Subchondral insufficiency fractures of the femoral head

Abstract

A subchondral insufficiency fracture (SIF) of the femoral head is a recently proposed concept, which needs to be differentiated from osteonecrosis. Clinically, SIF has generally been observed in the osteoporotic elderly women or renal transplant recipients. Radiographical changes are not obvious in its early phase, however, some cases undergo subchondral collapse (crescent sign). On the T1-weighted magnetic resonance images, a low intensity band is one of the characteristic imaging appearances, which corresponds histologically to the fracture line and associated fracture repair tissue. Therefore, the shape of the low intensity band generally tends to be irregular, disconnected, and convex to the articular surface. The prognosis of SIF is not clearly established. Some cases show resolution of the symptoms by the conservative treatments, while other cases show rapid progression of the collapse such as rapidly progressive arthrosis of the hip.

Keywords: Femoral head; Osteonecrosis; Osteoporosis; Subchondral insufficiency fracture.

Fig. 1

A 68-year-old woman with a subchondral insufficiency fracture of the right femoral head. (A) Radiograph obtained 8 weeks after onset shows subchondral collapse in the lateral portion of the femoral head. Joint space narrowing is also seen. (B) On the lateral view, a crescent sign is clearly seen (arrow). Final histopathological diagnosis in this case is subchondral insufficiency fracture.

Fig. 2

A 68-year-old woman with a subchondral insufficiency fracture of the right femoral head. (A) Radiograph obtained 4 weeks after onset shows no apparent abnormalities in the femoral head. (B, C) On magnetic resonance imaging obtained 4 weeks after onset, a diffuse bone marrow edema pattern is seen, with low signal intensity on T1-weighted imaging (B) and high signal intensity on T2-weighted imaging (C). A very low signal intensity band parallel to the articular surface is also seen (arrow). (D) On the cut section of the resected femoral head, a whitish line is seen just beneath the articular surface (arrow). (E) The specimen radiograph reveals an osteosclerotic line (arrow), which consists of callus formation along the fracture line (arrow). (F) Histology of the linear sclerotic area shows a fractured original bone trabecula with associated fracture callus formation and granulation tissue in the bone marrow space. No evidence of predisposing osteonecrosis is seen (H&E, ×100). Reprinted from Yamamoto et al.

Fig. 3

A 59-year-old woman with a subchondral insufficiency fracture of the right femoral head, which resulted in rapid destruction of the hip joint. (A) No apparent abnormality is seen on the radiograph obtained immediately after the onset of pain. However, a slight collapse was seen on the lateral side of the femoral head 1 week after onset (arrow). The collapse progressed until 4 weeks later, when joint space narrowing, particularly on the medial side, is seen and rapid destruction of the femoral head is observed. (B) Magnetic resonance imaging 2.5 weeks after onset shows a bone marrow edema pattern with two irregularly shaped low intensity bands with a convex shape on T1-weighted imaging. (C) On a cut section of the resected femoral head, a subchondral fracture line is observed with a whitish gray zone consisting of fracture callus and surrounding granulation tissue. The articular cartilage is thin especially in the weight-bearing portion, but its thickness is relatively preserved in the other regions, suggesting no evidence of chondrolysis. Reprinted from Yamamoto et al. with permission from American Roentgen Ray Society.

Fig. 4

Comparison of band images in subchondral insufficiency fracture (A) and osteonecrosis (B). Since the band in SIF corresponds to the fracture line, the shape is usually irregular, disconnected, convex and parallel to the cartilage surface. In contrast, the band in osteonecrosis corresponds to repair tissue formed around the necrotic area, which tends to show a smooth, well delineated and concave shape.

Fig. 5

A 23-year-old woman with a subchondral insufficiency fracture of the left femoral head. (A) Radiograph obtained 2 months after onset shows slight collapse in the lateral portion of the femoral head (arrow) where an irregular joint surface and partial sclerosis are also observed. (B) Bone scintigraphy shows diffuse increased uptake in the femoral head. (C) A low signal intensity area and a band-like pattern are seen on a T1 weighted image. (D) On gadolinium enhanced magnetic resonance imaging, the lesion totally shows diffuse high uptake, indicating that this area is alive. A bone biopsy was performed and the final histopathological diagnosis was subchondral insufficiency fracture in young age. (E) Since fractured lesion is located in the anterosuperior portion, anterior rotational osteotomy was performed to prevent further progression of collapse. Nine years after operation, no evidence of progression of collapse or osteoarthritic change is seen. The patient has no symptom. Partly reprinted from Yamamoto et al.

Fig. 6

A 69-year-old man with a subchondral insufficiency fracture of the medial femoral condyle. (A) Radiograph obtained 2 months after onset shows slight collapse of the medial femoral condyle (arrow). A low signal intensity area is seen on T1-weighted image (B) corresponding to high signal intensity on T2-weighted image (C). A bone biopsy was performed and the final histopathological diagnosis was subchondral insufficiency fracture of the medial femoral condyle.