Coronal alignment is a predictor of the rotational geometry of the distal femur in the osteo-arthritic knee

There is a lot of inter-individual variation in the rotational anatomy of the distal femur. This study was set up to define the rotational anatomy of the distal femur in the osteo-arthritic knee and to investigate its relationship with the overall coronal alignment and gender. CT-scans of 231 patients with end-stage knee osteo-arthritis prior to TKA surgery were obtained. This represents the biggest series published on rational geometry of the distal femur in literature so far. The posterior condylar line (PCL) was on average 1.6A degrees (SD 1.9) internally rotated relative to the surgical transepicondylar axis (sTEA). The perpendicular to trochlear anteroposterior axis (aSyenTRAx) was on average 4.8A degrees (SD 3.3A degrees) externally rotated relative to the sTEA. The relationship between the PCL and the sTEA was statistically different in the different coronal alignment groups (p < 0.001): 1.0A degrees (SD 1.8A degrees) in varus knees, 2.1A degrees (SD 1.8A degrees) in neutral knees and 2.6A degrees (SD 1.8A degrees) in valgus knees. The same was true for the aSyenTRAx in these 3 groups (p < 0.02).There was a clear linear relationship between the overall coronal alignment and the rotational geometry of the distal femur. For every 1A degrees in coronal alignment increment from varus to valgus, there is a 0.1A degrees increment in posterior condylar angle (PCL vs sTEA). The PCL was on average 1.6A degrees internally rotated relative to the sTEA in the osteo-arthritic knee. The relationship between the PCL and the sTEA was statistically different in the different coronal alignment groups. III.