Background/Purpose

Elevated body mass index (BMI) is associated with pain in knee OA.  However, it is unclear if adiposity closer in proximity to the knee might have a greater influence on pain in that joint.  To address this question, we assessed whether fat measured around the knee or around the hip was associated with prevalent knee pain. 

Methods

We performed a cross-sectional study of a subgroup of the incidence subcohort of the Osteoarthritis Initiative (OAI) who had DXA scans from the 72-month visit analyzed for knee and hip adiposity.  Participants from 2 clinical sites were included.  DXA scans of the right knee and one hip (usually the right) were acquired on identical GE Lunar Prodigy scanners, generating knee fat and hip fat percentages.  Knee pain was assessed using the question from the 72-month visit, “In the past 12 months, have you had pain, aching or stiffness in or around your knee on most days for at least one month?”  Posterior-anterior semiflexed knee radiographs were read for Kellgren-Lawrence (KL) grade (0-4) from the 48-month visit.  We performed logistic regression with knee fat percent quartiles as the predictors and frequent knee pain as the outcome.  Adjusted results included KL grade as a covariate.  We repeated these analyses evaluating hip fat percent quartiles as the predictor.

Results

359 participants, 51% female, were included with a mean age of 64.8 (8.0) years and BMI of 28.1 (4.9) kg/m².  The frequency of KL grades 0 – 4 included were 44%, 19%, 21%, 13%, and 3% respectively.  Table 1 illustrates that increasing knee fat percent quartiles were minimally associated with knee pain though both unadjusted and adjusted odds ratios were not statistically significant.  In contrast, hip fat percent quartiles were associated with knee pain with the p for trend for both unadjusted and adjusted odds ratios being statistically significant. 

Table 1.  Fat percentiles of the knee and hip as predictors for frequent knee pain.
Knee Fat Percent Quartiles	Prevalence of Knee Pain	Unadjusted OR	Adjusted OR (for KL Grade)
Quartile 1 (6-25%)	12/88 (14%)	Referent	Referent
Quartile 2 (25-34%)	21/90 (23%)	1.4 (0.7 – 2.8)	1.2 (0.6 – 2.7)
Quartile 3 (35-44%)	18/90 (20%)	1.3 (0.5 – 2.4)	1.0 (0.5 – 2.3)
Quartile 4 (44-64%)	22/90 (24%)	1.4 (0.7 – 3.0)	1.3 (0.6 – 2.9)
		p for trend = 0.13	p for trend = 0.40
Hip Fat Percent Quartiles	Prevalence of Knee Pain	Unadjusted OR	Adjusted OR (for KL Grade)
Quartile 1 (10-21%)	10/86 (12%)	Referent	Referent
Quartile 2 (22-26%)	20/88 (23%)	2.1 (1.0 – 4.7)	1.8 (0.8 – 4.2)
Quartile 3 (26-32%)	19/88 (22%)	2.0 (0.9 – 4.4)	1.8 (0.8 – 4.2)
Quartile 4 (32-44%)	27/88 (31%)	3.2 (1.5 – 6.9)	2.4 (1.1 – 5.6)
		p for trend = 0.005	p for trend = 0.05

Conclusion

Hip adiposity, not local knee adiposity, was associated with knee pain independent of radiographic OA severity.  These findings suggest that local adiposity may not have a clinically relevant influence on knee pain.  Instead adiposity of the hip, one adjacent joint away, has a greater influence on knee pain.  Understanding whether the mechanism of this relationship is biomechanically driven or driven by adipokines will be instructive in better understanding the causes of knee pain and identifying new targets of therapy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/hip-adiposity-not-local-knee-adiposity-is-associated-with-knee-pain-independent-of-radiographic-osteoarthritis-severity/