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Modeling of the Hand

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Francisco J. Valero-Cuevas, Ph.D.

NCMRR Symposium. January 4, 2001

I. Introduction

  • Motivation
    • Hand disabilities often result in a disproportionate reduction in our ability to interact with the physical world and each other.
    • The complexity of the hand makes it difficult to characterize the biomechanical consequences of hand disabilities and rehabilitation strategies.
  • Anatomy of forefinger
  • Utility of hand models
    • By describing individual anatomical structures and the interactions among them, computer models can predict the biomechanical consequences of hand disabilities and rehabilitation strategies.
    • Because of the complexity of the hand, most models are of individual digits, not of whole hands.
  • Research paradigm for modeling of the hand/digits
  • Restoring pinch function
  • Brief overview of hand models
    • Because of the versatility of the hand, a biomechanical model that encompasses all aspects of hand function is not yet available (and is perhaps not feasible).
    • Instead, models focus on specific aspects of hand/finger function such as motion and force production for prehension.
  • Non-clinically oriented models
    • 2D motion of single fingers:
      Leijnse et al ('92-'97): The effect of tendon excursion on finger motion.
      Harding et al ('93): Motion of the fingers during piano playing.
    • 3D motion of multiple fingers:
      Buchholz & Armstrong ('92): Wrapping grasps around objects.
    • 2D force production of single fingers:
      Lee and Rim ('91 & '92): maximal grip force.
    • 3D force production of multiple fingers:
      Chao et al ('76 & '78): Joint and finger forces.
  • Clinically oriented models
    • An, Chao, Linscheid, Cooney et al at Mayo Clinic ('79-'85): 3D Joint and finger forces in the normal and abnormal hand.
    • Spoor ('83): 2D force production in the paretic finger.
    • Thompson, Giurintano, Hollister, Brand, Buford et al ('88-'95): 3D finger and thumb models for tendon transfers and muscle forces.
  • To become part of clinical practice:
    • Modeling of the hand must:
      Have the necessary level of anatomical detail (e.g., complete musculature).
      Consider the neuromuscular aspects of control.
      Include experimental validation.
  • Modeling Challenges

II. Three clinical research questions being pursued using mechanics-based models

First question

What biomechanical disability can be expected following paralysis of specific muscles?
How should musculotendons be re-routed to maximize post-operative fingertip force?
How does the CNS dynamically control the redundant musculature of the digits?

  • Forefinger model case study
    • 3D model Includes all 7 muscles & adjustable extensor mechanism
  • Segments and joints Moment arms Extensor mechanism
  • Model predictions
  • Measured fingertip force
  • Simultaneous fine-wire EMG recordings
  • The model can predict the coordination patterns measured 3D force production
  • How to validate this prediction of weakness in pinch?
    • Developed hybrid cadaveric/optimization model to avoid the uncertainty in the anatomical assumptions made in classical computer models.
  • Apply known tensions to each tendon, measure output at fingertip Maximal predicted force
  • First finding
    • Somewhat counter-intuitively, the paralysis of extensor muscles of the forefinger weakens pinch force.
    • Thus, biomechanical modeling contributes to our understanding of the complex causes of disability.

Second question

What biomechanical disability can be expected following paralysis of specific muscles?
How should musculotendons be re-routed to maximize post-operative fingertip force?
How does the CNS dynamically control the redundant musculature of the digits?

    Biomechanical consequences of ulnar palsy and its treatment with tendon transfers
  • Second finding
    • Shifting by a few millimeters the insertion point of tendons transferred to prevent claw deformity in low ulnar palsy is predicted to greatly enhance fingertip forces.
    • Thus, biomechanical modeling can be used to improve the effectiveness of treatment strategies.

Third question

What biomechanical disability can be expected following paralysis of specific muscles?
How should musculotendons be re-routed to maximize post-operative fingertip force?
How does the CNS dynamically control the redundant musculature of the digits?

  • When producing sub-maximal forces:
    How do we select and implement coordination patterns from a large pool of valid alternatives in real-time? Hypothesis: the coordination pattern for the largest expected force is scaled to produce lower forces.
  • Modeling muscle redundancy
    • Predicted coordination patterns capable of producing 50% of maximal palmar force
  • Coordination patterns used for maximal and sub-maximal force
  • Coordination patterns used for different fingertip force magnitudes
  • Third finding
    • The CNS seems to simplify the control of redundant musculature by scaling whole muscle coordination patterns.
    • Thus, we can design surgeries to produce large forces knowing that the CNS can use a similar coordination pattern to produce post-operative forces of high and low magnitude.

III. Current research directions

  • To create a computer model to simulate dynamic interactions among multiple digits.
  • To design, compare and validate alternative surgical treatments and rehabilitation strategies.
  • To develop methods to evaluate hand function.
  • To understand the control of manipulation.

IV. Future work: Modeling unaffected and disabled manipulation ability

V. Conclusion

  • Mechanics-based modeling can be combined with neurophysiological and clinical principles to effectively describe the biomechanical consequences of hand disabilities and rehabilitation strategies.

Thank you

Last Updated Date: 11/30/2012
Last Reviewed Date: 11/30/2012
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