Neutral mechanical alignment: a requirement for successful TKA: opposes.

There is increasing evidence that for a number of patients, neutral alignment is not normal. Patients with so-called constitutional varus have been in varus alignment since the end of their growth. Restoring neutral alignment in these cases may not be the best option for these patients since it is abnormal to them. We recently performed a number of observational studies to find out how patients develop constitutional varus, how these patients can be recognized, and which factors contribute. A cohort of 800 young patients was analyzed to determine the influence of activity level on growth and the development of lower-leg alignment. At the same time, 250 asymptomatic adults between 20 and 27 years were analyzed to determine the incidence of constitutional varus. The results showed that 32% of adult men and 17% of adult women had constitutional varus knees with a natural mechanical alignment ≥3° varus. Constitutional varus was associated with increased sports activity during growth and began to become apparent at the time of growth spurt. Based on these data, we believe that an important fraction of the normal population has a natural alignment at the end of growth of ≥3° varus. This may be a consequence of Hueter-Volkmann's law. Restoration of mechanical alignment to neutral in these cases therefore may not be desirable and in fact unnatural for them.