The present study examined the link between LS and load-bearing joint pains in middle-aged or elderly Japanese cohort. Knee, hip, and low back pain were significantly associated with LS. Participants with hip pain were also more likely to have other load-bearing joint pain complications. This study also found that the LS odds ratio was 5.36 for 2 pain sites and 8.96 for more than 3 pain sites. To our knowledge, this is the first study to examine the association between LS and the number of pain sites.
Yoshimura et al. reported that 5.0% of males and 6.8% of females in their 50s, 11.4% of males and 16.6% of females in their 60s, 28.2% of males and 39.0% of females in their 70s, 62.1% of males and 76.0% of females in their 80s or older scored 16 or more points on the GLFS-25 in the general population health examination[8]. In our study, LS prevalence was relatively high in their 50s and relatively low in their 60s or older. Since villagers in their 50s generally undergo health checkups at their workplaces, it is possible that this checkup tended to be taken by those in their 50s who were not confident about their health. Also, Japanese workers usually retire or the ages of 63 or 65. Most of the residents of Miyagawa village are engaged in mountain forestry, and many of them are relatively active elderly people, so the prevalence of LS is thought to have been low.
Suka et al. reported that 41.2% of the adult population in Japan has musculoskeletal pain [9]. Of the 87.9 million Japanese aged 30 or older in 2005, the study estimated that the prevalence of back, hip and knee pain was 21.4 million (24.3%), 3.2 million (3.7%), and 9.1 million (10.4%), respectively, and that the prevalence of each would rise to 26.5%, 4.4%, and 12.9%, respectively, by 2055. In our study, the prevalence of low back, hip and knee pain (41.0%, 9.1% and 36.5%, respectively) were relatively higher than those in the previous report. This could be because our study consisted of community members aged 50 years and older. Nakatoh et al. reported that 56.6% of their study subjects complained of chronic pain somewhere in their body, and 39.2% complained of two or more pain sites in an evaluation of residents aged 50 years or older [10]. In our study, the number of subjects with load-bearing joint pain increased with age, accounting for 63.1% of participants with one or more pain sites and 26.2% of participants with two or more pain sites. Since we defined pain according to the LOCOMO study [11], it was difficult to directly compare the pain rate with that in the previously mentioned study [10]. Yoshimura et al. reported that the prevalence of low back pain and knee pain was 37.7% and 32.7%, respectively, and the prevalence of complicated low back pain and knee pain was 12.2% in those with this condition from a database of the integrated cohort of the LOCOMO study [11]. In the present study, among participants with multiple load-bearing joint pain, those with concurrent low back pain and knee pain were the most common. The percentage of participants with only low back and knee pain was 15.8%. This proportion was almost the same as that in the study by Yoshimura et al [11].
Leveille et al. reported that a greater number of painful sites increased the risk of falling [12]. In addition, Eggermont et al. reported that the number of painful areas was significantly more associated with lower limb function as measured by gait speed, balance, and chair stands than pain severity [13]. In this study, the LS odds ratio was 5.36 for 2 pain sites and 8.96 for more than 3 pain sites. Pain in many areas causes the muscles to move in a way that suppresses pain, leading to decreased lower limb function and reduced mobility, i.e., the development and progression of LS. Furthermore, we examined the extent to which each of the multiple load-bearing joints had coexisting pain. Among participants with hip, knee, or foot and ankle pain, about 40% of participants had pain at only one site each, but among those with hip pain, only about 10% participants had only hip pain without any other joint pain. Participants who complained of hip pain were more likely to have other coexisting load-bearing joint pain.
This study has several limitations. First, this study was a limited regional cohort study and does not necessarily reflect the population of our country. In 2020, Japan's population aging rate was 28.7%, while the aging rate in the region covered by this study was 49.7%. However, with our country's rapidly aging population, the number of elderly is expected to increase in the future. Hence, we believe that our data has potential clinical relevance. Second, the target population might have been limited to those with the ability to travel to the screening site. In addition, it is likely that those with an interest in health were more likely to be included in the study population. Third, the diagnosis of LS was made using only the GLFS-25 and not the two-step test or stand-up test [14]. Therefore, the prevalence of LS might be lower than it would be if these tests had been used. Fourth, pain was self-reported using a binary system of "yes" and "no", and the degree of pain was not assessed. Also, we did not assess the cause of pain. Fifth, because this study was a cross-sectional study, we did not evaluate the sequence of appearance of multiple pains.
In conclusion, 2 pain sites (OR 5.36), more than 3 pain sites (OR 8.96), low back pain (OR 2.42), hip pain (OR 2.99) and knee pain (OR 2.59) were statistically related to LS. Participants who complained of hip pain were more likely to have other coexisting load-bearing joint pain. Controlling load-bearing joint pain from an early stage and suppressing the number of load-bearing joint pain might lead to prevention of LS.