Using musculoskeletal modeling to evaluate the effect of ankle foot orthosis tuning on musculotendon dynamics: a case study

Abstract

Purpose: This case study examines the influence of an ankle foot orthosis footwear combination (AFO-FC) on musculotendon lengths and gait kinematics and kinetics after right thrombotic stroke resulting in left hemiplegia. Methods: Gait analysis was performed over three visits where the subject walked with an AFO-FC with two shank-to-vertical angle (SVA) alignments, a posterior leaf spring AFO (PLS AFO), and shoes alone. Biomechanical and musculoskeletal modeling was used to evaluate musculotendon lengths, kinematics, and kinetics for each condition. Results: The AFO-FC improved walking speed and non-paretic kinematics compared to the PLS AFO and shoes alone. The operating length of the paretic gastrocnemius decreased with the AFO-FC improving knee kinematics in swing, but not stance. As the SVA of the AFO-FC was reduced from 15° to 12°, internal ankle plantar flexor moment increased. Conclusions: Musculoskeletal modeling demonstrated that the AFO-FC altered gastrocnemius operating length during post-stroke hemiplegic gait. Using these tools to evaluate muscle operating lengths can provide insight into underlying mechanisms that may improve gait and guide future AFO-FC design.

Implications for Rehabilitation

• Modeling musculotendon operating lengths during movement has the potential to inform how ankle foot orthoses (AFO) affect tight muscles and improve mobility after stroke.

• Adjusting shank-to-vertical angle (SVA) of the AFO-footwear combination (AFO-FC) has the potential to improve gait kinematics by controlling length of the pathologic gastrocnemius and maximizing internal ankle plantar flexor moment of individuals with neuromuscular disorders.

Keywords:

• Ankle foot orthoses
• gait
• muscle length
• musculoskeletal modeling
• tuning

Acknowledgements

We wish to thank Donald McGovern, CPO, for his orthotic expertise in this case study and Rebecca Stine, MS, for data collection and processing. We also acknowledge use of the Jesse Brown VA Medical Center Motion Analysis Research Laboratory.

Declaration of interest

This case study was funded by National Institutes of Health (NIH) under Grant No. K12HD073945 (Principle Investigator: Katherine Steele) and the National Institute on Disability and Rehabilitation Research (NIDRR) of the U.S. Department of Education under Grant No. H133E080009 (Principle Investigators: Steven Gard and Stefania Fatone). The opinions contained in this publication are those of the grantee and do not necessarily reflect those of the Department of Education.