Abstract
Background
Authors sought to determine the degree of lateral condylar hypoplasia of distal femur was related to degree of valgus malalignment of lower extremity in patients who underwent TKA. Authors also examined the relationships between degree of valgus malalignment and degree of femoral anteversion or tibial torsion.
Methods
This retrospective study included 211 patients (422 lower extremities). Alignment of lower extremity was determined using mechanical tibiofemoral angle (mTFA) measured from standing full-limb AP radiography. mTFA was described positive value when it was valgus. Patients were divided into three groups by mTFA; more than 3 degrees of valgus (valgus group, n = 31), between 3 degrees of valgus to 3 degrees of varus (neutral group, n = 78), and more than 3 degrees of varus (varus group, n = 313). Condylar twisting angle (CTA) was used to measure degree of the lateral femoral condylar hypoplasia. CTA was defined as the angle between clinical transepicondylar axis (TEA) and posterior condylar axis (PCA). Femoral anteversion was measured by two methods. One was the angle formed between the line intersecting femoral neck and the PCA (pFeAV). The other was the angle formed between the line intersecting femoral neck and clinical TEA (tFeAV). Tibial torsion was defined as a degree of torsion of distal tibia relative to proximal tibia. It was determined by the angle formed between the line connecting posterior cortices of proximal tibial condyles and the line connecting the most prominent points of lateral and medial malleolus. Positive values represented relative external rotation. Negative values represented relative internal rotation.
Results
Greater lateral femoral condylar hypoplasia was related to increased valgus alignment of lower extremity. Correlation coefficient between mTFA and CTA was 0.253 (p < 0.001). Valgus group showed increased CTA, which was 10.2° ± 1.9°. CTA was 7.4° ± 2.5° in neutral group and 6.6° ± 4.8° in varus group. There was significant positive correlation between the degree of valgus alignment and the degree of femoral anteversion (r = 0.145, p = 0.003). pFeAV was 16.7° ± 5.8° in valgus group, 12.1° ± 6.0° in neutral group and 10.9° ± 7.0° in varus group. There was no correlation between degree of valgus alignment and degree of femoral anteversion (r = 0.060, p = 0.218). In terms of tibial torsion, increased valgus malalignment was associated with increased tibial torsion (r = 0.374, p < 0.001). Valgus group showed increased tibial torsion than other groups. Tibial torsion was 32.6° ± 6.2° in valgus group, 26.3° ± 6.9° in neutral group and 22.6° ± 7.2° in varus group.
Conclusions
Increased valgus alignment of lower extremity was related to greater lateral femoral condylar hypoplasia. However, increased valgus alignment was not related to degree of femoral anteversion whereas it was related to increased external tibial torsion. Our findings should be considered when determining proper rotational alignment in TKA.
