Accurate and reliable pose recovery of distal locking holes in computer-assisted intra-medullary nailing of femoral shaft fractures: a preliminary study.
OBJECTIVE
One of the difficult steps in intra-medullary nailing of femoral shaft fractures is distal locking - the insertion of distal interlocking screws. Conventionally, this is performed using repeated image acquisitions, which leads to considerable irradiation of the patient and surgical team. Virtual fluoroscopy has been used to reduce radiation exposure, but can only provide multi-planar two-dimensional projection views. In this study, two calibrated fluoroscopic images were used to automatically recover the positions and orientations of the distal locking holes (DLHs). The ultimate goal is to provide precise three-dimensional guidance during distal locking.


METHODS
A model-based optimal fitting process was used to reconstruct the positions and orientations of the DLHs from two calibrated fluoroscopic images. No human intervention is required. A preliminary in vitro validation study was conducted to analyze the accuracy and reliability of the technique using images acquired from different viewpoints. The ground truths of the DLH were obtained by inserting a custom-made steel rod through the hole and then digitizing both the top and bottom centers of the rod using a sharp pointer. The recovery errors were computed by comparing the computed results to the ground truths.


RESULTS
In all experiments, the poses of the DLHs could be recovered fully automatically. When the recovered positions and orientations of the DLHs were compared to their associated ground truths, a mean angular error of 0.5 degrees (STD = 0.2 degrees ), and a mean translational error of 0.1 mm (STD = 0.0 mm) were found.


CONCLUSIONS
Accurate and reliable pose recovery of distal locking holes from two calibrated fluoroscopic images is achievable. Our preliminary in vitro experimental results demonstrate that the recovered poses of the distal locking holes are sufficiently accurate for intra-operative use.
Zheng
Guoyan
G
MEM Research Center ISTB, University of Bern, Bern, Switzerland. Guoyan.Zheng@MEMcenter.unibe.ch
Zhang
Xuan
X
Haschtmann
Daniel
D
Gédet
Philippe
P
Langlotz
Frank
F
Nolte
Lutz P
LP
D000465:Algorithms; D001858:Bone Nails; D001863:Bone Screws; D002138:Calibration; D003198:Computer Simulation; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000601:surgery*; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D005471:Fluoroscopy / Q000295:instrumentation*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D008953:Models, Anatomic; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity; D012984:Software; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*