J. Sharma et al., The mechanism of the effect of obesity in knee osteoarthritis - The mediating role of malalignment, ARTH RHEUM, 43(3), 2000, pp. 568-575
Objective. Obesity is most strongly linked to osteoarthritis (OA) at the kn
ee. Varus malalignment was examined as a possible local mediator that may i
ncrease the impact of body weight at the knee, versus the hip or ankle, Com
partment load distribution is more equitable in valgus than in varus knees,
and valgus knees may better tolerate obesity. We therefore tested whether
1) body mass index (BMI) is correlated with OA severity in vans knees, 2) t
he BMI-OA severity correlation is weaker in valgus than in varus knees, 3)
BMI is correlated with the severity of varus malalignment, and 4)the BMI-me
dial tibiofemoral OA severity relationship is reduced after controlling for
vans malalignment.
Methods. In 300 community-recruited patients with knee OA, 2 groups (varus
and valgus) were identified based on dominant knee alignment on a full-limb
radiograph, i,e,, the angle formed by the intersection of the femoral and
tibial mechanical axes. Severity of knee OA was assessed by measurement of
the narrowest joint space width on radiographs of knees in a fluoroscopy-co
nfirmed semiflexed position.
Results. Alignment direction was symmetric (or neutral in 1 limb) in 87% of
patients, One hundred fifty-four patients had varus knees and 115 had valg
us knees. BMI correlated with OA severity in the vanes group (r = -0.29, P
= 0.0009) but not in the valgus group (r = -0.13, P = 0.17). BMI correlated
with malalignment in those with varus knees (r = 0.26) but not in those wi
th valgus knees (r = 0.16). The partial correlation of BMI and OA severity,
controlling for sex, was reduced from 0.24 (P = 0.002) to 0.04 (P = 0.42)
when varus malalignment was added to the model,
Conclusion. BMI was related to OA severity in those with varus knees but no
t in those with valgus knees. Much of the effect of BMI on the severity of
medial tibiofemoral QA was explained by varus malalignment, after controlli
ng for sex. Whether it precedes or follows the onset of disease, varus mala
lignment: is one local factor that, may contribute to rendering the knee mo
st vulnerable to the effects of obesity.