Disability assessment should be viewed as an attempt to determine
the behavior or performance of an individual in a specific context.16 Loss
of a specific function such as the inability to bend to pick up
a 15-lb box at work may coexist with the ability to bend and pick
up a 30-lb, 3-year-old child. This functional dissonance can exist
without conscious malingering because of the powerful differences
between the absolute inability to perform a task versus the inability
to perform a certain task comfortably in a specific environmental
context. This makes the differentiation between those who cannot
work from those who do not want to work quite difficult. Pain is
subjective and is influenced by environmental factors. Impairments
and disabilities may fluctuate depending on the situation in which
a chronic pain patient finds himself.
There are a wide range of functional assessment methods available,
which vary from simple range-of-motion measurements that can be
easily performed in the office setting, to sophisticated, 2-day
functional capacity evaluations that require expensive equipment
and trained personnel. The most commonly used methods are pain measurement
tools, functional assessments (by patient report or examination),
psychological measurements, and information about the general health
status. The use and combination of these different methods depends
largely on the goal of the assessment. These goals may be a medicolegal
disability rating in a workers’ compensation case, identification
of limitations to direct the patient to an appropriate therapy program,
or for research purposes. Table 84-1 gives an overview of the different
categories and frequently used assessment methods in pain patients.
The most widely used measurements are discussed in the following
Since pain is a multidimensional experience and is private and
subjective in nature, it may be the most difficult measurement to
perform in health assessment. Its results often do not follow the basic
requirements of psychometric measurement, that is, reliability and
validity. Pain measurement can capture two dimensions of the pain
experience; namely, the sensory aspects of the pain and the person’s
emotional reaction to the pain. Although most clinical applications
use fairly simple intensity scales, newer measurement methods are
starting to evolve. Based on sensory decision theory, these methods
attempt to distinguish the stimulus strength from the subjective response.
It has been demonstrated, for example, that a placebo works as an
analgesic primarily by reducing the respondent’s tendency
to label an experimental stimulus as “painful” rather
than by altering the person’s ability to feel it. Thus,
the placebo seems to alter the affective response, not the perception
of the stimulus.17
Most pain measurement methods can be divided in the following
categories: pain questionnaires that record verbal or written responses
to pain; behavioral measurements of pain that depend on observed
pain behaviors of the subject; and analog methods, commonly used
in laboratory studies, in which the respondent compares his pain
with an experimentally induced pain stimulus of known intensity.18 However,
these different approaches measure different aspects of pain, and
there appears to be little correlation between them.
The most commonly known and widely accepted questionnaires are
the different subtypes of the visual analog pain rating scales.
They provide a simple way to record a subjective estimation of pain
intensity. Several types have been used, but the original scale,
popularized by Huskisson, consisted of a straight line, 10-cm long,
that represented the range of pain to be rated.19 The
visual analog scale (VAS) has been studied extensively, showing
excellent reliability and adequate validity. In the comparison of
different types of pain rating scales, it has been demonstrated
that the numerical ratings are preferable to the verbal rating scales.
For children and illiterate patients, a version showing faces is
available. Overall, the VAS provides a robust, sensitive, and reproducible
method of expressing pain severity that is applicable to a wide
age range (children age 5 and older to adults that are cognitively
intact) and is easily applied in a clinical setting.
Melzack’s McGill Pain Questionnaire (MPQ) is the most
commonly used measurement to describe the diverse dimensions of
pain. The MPQ was initially presented in 1975 as a preliminary method.
However, the questionnaire continues to be used in its original
form and is considered the gold standard against which other, newer
instruments are compared.18 An attempt to address
three major dimensions of pain—sensory-discriminative,
motivational-affective, and cognitive-evaluative—are represented
on the MPQ. The complete MPQ includes the patient’s history
and diagnosis, drug regimen, symptoms, and the effects of pain on
the patient. The most commonly used section, however, is the 102-word
questionnaire in which the patient has to mark pain attributes (i.e.,
sharp, burning, lancinating, punishing), pain intensity, accompanying
symptoms (i.e., headache, dizziness), sleep, food intake, activity,
and time course. It also includes a dermatomal pain drawing.
Four different scoring methods have been described by Melzack.
The reliability of the MPQ is only weak, and the validity is adequate.
There have been considerable discussions whether the selection and
grouping of words reflect the dimensions he proposed.20 Nevertheless,
the importance of the MPQ is demonstrated by the incorporation of
certain of its sections into several other scales and its use in
many study protocols. The questionnaire takes about 15 to 20 minutes
to administer, and is therefore probably too long for a routine
office visit, but it may be helpful for an initial evaluation.
Limitations at the impairment level can be easily measured with
the addition of a small number of functionally oriented examination
techniques. Determining physical parameters such as range of motion,
strength, lifting, and endurance can be incorporated in routine
office visits or evaluation protocols and enables numeric documentation
of structural impairment. Waddell studied the correlation between
physical examination findings and self-reported disability in low
back pain patients, demonstrating that total lumbosacral flexion
measured at the T12-L1 interspace explained the greatest proportion
of variance in disability scores when compared with any other physical
examination test performed to assess chronic low back pain.21 Once
impairments are identified, treatment can focus on improvement of
these functions rather than pain reduction. This becomes increasingly
important in chronic pain patients, in which a pain elimination
treatment approach is rarely successful.
Inclinometer techniques have become increasingly popular, especially
in the physical assessment of back pain patients, since they are
easy to apply.22 They have become standard measurements
in functional restoration programs for chronic back pain. Total
lumbosacral flexion and extension can be assessed by placing a single
inclinometer over the T12-L1 spinous processes. Straight leg raising
can be tested by using the inclinometer placed on the tibial tuberosity.
Suggested normal range of motion values for lumbosacral mobility are
a minimum of 100 degrees of flexion and 25 degrees of extension,
and for straight leg raising, a minimum of 75 degrees. Recorded
measurements can be documented on graphs for quick reference (Fig.
84-2). Initial measurements in pain patients are likely to be influenced
by psychological issues as well as physical tolerances, since patients
may be inhibited by emotional distress, fear of injury, and pain.
Therefore, although measurements may not represent true physiologic abilities,
they still provide a numeric measure of the patient’s psychophysical
status and a meaningful starting point for treatment decisions.
Graph for lumbosacral flexion and extension measured
with the single inclinometer technique.
The testing of strength, lifting, and endurance can be performed
in a number of ways. None of the strength measure methods (isometric,
isotonic or isokinetic) is superior in this setting, since all provide
quantification of strength impairments. One relatively inexpensive
method of lower back extension strength testing was developed using
a standard back extension unit found in many fitness facilities
(Fig. 84-3).23 The testing protocol determines
the maximum amount of weight that a subject can lift for four repetitions.
Testing weight is begun at 9 kg. The endpoints for the test are
psychophysical (subjective maximum), form (poor performance), or
safety (more than 120% of the body weight). Based on normative
data, the trunk extensor strength for a non-impaired person should
be around 100% to 110% of ideal body weight.23 Chronic
back pain patients typically have an isometric extension strength
that shows an approximate 50% reduction compared with non-impaired
persons. Although other measurements of impairments have been described
in the literature, this method illustrates the basic concept that the
effects of pain on physical performance rather than solely the pain
intensity itself should be measured. Similar strategies should be
adopted for other pain syndromes not related to the spine.
Lower back-extension strength testing with a standard
back extension unit.
The role of functional capacity evaluations (FCEs) has considerably
increased over the last several years. They are used for work injury
prevention and in rehabilitation to define an individual’s functional
abilities or limitations. By asking the patient to perform a set
of certain test activities, the individual’s ability to
meet the required work demands can be assessed. FCEs are increasingly used
to determine a patient’s ability to return to his workplace,
for pre-employment screening, for disability determinations, and
to assist in determining case closure in medicolegal cases.24 Although
all systems share the common goal of attempting to measure work-related
functional performance objectively, considerable differences in
length of assessment, psychometric evaluation, costs, and standardization
exist. Research to justify the use of FCEs for disability determination
is sparse and the testing measures of consistency should not be
inappropriately used to make a determination of possible malingering.