Osteonecrosis

Trauma

Femoral neck fracture

Hip dislocation

Atraumatic

Alcoholism

Corticosteroids

SLE

Caisson disease

Coagulopathies

Sickle cell disease

Cushing disease

Gaucher disease

Pancreatitis

Chronic renal failure

Pregnancy

Smoking

Oral contraceptives

Hemoglobinopathies

Clinical Presentation

Atraumatic cases may be asymptomatic and may only be diagnosed when incidentally imaged, e.g., AVN femoral head/s identified during MRI examination for assessment of a pelvic renal transplant. Patients may complain of nonspecific groin pain, worse on weight bearing with progression over time. Larger infarcts may present with more severe pain. Clinical examination demonstrates a decreased range of motion. There is progressive disability with femoral head collapse and secondary degeneration.

Staging

There are multiple staging systems available. The most commonly used are detailed in Tables 12.2 and 12.3.

Table 12.2

Classification of AVN of the femoral head

Stage	Radiograph	Diagnosis	Clinical
Stage 0 preclinical	Normal	Biopsy positive	Osteonecrosis suspected when definite disease in contralateral hip
Stage 1 preradiographic	Normal or subtle loss of clarity trabecular pattern, patchy osteopenia	Biopsy, bone scan, MRI^a positive	50 % sudden pain in groin, limited range of motion
Stage 2a precollapse	Changes in trabecular pattern, sclerosis may be localized or diffuse, cysts may develop, mixed pattern	Radiograph, bone scan, MRI^a positive	Clinical signs persist or worsen over several months
Stage 2b transition	Flattening, crescent sign (subchondral fracture)	Radiograph, bone scan, MRI^a positive
Stage 3 collapse	Sequestrum, break articular margin on both sides of the affected bone followed by collapse, normal joint space	Radiograph, bone scan, MRI^a positive	Progressive increase and more constant pain, functional incapacity
Stage 4 osteoarthritis	Osteoarthritis superimposed on a deformed femoral head	Radiograph, bone scan, MRI^a positive	Progressive decrease in range motion

From Ischemia and Necroses of Bone, by R. Paul Ficat, Jacques Arlet; edited and adapted by David S. Hungerford, Williams & Wilkins, 1980

^aMRI was not included in original staging

Table 12.3

ARCO classification system 1992

Stage	Imaging	Subdivisions
Stage 0	Positive biopsy, negative imaging
Stage 1	Positive MRI +/− bone scan, negative radiograph, CT	Lesion location: medial, central, or lateral
Stage 2	Radiograph positive: sclerotic/cystic/osteopenia	% femoral involvement
Stage 3	Radiograph: crescent sign (subchondral fracture)	Head a <15 % b 15–30 c >30 %
Stage 4	Radiograph: flattening of the femoral head	Head a <15 % b 15–30 c >30 %
Stage 5	Radiograph positive: flattening of the femoral head and osteoarthritis	Depression femoral head when fracture present (stages 4 and 5) a <2 mm b 2–4 mm c >4 mm
Stage 6	Complete joint destruction

Reprinted with permission from ARCO (Association Research Circulation Osseous): Committee on terminology and classification. ARCO News. 1992;4:41–46

Imaging

Radiographs (Fig. 12.1)

Fig. 12.1

(a) Modified AP radiograph of the left hemi-pelvis, surgical clips related to renal transplant, left hip pain, generalized osteopenia, no radiographic changes AVN, stage 1 AVN. (b) AVN of bilateral hips on AP radiograph, stage 4. The right hip demonstrates partial collapse of the femoral head and secondary degenerative changes, stage 2a; the left femoral head demonstrates localized sclerosis in a patient on long-term steroids. (c) AP radiograph of the right hip with stage 3 AVN, with collapse of the femoral head with maintenance of joint space. See Table 12.2 for detailed description of the staging of AVN

Radiographs may be normal or demonstrate only subtle changes. Radiographs have a low sensitivity in early disease. In patients with suspected AVN, MRI is advised.

Early changes include patchy osteopenia and loss of clarity of the trabecular pattern. This progresses to areas of ill-defined sclerosis. The subchondral region should be closely evaluated for development of a lucent line, the “crescent sign,” a subchondral fracture that heralds impending collapse. The convex outline of the femoral head should be maintained; any loss of convexity or flattening indicates early collapse. Collapse progresses with deformity of the femoral head and development of secondary degenerative changes such as joint space loss, osteophytes, subchondral sclerosis, and cyst formation. These latter changes may be more evident on the acetabular aspect of the joint as the femoral head collapses. Radiographic findings are detailed in Table 12.2.

MRI (Figs. 12.2, 12.3, 12.4, and 12.5)

Fig. 12.2

(a, b) Cor T1 and T2FS, respectively, demonstrate bilateral AVN and chronic AVN of the left femoral head (note the double-line sign and acute AVN of the right femoral head with extensive bone marrow edema and small joint effusion). (c, d) Sag and axial T2FS, respectively, in a different patient, with subchondral fracture line (arrow), linear high signal intensity, and early cortical collapse

Fig. 12.3

(a) AP radiograph of the left shoulder demonstrating AVN of the humeral head, stage 2b, in a patient with Crohn’s disease. (b) Corresponding Cor T2FS MRI. (c) 6 years later, AP radiograph, stage 3 AVN. (d) AVN of the right humeral head in a different patient with subchondral fracture (black arrows) and early collapse with flattening cortical margin

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