Hypoplasia of the Lateral Femoral Condyle is Not Associated with Valgus Knee Alignment.

Abstract

Background: Valgus lower limb alignment has anecdotally been associated with lateral femoral condyle (LFC) hypoplasia. However, limited scientific evidence exists to substantiate this doctrine. This study aimed to investigate the association between coronal plane alignment (CPA) and bony distal femoral geometry.

Methods: Routine preoperative computed tomography (CT) scans and full-length weight-bearing radiographs were analyzed for patients undergoing primary total knee arthroplasty, and standardized measurements of bony distal femoral geometry were recorded. Ratios between lateral to medial structure measurements were used to adjust for size differences between patients. Patients were grouped by CPA and sex with statistical analysis performed to determine any significant groupwise differences for each measurement/ratio.

Results: There were 156 patients included, with 83 women (53.2%) and 73 men (46.8%). There were 100 patients (64.1%) who demonstrated varus (women n = 49; men n = 51) and 56 patients (35.9%) who had valgus alignment. No significant differences were observed between groups in age, body mass index, race, or laterality of the imaged knee. Linear regression modeling demonstrated no significant groupwise differences in lateral/medial condyle antero-posterior (AP) distance or lateral/medial posterior condyle offset ratios in relation to CPA and sex, or in lateral/medial condyle diameter ratio in relation to CPA alone. Valgus alignment was associated with significantly reduced lateral/medial epicondyle to posterior condyle distance ratio, lateral/medial femoral column length ratios, and increased lateral femoral AP condyle distance to trans-condylar width.

Conclusion: No statistically significant differences exist across most standardized measurements of lateral distal femoral geometry in relation to CPA. Contrary to conventional thought, patients who had valgus alignment did not demonstrate reduced bony AP diameter of the LFC. Perceived LFC hypoplasia in patients who have valgus alignment may be attributable to differences in cartilage wear of the LFC, relative shortening of the lateral femoral column, or a relative posterior position of the lateral epicondyle resulting in an internally rotated appearance of the distal femur in the axial plane relative to the TEA.