3D atlas-based registration can calculate malalignment of femoral shaft fractures in six degrees of freedom.
OBJECTIVE
This study presents and evaluates a semi-automated algorithm for quantifying malalignment in complex femoral shaft fractures from a single intraoperative cone-beam CT (CBCT) image of the fractured limb.


METHODS
CBCT images were acquired of complex comminuted diaphyseal fractures created in 9 cadaveric femora (27 cases). Scans were segmented using intensity-based thresholding, yielding image stacks of the proximal, distal and comminuted bone. Semi-deformable and rigid affine registrations to an intact femur atlas (synthetic or cadaveric-based) were performed to transform the distal fragment to its neutral alignment. Leg length was calculated from the volume of bone within the comminution fragment. The transformations were compared to the physical input malalignments.


RESULTS
Using the synthetic atlas, translations were within 1.71 ± 1.08 mm (medial/lateral) and 2.24 ± 2.11 mm (anterior/posterior). The varus/valgus, flexion/extension and periaxial rotation errors were 3.45 ± 2.6°, 1.86 ± 1.5° and 3.4 ± 2.0°, respectively. The cadaveric-based atlas yielded similar results in medial/lateral and anterior/posterior translation (1.73 ± 1.28 mm and 2.15 ± 2.13 mm, respectively). Varus/valgus, flexion/extension and periaxial rotation errors were 2.3 ± 1.3°, 2.0 ± 1.6° and 3.4 ± 2.0°, respectively. Leg length errors were 1.41 ± 1.01 mm (synthetic) and 1.26 ± 0.94 mm (cadaveric). The cadaveric model demonstrated a small improvement in flexion/extension and the synthetic atlas performed slightly faster (6 min 24 s ± 50 s versus 8 min 42 s ± 2 min 25 s).


CONCLUSIONS
This atlas-based algorithm quantified malalignment in complex femoral shaft fractures within clinical tolerances from a single CBCT image of the fractured limb.
Orthopaedic Biomechanics Laboratory, Sunnybrook Health Sciences , Toronto .
Meghan C
MC
Crookshank
Maarten
M
Beek
Michael R
MR
Hardisty
Emil H
EH
Schemitsch
Cari M
CM
Whyne
D000465:Algorithms; D002102:Cadaver; D054893:Cone-Beam Computed Tomography; D018483:Diaphyses / Q000000981:diagnostic imaging / Q000293:injuries; D005264:Femoral Fractures / Q000000981:diagnostic imaging*; D018460:Fractures, Comminuted / Q000000981:diagnostic imaging; D017759:Fractures, Malunited / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged
Cone-beam CT; femoral fracture; malalignment