This is one of the first studies to report on the relationship between summary measures of pain location and pain severity and lower extremity function measured by physical performance testing in a population of older persons. Results show that presence of multisite pain was associated with about a 1-point difference in SPPB performance compared with persons reporting no pain. A recent longitudinal study found that a change of one point in the SPPB score was clinically meaningful in a community-dwelling older adult population (29
). Similarly, the differences we observed across groups in gait speed were also in the clinically meaningful range (29
). However, our observed cross-sectional differences may not compare directly with longitudinal changes reported by Perera and colleagues (29
). Our findings are in contrast to findings from previous studies that focused on selected pain sites (back and lower extremity pain) or studied an already disabled population. Those studies did not report consistent findings in the relationships between chronic pain and lower extremity function (15
). With respect to pain severity, our study shows that the highest quartile of pain severity was significantly associated with SPPB performance, but when pain locations and pain severity were included in the same model, only presence of multisite or widespread pain remained significantly associated with lower extremity function.
We also found that of all the different pain sites, knee pain was the only site independently associated with SPPB performance. Most studies of pain and lower extremity function in older adults have focused on single-site pain such as knee or back pain and have not accounted for pain in multiple other joints (11
). However, our results show that most older people who experience pain report multisite
pain, consistent with a number of studies from the United Kingdom (14
). Therefore, site-specific analyses may be missing a key element of chronic pain in older people. It can be argued that multisite pain may be an important measure in the clinical setting, even more so than pain severity or site-specific pain.
In the MBS population, elders who had multisite pain demonstrated poorer standing balance. Few studies have examined the relationship between chronic pain severity or number of pain sites and balance in older adults. In the Health ABC study, more severe back pain was independently associated with poorer scores on balance tests, but other sites of pain were not examined (32
). In another report, knee pain severity was inversely correlated with balance performance in older adults, but this relationship was dependent on ankle strength (36
). Our findings suggest that in older adults, there may be multiple pathways through which pain may influence balance and lower extremity function in general. Persons experiencing pain may move their muscles in such a way to minimize the sensation of pain, thus compromising lower extremity function (37
). It is also possible that multisite pain may be distracting, thus interfering with balance and contributing to a compensatory slowing of lower extremity function in general. Pain is known to have a strong attentional component (38
) and distracting factors during walking, for instance performing a dual-task, limit lower extremity function in older adults (39
). Limitations in lower extremity function caused by distraction by pain could potentially lead to falls. Indeed, widespread musculoskeletal pain contributed to falls in older women with disabilities (40
With respect to chair stands performance, both pain location and the highest quartile of pain severity were associated with poorer chair stands performance, but when adjusting for both, only the association with pain severity remained significant. The variance that was explained by these models was relatively limited compared with models of other performance tests (data not shown), which may be explained by the missing values on this test; more people with pain did not perform the chair stands. In other words, the repeated chair stands test is more burdensome than simple gait and balance tests for older persons. Thus, persons with symptomatic musculoskeletal or cardiovascular conditions were generally less likely to perform the test, possibly explaining the somewhat lower variability in the measure across pain groups.
In contrast to overall mobility function and standing balance, our results showed that pain severity has a stronger association with individual tests of gait speed and chair stands than does pain location. Previously, pain severity was associated with gait speed in old-old community-dwelling adults and older women with disabilities (33
). It is noteworthy that the association found in the present study between pain severity and gait speed was only significant for the highest quartile of pain severity. There may be a threshold of pain severity, beyond which lower extremity function is significantly affected. The highest quartile of pain severity in our population was based on a cut point of 4 or higher on the average of the four BPI 0–10 severity ratings. In general, pain rated as 4 or higher on a single-item rating of pain intensity is interpreted as moderate or severe pain. Because the BPI scale consists of pain ratings under four conditions, it is not directly comparable with a single-item rating that is often used in clinical settings. However, further studies are needed to determine whether there is a threshold effect of pain severity on mobility function, a factor that could have important clinical implications for the management of pain. As noted previously (15
), it is possible that even modest pain relief could lead to significant changes in lower extremity function, particularly among persons who have moderate or severe pain.
Our measure of pain severity, the BPI subscale, is a measure of overall
pain severity, not accounting for varying pain severity across multiple pain sites. It is possible that a person could have severe pain at one site and have the same BPI severity score as a person with severe pain in multiple sites. Given that most older persons who have chronic pain report pain in multiple sites, a summary assessment of pain severity may have some limitations in older adults, even though the BPI specifically is currently recommended in guidelines for pain assessment in older patients (22
). Nonetheless, our findings suggest that the BPI severity measure is generally comparable with pain location assessment for their respective impact on lower extremity mobility in the older population.
There are some limitations of this study that should be mentioned. First, the cross-sectional design of the present study precludes inferences on causal relationships between pain and lower extremity function. Whether increased pain sites and/or pain severity actually lead to lower extremity limitations should be addressed in future longitudinal studies. Second, we may not have adequately accounted for the influence of comorbidity because our assessment of comorbid conditions was based on self-report. Last, other factors such as medication use, self-efficacy related to mobility, and aspects of executive function may have influenced the observed relationships, but it was beyond the scope of this study to examine the many possible mediators of the pain–function relationship. Future studies could examine these and other factors that would provide a better understanding of the pathway from chronic pain to limitations in lower extremity function.
In conclusion, presence of multisite pain is associated with poorer lower extremity mobility performance on the SPPB cross-sectionally in the MBS population. However, pain severity, more so than pain locations, was associated with poorer performance in the individual tests of gait speed and repeated chair stands. These provocative findings demonstrate the need for further investigation into measures of pain characteristics that pose the greatest hazards to daily functioning of older adults. Longitudinal research is essential to inform clinical care of the many older adults who live with chronic multisite pain.