors would like to thank Christina Gravel, Myriam Gauvin, Anne-Marie Jean, Ariane Viau and Cynthia Appleby for data collection, Hakim Mecheri for data processing, as well as Amir Hossein Eskandari for his comments and helps.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST-2019-0018), fonds de recherche du Québec en nature et technologies (FRQNT-200564) and Mitacs (IT18289).