What Causes Osteoarthritis?

A study published in the October issue of Arthritis & Rheumatology assessed factors associated with osteoarthritis (OA) afflicting various joints.

“There is no curative treatment for osteoarthritis (OA), which is the most common form of arthritis,” the researchers wrote. “This study was undertaken to identify causal risk factors of knee, hip, and hand OA.”

The study included data on 384,838 patients, gathered from the UK Biobank study. Researchers performed mendelian randomization (MR) analyses to test for causality for body mass index (BMI), bone mineral density (BMD), serum high‐density lipoprotein cholesterol, low‐density lipoprotein cholesterol, and triglyceride levels, type 2 diabetes, systolic blood pressure (BP), and C‐reactive protein levels. The main outcome was OA as determined by hospital diagnoses (all sites, n = 48,431; knee, n = 19,727; hip, n = 11,875; hand, n = 2,330).

Osteoarthritis Causal Factors Vary by Joint

MR analyses found a causal relationship between genetically determined BMI and all OA (odds ratio [OR] per SD increase 1.57 [95% CI 1.44–1.71]), and with OA of the hip and knee, but not the hand. An increase in genetically determined femoral neck BMD was causally correlated with all OA (OR per SD increase 1.14 [95% CI 1.06–1.22]), knee OA, and hip OA; low systolic BIP was also causally associated with all OA (OR per SD decrease 1.55 [95% CI 1.29–1.87]), knee OA, and hip OA. None of the other tested factors were correlated with OA.

One of the study’s limitations is that it relied on hospital diagnoses to determine OA, so radiographic progression and pain could not be determined, and there was no way to exclude potential misdiagnoses.  This primarily applies to hand OA, the researchers noted, adding that posttraumatic OA may also be overrepresented in hospital diagnoses of knee OA. This study also had no data on the effect of physical activity. Lastly, the patient population was limited to white patients.

“In conclusion, BMI exerts a major causal effect on the risk of OA at weight‐bearing joints, but not at the hand. Evidence of causality of knee OA and hip OA was observed for high femoral neck BMD and low systolic BP,” the authors wrote in sum. “These results should be considered in the future research of OA and for the elaboration of prevention or therapeutic strategies for the different OA sites.”