[Translated article] Coronal and rotational femoral anatomy in a Spanish cohort: Anatomical description and surgical implications for total knee arthroplasty.

Abstract

Purpose The primary objective is to analyse the distribution of three femoral anatomical parameters in a Spanish osteoarthritic population using CT-based measurements: (1) anatomical-mechanical axis (AA-MA), (2) posterior condylar-transepicondylar axis (PCA-TEA) and (3) lateral distal femoral angle (LDFA). The secondary objective is to assess the surgical relevance of these findings in TKA. Methods It is a multicentric cross-sectional observational study. Preoperative CT-scans of 318 patients from a Spanish cohort were analysed to determine AA-MA, PCA-TEA and LDFA. Then, femoral implant positioning was simulated as 5° of valgus from the AA and 3° of external rotation from the PCA. For each patient, this simulated positioning was compared to the theoretical mechanical alignment target. Finally, the native femoral JLO (LDFA) of each patient was compared to the mechanical alignment target (90°). Results Mean AA-MA relationship was 6.0° ± 0.9°, mean PCA-TEA angle was 3.1° ± 1.8° and mean native LDFA was 87.3° ± 2.9°. Positioning the femoral component systematically at 5° of valgus from the AA and 3° of external rotation from the PCA would result in 74.7% of implants being placed in varus and 46.1% in internal rotation from the TEA. Moreover, mechanically alignment would produce a more varus femoral JLO than the native LDFA in 78.1% of patients. Conclusions There is considerable variability in femoral anatomy within the osteoarthritic Spanish population. The 6.7% of patients had AA-MA values outside the 5-7° range. The 41.8% of patients showed PCA-TEA angles smaller than 2° or greater than 4°. The 30.6% of LDFA were outside the 85-90° interval. Simulating a femoral component positioned using only AA and PCA references was associated with deviations from the intended mechanical alignment, most commonly resulting in varus deviation and internal rotation from the TEA.