Posture shifting after spinal cord injury using functional neuromuscular stimulation – a computer simulation study

J Biomech, 2011 · DOI: 10.1016/j.jbiomech.2010.12.020 · Published: June 3, 2011

Spinal Cord Injury Neurology Biomechanics

Simple Explanation

This study uses a computer model to explore how people with spinal cord injuries (SCI) might be able to shift their posture while standing, using electrical stimulation of their muscles. The model includes the trunk, pelvis, and legs. The model simulates forward and sideways leaning movements, taking into account the forces applied by the upper body when using a support device like a walker. The goal is to identify which muscles need to be stimulated to allow these shifts with minimal effort from the upper body. The findings suggest that stimulating specific trunk and leg muscles can help people with SCI change their standing posture using minimal effort from their upper body. This could allow them to reach for things more easily and increase their overall standing work volume.

Study Duration

Not specified

Participants

Modeled on an average healthy male (weight 840.7 N, height 1.72 m)

Evidence Level

Level 5: Computer simulation study

Key Findings

1
For anterior shifting, inclusion of the Psoas and External Obliques bilaterally resulted in the least relative UE effort (0.119, mean UE effort = 45.3N ≡ 5.4% BW).
2
For lateral shifting, the set including the Psoas and Latissimus Dorsi bilaterally yielded the best performance (0.025, mean UE effort = 27.8 N ≡ 3.3% BW).
3
Adding the Psoas alone bilaterally competed favorably in overall best performance across both maneuvers.

Research Summary

This paper explored the theoretic feasibility of enabling individuals with SCI to undertake posture shifts while standing with FNS using a 3D musculoskeletal model adjusted for muscle properties typically observed in individuals with SCI and a powerful dynamic optimization software package. Muscle Sets 5, 8 and 9 clearly outperformed the others in terms of minimizing overall UE effort. Whereas only Psoas would be sufficient for the forward lean maneuver, adding either External Obliques or Latissimus Dorsi would be essential for sideways lean. Overall, this analysis demonstrated that it is possible to identify and activate an optimal set of paralyzed lower extremity and trunk muscles to carry out useful standing maneuvers with minimal upper extremity effort.

Practical Implications

FNS System Development

These findings are valuable for developing future FNS standing systems, particularly in selecting the optimal muscle combinations for stimulation.

Increased Work Volume

By enabling postural shifting, individuals with SCI can increase their work volume and independence during activities of daily living.

Balance Control

The attained postures can serve as set-points for controllers that maintain balance in the presence of destabilizing factors.

Study Limitations

1
Only one of the muscle characteristics (maximum isometric force) was adjusted for effect of paralysis.
2
The maximum isometric force was scaled by a single factor (50%) for all muscles. It is possible that different muscles could be affected differently by SCI.
3
The optimization algorithm required otherwise continuous variables to be discretized and interpolated to estimate values between samples. This could have compromised the smoothness of the results.

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