The role of knee alignment in disease progression and functional decline in knee osteoarthritis

Context Knee osteoarthritis (OA) is a leading cause of disability in older persons. Few risk factors for disease progression or functional decline hav e been identified. Hip-knee-ankle align ment influences load distribution a t the knee; varus and valgus alignment increase medial and lateral load, re spectively. Objective To test the hypotheses that (1) varus alignment increases risk of medial knee OA progression during the subsequent 18 months, (2) valgus ali gnment increases risk of subsequent lateral knee OA progression, (3) greate r severity of malalignment is associated with greater subsequent loss of jo int space, and (4) greater burden of malalignment is associated with greate r subsequent decline in physical function. Design and Setting Prospective longitudinal cohort study conducted March 19 97 to March 2000 at an academic medical center in Chicago, ill. Participants A total of 237 persons recruited from the community with prima ry knee OA, defined by presence of definite tibiofemoral osteophytes and at least some difficulty with knee-requiring activity; 230 (97%) completed th e study. Main Outcome Measures Progression of OA, defined as al-grade increase in se verity of joint space narrowing on semiflexed, fluoroscopically confirmed k nee radiographs; change in narrowest joint space width; and change in physi cal function between baseline and 18 months, compared by knee alignment at baseline. Results Varus alignment at baseline was associated with a 4-fold increase i n the odds of medial progression, adjusting for age, sex, and body mass ind ex (adjusted odds ratio [OR], 4.09; 95% confidence interval [CI], 2.20-7.62 ). Valgus alignment at baseline was associated with a nearly 5-fold increas e in the odds of lateral progression (adjusted OR, 4.89; 95% CI, 2.13-11.20 ). Severity of varus correlated with greater medial joint space loss during the subsequent 18 months (R=0.52; 95% CI, 0.40-0.62 in dominant knees), an d severity of valgus correlated with greater subsequent lateral joint space loss (R=0.35; 95% CI, 0.21-0.47 in dominant knees). Having alignment of mo re than 5 degrees (in either direction) in both knees at baseline was assoc iated with significantly greater functional deterioration during the 18 mon ths than having alignment of 5 degrees or less in both knees, after adjusti ng for age, sex, body mass index, and pain. Conclusion This is, to our knowledge, the first demonstration that in prima ry knee OA varus alignment increases risk of medial OA progression, that va lgus alignment increases risk of lateral OA progression, that burden of mal alignment predicts decline in physical function, and that these effects can be detected after as little as 18 months of observation.