Age and BMI Are Not Associated with Fatigue in Hip and Knee Osteoarthritis | Article of The Week #41

Osteoarthritis is the most common chronic condition of the joints and is something we all see everyday in clinical practice. The condition can manifest in any joint but is most commonly occurring in the knees and hips. This is reflected in the fact that OA in these joints is expected to be the 9th leading cause of years lived with disability by 2030.

Joint pain is the hallmark sign of osteoarthritis and arguably the leading cause of disability but the way we consider diasbility in arthritis is changing. Fatigue has recently emerged as an important and prevalent symptom for people living with osteoarthritis and could be big contributor to the high rates of disability associated with the condition. This leads to the immediate question – how do we treat fatigue in OA?

New Insights into Patellofemoral OA

A new systematic review has been published in the journal Rheumatology Advances in Practice which has set out to try to identify and evaluate factors related to fatigue in individuals with hip and or knee osteoarthritis.


This systematic review followed the PRISMA guidance and the protcol was registered with PROSPERO in July 2019, both are hallmarks of a good systematic review. A quick check of the PROSPERO database shows that the authors followed their protocol as intended.

In total five databases were searched from inception to March 2020 and these were AMED, CINAHL, MEDLINE, ProQuest and Web of Science core collection. The search strings were adapted for each database, were created by experienced systematic reviewer and can be found in the supplementary information within the article.

Articles were included within the review if they were peer-reviewed, included a hip and or knee osteoarthritis diagnosed using radiographic evidence or a clinical diagnosis using ACR criteria or KL grading and measured fatigue using outcome measures such as the SF-36 vitality scale. If studies involved joint replacements, were published in non-english and were review or grey literature were excluded.

“Two individual factors (age and BMI) had moderate evidence of no association with fatigue.”

Data was extracted by two authors with a third available if consensus needed to be reached. Article quality was assessed using the National Heart, Lung, and Blood Institute (NHLBI) quality appraisal tool. This tool rates studies as having a high, moderate or low risk of bias and is similar to the Cochrane Risk of Bias Tool but is used less frequently because it doesn’t assess for attrition bias.

The results of this study were presented as a narrative synthesis to report factors which were or were not associated with fatigue. Two authors grouped and classified identified factors into individual, disease-specific, psychosocial, behavioural and biologial groups using the bio-behavioural conceptual framework of fatigue in OA.

A best evidence synthesis and ranking system was used to grade the level of evidence supporting the associations found in the results. The details of how this was achieved is fairly complex and a breakdown can be found in the article in full text in the supplementary information.

Results & Clinical Take Home

In total 24 studies were included within the results which involved a total of 9475 patients with knee and or hip osteoarthritis. Of the 24 studies nineteen were rated as having a high quality, four were of moderate quality and one of low quality. Sample sizes varied greatly between studies from 3815 or 68 and the most commonly used fatigue outcome measure was the visual anaogue scale which was used in a third of studies.

Looking at individual factors interestingly age and BMI had moderate evidence of no association with fatigue which is likely contrary to many clinicians presumptions. Race, level of education and gender are not associated with levels of fatigue. Higher rates of co-morbidities however has moderate association with fatigue which is commonsensical and aligns to concepts of frailty and burden of disease.

Looking at the burden of disease further, sixteen studies examined the relationship between disease specific factors and fatigue. There was  moderate evidence to support the association between high pain and higher fatigue. Interestingly there was no evidence to suggest a relationship between worse radiographic severity and fatigue reinforcing the importance of correlating radiology with clinical presentation.

Quick Summary of Factors Associated with Fatigue in Lower Limb OA

  • Age and BMI had moderate evidence of no association with fatigue
  • Worse x-ray evidence is not related to levels of fatigue
  • Signs of depression is associated with higher rates of fatigue
  • Unsurprisingly low levels of physical activity are related to higher rates of fatigue
  • High levels of pain is associated with higher levels of fatigue

Eleven studies assessed the association between psychological factors and fatigue. There is strong evidence to suggest an association between depresive symptoms and higher levels of fatigue. This likely explains why related to low self-reported physical function is also associated with higher rates of fatigue. Unsurprisingly low rates of physical activity are associated with higher rates of fatigue.

Looking at strengths and weaknesses of this study the fact that only articles written in English were included limits the real-world applicability of behavioural factors in clinical practice and it can’t be ingnored that some factors may not have been identified at all because of this.

Fatigue outcome measures have not been validated for hip or knee OA which likely explains why the VAS was the most commonly used tool in the studies included. This will have had some impact on the results of the synthesis however in clinical practice it’s likely that VAS is the most used tool.

In terms of how you can use this information in clinical practice the current evidence strongly suggests that to manage fatigue in hip and knee OA modfifiable factors such as physical activity, physcial function, pain and depressive symptoms need to be targeted.