Is there a Relationship between Distal Femoral Hypoplasia and Coronal and Rotational Alignments in Osteoarthritis Knees?

Abstract

Introduction: There have been studies with regard to anatomic variances of distal femoral condyles, such as lateral femoral condylar hypoplasia, in osteoarthritic knees with valgus deformity. These studies suggested that the posterior condylar axis (PCA) is not a reliable method to determine the axial rotation of femoral component. Even if this is useful information when performing TKA in patients with valgus deformity, the axial anatomic variance of lateral femoral condylar hypoplasia was not evaluated using more comprehensive methods in terms of the relationships with proximal femoral and tibial rotational profiles. Therefore, the authors analyzed the degree of lateral femoral condylar hypoplasia according to the coronal alignment of the lower limb in patients with knee osteoarthritis. The authors also aimed to determine whether rotational profiles, including femoral anteversion and the tibial rotation, differed according to the coronal alignment of the lower limb.

Materials and Methods: From November 2011 to May 2015, 422 knees from 211 patients (20 male, 191 female), who were examined with a standing full-limb anteroposterior (AP) radiograph and computed tomography (CT) before total knee arthroplasty (TKA), were included. Coronal alignment of the lower limb was assessed using a mechanical tibiofemoral angle (mTFA), and it was measured using the standing full-limb AP radiograph. Then, the patients were divided into three groups based on the degree of the mTFA

more than 3 degrees of valgus (n = 31), 3 degrees of valgus to 3 degrees of varus (n = 78), and more than 3 degrees of varus (n = 313). To measure the rotational profiles of the lower limb, CT of the lower extremity was used. Condylar twisting angle (CTA) was defined as the angle formed by clinical transepicondylar axis of distal femur (TEA) and PCA. Femoral anteversion (FeAV) was measured based on TEA (tFeAV) and PCA (pFeAV), respectively. Tibial torsion was measured using the angle formed between a line that is connecting the posterior aspects of the proximal tibia condyles and a line that is connecting the most prominence of lateral and medial malleolus. Relationships between the indicators were analyzed.

Results: Increased valgus alignment of the lower limb was related to greater lateral femoral condylar hypoplasia. Correlation coefficient between mTFA and CTA was 0.253 (p < 0.001). In contrast, there was no difference in terms of degree of femoral anteversion between the three groups. Because of the hypoplasia of the lateral femoral condyle, there was significant positive correlation between degree of valgus deformity and the pFeAV (r = 0.145, p = 0.003). In the subgroup analysis, the pFeAV was greater in the valgus group than the neutral and varus groups. The pFeAV was 16.7° ± 5.8° in the valgus group, 12.1° ± 6.0° in the neutral group and 10.9° ± 7.0° in the varus group. However, when assessing the femoral anteversion using TEA, there was no correlation between the degree of valgus deformity and the tFeAV (r = 0.060, p = 0.218). In addition, there was no difference in the degree of femoral anteversion among the three subgroups. The tFeAV was 6.5° ± 5.6° in the valgus group, 4.7° ± 5.6° in the neutral group and 4.3° ± 7.0° in the varus group. In terms of tibial torsion, the valgus group showed increased tibial torsion than the neutral and varus groups. Tibial torsion was 32.6° ± 6.2° in the valgus group, 26.3° ± 6.9° in the neutral group and 22.6° ± 7.2° in the varus group. In the correlation analysis, there was positive correlation between degree of valgus deformity and increased tibial torsion (r = 0.374, p < 0.001).

Conclusions: The CTA was significantly greater in valgus group, indicating the lateral condyle had hypoplastic change relative to medial condyle. This anatomic difference of distal femur is important to determine proper femoral component rotation during TKA in patients with valgus deformity. Even if the degree of valgus deformity was not related to the degree of femoral anteversion, it was related to increased tibial torsion. Therefore, these rotational profiles should be preoperatively evaluated and the degree of hypoplasia of lateral femoral condyle and the increased torsion of tibia should be considered to obtain satisfactory rotational alignment after TKA in patients with valgus deformity.