Other factors include female gender, previous knee injury, age, and presence of hand OA.
Familiar risk factors for knee osteoarthritis (OA) in individuals 50 years and older — high body mass index (BMI), previous knee injury, age, female sex, and the presence of hand OA — were confirmed as the condition’s top drivers in a new systematic review and meta-analysis with an updated evidence base.
One-fourth of cases of onset of knee pain could be attributable to being either overweight or obese, according to Victoria Silverwood and colleagues at the Arthritis Research UK Primary Care Centre at Keele University in Staffordshire, England.
The finding emphasizes “the continued importance of weight loss as a management option for OA,” they wrote in Osteoarthritis and Cartilage. “Our calculated PAF [population attributable fraction] values demonstrate that 24.6% of cases of onset of knee pain could be attributed to being either overweight or obese.”
Data from 46 published studies up to December 2012 were extracted for the systematic review to assess the association between potential risk factors and knee pain/knee OA in study cohorts with a mean age of 50 years and older. Thirty-four studies in which risk factors had consistent definitions across studies were included in the meta-analysis.
Meta-analysis was performed for five risk factors where a sufficient number of studies reported findings. These were: BMI, female gender, smoking, previous knee injury, and the presence of hand OA or Heberden’s nodes.
There was consistent demonstration that being overweight was a risk factor for the onset of knee OA. Among 22 such studies included in the meta-analysis, the pooled odds ratio (OR) was 1.98 (95% CI 1.57-2.20).
Among 22 studies investigating obesity as a risk factor for onset of knee OA, all studies were generally consistent in reporting obesity as a risk factor despite a large amount of heterogeneity between study findings. The pooled OR of these studies was 2.66 (95% CI 2.15-3.28), a slightly larger effect on onset of knee OA than being overweight.
In 25 cohort studies reporting results, or from which results could be deduced, on the effect of being either overweight or obese on knee OA, the pooled OR was 2.10 (95% CI 1.82-2.42) with a large amount of heterogeneity between studies.
The pooled OR for previous knee injury as a risk factor for knee OA was 2.83 (95% CI 1.91-4.19) in 12 studies, which all showed an increased risk of knee OA with a prior injury, although heterogeneity between studies was considerable.
Evidence was consistent across 10 cohort studies that female gender was a risk factor, with a pooled OR of 1.68 (95% CI 1.37-2.07).
In six cohort studies, the pooled OR of hand OA as a risk factor for knee OA was 1.30 (95% CI 0.90-1.87) with moderate heterogeneity, indicating that it may potentially be a risk factor.
A pooled OR of 0.92 (95% CI 0.83-1.01) suggests that, overall, smoking is not associated with knee OA.
Among 19 studies assessing increasing age as a risk factor for knee OA, there was general agreement that increasing age is a significant risk factor, although establishing a pooled OR was not possible because of the range of different age categorizations.
Kneeling, lifting, and farm and construction work were each evaluated in fewer than five studies. “In summary, it would appear that individuals who are exposed to certain physically demanding activities in their daily working lives may be at an increased risk of developing knee pain and knee OA,” the authors conclude.
Of 16 studies that assessed the effect of high levels of physical activity, 11 showed no statistically significant effect on development of knee OA, three showed a significant effect of intense activity, one found a significant effect of habitual activity, and another found a significant effect only in those who ran 20 or more miles per week.
Population attributable fractions were calculated for being overweight or obese, and indicated that 5.1% of new knee pain/knee OA could be attributed to a previous injury and 24.6% could be attributed to being overweight or obese.
“The results of this review can be used clinically to help healthcare professionals identify and manage patients at risk of developing or increasing knee OA,” the authors wrote. “Some, such as weight, can be targeted clinically in order to reduce the number of patients who suffer from knee OA. Patients with other risk factors such as previous knee injury, age, and female gender can be managed to reduce progression of the condition.”
The authors did not assess the quality of the studies in their review but noted that a previous review they conducted that did take into account the quality of studies made no difference in their findings. Not all potential risk factors (such as low muscle strength or malalignment) were considered. In addition, the definition of knee pain was self-reported and may not reflect radiographic knee OA.