In Vivo Assessment of Distal Femur Fracture Motion via Weightbearing CT

Distal femur fractures have a significant risk of healing complications, with potentially suboptimal fracture motion. We developed an in vivo method of quantifying fracture motion to support translational research. Five men and one woman (age 48.3 ± 24.9 years; weight 79.8 ± 12.9 kg, mean ± SD) underwent non-weightbearing and weightbearing CT following plate (4) or nail (2) fixation of distal femur fractures (AO/OTA 33) while recording static ground reaction forces. Subject-specific models were generated, coordinate systems were established, and fragment poses were reconstructed to assess motion. Fracture motion was measurable and greater at the medial than the lateral aspects of fractures, with notable axial plane motion. Three-dimensional (3D) displacement (mean ± standard deviation [SD]) was greater at the medial than lateral fracture (4.4 ± 2.6 vs. 3.5 ± 2.6 mm, p = 0.047), including mean proximal-distal displacement at the medial fracture (2.0 ± 3.0 mm) versus lateral fracture (0.8 ± 3.2 mm, p = 0.030), and mean axial plane displacement at the medial (3.5 ± 1.6 mm) versus lateral (2.6 ± 1.6 mm, p = 0.009) fracture. Axial plane displacement was similar to proximal-distal displacement at the medial (p = 0.318) and lateral (p = 0.488) fracture. 3D and axial plane displacement were moderately associated with load, while proximal-distal displacement was minimally associated with load. Weightbearing magnitude only modestly explained intersubject differences in motion. This method allows exploration of relationships between fracture motion, fracture pattern, fixation, loading, and healing.