Evaluating Function/Impairment of Low Back Pain Using SEMG
by Robert J. Gatchel, PhD, ABPP; Mark D. Ricard, PhD; Emily Brede, RN; and Krista J. Howard, MS
 Electrodiagnostic evaluations, with one type being electromyography
(EMG), are commonly performed in diagnosing nerve and muscle pain disorders. Conventional
EMG assessment is usually referred to as “needle EMG,” where a fine concentric
or monopolar needle electrode is inserted into a particular muscle. Quantitative analyses
are then conducted on needle insertion-generated activity, as well as motor unit action
potential waveforms. Another less intrusive form of EMG evaluation is surface EMG (SEMG).
Rather than inserting needles, which many patients complain of as being painful and too
invasive, electrodes are placed on the skin using simple adhesive collars and overlying
the muscle(s) being studied. One drawback of SEMG, as compared to needle EMG, is that only
superficial muscle activity can be recorded. Nevertheless, as will be reviewed, SEMG has
been found to be useful in evaluating movement, gait, postural, and functional
disturbances.
In this present article, we will focus on the use of SEMG in evaluating the degree of
physical impairment in low back pain (LBP). Indeed, whenever one evaluates painful spinal
disorders such as LBP—especially in workers’ compensation or personal injury
populations—as recently reviewed by Gatchel, Ricard et al,1 the degree of
potential physical impairment needs to be considered for employment/ injury compensation
issues. Impairment refers to the alteration of a person’s usual health status due to
anatomic or pathophysiologic abnormalities. For back pain, it is frequently evaluated by
measuring strength, lifting capacity, range-of-motion, aerobic capacity, as well as
measures of human performance.2 A traditional problem, though, has been the
lack of universal agreement about what measure(s) should be used in impairment
evaluations. The American Medical Association identified only range-of-motion in earlier
versions of its Guides to the Evaluation of Permanent Impairment, but it is no longer
included in the most recent 6th Edition. There are growing annual costs associated with
the diagnoses and care of musculoskeletal disorders such as LBP, amounting to tens of
billions of dollars in the United States alone.3 In fact, in a most recent
survey of expenditures among adults with back and neck problems, Martin et al reported a
65% increase (adjusted for inflation) of expenditures from 1997 to 2005, which was a more
rapid increase than overall health expenditures.4 Thus, there is a great need
to develop valid measures to objectively quantify physical function in patients with these
disorders. Such objective measures would aid in assessing both physical impairment needed
to address compensation issues, as well as use in determining a therapeutic endpoint
following treatment.
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— March 2009
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