Objective To analyze the femoral head collapse and the operation of osteonecrosis of the femoral head (ONFH) in different Japanese Investigation Commitee (JIC) types, in order to summarize the prognostic rules of each type of ONFH, and explore the clinical significance of CT lateral subtypes based on reconstruction of necrotic area of C1 type and verify their clinical effect. Methods A total of 119 patients (155 hips) with ONFH between May 2004 and December 2016 were enrolled in the study. The total hips consisted of 34 hips in type A, 33 in type B, 57 in type C1, and 31 in type C2, respectively. There was no significant difference in age, gender, affected side, or type of ONFH of the patients with differenct JIC types (P>0.05). The 1-, 2-, and 5-year femoral head collapse and operation of different JIC types were analyzed, as well as the survival rate (with femoral head collapse as the end point) of hip joint between different JIC types, hormonal/non-hormonal ONFH, asymptomatic and symptomatic (pain duration >6 months or ≤6 months), and combined preserved angle (CPA) ≥118.725° and CPA<118.725°. JIC types with significant differences in subgroup surgery and collapse and with research value were selected. According to the location of the necrotic area on the surface of the femoral head, the JIC classification was divided into 5 subtypes in the lateral CT reconstruction, and the contour line of the necrotic area was extracted and matched to the standard femoral head model, and the necrosis of the five subtypes was presented by thermography. The 1-, 2-, and 5-year outcomes of femoral head collapse and operation in different lateral subtypes were analyzed, and the survival rates (with collapse of the femoral head as the end point) between CPA≥118.725° and CPA<118.725° hip in patients with this subtype were compared, as well as the survival rates of different lateral subtypes (with collapse and surgery as the end points, respectively). ResultsThe femoral head collapse rate and operation rate in the 1-, 2-, and 5-year were significantly higher in patients with JIC C2 type than in patients with other hip types (P<0.05), while in patients with JIC C1 type than in patients with JIC types A and B (P<0.05). The survival rate of patients with different JIC types was significantly different (P<0.05), and the survival rate of patients with JIC types A, B, C1, and C2 decreased gradually. The survival rate of asymptomatic hip was significantly higher than that of symptomatic hip, and the survival rate of CPA≥118.725° was significantly higher than that of CPA<118.725° (P<0.05). The lateral CT reconstruction of type C1 hip necrosis area was selected for further classification, including type 1 in 12 hips, type 2 in 20 hips, type 3 in 9 hips, type 4 in 9 hips, and type 5 in 7 hips. There were significant differences in the femoral head collapse rate and the operation rate among the subtypes after 5 years of follow-up (P<0.05). The collapse rate and operation rate of types 4 and 5 were 0; the collapse rate and operation rate of type 3 were the highest; the collapse rate of type 2 was high, but the operation rate was lower than that of type 3; the collapse rate of type 1 was high, but the operation rate was 0. In JIC type C1 patients, the survival rate of the hip joint with CPA≥118.725° was significantly higher than that with CPA<118.725° (P<0.05). In the follow-up with femoral head collapse as the end point, the survival rates of types 4 and 5 were all 100%, while the survival rates of types 1, 2, and 3 were all 0, and the difference was significant (P<0.05). The survival rate of types 1, 4, and 5 was 100%, of type 3 was 0, and of type 2 was 60%, showing significant difference (P<0.05). Conclusion JIC types A and B can be treated by non-surgical treatment, while type C2 can be treated by surgical treatment with hip preservation. Type C1 was classified into 5 subtypes by CT lateral classification, type 3 has the highest risk of femoral head collapse, types 4 and 5 have low risk of femoral head collapse and operation, type 1 has high femoral head collapse rate but low risk of operation; type 2 has high collapse rate, but the operation rate is close to the average of JIC type C1, which still needs to be further studied.
Objective To investigate the biomechanical characteristics of the CT-based lateral classification of Japanese Investigation Committee (JIC) type C1 osteonecrosis of the femoral head (ONFH) under different necrotic extents using finite element analysis, and to evaluate the validity of the CT-based lateral classification for assessing the risk of femoral head collapse. MethodsA finite element model of the hip joint was established based on CT data from a healthy 35-year-old male volunteer. According to the JIC C1 classification criteria, three necrotic extents were defined in the coronal plane: M1 (30%), M2 (50%), and M3 (70%). According to the sagittal location of the necrotic lesion, the femoral head was equally divided into anterior, middle, and posterior regions, and five types of the CT-based lateral classification were defined: type 1, involvement of the anterior region only; type 2, involvement of the anterior and middle regions; type 3, involvement of the anterior, middle, and posterior regions; type 4, involvement of the middle and posterior regions; and type 5, involvement of the posterior region only. A total of 15 finite element models were constructed by combining the three necrotic extents with the five CT-based lateral classification types. Bilateral standing loading was simulated, and the maximum von Mises stress and maximum displacement of the femoral head surface and necrotic region were recorded. Results Stress concentration was mainly located in the superolateral region of the femoral head directly above the necrotic lesion, consistent with previous studies. Within the same CT-based lateral classification type, increases in necrotic extent from M1 to M3 were associated with significant increases in the maximum von Mises stress and maximum displacement of the femoral head surface, as well as the maximum displacement of the necrotic region. No significant difference was found in the maximum von Mises stress in the necrotic region among M1, M2, and M3 groups (P>0.05). Except for the differences in the maximum von Mises stress on the femoral head surface between groups M2 and M3, and the differences in the maximum displacement in the necrosis region between groups M1 and M2 (P>0.05), there were significant differences in the maximum von Mises stress on the femoral head surface, the maximum displacement on the femoral head surface, and the maximum displacement in the necrosis region between other groups (P<0.05). At the same necrotic extent, the maximum von Mises stress and maximum displacement on the femoral head surface and in the necrosis region were significantly higher in type 3 than in other types; followed by type 2>type 1>type 4>type 5. Among them, there was no significant difference in the maximum von Mises stress on the femoral head surface between types 1 and 4, types 2 and 3, and the maximum displacement on the femoral head surface between types 1 and 2, types 2 and 3, types 4 and 5, as well as the maximum von Mises stress in the necrosis region between types 4 and 5, and the maximum displacement in the necrosis region between types 1 and 2, types 4 and 5, types 2 and 3, and types 4 and 5 (P>0.05); all other comparisons between different types showed significant differences (P<0.05). ConclusionBoth the location and extent of osteonecrosis affect the biomechanical stability of the femoral head, with lesion location, particularly involvement of the anterior weight-bearing region, exerting a greater influence on stress distribution. The CT-based lateral classification can effectively distinguish biomechanical differences associated with different necrotic locations and may provide a useful reference for evaluating the risk of femoral head collapse and guiding individualized treatment in patients with JIC type C1 ONFH.