COMMENTARY
Use of the Medical Research Council
Muscle Strength Grading System in the
Upper Extremity
Michelle A. James, MD
From Shriners Hospital for Children Northern California and University of California Davis School of
Medicine, Sacramento, CA.
History of Muscle Strength Grading
The Medical Research Council of Great Britain
(MRC) system is the best known and most commonly used muscle strength grading system for manual muscle testing (MMT) worldwide. Dyck et al1
trace the development of the MRC system to the
treatment of war injuries and poliomyelitis. S.W.
Mitchell, a Civil War surgeon, recognized nerve
damage as a cause of muscle weakness in 1872.
Mitchell and M.J. Lewis were later responsible for
the first known effort to grade neuromuscular signs
when they classified ataxic gait in 1886. In 1917,
R.W. Lovett, a Boston orthopedist, published the
muscle scoring system later adapted by the MRC
based on his experience treating poliomyelitis; he
credited W. Wright, a physical therapist, with developing the muscle testing methods.2 As a result of
their experiences treating World War II injuries, 12
surgeons formed the Nerve Injuries Committee of the
British Army (G. Riddoch [Chair], W.R. Bristow,
H.W.B. Cairns, E.A. Carmichael, M. Critchley, J.G.
Greenfield, J.R. Learmonth, H. Platt, H.J. Seddon,
C.P. Symonds, J.Z. Young, F.J.C. Herrald) and developed the classic handbook Aids to the Investigation of Peripheral Nerve Injuries.3 This manual illustrates the major actions of limb muscles and how
they should be tested; defines the concepts of prime
movers, synergists, and antagonists; and includes the
muscle grading scale familiar to all orthopedic surgeons (Table 1). A modified version of this manual,
Aids to the Examination of the Peripheral Nervous
System, fourth edition, was published in 2000.4 Because the MRC system was intended to be used to
grade recovery from paralysis (grade 0) attributable
to nerve repair, the greatest emphasis is placed on
severe degrees of weakness (grades 1, 2, 3); although
this system is ordinal, the difference in strength between different grades was not assumed to be constant. In general, the intertester and intratester reli154
The Journal of Hand Surgery
ability of MMT graded with the MRC system has
proven acceptable.2
Problems With the MRC
Not surprisingly, the MRC system has been widely
used to describe muscle strength in the upper extremities of people with conditions other than war
injuries and poliomyelitis. It has been modified
almost as often as it has been used, primarily
because of the wide, difficult-to-quantify gaps between grades 3 and 4 and grades 4 and 5 and
because large joint motors such as the deltoid may
recover enough strength to provide resistance to
MMT (grade 4) without having enough strength or
strong enough synergists to provide full motion
against gravity (grade 3). Another problem with
this system is inherent intersubject variability in
muscle strength, rendering it useful primarily for
intrasubject changes in strength rather than intersubject comparisons. In addition, this system
tempts the examiner to consider a muscle with a
certain grade of strength as having the same degree
of recovery as another muscle with the same grade,
when in fact the amount of recovery necessary to
enable the deltoid to be graded 3 may be considerably different than the amount of recovery necessary to enable a wrist extensor to be graded 3.
The challenges of applying MMT graded by the
MRC to all types of nerve injuries as a measurement of the results of modern repair techniques,
combined with the fact that no other muscle grading scales are widely accepted, have led to attempts to modify this system. “Critical Reappraisal
of MRC Muscle Testing for Elbow Flexion” by
MacAvoy and Green quantifies some of the problems encountered when the MRC is used other
than as originally intended—for instance, to quantify improvement between grades, especially
grades 3, 4, and 5.
Michelle A. James / MRC Grading in the Upper Extremity
Table 1. Medical Research Council Grades
Grade
Muscle State
0
1
2
No contraction
Flicker or trace of contraction
Active movement with gravity
eliminated
Active movement against gravity
Active movement against gravity
and resistance
Normal power
3
4
5
Data from the Medical Research Council.3
Modifications of the MRC
In the past 6 years at least 8 publications in The
Journal of Hand Surgery have referred to this grading system to quantify the results of surgical reconstruction in tetraplegia,5 nerve repair,6 brachial
plexus birth palsy,7–9 brachial plexus injury,10,11 and
opposition transfer for carpal tunnel syndrome.12 All
cited the MRC (although Leechavengvongs et al10,11
did not cite an original MRC publication), but all
modified its intended use by presenting only preoperative data5,8; reporting only “average increase of
British Medical Research Council units”12; subdividing grade 4 into 4 –, 4, and 4⫹5; adding together the
scores of muscles sharing the innervation of a peripheral nerve to create a composite score6; describing deltoid function as grade 4 without full shoulder
abduction against gravity9,11; or eliminating grades 4
and 5 but expanding grades 2 and 3.7 Of all these
recent Journal of Hand Surgery publications, only
Chen et al9 and Curtis et al7 note that they have used
a modified version of the MRC, and only Curtis et al7
formally validated their modification, the Active
Movement Scale, by studying interrater reliability.
Discussion
Perhaps World War II surgeons using early techniques of nerve repair were gratified to achieve grade
3 strength in a previously paralyzed muscle, and the
differences between grades 3, 4, and 5 did not concern them, because this level of recovery was usually
not attained. Modern techniques may achieve better
results and engender higher expectations of a measurement system.
A new system of grading for MMT should retain
the advantages of the MRC (wide acceptability, ease
of use, usefulness for most muscles, applicability to
motor recovery from all types of nerve injury). Useful potential modifications of the MRC include a
grade for a muscle that achieves strength against
155
resistance but not against gravity and a standardized
subdivision of grade 4.
At the cost of the convenience of MMT, actual
measurement of torque provides much more detailed
and accurate measurement of muscle strength, especially for the shoulder and elbow.13–16 The gold standard is isokinetic dynamometry using machinery (eg,
Cybex [Medway, MA], KinCom [IsoKinetic International, Harrison, TN]). The clinical usefulness of such a
machine, however, is limited by the cost and size of the
apparatus and the time required for positioning and
testing.15 In addition, the minimum measurable strength
on some isokinetic dynamometers may be more than
that recoverable by nerve repair. Specialized devices
have been developed for measuring isometric elbow
and shoulder strength13,14 and hand and wrist twisting
strength,17 but these are not widely available. A handheld dynamometer (HHD) provides more accurate
measurements of isometric muscle strength than MMT
and is easy to use as long as the examiner has sufficient
strength to stabilize the device.15,16 Methods of increasing reproducibility and reliability using a HHD have
been developed, and normative data are available for
different populations.16 (An example of such a device
available in the United States is the microFET 2 Dynamometer; Hoggan Health Industries [West Jordan, UT]).
Unless HHD is widely adopted or until a better
grading system is developed and well validated, the
MRC will continue to be used. When it is altered,
these alterations should be specifically described and
enumerated, and the resulting system should be referred to as a modification. Otherwise, tinkering with
the MRC erodes the elegant and prescient intent of
the Nerve Injuries Committee. With their publication
of the MRC, this group of surgeons accomplished a
remarkable achievement: a simple grading system
used worldwide for over 60 years, applied with extraordinary success despite its shortcomings. Its wide
acceptance precludes the need for further validation of
the MRC, but any substantial alterations should be
validated before presentation to show that they reliably
and reproducibly achieve the goals of the investigators.
Received for publication November 13, 2006; accepted in revised form
November 15, 2006.
No benefits in any form have been received or will be received from
a commercial party related directly or indirectly to the subject of this
article.
Corresponding author: Michelle A. James, MD, Shriners Hospital for
Children, 2425 Stockton Blvd, Sacramento CA 95817; e-mail:
mjames@shrinenet.org.
Copyright © 2007 by the American Society for Surgery of the Hand
0363-5023/07/32A02-0002$32.00/0
doi:10.1016/j.jhsa.2006.11.008
156
The Journal of Hand Surgery / Vol. 32A No. 2 February 2007
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