gms | German Medical Science

Objectives: The natural history of osteonecrosis of femoral head (ONFH) generally includes the collapse of the femoral head, and it is influenced by the extent and location of the necrotic lesion. Most orthopedic surgeons have measured and categorized the extent of ONFH using two-dimensional (2-D) slice images of simple radiography or magnetic resonance imaging (MRI). However, as the conventional measurement methods are based on specific 2-D slice images, the extent and location of the necrotic lesion can't be evaluated exactly. To address this issue, we performed MRI-based three-dimensional (3-D) analysis of the necrotic lesions using images of 3-D reconstructed bone models.

Methods: We included twenty cases of ONFH, which were categorized based on the scale by the Japanese Investigation Committee (JIC) classification system (type A in 2 cases, type B in 3, type C1 in 7, and type C2 in 8). For each slice of MR images, parts of the necrotic lesions were segmented, and reconstructed as 3-D bone models along with entire femoral head and acetabulum with Mimics® (Materialize, Leuven, Belgium). Identifying the extent and location of the necrotic lesions was performed with 3-Matics® (Materialize, Leuven, Belgium).

Results and Conclusion: In 17 of 20 cases (type A in 2 cases, type B in 3, type C1 in 6, and type C2 in 6), the surface areas of midcoronal planes were not the largest, and in 18 of 20 cases (type A in 2 cases, type B in 3, type C1 in 6, and type C2 in 7), those of midaxial and midsagittal planes were not also maximal. Although the conventional methods using specific 2-D slice images is simple and easy to measure the extent and location of the necrotic lesions, to assess them only with a few imaging planes is high probability of misinterpretation. Therefore, MRI-based 3-D analysis using images of 3-D reconstructed bone models can be a good alternative to the conventional methods for estimating the extent and location of the necrotic lesions in ONFH.