Evolutionary course of the femoral head osteonecrosis: Histopathological - radiologic characteristics and clinical staging systems

Abstract

Osteonecrosis of the femoral head (ONFH) is a recalcitrant ischemic disorder, which could be classified into two major categories: traumatic and nontraumatic. Regardless of different risk factors, it has been testified that ONFH results from primitive vascular problems, leading to temporary or permanent loss of blood supply to bone tissue. Histopathological and microarchitectural alterations ensues, which is a gradual evolutionary process involving bone marrow and osteocyte necrosis, progressive destruction of subchondral bone, unsuccessful reparative process, and eventual articular collapse and degenerative arthritis. Based on the imaging features of ONFH, different classification systems have been developed to evaluate the severity and prognosis of the disease, which is pivotal for implementation of treatment strategy, especially the joint-preserving surgery. However, patients classified with the same severity stage, especially in the peri-collapse stage, sometimes responded differently after similar joint-preserving surgery. The unusual phenomenon may be attributed to the limitation of the current imaging classification systems, which might underestimate the disease severity, especially when referring to the early stages. In this review, we briefly summarize the etiology and pathogenesis of ONFH. The imaging features and staging classification systems of ONFH are also described. More importantly, we focus on histopathological and microstructural alterations of the femoral head, and provide an overview of their essential contribution to ONFH progression. Given the observation of discordance between imaging characteristics and histopathological alterations, a substantial amount of research on the relationship between imaging and histopathological features is required to further modify and revise the current wide-accepted classification systems.

Keywords: Histopathology; Imaging; Microarchitecture; Osteonecrosis of the femoral head; Pathogenesis; Staging.

Figure 1

Histopathological alterations of osteonecrotic femoral heads in Stage II (A) Coronally sectioned gross specimen. The articular surface is not altered considerably as in stage I (b, B1, B2) Necrotic area: There is an accumulation of bone marrow cell debris and bone trabeculae demonstrating empty lacunae, occasionally containing some pycnotic nuclei of osteocytes (c, C1, C2) Lateral transitional zone: Increased vascularity and marrow reaction with inflammatory fibrovascular infiltration is observed, leading to the eventual formation of subchondral cyst (d, D1, D2) Inferior transitional zone: The proliferating capillaries and fibroblasts extend into the necrotic area, and viable new bone tissue is regenerated by osteoblasts, resulting in the sclerotic rim (e, E1, E2) Medial transitional zone: New blood vessels propagate into the peripheral region of the necrotic lesion, and dead bone trabeculae are removed by osteoclasts. Stain: Haematoxylin and Eosin (B1-E1), Goldner's Trichrome (B2-E2), Magnification: ​× ​10.0.

Figure 2

Histopathological alterations of osteonecrotic femoral heads in stage III (A) Coronally sectioned gross specimen. Subchondral collapse is observed just beneath the osteochondral junction, which is verified by the histological section (b, B1, B2) Necrotic area: Subchondral trabecular fracture is located just beneath the subchondral bone plate level (c, C1, C2) Lateral transitional zone: The initial fracture of the subchondral plate, which is mostly located in the region between necrotic and sclerotic bone tissue, is considered as a starting point to further trigger the collapse of the femoral head (d, D1, D2) Inferior transitional zone: The reactive interface undergoes progressive remodeling at the junction with regenerated bone tissue observed, and vascular-rich granulation tissue is detected in the marrow space (e, E1, E2) Medial transitional zone: When the medial boundary of the necrotic lesion is located lateral to the fovea of the femoral head, revascularization and active bone remodeling occurs in the region. Stain: Haematoxylin and Eosin (B1-E1), Goldner's Trichrome (B2-E2), Magnification: ​× ​10.0.

Figure 3

Histopathological alterations of osteonecrotic femoral heads in stage IV (A) Coronally sectioned gross specimen. The shape of the femoral head is severely deformed at this stage (b, B1, B2) Necrotic area: Chondrocytes close to the necrotic lesion preserve the morphology integrity, but when it progresses towards the superficial layer of cartilage, chondrocytes vary in the shape and structure. Weight-bearing zone of the femoral head is replaced by fibrous tissue, secondary collapse ensues (c, C1, C2) Lateral transitional zone: The osteochondral structure is obviously damaged and shows a chaotic, irregular morphology (d, D1, D2) Inferior transitional zone: Histomorphological characteristics of this region in stage IV is similar to that in stage III (e, E1, E2) Medial transitional zone: Despite the reparative process and reactive woven trabeculae in the area, substitution of necrotic bone with viable new bone tissue fail, exhibiting apparently disarranged structure. Stain: Haematoxylin and Eosin (B1-E1), Goldner's Trichrome (B2-E2), Magnification: ​× ​10.0.

Figure 4

ON (ARCO Stage I) of the right femoral head in a 38-year-old male patient (A) Frontal radiograph (B) Frog-leg lateral radiograph (C) Coronal CT image (D) Coronal T1-weighted MR image.

Figure 5

ON (ARCO Stage II) of the right femoral head in a 30-year-old male patient (A) Frontal radiograph (B) Frog-leg lateral radiograph (C) Coronal CT image (D) Coronal T1-weighted MR image.

Figure 6

ON (ARCO Stage III) of the right femoral head in a 24-year-old female patient (A) Frontal radiograph (B) Frog-leg lateral radiograph (C) Coronal CT image (D) Coronal T1-weighted MR image.

Figure 7

ON (ARCO Stage IV) of the right femoral head in a 30-year-old male patient (A) Frontal radiograph (B) Frog-leg lateral radiograph (C) Coronal CT image (D) Coronal T1-weighted MR image.