As pain alleviation is one of the principal therapeutic outcomes for musculoskeletal physiotherapists, it is imperative that we are able to accurately evaluate and measure pain.
Multifaceted interactions between nociceptive transmission, centralised pain mechanism, psychosocial belief and environmental factors influence pain perception (Jensen 2011), even so there has been little headway in development of objective measures of pain, despite decades of research into causes, mechanisms and measurements of pain, therefore pain remains a subjective personal experience of the patient rather than a systematic quantification by physiotherapist in clinical practice. Pain, being the principal presentation for which patients seek physiotherapy treatment, should have clear, objective evaluation processes as pain has been shown to be predictive of functional disability, resumption of work activities and is a sensitive measure of effectiveness of treatment.
Another aspect of patient’s pain experience which is critical to physiotherapy practice is the impact on functional outcomes e.g. mobility, participation in activities etc. The goal of physiotherapy in most cases includes facilitating a return to patient specific functional activities (Peiris 2011). This resulted in the development and validation of the Functional Pain Scale (FPS) (Gloth 2002).This scale included a functional component into the self reported pain rating intensity, thereby providing an objective dimension to a subjective measure. This article aims to highlight the deficiencies of using uni-dimensional subjective reports of pain intensity and the need for clinicians to consider utilising FPS as an objective tool to evaluate pain.
Pain measurement – Current clinical approach and available tools
In clinical practice, physiotherapists focus on pain intensity as the primary indicator of the pain experience. Patients are asked to self report their pain intensity on a uni-dimensional scale such as numerical rating scale, verbal rating scale or visual analogue scales (Jensen 2011). There are a wide variety of pain rating tools available which differ in the number of response options, lengths of scales, verbal descriptors, space orientations and the time spans covered. Usually a short description of the tool is given to the patient so that they can identify where they are on the pain scale. This means of rating is sufficient for the patients however; instructions need to be clear and specific to clarify in order to relate current, maximum, usual or average pain over a period of time.
Ferreira-Valente (2011) compared the relative validity of Visual Analogue Scale (VAS), Numerical Rating Scale (NRS), Verbal Rating Scale (VRS), and the Faces Pain Scale-Revised (FPS-R) to evaluate differences in experimentally induced pain in between 127 men and women. All of the scales detected varying levels in pain perception, when exposed to 4 different temperatures; these variations in temperature resulted in statistically significant differences in the pain intensity ratings, with lower temperatures for example resulting in higher pain ratings for each of the 4 scales studied.
Even though the above research demonstrates the validity of all the scales, clinically physiotherapists and patients often struggle with consistent ratings due to the lack of clear definitions of what each rating represents. Because pain is subjective, patients often express difficulty choosing a number to represent their pain level, and at times, clinicians may not believe the number identified by the patient. For e.g. it has been demonstrated that most patients treat a 101 point NRS as a 11- or 21- point scale providing their responses in multiples of 5 or 10 only (Jensen 1994).
In clinical experience, the author has encountered several patients who, when asked to rate their pain from 0-10 on a scale where 0 represents no pain and 10 as the maximum pain tend to answer as –‘Oh its worse.. I would probably rate it as an 11 out of 10 at its worst’. This may represent a lack of understanding of the utility and purpose of scale on the part of patient, an exaggeration of pain response or individualistic pain thresholds. This lack of clarity is unhelpful in terms of evaluating the effectiveness of intervention provided to the patient. Similarly, there are others who will rate their pain as 9 or 10, when they appear comfortable and able to participate in the subjective assessment. In a recent assessment report the author reviewed, the patient rated her pain as 10 on a scale of 0-10; however she reported no negative pain impact on her activities of daily living, hobbies or work related activities. This inconsistency highlights the practical problems of using such scales in clinical practice even though they have demonstrated psychometric validity. Similarly, response to VAS’s may be dependent on the visuospatial abilities of the patient and can thus be impacted by patients with physical or cognitive impairments or in the elderly (Gagliese 2005).
There are Quality of Life scales that can be utilised, such as Oswestry scale for low back pain and Neck Disability Index (NDI) for evaluation of the impact of pain upon function and activities of daily living, these are more detailed and require more clinical time to complete thus may not be feasible within the limited time available at a physiotherapy appointment. Speed of administration is a useful property of uni-dimensional scales which is one of the reasons for continued use of previously mentioned pain scales.
Functional Pain Scales
As highlighted above, patients may fail to decipher the actual meaning of scores on a linear uni-dimensional scale. Gloth (2002) posited that to overcome this deficiency and to enhance the utility of pain scales, it should be associated with function as people are readily able to perceive the impact of their pain on their functional ability. By testing patients’ level of pain with respect to its interference with their daily function, a more accurate measure of their pain may be ascertained.
The Functional Pain Scale developed by Gloth (2002) is a 6 point scale rated from 0 to 5 with 0 being no pain and 5 being intolerable pain which disallows patients to verbally communicate because of pain. Each score is rated in terms of the impact of pain on function i.e. whether it is tolerable and doesn’t prevents any activities (1), some activities (2), intolerable but allows use of telephone, watch TV or read (3), doesn’t allow these activities (4).
Gloth (2002) provided evidence of the psychometric properties of the FPS in their study on 100 elderly patients from a residential nursing home setting. Inter-rater reliability for FPS exceeded 0.95 while validity testing showed high correlations with other instruments tested (r = 0.62, r = 0.85, r = 0.80, r = 0.90 for the VAS, the PPI, the MPQ-SF, and the NPS respectively). FPS also demonstrated better overall responsiveness index than other tested instruments. While the basic theoretical concept of the scale is sound, most patients present to physiotherapy departments with pain levels ranging from 1, no pain to 2,tolerable pain but with some restriction on physical activity. This would lead them to rate their pain between 0 to 2 whereas a rating of 3 means that they are restricted to sedentary activities like watching television and use of telephone.
While this would facilitate relevance of the pain rating as well as its correlation with function which can be demonstrated objectively, FPS is impractical to assess the effectiveness of treatment or to note the change in pain status pre- and immediately post- intervention.
Another such scale which focuses on function is the ‘Effect of Pain’ scale (EOP) which has been developed by Hunt et al (2011). It is a self rating scale used to determine a client’s opinion of the extent to which pain is affecting their ability to perform activities and rated from A (normal ability) to E (inability to apply strength, move or stay in one position). The authors of EOP have provided anecdotal evidence that it can be employed by clinicians to match the client’s report of pain with their objective functional performance. This scale is still under development and has not yet been tested for its psychometric properties.
Matheson (2013) have developed an 11 point functional pain scale where patients rate their pain levels from 0 to 10 in increments of 0.25. While it seems like the traditional numerical rating scale with 0 as no pain and 10 rated as worst imaginable pain, the difference is in the way scores are defined and evaluated. While scores between 0-2.75 indicate non disabling pain, yet is getting progressively worse, it does not hamper functional activities. A score of 3 indicates pain impacting patient’s functional capability e.g. having to slow down or stop movement and stretch in order to continue with the activity. The score from 3 to 4.75 indicates progressively worsening impact on the functional activity and a score of 5 indicates that the patient is unable to complete the activity. A score of 7 indicates severely disabling pain where the patient cannot use or move the painful area and is unable to focus on anything else but the pain; the patient may also need to lie down and exhibit tearfulness. Beyond the score of 7, pain worsens progressively such that the patient is near hospitalisation and at a rating of 10, the patient is defined as completely incapacitated due to pain and requires immediate hospitalisation. It is apparent that the definition and scoring criteria in the Matheson FPS is well defined and related to functional activities, thus easier for the physiotherapists to correlate with other objective tests and tasks.
Generally it would be expected that the patient reported pain scores will vary between 0 (no pain) to 5 (very disabling pain causing inability to complete the task) and rarely to 7 (severely disabling pain which can cause tearfulness). As discussed above, one of the limitations of the traditional numerical rating scales is exaggeration of pain rating by patients in the absence of clear concise definitions. Use of Matheson FPS would allow physiotherapists to clarify the ratings and definitions with the patients and check that the rating provided is an accurate assessment of their pain levels. For e.g. if a patient rates their pain as 6 or 7 but is able to continue their activity albeit with some pain, the physiotherapist can inform the definitions of pain rating and help the the patient to reconsider their pain rating at between 3 and 5.
FPS can also be used to determine the impact of interventions through a pre- and post-assessment, especially in application of manual therapy techniques where it is important to judge the immediate post intervention impact on pain levels along with performance of offending movement. Matheson’s FPS is an integral part of the Matheson Functional Capacity Evaluation (FCE) protocol. A functional capacity evaluation (FCE) evaluates an individual’s capacity to perform work activities related to his or her participation in employment (Soer et al., 2008). The FCE process compares the individual’s health status and body functions to the structures and demands of the job and the work environment. FPS is one of the tools utilised to establish the reliability of pain and disability reports (RPDR) of the patient. RPDR is a battery of tests that is designed to assess the dependability and accuracy of the client’s subjective reports of pain and disability. FPS is utilised along with several other subjective measures of pain by patients to rate their pain levels at various stages of testing which is then correlated with their physical performance during standardised assessments as well as use of placebo tests. Discrepancy between the patient’s report of pain and their actual performance form the basis of judgement of reliability of the patient’s report of pain and disability.
Though used extensively within the Matheson system, the author was not able to find any supporting literature for its psychometric properties (reliability, validity or responsiveness) through an extensive search of literature using MEDLINE, CINAHL, AMED, SPORTDiscus and Health Source Nursing databases. While lack of data on the reliability and validity indicates that further research is needed on the utilisation of this scale, subjectively, it does seem to have face validity which is an indicator of whether the instrument appears to measure what it is supposed to measure. Considering the obvious advantages of ease of use, correlation with function which can be objectively evaluated and ability to evaluate the effect of any intervention, it is suggested that physiotherapy clinicians must make use of functional pain scale over traditional scales to evaluate pain intensity.
Within physiotherapy clinical practice, pain evaluation remains a subjective assessment report of the patient through the utilisation of various numerical rating or visual analogue scales. Physiotherapists and patients often struggle with these scales because of the lack of understanding of what each rating represents. In this article, the author has highlighted the development of functional pain scales and argued for their increased utility within clinical setting to increase correlation of pain evaluation with functional performance which can be objectively evaluated. However, the functional pain scales currently available have not been tested for their psychometric properties and therefore further research is needed to validate the use of their instruments in routine clinical practice.