Kenji Tobita*, Hiroshi Okazaki, Yoshinao Koike, Yoshiharu Simozono, Masahiko Bessho, Sakae Tanaka and Isao Ohnishi
Background: Assessment of lower extremity alignment is important. The malalignment test is generally assessed two-dimensionally on plain radiographs. In patients with complex deformities, the key points are set inaccurately on Roentgenogram images, leading to problems with both accuracy and reproducibility. Computed tomography (CT) is the current gold standard for evaluating femoral torsion measurements. However, CT images vary depending on slice orientation during scanning, images of flexion deformities are affected by the orientation of the CT slice, making accurate evaluation impossible should a flexion deformity be present. For this reason, three-dimensional preoperative analysis is required. We report a case in which three-dimensional preoperative analysis was used for a patient with leg deformity after injury to the distal femoral epiphysis, with good results.
Methods: CT scanning was used to establish a preoperative plan and produced a surface morphology model from CT axial data. Free software was then used to create mirror images of the affected and unaffected sides from these data. The mirror image of the unaffected side was then positioned in three-dimensional space, and vectors were set. The fragment proximal to the osteotomy plane was defined as the reference fragment (RF) and the distal fragment as the corresponding fragment (CF), with the functional axis of the unaffected side forming the helical axis (HA). The amount of deformity correction of the CF required was then calculated automatically in terms of the two parameters of rotation and translation in three dimensions by shifting the CF along the HA. A Taylor spatial frame (TSF) was used to perform gradual correction surgery.
Results: The rotational deformity was corrected, a 20-mm medial shift and 12-mm posterior shift persisted. Correction was carried out a second time to correct this deformity.
Conclusion: Three-dimensional analysis of long-bone may prove useful for the correction of long bones deformities in the legs when complex deformity is present.
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