The accuracy and precision of computer assisted surgery in the assessment of frontal plane deviations of the lower extremity: a femoral fracture model

Mechanical axis deviation of the lower extremity as a result of malreduction or malunion of fractures plays an important role in the development of arthritis. Therefore it is crucial to restore the limb alignment as accurate as possible. The purpose of this study was to evaluate the accuracy and precision of navigation in assessing isolated frontal plane (varus/valgus) deviations of the lower limb in a simulated fracture model of the femur.

Three fracture models with ten specimens in each were created in femoral synthetic composite bones to simulate a subtrochanteric (AO/OTA 31-A1), mid-diaphyseal (AO/OTA 32-A3), and supracondylar (AO/OTA 33-A1) femur fracture. Each specimen was mounted on a custom holding device and registered with the navigation system. Eight custom-made aluminum wedges of varying angles (5°–26°) were used to create varus/valgus angulations at the fracture site. After wedge placement, the frontal plane deformity was recorded and registered by the navigation system. The means and standard deviations for each navigated wedge angle were calculated and compared to the actual wedge angle using a one sample t test. A single factor ANOVA test was subsequently performed to see if the differences between the navigated mean angles in each fracture group were statistically significant. The level of significance was defined as P < 0.05.

None of the navigated mean angles were found to be significantly different from the actual wedge angles (P = 0.05–1.00). More specifically, the differences between the navigated mean angles and the actual wedge angles ranged from 0° to 0.7°. Furthermore, the differences between the navigated mean angles in each angle group were found to be statistically insignificant (P = 0.53–0.99).

The high accuracy and precision of navigation systems in determining frontal plane deformities of long bones can make them an invaluable tool for the exact reduction and realignment of lower extremity fractures.