Subtalar axis determined by combining digital twins and artificial intelligence: influence of the orientation of this axis for hindfoot compensation of varus and valgus knees.

PURPOSE

Previous studies evaluating hindfoot and knee alignment have suggested compensation between the knee and the hindfoot deformities. However, these studies did not investigate the influence of the orientation of the subtalar axis on the results.

MATERIAL AND METHODS

Using computed tomography data of patients without osteoarthritis, digital twins, and artificial intelligence, we identified the orientation of the axis of the subtalar joint. Compensation was evaluated in the subtalar joint according to angular knee deformity and subtalar axis direction.

RESULTS

With the inclination angle defined as the angle between the axis and the XY plane (horizontal) and the deviation angle defined as the angle between the projection of axis on the XZ plane, the inclination angle of the subtalar helical axis showed an average angle of 35.3° (range 5° to 48°). The mean deviation angle for the helical axis was 6.4° (range - 4° to + 12°). Our findings indicated that an increase of the inclination angle of the subtalar axis tends to limit adjustment in the hindfoot alignment toward re-balance of the whole lower limb toward a neutral weight-bearing axis when malalignment of the knee occurs.

CONCLUSION

Malalignment of the knee and different compensations in the hindfoot contribute to various combined deformities in the population: associated valgus or varus deformities and inverse associations of varus/valgus deformities.