Abstract
BACKGROUND:
Along with quantitative measures, pain symptoms may help inform early interventions to prevent prolonged standing induced low back pain (LBP); however, the relationship between quantitative and qualitative measures has not been assessed.
OBJECTIVE:
Determine the relationship between qualitative and quantitative measures of pain development during prolonged standing induced LBP development.
METHODS:
Thirty-five participants performed two-hours of standing. A visual analog scale (VAS) and the Short-Form McGill Pain Questionnaire were used to assess the participant’s LBP every 7.5-minutes. Participants were classified as a pain developer (PD) based on VAS scores or three consecutive pain symptom reports.
RESULTS:
Pain symptom reports occurred 31.3 (±24.8) minutes earlier than the VAS reports. Eight participants (44%) were non-PDs with the VAS and PDs with the symptom method (p = 0.0047).
CONCLUSIONS:
A subset of participants who were not categorized as LBP developers during prolonged standing using the VAS method still report LBP symptoms. The inclusion of pain symptom reporting could provide additional information for practitioners when identifying individuals who would benefit from early interventions for standing induced LBP.
Keywords
Introduction
Between 40 and 71% of sample populations report developing low back pain (LBP) during two-hours of prolonged constrained standing [1–6]. Those who can be described as a pain developer (PD) during prolonged standing are three times more likely to experience episodes of clinical LBP during the two years following their initial data collection than individuals classified as non-PDs [7]. Clinical tests [8], visual analog scales [9], and pain symptom reports [10] are typically used to assess people’s potential for pain development during prolonged standing; however, qualitative reports of pain symptoms, such as the individual describing their pain as “aching” or “sharp”, and their relationship to quantitative severity reports have not been examined. A better understanding of the relationship between pain symptom and its severity during prolonged standing could help practitioners better identify individuals who would benefit from early interventions for standing induced LBP.
Over the last few decades, the recording of LBP has shifted from physician-based assessment to patient self-report of pain [11]. The visual analog scale (VAS) is a 100 mm horizontal line where patients indicate their level of LBP from no pain to worst possible pain using a single vertical mark. The clinician records the patient’s pain before treatment and during follow-up appointments to compare score changes to determine the effect of the treatment [11]. For LBP, the VAS is responsive enough to detect pain with a minimal clinically important difference of 8 mm on the 0 mm–100 mm scale [11]. Over a two-hour prolonged standing trial, a 10 mm threshold from a baseline measure has been used to classify PDs using the VAS. In multiple studies, using this threshold, participants clearly separate into PD and non-PD groups during two-hours of prolonged standing [3, 12–15]. The VAS is not perfect in separating these two groups; 17% of a sample population will be categorized in the opposite pain group during a second bout of prolonged standing performed four weeks later [16]. Overall, the protocol yielded excellent day-to-day repeatability with ICC scores greater than 0.80 [16].
Clinicians can also ask their patients to describe their LBP from a list of common symptoms. The Short-Form McGill Pain Questionnaire is a useful instrument in measuring pain for a limited amount of time and employs qualitative and quantitative measures [17]. A previous study determined that qualitative measures for people who were classified as standing induced PDs were similar to people that were known to have LBP, with the most common qualitative measures reported during prolonged standing being aching, stiffening, cramping, and tightness [10]. There are modified versions of the Short-Form McGill Pain Questionnaire, one of which was used in this study [17]. No research has been done to see if pain symptom descriptors could help identify the initial states of LBP during prolonged standing. Pain developers may be able to be identified earlier and we would have a better understanding of their symptoms. Also, some non-PDs may still report pain symptoms that are being missed by quantitative measures only. That is, a person may not report pain on a VAS but still may report pain symptoms such as aching or cramping. Rather than invalidating the VAS, using the symptom and severity reports together may identify an additional sub-group of individuals who are currently not affected by standing, but with cumulative exposure, would be on a path to prolonged standing induced LBP.
Ultimately, combining symptom and severity measures could provide a more comprehensive understanding pain development during prolonged standing to guide early interventions with the goal of reducing the likelihood that a person will develop clinical LBP. We could use this model to provide additional guidance for jobs that typically require prolonged standing (such as cashiers) or when developing guidelines for sit-stand workstations [18–21]. For example, previous work using a 3:1 stand-sit work schedule (45 minutes standing, 15 minutes sitting) showed that once prolonged standing induced LBP occurs, as measured using a visual analog scale, pain is decreased upon sitting but quickly returns and continues to rise when a person stands again [14]. As mentioned in the previous paragraph, it is unknown if individuals who do not quantitatively report pain on a VAS would report pain symptoms. Early diagnosis of this sub-group may prevent the worsening of the pain symptom reports over time through early interventions and individualized sit-stand or active break work schedules.
The purpose of this study was to determine the relationship between quantitative (VAS) and qualitative (symptom) reports of pain development. We hypothesized that 1) a portion of non-PDs, with a maximum VAS difference of less than 10 mm, would report LBP symptoms during two-hour prolonged standing, and 2) PDs would report symptoms before exceeding the 10 mm difference on the VAS. The results of this study will help practitioners continue to develop guidelines and developing early intervention strategies.
Materials and methods
Participants
Thirty-five participants, (18 male and 17 female) were recruited to participate in this study. The inclusion criterion was individuals between 18–35 years old. Participants could not have had a previous history of LBP that required medical intervention or time off from work longer than three days, previous lumbar or hip surgery, employment in a task that required prolonged static standing during the past 12 months, and the inability to stand for at least two hours. This research was approved by the Office of Research Ethics at the University of Waterloo. Informed consent was obtained from each participant.
VAS pain symptom reporting
The VAS and Short-Form McGill Pain Questionnaire [17] were used to assess the participant’s current level of LBP at the start of the trial.
For the VAS, participants were asked to indicate their CURRENT level of LBP from no pain to worst possible pain using a single vertical mark on the 100 mm scale and indicate on the body diagram where their pain was felt.
For the pain symptoms, participants were asked to check as many of the listed symptoms. The choices that were used to describe the participants’ current level of pain quantitatively in their low back were throbbing, shooting, stabbing, sharp, cramping, gnawing, hot-burning, aching, heavy, tender, tiring-exhausting, sickening, fearful, and cruel-punishing [17].
Experimental protocol
After providing informed consent, participants completed a baseline VAS. Participants then performed two hours of prolonged standing while doing light assembly and sorting tasks –assembling and dissembling mechanical pens, nuts, bolts, and washers and sorting cards and money into predetermined piles in random 15-minute blocks for each participant. A height adjustable table was placed 5–6 cm below the participant’s wrist when elbows were placed at 90 degrees. They were not allowed to lean on the table and were instructed to do the tasks within a primary reach zone with a depth of 25.4 cm from the edge of the table, width of 101.6 cm, and a diameter of 33–43 cm with respect to the shoulder joint [22]. Every 7.5 minutes, the participants were asked to complete a VAS and pick as many words as they wanted from the Short Form McGill Pain Questionnaire to describe their CURRENT pain, totaling 16 entries per participant.
Definition of pain developers
Pain development from prolonged standing was determined using two separate methods (1) pain symptom and (2) VAS method. With the pain symptom method, participants with three or more consecutive symptom descriptors during the two-hour prolonged standing were classified as PDs. That is, the participant needed to have this pain symptom for at least 22.5 consecutive minutes (three reports at 7.5-minute intervals). We chose this threshold because it established a consistent report of the pain symptom. The minimum consecutive reports of pain symptoms across all participants who reported symptoms was four (30-minutes). For the VAS method, participants were classified as PDs if at any point during the two-hour prolonged standing the VAS was 10mm or greater from their baseline measurement. Pain groups were classified individually for VAS and pain symptom method.
Statistical analysis
For each participant, an agreement (non-PD/ non-PD, PD/ PD) or disagreement (non-PD/ PD, PD/non-PD) was recorded between the VAS and symptom descriptors, respectively. A two-way chi-square test was used to compare the pain categorization using the pain symptoms to those expected from the VAS scores.
For those who were PDs in both methods, the time between VAS exceeding 10 mm and first symptom descriptor were evaluated to assess if symptoms occurred earlier than when they reached a 10 mm difference on the VAS. A description of the symptoms reported, the most common symptoms reported overall, and max VAS were also compiled for each participant.
Results
Pain scores and questionnaire items
A significant number of participants switched from non-PDs to PDs when assessed with the pain symptoms method (p = 0.0047, Table 1). Seventeen of the 35 participants (48.6%) were categorized as PDs using the VAS method. Twenty-five participants (71.4%) were categorized as PDs for the pain symptom method. Eight participants changed from a non-PD with the VAS method to a PD with the symptom method (Tables 1 and 2). No participants switched from PD with the VAS to non-PD with the pain symptom method.
Frequency of pain developers (PDs) and non-PDs categorized using the VAS and pain symptom methods
Frequency of pain developers (PDs) and non-PDs categorized using the VAS and pain symptom methods
Time each participant exceeds the VAS and symptom reporting threshold
Note: PD = pain developer; non-PD = non-pain developer; N/A means that person never reached the threshold for PD categorization.
Pain scores that exceeded the 10 mm threshold for the VAS method occurred on average at 42.8 (±27.8) minutes into the two-hour prolonged standing protocol. Pain developers with at least three consecutive symptoms reached this threshold at 11.5 (±22.8) minutes into the prolonged standing protocol. The average time between the VAS method and symptom method was 31.3 (±24.8) minutes, with the symptom method being reported earlier for every participant (Table 2).
Aching was the most common descriptor chosen by those who were symptom classified PDs (Table 3), with 72% of participants choosing this symptom. Those classified as both symptom and VAS PDs selected a range of symptoms, including “tiring”, “heavy”, “throbbing”, “gnawing”, and “stabbing”, which were not selected by symptom-only PDs.
Number of participants reporting each pain symptom at least once over the prolonged standing trial
Number of participants reporting each pain symptom at least once over the prolonged standing trial
The purpose of this study was to investigate differences in quantitative versus qualitative measures of defining prolonged standing induced LBP development. The first hypothesis that a portion of non-PDs with a VAS difference of less than 10 mm would report LBP symptoms during two-hour prolonged standing was supported. Of the 18 participants classified as non-PDs based on the VAS, eight (44%) changed to PDs based on their symptom descriptors. Our second hypothesis that PDs would develop symptoms before they reached a 10 mm difference on the VAS was also supported. Of the participants that remained in the PD group for both methods, 100% (17/17) were categorized as pain developers using the symptom method and were identified on average as early as approximately 11 minutes into the standing exposure, 31 minutes before the VAS approach classified them as PDs.
Previous research on LBP during prolonged standing and pain symptom reporting used five similar symptoms (stabbing, cramping, burning, aching, and sensitive) [10] out of 14 symptoms used in this study. Aching, stiffening, and tightness were the most frequent symptoms reported during prolonged standing for the previous study [10]. This supports our results, as aching was the most common symptom reported during our study.
PDs categorized with the VAS chose a more diverse group of symptoms to describe their pain compared to VAS non-PDs. PDs categorized with the VAS were also the only group who selected one of the “affective descriptors”; eight of the 17 VAS PDs used the word “tiring-exhausting” when asked to describe their current low back pain symptoms. As a result, LBP development during prolonged standing could also influence the person’s mood and feelings. Previous work on the psychosocial aspect of prolonged standing induced low back pain development presents conflicted results. Some studies show no difference between PD and non-PD [9, 13], while a more recent study reported a relationship between LBP symptom (VAS greater than 20 mm) and the Fear of Pain Questionnaire-III and the Pain Catastrophizing Scale [23]. These results emphasize the importance of further research on the psychological factors related to prolonged standing induced low back pain.
The eight participants who switched groups averaged a max VAS of 4.9 mm, while the ten participants that remained non-PDs had a max VAS of 1.9 mm. We do not feel that the reporting of pain symptoms in this subgroup invalidates the use of a VAS or the 10 mm threshold because it reflects that these symptoms are of a very low severity; however, continued exposure over time in this sub-group may result in worsening pain in the future. Individuals who were classified as PDs based on the VAS were found to be three times more likely to experience episodes of clinical LBP two years following data collection compared to those placed in the non-PD group [7]. Symptom PDs could be on the same path as those individuals and could have more LBP with continued exposure to long periods of constrained standing.
Future work should continue to look at the symptom reporting sub-group found in this study to assist with the prevention of prolonged standing induced LBP development as this sub-group could be the target of early intervention strategies. Early identification is a critical component for developing intervention strategies to avoid the pathway of PDs progressing to clinical LBP cases. Once PDs report pain during standing, a seated break will not alleviate the pain during a subsequent bout of standing [14]. Pain symptom reporting could be an initial way for practitioners to determine individualized recommendations for a sit-stand or active break schedule. People’s preferences on different sit-stand workstation schedules can vary [24] so one standard schedule may not work for everyone. Since pain symptom reports occurred very early for many participants, a short trial of prolonged standing, along with qualitative and quantitative reports of pain, could be used to determine intervention strategies.
A third way to define PDs could be to use objective measures to predict a person’s pain status. The primary mechanism for low back pain development is unknown; and as a result, it is challenging to determine objective measures that can be used to identify PDs. Some variables that have been assessed are movements at the lumbar spine level and body weight shifting between two legs [13], gluteus medius muscle co-activation [9, 25], and lumbar spine and lower limb kinematics [15, 26]. The success of determining objective measures that can predict pain development or identify risk factors related to prolonged standing induced LBP depends on our ability to classify people into the proper pain groups. Improper classification affects statistical significance and it will be harder to determine objective measures that distinguish the two groups. One study has assessed the repeatability of the VAS method for defining pain groups, with 83% of participants being defined the same group when two prolonged standing simulations were separated by four weeks [16]. We also did not assess the repeatability of this symptom reporting; therefore, future work should assess the repeatability of these LBP symptom reports.
A second limitation of this study is the age of the participants, who ranged from 18–35 years old. While this group represents a portion of the working population, the results may not be generalizable to older populations. However, most of the individuals who report developing LBP during prolonged standing are younger [27, 28].
Finally, many clinicians use numerical rating scales (NRS) to assess patient self-reports of LBP [29]; however, we believe that for our purposes VAS is better for assessing the changes in LBP development within a session. With the NRS, participants are required to circle or say their rating. With the VAS, they are not aware of their numerical score and are not able to reference it when filling the next VAS. As a result, participants are reflecting on their current level of pain, not in comparison to their previous ratings.
When assessing prolonged standing induced LBP, we recommend the combined use of qualitative and quantitative methods. By collecting symptom reports, you can assess the sub-group of participants or patients who may potentially develop more intense pain symptoms over time. These individuals can then utilize early intervention strategies to mitigate their pain development in the future.
Conclusions
Categorization of participants with LBP development during prolonged standing using LBP symptoms to assess pain provided differing results compared to the typically used quantitative measure. All PDs reported pain symptoms before exceeding a 10 mm difference on the VAS (100%). Fifty-six percent of non-PDs reported LBP symptoms during two-hours of prolonged standing. In line with previous work, “aching” was the most commonly reported symptom. Practitioners should consider these findings to aid in defining LBP for those who stand for prolonged periods. Awareness of the commonly induced symptoms and the time of pain development can help in educating and training workers appropriately so their LBP can be reduced or managed. Early intervention could result in a reduction in the number of these cases that become clinical cases and require medical visits. The addition of symptom reporting can inform best practices for early interventions, especially in people who were categorized as PDs based on their reported symptoms. Future studies should look at the repeatability of symptoms and the ability of practitioners to use this data to recommend individualized interventions.
Conflict of interest
None to report.
Footnotes
Acknowledgments
A Natural Science and Engineering Research Council (NSERC) Doctoral Scholarship supported KMG during her doctoral studies. A Tier I Canada Research Chair and NSERC Discovery grant supported JPC.