Dynamic deformation of femur during medial compartment knee osteoarthritis

Objectives
The aim of this study was to evaluate the morphological changes of the femur in the coronal plane in progressing varus gonarthrosis and to explore the interrelation of each component.
Patients and methods
From January to July 2017, radiographic images of 1538 knees of 883 consecutive patients were collected and analyzed. We drew the alignments and measured the orientation angles of the lower extremities and compared the results among age groups for each sex. Correlation and regression tests were used to analyze the measurements.
Results
There were significant differences in the neck-shaft angle (NSA), femoral bowing angle (FBA) and anatomic medial distal femoral angle (aMDFA) by age group in females, whereas the differences were not significant in males. In females, a positive correlation was found between age and the FBA and aMDFA (r = 0.253, 0.141, p<0.01), and a negative correlation was found between age and the NSA while the FBA was controlled (r = -0.065, p<0.05). The FBA was positively correlated with the NSA (r = 0.312, p<0.01) and aMDFA (r = 0.233, p<0.01). The NSA, FBA, and aMDFA together affected 72.2% of the mechanical medial distal femoral angle (mMDFA) (β = 0.071, -0.528, 0.803, p<0.01).
Conclusion
As knee osteoarthritis (KOA) progressed, dynamic deformation of the femur was found in females, while no obvious changes were found in males. Femoral mechanical axis varus (mMDFA decrease) was the result of changes in the NSA, FBA and aMDFA. The deformation was throughout the femur rather than in a local area, as femur bowing can lead to corresponding changes in both ends of the femur. We provided a theoretical basis for TKA and knee-salvage treatment, and more attention should be paid to aging patients, especially females, in the preoperative protocol for orthomorphia.