Three-dimensional distribution of subchondral fracture lines in osteonecrosis of the femoral head

Abstract

Objective: To investigate the characteristics of three-dimensional distribution of subchondral fracture lines on the surface of the osteonecrosis femoral head, and to discuss the underlying mechanisms that contribute to its collapse.

Methods: We retrospectively analyzed computed tomography (CT) images from 75 patients (comprising a total of 77 femoral heads) diagnosed with Association Research Circulation Osseous (ARCO) stage IIIA or IIIB femoral head necrosis. The three-dimensional structures of both the femoral head and the subchondral fracture line were reconstructed and subsequently fitted into normal femoral head model. A heat map of fracture line was generated to visualize its spatial distribution across the femoral heads surface.to observe its distribution. In addition to that, the femoral head was partitioned into four zones, and the frequency of each fracture line traversing different zones was calculated and analysed.

Results: Highest and lowest density of subchondral fracture lines was demonstrated in anterolateral and posterolateral zone respectively. and most sparse in posterolateral. Furthermore, the three-dimensional heat map of fracture lines highlighted their most frequent occurrence in the anterolateral area, particularly near the junction of the femoral head and neck. One fracture line may pass through multiple areas, passage frequencies for fracture lines was observed in zones I, II, III and IV for 66 times (85.7 %), 52 times (67.5 %), 25 times (32.5 %) and 46 times (59.7 %), respectively, with a significant difference between zone I and other zones (P < 0.001).

Conclusion: Subchondral fracture line of femoral head occurs most frequently in anterolateral femoral head, suggesting that the anterolateral part may be the initial location of collapse.

Translational potential of this article: We found that the subchondral fracture line was most frequently located anterolateral to the femoral head, suggesting that this may be the site of initiation of collapse. Furthermore, we propose an innovative method for analyzing and visualizing subchondral fracture distribution in femoral head necrosis in the form of fracture line heat maps. By doing so, we provide a valuable reference for physicians, enabling them to enhance their management strategies for femoral head necrosis. Ultimately, this approach holds the promise of significantly improving the prognosis and outcomes for patients afflicted with this condition.

Keywords: Collapse; Computed tomography; Osteonecrosis of the femoral head; Three-dimensional distribution.

Graphical abstract

Figure 1

Reconstruction of template femoral head and subchondral fracture line. Areas of interest in CT images were colored in red (A1-A3). The contours of a healthy femoral head was derived through a combination of semi-automatic software tools and manual refinement (A4). Subchondral fracture lines were traced layer by layer from axial, coronal and sagittal positions(B1–B3), the red dots in B1–B3 are markers depicting the subchondral fracture line. (B4) Fracture line projection after reconstruction.

Figure 2

Fracture line projection. A. Superimpose the reconstructed 3D model of collapsed femoral head onto the template femoral head; B. Through adjustment of position, size and other parameters, merging the 2 femoral head models and project the fracture line onto the template; C. The fracture line was reconstructed on the template femoral head.

Figure 3

Femoral head partitioning method. Figure A: The green dot corresponds to the center of the femoral head. Figure B: The blue dot represents the midpoint of the femoral calcar. Figure C: Another blue dot signifies the midpoint of the concavity within the femoral head. In figure D, two perpendicular planes were constructed by intersecting through these three points. Femoral head surface was divided into 4 zones: Zone III (Figure E): Represents the posteromedial region. Zone IV (Figure E): Corresponds to the posterolateral region. Additionally, in Figure F: Zone I: Encompasses the anterolateral region. Zone II: Refers to the anteromedial region. The green curve is the projection of one fracture line, passing through Zone I and II simultaneously.

Figure 4

Patient Enrollment Flowchart. Final group includes 75 patients with 77 femoral heads. ARCO =Association Research Circulation Osseous; ONFH=Osteonecrosis of the Femoral Head; CT=Computed tomography.

Figure 5

Subchondral fracture lines distribution of femoral head. A. anterior view; B. view from above; C. medial view; d. Posterior view.

Figure 6

Heat Map of the distribution of subchondral fracture line of femoral head. A. anterior view; B. view from above; C. medial view; D. Posterior view.

Figure 7

map of subchondral fracture line distribution involving two or fewer areas. A. anterior view; B. view from above; C. medial view; D. Posterior view.

Figure 8

The subchondral fracture lines of the femoral head after reconstruction in two cases. A. An early-stage fracture line in femoral head collapse (marked by the green line). B. A late-stage fracture line in femoral head collapse (marked by the green line). In figures A and B, I, II, III, and IV represent four different regions on the surface of the femoral head.