**2. Clinical stage assessed by radiographic image and prognosis**

The clinical stages of FHN progression are classified based on radiographic examination, with magnetic resonance imaging (MRI) and bone scintigraphy used in the early stages. Although different radiographic classifications of clinical stage have been proposed, the underlying concept and indices of change are comparable between each classification [7–9]. The stage and classification, evaluated from plane, anterior–posterior, radiography images, are useful to understand the prognosis of FHN and to plan for treatment (**Table 1**). The classification of the Association Research Circulation Osseous (ARCO) Committee is the most widely used clinical grading classification for osteonecrosis of the femoral head (ONHF). The stages of FHN are defined as follows. Stage 1 is the identification of an osteonecrosis lesion by MRI and bone scintigraphy, with a marginal reaction emerging as a band of low signal intensity on T1 weighted images and a band of high signal intensity on T2-weighted images. Stage 2 is defined by radiographic appearance of demarcated regions of sclerosis and lucency. Blood vessels enter the necrotic zone as part of a repair process of bone resorption and formation, while toward the margin of the reactive interface, dead cancellous bone is invested by fibrous and lamellar tissues. In stage 3, resorption of bone causes fractures within the subchondral bone, with resulting segmental fractures identified on the radiographs by the 'crescent sign.' Stage 3 is subdivided into stage 3A, collapse of the femoral head <3 mm, and stage 3B, collapse of the femoral head ≥3 mm. In stage 4, osteoarthritic joint space narrowing, with osteophyte formation, is identified. According to Steinberg's classification, after stage 5, osteoarthritic changes are advanced.

The radiographic classification of the Specific Disease Investigation Committee (SDIC), under the auspices of the Japanese Ministry of Health, Labour and Welfare, defines the progression of FHN based on the extent of involvement of the weight-bearing surface of the femoral head (**Figure 1**) [9]. Plane, anterior–posterior radiographs are used to evaluate the necrotic area, and the three types of lesions are defined as follows. The type A lesion occupies the medial onethird or less of the weight-bearing surface of the femoral head, while the type B lesion occupies the medial two-thirds or less of the weight-bearing surface. The type C lesion occupies more than two-thirds of the weight-bearing surface and is subdivided into C1 and C2 types: the C2 lesion extends laterally to the edge of the acetabulum, whereas the C1 lesion does not. Mont et al. [5] reported a risk for progression to collapse of 9% for type A lesions, 19% for type B lesions, and 59% for type C lesions. Nishii et al. [10] calculated an odds ratio (OR) for the incidence of collapse of the femoral head with type C lesions of 10.8 (95% confidence interval, 2.4–48.0), and an OR for progressive collapse of 26.0 (95% confidence interval, 1.9–358.5).


Notes: ARCO, Association Research Circulation Osseous; MRI, magnetic resonance imaging.

**Table 1.** Clinical staging of osteonecrosis.

In the natural history of FHN, 59% of cases progress to symptomatic disease and collapse of the femoral head [5]. The prognosis is different depending on the etiology. FHN resulting from sickle cell disease has the highest risk for progressing to collapse (73%), while 47% of cases due to excessive alcohol consumption are at risk of collapse and 46% of cases resulting from renal failure. The risk for collapse associated with corticosteroid use (26%) and for idiopathic FHN (38%) is comparable to the overall prevalence of collapse (38%). Cases of FHN associated with human immunodeficiency virus infection (15%) or systemic lupus erythematosus (7%) have a relatively lower risk for collapse, compared to the overall prevalence [5]. Therefore, under‐

Nonoperative treatment of FHN has been shown to have limited success in preventing disease progression [2]. Consequently, the use of joint preserving procedures has decreased in the United States, from being the treatment of choice in 25% of cases of FHN in 1992 compared to 12% of cases in 2008. Over the same period, total hip replacement for the management of FHN

The clinical stages of FHN progression are classified based on radiographic examination, with magnetic resonance imaging (MRI) and bone scintigraphy used in the early stages. Although different radiographic classifications of clinical stage have been proposed, the underlying concept and indices of change are comparable between each classification [7–9]. The stage and classification, evaluated from plane, anterior–posterior, radiography images, are useful to understand the prognosis of FHN and to plan for treatment (**Table 1**). The classification of the Association Research Circulation Osseous (ARCO) Committee is the most widely used clinical grading classification for osteonecrosis of the femoral head (ONHF). The stages of FHN are defined as follows. Stage 1 is the identification of an osteonecrosis lesion by MRI and bone scintigraphy, with a marginal reaction emerging as a band of low signal intensity on T1 weighted images and a band of high signal intensity on T2-weighted images. Stage 2 is defined by radiographic appearance of demarcated regions of sclerosis and lucency. Blood vessels enter the necrotic zone as part of a repair process of bone resorption and formation, while toward the margin of the reactive interface, dead cancellous bone is invested by fibrous and lamellar tissues. In stage 3, resorption of bone causes fractures within the subchondral bone, with resulting segmental fractures identified on the radiographs by the 'crescent sign.' Stage 3 is subdivided into stage 3A, collapse of the femoral head <3 mm, and stage 3B, collapse of the femoral head ≥3 mm. In stage 4, osteoarthritic joint space narrowing, with osteophyte formation, is identified. According to Steinberg's classification, after stage 5, osteoarthritic

The radiographic classification of the Specific Disease Investigation Committee (SDIC), under the auspices of the Japanese Ministry of Health, Labour and Welfare, defines the progression of FHN based on the extent of involvement of the weight-bearing surface of the femoral head (**Figure 1**) [9]. Plane, anterior–posterior radiographs are used to evaluate the necrotic area, and

standing the etiologic factor of FHN is important for treatment planning.

**2. Clinical stage assessed by radiographic image and prognosis**

has increased from 75% in 1992 to 88% in 2008 [6].

92 Advanced Techniques in Bone Regeneration

changes are advanced.
