DENVER – The relationship between nighttime knee pain from osteoarthritis and sleep disturbances is more complex than a simple association, according to new research presented at the Osteoarthritis Research Society International 2023 World Congress.
The findings suggested that the association between knee OA pain and sleep problems was also linked to activities of daily living, which can contribute to pain but are also affected by OA, Takahiro Sasahara, of the department of orthopedics at Juntendo University, Tokyo, and Koshigaya Municipal Hospital, Saitama, Japan, told attendees. The study also found that knee pain and mobility impairment were associated with sleep disturbances in older adults regardless of the severity of knee OA.
Luisa Cedin, a PhD student at Rush University, Chicago, who attended the presentation, noted the clinical implications of the interaction of daily activities with knee pain.
”I’m a physical therapist, and this could have a significant impact on the performance of the exercises that I’m requiring as a physical therapist,” Ms. Cedin said in an interview. “When you ask somebody who is not getting enough rest during the night – not only enough time but enough quality of rest – we know that we can expect a lower performance with any type of exercises, whether it’s less strength or force, less power, less agility, or less resistance or endurance, so this has a big impact on their quality of life.”
Mr. Sasahara cited research noting that acute pain occurs at the beginning of movement and during weight bearing and walking while chronic pain frequently occurs at night and in early morning awakenings. The prevalence of sleep disturbances in patients with chronic pain ranges from 50% to 80%, he said, and past evidence has shown the relationship between sleep and pain to be bidirectional.
For example, insomnia frequency and severity, sleep-onset problems, and sleep efficiency are all positively associated with pain sensitivity, and increasing severity of OA is linked to increasing prevalence of night knee pain and sleep problems, affecting quality of life, he said.
In this new study examining the relationship between sleep disturbance and knee pain and mobility, the researchers focused specifically on a population of older adults with knee OA. They analyzed data from the Bunkyo Health Study, which was conducted at Juntendo University’s Sportology Center to examine the association between metabolic, cardiovascular, cognitive dysfunction, and motor organ disorders in older adults from November 2015 to September 2018.
From the initial population of 1,630 adults, aged 65-84, who did not need medical treatment because of knee pain, the researchers analyzed data from 1,145 adults who the met this study’s criteria, which included MRI imaging of medial type knee OA. A little over half (55.7%) were women, with an average age of 73 and an average body mass index (BMI) of 22.8 kg/m2.
In addition to blood and urine sampling, the researchers determined the severity of knee OA based on joint space width, femorotibial angle, and Kellgren and Lawrence (K/L) grade from x-rays in standing position. They also assessed the structure of knee OA using a whole-organ MRI score (WORMS), and pain and mobility with a visual analog scale, the Japan Knee Osteoarthritis Measure (JKOM), and the 25-question geriatric locomotive function scale.
The JKOM, based on the Western Ontario and McMaster Universities quality of life index for general knee OA, is adjusted to account for the Japanese lifestyle and covers four categories: knee pain and stiffness, a score for activities of daily living, a social activities score, and the patient’s health conditions.
Overall, 41.3% of the participants had sleep disturbances, based on a score of 6 or higher on the Pittsburgh Sleep Quality Index–Japanese. More women (55.7%) than men experienced sleep problems (P < .001), but there were no significant differences in the average age between those who did and those who did not have sleep issues. There were also no significance differences in BMI, joint space width, or femorotibial angle, which was an average 177.5 degrees in group with no sleep problems and 177.6 degrees in the group with sleep disturbances.
The proportion of participants experiencing sleep disturbances increased with increasing K/L grade of OA: 56.8% of those with K/L grade 4 had sleep problems, compared with 40.9% of those with K/L grade 3, 42.1% of those with K/L grade 2, and 33.7% of those with K/L grade 1, resulting in 30% greater odds of sleep disturbance with a higher K/L grade (odds ratio, 1.3; P = .011).
Knee pain at night was also significantly associated with severity of OA based on the K/L grade. While only 6.9% of participants reported pain at night overall, nearly 1 in 3 (29.5%) of those with K/L grade 4 reported pain at night, compared with 3.4% of those with K/L grade 1 (P < .001). (Night pain occurred in 5.4% of those with K/L grade 2 and 16.1% with K/L grade 3.)
However, after adjusting for age, gender, and BMI, the severity of knee OA was not significantly associated with sleep disturbance based on K/L grade, joint space width, femoro-tibial angle, and/or WORMS. But knee pain remained significantly associated with sleep disturbance after adjustment based on the visual analog scale and the JKOM (P < .001 for both).
Sleep problems were also significantly associated with each subcategory of the JKOM after adjustment (P < .001 for all but social activities, which was P = .014).
“Activities of daily living may affect the occurrence of knee pain at night,” Mr. Sasahara said, and “sleep disturbance may also disturb quality of life.” If sleep disturbances related to nighttime knee pain are linked to activities of daily living, then “not only knee pain but also activities of daily living need to be improved in order to improve sleep.”
He noted several of the study’s limitations, including the fact that lifestyle habits and work were not taken into account, nor did the researchers evaluate sleep disturbances potentially resulting from a medical illness. The researchers also only examined knee pain, not pain in other parts of the body.
The research was funded by Juntendo University; the Strategic Research Foundation at Private Universities; KAKENHI from the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Mizuno Sports Promotion Foundation; and the Mitsui Life Social Welfare Foundation. Mr. Sasahara and Ms. Cedin had no disclosures.