Written by Catharine Paddock
It appears that knee pain of some kind is a common complaint in middle-aged and mature women, with varying possible causes leading to varying types of pain. A new study on knee-pain patterns assessed periodically over 12 years in a representative UK population finds that nearly two-thirds (63%) of women aged 50 and over experience knee pain at least once, persistently, or intermittently over such a period. The authors found these patterns were more likely in women with higher BMI, with a previous knee injury, or whose scans showed they had osteoarthritis (OA). They write about their findings in the 19 December online issue of the journalArthritis & Rheumatism.
Senior author Dr Nigel Arden, a Professor of Rheumatology at the University of Oxford in the UK, told the media that this was the first study involving community-based participants that investigates patterns of knee pain using “multiple assessment points” over a period of 12 years: “Understanding the prevalence and predictors of knee pain is the first step in developing comprehensive pain assessment plans that could lead to more targeted treatment options for those burdened by OA.”
For their analysis, Arden and colleagues used data gathered in the Chingford Study, a prospective population-based study of OA and osteoporosis established in 1989. This started with more than 1,000 women aged from 44 to 57 (median 52) years. The cohort is described as representative of women in the UK in general in terms of height, weight, and smoking status. At four times over the 12 years of the study, the participants completed questionnaires about their knee pain. From their responses the researchers classed the 489 participants who were still in the study at the end into one of four groups, depending on their pain characteristics: asymptomatic, persistent, incident, and intermittent.
The results showed that:
- 44% of women reported experiencing “any days of pain”.
- 23% reported experiencing “pain on most days of the previous month”.
- Of those experiencing “any pain”, 9% had persistent pain, 24% had incident pain, and 29% had intermittent pain.
- Of those experiencing “pain on most days”, these figures were 2%, 16% and 18% respectively.
- A higher BMI predicted persistent and incident patterns of pain, while radiographic OA predicted persistent pain.
- Those who reported a previous knee injury were more likely to have persistent or intermittent patterns of pain.
The researchers conclude the results show a “significant variability” in patterns of knee pain over time in this representative population, with few participants “consistently reporting knee pain at each time point”. They also suggest that a strength of the study is that it describes a natural history of knee pain over a long period of time, taking data from several points along that timescale. Finding that separate factors appear to predict pain patterns differently (eg BMI predicted persistent and incident patterns while OA predicted only persistent pain patterns) may be why studies that measure pain at one time point seem to show inconsistent relationships between pain predictors and pain patterns, they add.
Arden said: “Validation of our findings through reproduction in other patient groups is needed to advance knowledge of knee pain predictors that will ultimately enhance prevention and treatment strategies for those with OA.”
OA is a leading cause of disability throughout the world. In the US, the American College of Rheumatology estimates that over 27 million Americans over the age of 25 are living with the disease, with pain being the most problematic symptom. The damage to the economy that can be linked to OA is substantial. In the UK, reports suggest it accounts for £3.2 billion a year loss in productivity. The US Centers for Disease Control and Prevention (CDC) puts the cost of job-related OA at between $3.4 and $13.2 billion a year. Previous studies indicate that OA of the knee in particular is linked to reduced physical function and is a substantial burden to society. According to figures from the CDC, nearly half a million total knee replacements were carried out in the the US in 2004, with around $14 billion spent on the hospital costs of such an operation.