Wendy Murray
Northwestern University

Computer models of the musculoskeletal system provide quantitative representations of anatomy
and function from which we can derive a better understanding of the neural control of
movement. This talk will:
• describe the development and validation of a general computer-graphics-based
musculoskeletal model that accurately represents the biomechanics of the upper
extremity, and
• demonstrate how computer simulations of orthopaedic surgical procedures that restore
function following cervical spinal cord injury have generated hypothesis-driven
experimental studies that will ultimately provide a scientific basis for surgical decisionmaking.
This work illustrates how biomechanical modeling can provide both a meaningful entry point
and a logical research direction for complicated clinical questions.
A three-dimensional biomechanical model of the upper extremity has been developed
that includes 15 degrees of freedom representing the shoulder, elbow, forearm, wrist, thumb, and
index finger, and 50 muscle compartments crossing these joints. The model characterizes the
mechanical actions of the muscles of the upper extremity, as determined by comparisons to
experimentally measured moment arms. The force-generating characteristics of the muscles are
derived from detailed anatomical studies of muscle architecture. Total isometric joint moments
estimated using the model are comparable to the isometric moments produced by healthy adult
subjects during maximum voluntary effort.
The upper extremity model has been applied to simulate tendon transfers that restore
important aspects of hand function to individuals who are paralyzed. Tendon transfers are
reconstructive surgical procedures that involve transferring the tendon of a non-paralyzed muscle
to that of a paralyzed muscle to restore voluntary control of the paralyzed function. The surgical
simulations have been integrated with both intra-operative measurements of muscle sarcomere
lengths (obtained using laser diffraction) and post-operative assessments of hand impairment
(quantified with custom-designed transducers). The results suggest that the choice of surgical
attachment length has the potential to predictably alter functional outcomes. The hypotheses
from our surgical simulations have generated a multi-center trial; we are currently quantifying
both surgical attachment lengths and post-operative outcomes to characterize the link between
surgical technique and clinical outcome.

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