From a random sample comprising 5,655 households within the target area, recruitment staff confirmed that 4,319 persons aged 70 years and older resided at the sampled addresses. Of these, 1,610 were ineligible, 1,916 were of unknown eligibility (including refusal to complete screening), 44 persons were eligible but did not complete the interview, and 749 persons were eligible and completed the baseline home interview and clinic examination. Ineligibility was most commonly related to language, poor health, mobility, and cognitive status.
To determine the response rate among those eligible to participate, which was 53%, we applied our observed eligibility rate (33%) to estimate the proportion of those we contacted whose eligibility was unknown would have been eligible to participate (American Association of Public Opinion Research40
). Participants were younger than non-participants [mean in years (SD), 78 (5) and 79 (7) respectively, P < 0.001] and more likely to be white, non-Hispanic (81% vs. 77%, P = 0.02) but no more likely to be women (63% vs 64%, P = 0.81).
At baseline, 40% of participants reported chronic polyarticular pain. Another 24% reported chronic pain in only one joint area. The number of musculoskeletal pain locations was highly correlated with the tertile classifications of both BPI pain severity and pain interference (r = 0.55 for each). The two BPI subscales also were highly correlated (r = 0.70). Older adults who had polyarticular pain were more likely to be women, have fewer years of education, to be obese, have fallen in the previous year, and have poorer performance in tests of balance and mobility (). Medical conditions associated with chronic musculoskeletal pain included spinal stenosis/disc disease, hand and knee osteoarthritis, rheumatoid arthritis, depression, peripheral arterial disease, and heart disease ().
Baseline characteristicsa according to chronic musculoskeletal pain categories.
Baseline medical conditions according to pain categories.
Overall, 76% of participants completed 18 monthly calendars, 90% completed 15 or more monthly calendars and 94% completed at least 12 monthly calendars. On average, 98% of falls calendar information was completed each month either by returned postcards or by telephone; specifically, the proportions of completed calendars at 6, 9, 12, and 18 months were 97%, 97%, 98% and 98%, respectively, among persons currently enrolled at each time point. A total of 1,029 falls were reported by the 749 participants on the monthly fall calendars during up to 18 months of follow-up. More than half of participants (n=409; 55%) fell at least once during the follow-up. Older persons who had chronic pain, whether measured by location, severity, or pain interference with activities, had higher rates of falls during follow-up compared to those who had no pain (p<0.05, ). After multivariable adjustment for chronic conditions and fall risk factors, each measure of chronic pain continued to be independently associated with increased occurrence of falls (). Adjustment for balance and mobility performance, use of psychotherapeutic medications, and, in subsequent models, adjustment for use of analgesics and clinical criteria for osteoarthritis of the hand and knee had little influence on the rate ratios (RR). When we adjusted for history of falls, the association with each pain measure was attenuated but remained significant (eTable 1
online). We found no evidence of an interaction between musculoskeletal pain and use of daily analgesics in relation to falls (test for interaction, p=0.78).
Age-adjusted fall rates according to pain measuresa
Rate ratios for the occurrence of fallsa according to baseline pain measures.
We considered individual musculoskeletal sites alone or in combination with other sites of pain in relation to falls. For each site of joint pain, risk for falls increased only when polyarticular pain was present (). The one exception was back pain, which was not associated with an increased rates of falls compared to persons without pain.
Rate ratios for the occurrence of fallsa according to pain sites.
In about one-third of the monthly postcards, participants rated their pain on average for the month as moderate to very severe. We observed a strong graded relationship in the short term between pain severity ratings each month with risk for falls in the subsequent month (). For example, among persons who reported severe or very severe pain for any given month on their calendar postcard, there was a 77% increased likelihood for a fall in the subsequent month, compared to those who reported no pain (multivariable adj. OR 1.77, 95%CI 1.32 – 2.38). Persons reporting even very mild pain also had an elevated risk for falls in any given month (adj. OR 1.36, 95%CI 1.08 – 1.71). Further adjustment for baseline pain status led to only a modest attenuation of the association with no change in the significance of the findings.
Adjusted odds ratiosa for falls in the subsequent month according to monthly pain ratings.