IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING, VOL. 16, NO. 3, JUNE 2008 255
Musculoskeletal Model-Guided, Customizable
Selection of Shoulder and Elbow Muscles
for a C5 SCI Neuroprosthesis
Juan Gabriel Hincapie, Dimitra Blana, Edward K. Chadwick, and Robert F. Kirsch, Member, IEEE
Abstract—Individuals with C5/C6 spinal cord injury (SCI) have
a number of paralyzed muscles in their upper extremities that
can be electrically activated in a coordinated manner to restore
function. The selection of a practical subset of paralyzed muscles
for stimulation depends on the specific condition of the individual,
the functions targeted for restoration, and surgical considerations.
This paper presents a musculoskeletal model-based approach for
optimizing the muscle set used for functional electrical stimulation
(FES) of the shoulder and elbow in this population. Experimen-
tally recorded kinematics from able-bodied subjects served as
inputs to a musculoskeletal model of the shoulder and elbow,
which was modified to reflect the reduced muscle force capacities
of an individual with C5 SCI but also the potential of using FES
to activate paralyzed muscles. A large number of inverse dynamic
simulations mimicking typical activities of daily living were per-
formed that included 1) muscles with retained voluntary control
and 2) many different combinations of stimulated paralyzed
muscles. These results indicate that a muscle set consisting of
the serratus anterior, infraspinatus and triceps would enable the
greatest range of relevant movements. This set will become the
initial target in a C5 SCI neuroprosthesis to restore shoulder and
elbow function.
Index Terms—Functional electrical stimulation (FES), muscu-
loskeletal modeling, neural prostheses, spinal cord injury (SCI).
I. INTRODUCTION
APPROXIMATELY 11 000 new cases of spinal cord injury(SCI) occur each year in the U.S. and a total of 250 000
individuals live today with SCI. Cervical SCI comprises 51%
of the total number of SCI cases, with 26% of all SCI cases
occurring at the C5/C6 level [1]. Individuals with complete in-
juries at the cervical level lose control over a number of muscles
in their upper extremity and their lower extremities are totally
paralyzed. A complete C5/C6 SCI results in hand muscle paral-
ysis and loss of wrist and elbow extension. Paralysis at the more
proximal joints is partial. Typically, muscles providing forearm
Manuscript received August 1, 2007; revised December 10, 2007; accepted
February 9, 2008. This work was supported by the National Institutes of Health
National Institute of Neurological Disorders and Stroke (NIH NINDS) under
Contract N01-NS-1-2333 and Contract N01-NS-5-2365.
J. G. Hincapie, D. Blana, and E. K. Chadwick are with the Department of
Biomedical Engineering, Case Western Reserve University, Cleveland, OH
44106 USA and with the VA Cleveland Functional Electrical Stimulation
Center, Cleveland, OH 44106 USA (e-mail: juan.hincapie@case.edu; dimitra.
blana@case.edu; edward.chadwick@case.edu).
R. F. Kirsch is with the Department of Biomedical Engineering, Case
Western Reserve University, Cleveland, OH 44106 USA and also with the
Louis Stokes Cleveland Department of Veterans Affairs Medical Center,
Cleveland, OH 44702 USA (e-mail: robert.kirsch@case.edu).
Digital Object Identifier 10.1109/TNSRE.2008.922681
pronation, elbow extension, and shoulder adduction and hori-
zontal flexion are paralyzed, while their antagonists (performing
forearm supination, elbow flexion, and shoulder abduction and
horizontal extension) retain at least partial voluntary control.
Glenohumeral and scapular stability can be severely impaired
by paralysis of rotator cuff and serratus anterior muscles, re-
spectively [2]. This paralysis pattern greatly limits the ability to
reach specific areas of the arm’s workspace and also prevents
mechanical coordination between different motions needed for
other functions.
Neuroprostheses are systems that use functional electrical
stimulation (FES) to activate paralyzedmuscles in a coordinated
way so that useful function can be provided. A neuroprosthesis
activates the peripheral nervous system by delivering electrical
impulses to the motor neurons innervating the paralyzed mus-
cles, thus replacing the electrical signals coming from the brain
through the injured spinal cord. Individuals with a C5/C6 SCI
have been provided with functional hand grasp through the use
of an upper extremity neuroprosthesis, improving their ability
to handle objects [3], [4]. However, paralysis and weakness of
shoulder and elbow muscles results in a considerable reduction
in the person’s ability to perform basic daily activities that
require positioning of the arm in space. FES to restore proximal
arm function has been explored experimentally but has not
been widely deployed into clinical settings. Percutaneous and
surface FES systems developed for C4 SCI have used prepro-
grammed patterns of stimulation of arm muscles to restore
simple functions like feeding [5]–[7]. In the C5-C6 SCI popula-
tion, the conditions are very different than for C4 because many
proximal muscles retain voluntary control and there is less
proximal denervation [8]. Crago et al. [9] stimulated the triceps
muscles of two C6 SCI individuals to restore elbow extension
sufficient to allow the users to efficiently move objects within
an expanded workspace. Although they demonstrated the basic
feasibility of stimulating proximal muscles to restore function,
none of these earlier studies systematically investigated the im-
portance of stimulating specific muscles for increasing function
while simultaneously maintaining shoulder (glenohumeral and
scapular) stability.
The complexity of the shoulder has been a particular chal-
lenge for movement restoration. The shoulder mechanism con-
sists of several joints (sternoclavicular, acromioclavicular, and
glenohumeral) and an articulation between the medial border
of the scapula and the thorax. The coordinated actions of sev-
eral muscles acting across these joints results in a very large
range of shoulder motion and the ability to reach, lift, and move
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