ARTHRITIS & RHEUMATISM
Vol. 50, No. 12, December 2004, pp 3904–3909
© 2004, American College of Rheumatology
The Effect of Body Weight on Progression of
Knee Osteoarthritis Is Dependent on Alignment
David T. Felson, Joyce Goggins, Jingbo Niu, Yuqing Zhang, and David J. Hunter
Objective. Whereas obesity increases overall load-
ing of the knee, limb malalignment concentrates that
loading on a focal area, to the level at which cartilage
damage may occur. This study evaluated whether the
effect of body weight on progression of knee osteoarthri-
tis (OA) differs depending on the degree of limb mal-
Methods. The study population comprised 228
veterans and community recruits with symptomatic
knee OA (pain on most days and radiographic disease)
who volunteered to participate in a natural history
study and from whom baseline radiographs were ob-
tained to assess alignment; 227 (99.6%) completed a
30-month followup. Of 403 knees assessed at baseline,
394 (97.8%) were followed up. Participants’ body mass
index (BMI) was assessed at each examination. The
main outcome measure was progression of knee OA,
defined as narrowing of the tibiofemoral joint space by
1 grade (semiquantitative scale 0–3) on radiographs of
the fluoroscopically positioned knee. The association
between BMI and the risk of knee OA progression was
assessed after adjusting for age, sex, and limb align-
ment, using logistic regression and generalized estimat-
Results. Of 394 knees, 90 (22.8%) showed disease
progression, and limb alignment was strongly associ-
ated with progression risk. The risk of progression
increased with increasing weight (for each 2-unit in-
crease in BMI, odds ratio [OR] for progression 1.08,
95% confidence interval [95% CI] 1.00–1.16). However,
among those knees with neutral alignment (0–2°), in-
creases in BMI had no effect on risk of progression (OR
1.00), and in those with severe malalignment (>7°), the
effect was similarly null (OR 0.93). The effect of BMI on
progression was limited to knees in which there was
moderate malalignment (OR per 2-unit increase in BMI
1.23, 95% CI 1.05–1.45).
Conclusion. Although elevated BMI increases the
risk of knee OA progression, the effect of BMI is limited
to knees in which moderate malalignment exists, pre-
sumably because of the combined focus of load from
malalignment and the excess load from increased
weight. This has implications for clinical recommenda-
tions and for trials testing weight loss in those with
Knee osteoarthritis (OA) affects ?6% of adults
ages 30 years and older (1). There are no treatments
available that would impede the course of this disease,
which is generally characterized as progressive cartilage
loss. Persons with knee OA are, on average, heavier than
those without disease, and longitudinal studies have
shown that being overweight increases the risk of devel-
oping disease (2–4). Since disease incidence is influ-
enced by a person’s weight, it is possible that being heavy
also has an effect on the risk of disease progression in
those who already have OA in which case weight loss
might be an effective treatment to prevent structural
However, the effect of body weight on disease
progression has been less consistently demonstrated
than its effect on disease incidence. Some longitudinal
studies of patients with knee OA have shown that,
compared with nonobese subjects, those who are obese
have a higher risk of joint space loss, suggestive of
cartilage loss, as visualized on radiographs (5–7), but
these findings are not universally reported. Indeed, some
prospective studies of knee OA have shown no associa-
tion between being overweight and disease progression
Supported by the NIH (grant AR-47785) and by the Arthritis
Foundation (Clinical Sciences grant).
David T. Felson, MD, Joyce Goggins, MPH, Jingbo Niu, MD,
Yuqing Zhang, DSc, David J. Hunter, MD: Boston University Clinical
Epidemiology Research and Training, and the Arthritis Center, Bos-
Address correspondence and reprint requests to David T.
Felson, MD, A207, 715 Albany Street, Boston, MA 02118. E-mail:
Submitted for publication April 11, 2004; accepted in revised
form September 2, 2004.
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BODY WEIGHT, ALIGNMENT, AND KNEE OA PROGRESSION3909