Data beats dogma-Valgus knees are not associated with a hypoplastic lateral femoral condyle: A CT-based analysis from...

Observations following the mechanical alignment principle have led to the concept that the lateral femoral condyle (LFC) is hypoplastic in valgus knee. This study aimed to investigate if this assumption is correct-the hypothesis was that there is no relationship between the radius of curvature of the LFC and coronal alignment.

This is a retrospective study of prospectively collected patients who underwent primary robotic TKA between 2021 and 2023. Segmentation of the preoperative computerised tomography scan was performed to obtain a three-dimensional model of the knee. A semi-automated algorithm was used to create a circle of best fit to obtain the radius of each femoral condyle. The size of the condyles was expressed as the lateral-to-medial (L2M) condylar radii ratio. Patients were stratified based on hip-knee-ankle (HKA) angle and L2M ratio, and the association with the alignment was analysed. Distal and posterior offset were investigated and analysed. Significance was for p values < 0.05.

Overall, 498 consecutive knees were investigated. The mean HKA was 4.1 ± 5.4° varus. The mean L2M condylar ratio was 0.95 in patients with neutral alignment, 0.98 in varus alignment and 0.96 in valgus alignment. The L2M ratio was <1 in all alignment groups, with no significant differences between varus and valgus. The knees with a hypoplastic LFC (L2M ratio <0.9) showed a similar HKA distribution to those with L2M > 0.9. No differences in posterior offset of the LFC were noted between valgus, neutral and varus knees. The lateral distal offset was greater in valgus than neutral knees (27.1 ± 2.7 mm vs. 25.9 ± 2.9 mm).

The LFC is on average smaller than the MFC regardless of the coronal alignment, with no correlation with the HKA. These findings add evidence against the concept of a hypoplastic LFC in valgus knees.

Level III, retrospective cohort study.