gms | German Medical Science

Objectives: Transtrochanteric anterior rotational osteotomy (TARO) is a joint-preserving surgical procedure which involves transposing an intact posterior part of femoral head to a weight-bearing portion of hip joint. The radiographic and clinical prognosis after TARO is influenced by the proportion of the intact area to acetabular weight-bearing portion. Most orthopedic surgeons have predicted and estimated the results of TAROs based on two-dimensional (2-D) slice images of simple radiography or computed tomography. However, there is a limit to forecast and evaluate the outcomes exactly by using the 2-D slice images alone. To address this issue, we performed magnetic resonance imaging (MRI)-based three-dimensional (3-D) simulation of TARO for osteonecrosis of femoral head (ONFH) using images of 3-D reconstructed bone models.

Methods: We selected 3 cases of ONFH (Type B, C1, and C2) based on the scale by the Japanese Investigation Committee (JIC) classification system. Each case had a necrotic lesion which was positioned in the mid-to anterior portion of the femoral head. Selected MRI images were formatted as Digital Imaging and Communications in Medicine (DICOM) image files and were managed with Mimics® (Materialize, Leuven, Belgium) to reconstruct the 3-D bone models. Measurement using the images of 3-D reconstructed bone models was conducted with 3-Matics® (Materialize, Leuven, Belgium).

Results and Conclusion: In case of type B lesion, initial surface areas that were located under the acetabular weight-bearing portion at zone 1, 2, and 3 were 232 mm2, 350.93 mm2 and 18.2 mm2, respectively. Each surface area showed a tendency to decline in accordance with the increase of anterior rotation angle. With the 1st osteotomy plane that had no inclination, the surface areas were changed to 180.7 mm2, 19.79 mm2 and 0 mm2, respectively. With the plane which had a 10 degree inclination, those decreased to 112.96 mm2, 0 mm2 and 0 mm2, respectively. In case of type C1 lesion, initial surface areas at each zone were 238.3 mm2, 470.2 mm2 and 69.83 mm2, respectively. With no inclined osteotomy plane, the surface areas lessened to 129.14 mm2, 285.2 mm2 and 0 mm2, respectively. With the 10 degree inclined osteotomy plane, those decreased to 109.86 mm2, 216.24 mm2 and 0 mm2, respectively. However, in case of type C2 lesion, initial surface areas at zone 1 and 3 were minimal regardless of anterior rotation and inclination angle.

We could measure and predict the surface areas of the ONFH lesions which were positioned under the acetabular weight-bearing portion at each zone after TARO. In conclusion, preoperative MRI based 3-D simulation using the images of 3-D reconstructed bone models appears to be effective for predicting and evaluating the outcome after TARO.