Reassessing Valgus Lower Extremity Alignment: Is Lateral Condyle Hypoplasia a Myth?

BACKGROUND: Lower-extremity coronal alignment influences joint loading, gait mechanics, and the progression of osteoarthritis, yet the relative contributions of hip and knee anatomy remain incompletely defined. Valgus lower extremity alignment has traditionally been attributed to lateral femoral condyle hypoplasia, but the major contributor to valgus alignment and that femoral version and tibial bowing are more strongly associated with valgus deformity. METHODS: We performed a retrospective review of 122 consecutive primary total knee arthroplasties (57 valgus, 65 varus) with preoperative long-leg radiographs and hip-to-ankle computed tomography. Hip-knee-ankle angle, tibial shaft angulation, femoral version, and medial and lateral femoral condyle heights were independently measured by three blinded observers. Multivariate analyses of covariance were used to determine differences between groups for femoral version and bowing angle with age and sex as covariates; all other continuous variables were compared with two-tailed t-tests, and categorical variables with Chi-square analyses (α = 0.05). RESULTS: Valgus alignment demonstrated significantly lower femoral anteversion than varus alignment (5.5 [95% confidence interval (CI) 3.1 to 7.9] versus 10.3 [95% CI 8.0 to 12.5], P = 0.005) and a markedly higher prevalence of femoral retroversion (30 versus 3%, P < 0.001). Medial tibial bowing greater than 3° occurred in 50.9% of valgus knees compared with 3% of varus knees (P < 0.001). Unexpectedly, lateral femoral condyle height was slightly greater in the valgus group compared with the varus group (62.8 versus 60.9 mm, P = 0.025). CONCLUSIONS: Valgus lower extremity alignment is strongly associated with femoral retroversion and medial tibial bowing, but not lateral femoral condyle hypoplasia. These findings challenge long-standing assumptions about the pathogenesis of valgus deformity and underscore the importance of assessing femoral version and tibial morphology when planning total knee or hip arthroplasty.