Diagnostic criteria
I. Main criteria
1. Clinical symptoms, signs and medical history: inguinal and hip. Arthralgia mainly in the thigh area, limited internal rotation of the hip joint, history of hip trauma. History of corticosteroid application. History of alcohol abuse.
2.X-ray changes: femoral head collapse without joint space narrowing; sclerotic zone in the femoral head; subchondral bone with translucent X-ray zone (crescent sign, subchondral fracture).
3. Nuclear scan shows a cold zone within a hot zone in the femoral head.
4. The T1-weighted phase of MRI of the femoral head shows a banded low signal (banding type) or the T2-weighted phase has a bilinear sign.
5. Bone biopsy shows more than 50% osteocyte vacuolation foci in the trabeculae, and involves multiple adjacent trabeculae with bone marrow necrosis.
Secondary criteria
1. X-ray shows collapse of the femoral head with narrowing of the joint space, cystic degeneration or speckled sclerosis in the femoral head, and flattening of the upper part of the femoral head.
2.Nucleotide bone scan shows cold or hot areas.
3. MRI shows a band type with homogeneous or heterogeneous low signal intensity without T1 phase.
The diagnosis can be confirmed if two or more major criteria are met. If one major criterion is met, or the number of positive secondary criteria is ≥4 (including at least one positive radiographic change), the diagnosis is likely to be made.
Key points of each diagnostic method
Femoral head necrosis can be diagnosed by history taking, clinical examination, X-ray, magnetic resonance imaging (MRI), nuclear scan, computerized tomography (CT) and other methods.
I. Clinical diagnosis
The medical history should be carefully inquired, including the history of hip trauma, application of corticosteroids, alcohol consumption or anemia, etc. The clinical symptoms should clarify the pain location, nature and relationship with weight-bearing. Physical examination should include the rotational activity of the hip joint.
Early clinical symptoms of femoral head necrosis are not typical, and internal rotation of the hip joint leading to pain is the most common symptom. After the femoral head collapses, the range of motion of the hip joint may be limited.
Signs : Local deep pressure pain, pressure pain at the stop point of the adductor muscle, and axial percussion pain may be positive in some patients. In the early stage, the hip joint pain, Thomas sign and 4-character test are positive; in the late stage, the femoral head collapse, hip dislocation, Allis sign and single leg independence test are positive.
Other signs include limited abduction, external rotation or internal rotation, shortening of the affected limb, muscle atrophy, and even signs of subluxation. In the presence of hip dislocation, there may be upward shift of the Nelaton line, the bottom edge of the Bryant triangle is less than 5 cm, and the Shenton line is discontinuous.
Radiographs
X-rays are difficult to diagnose early-stage (stage 0 and I) femoral head necrosis, but can show positive changes in stage II and above, such as sclerotic bands, cystic changes on X-ray, speckled sclerosis, subchondral fractures and femoral head collapse. It is recommended to take X-rays in both posterior anterior (orthogonal) and frog lateral views, the latter of which can show the changes in the necrotic area of the femoral head more clearly.
MRI
The T1-weighted phase of typical femoral head necrosis is characterized by the residual epiphysis of the femoral head, sinuous bands of low signal adjacent to or crossing the epiphysis, and low signal bands encircling high signal areas or mixed signal areas.
The recommended sequence is T1- and T2-weighted, with the addition of T2 lipid suppression or short T1 inversion recovery (STIR) sequences for suspicious lesions. Coronal and cross-sectional scans are generally used, and additional sagittal scans may be added for more accurate estimation of necrosis volume and for clearer visualization of the lesion. Roll-enhanced MRI is particularly effective for early detection of femoral head necrosis.
Nuclear scan
The sensitivity of nuclear scan is high but the specificity is low for the diagnosis of early femoral head necrosis. The diagnosis can be confirmed by using 99 Tc diphosphate scan if there is a cold area in the hot area. However, the concentration of nuclide alone (hot zone) should be differentiated from other hip diseases. This test can be used to screen for lesions and to look for multisite necrotic foci. Single photon emission tomography (SPECT) may increase sensitivity, but specificity is still not high.
V. CT
For stage II and III lesions, CT can clearly show the border, area, sclerotic zone, self-repair and subchondral bone of the necrotic lesion, etc. CT shows subchondral fracture with better clarity and positive rate than MRI and X-ray, and with the addition of two-dimensional reconstruction, it can show the overall situation of the femoral head in the coronal position.
Differential diagnosis
Differentiation of lesions with similar radiographic or MRI changes should be noted.
I. Differential diagnosis of diseases with similar X-ray changes
1. Intermediate and advanced osteoarthritis: when the joint space is narrowed and subchondral cystic changes appear, it may be confused, but the CT shows sclerosis with cystic changes, and MRI changes are mainly low signal, which can be differentiated accordingly.
2, acetabular dysplasia secondary to osteoarthritis: the femoral head is incompletely wrapped, the acetabular line is in the upper part of the femoral head, the joint space is narrowed and disappeared, osteosclerosis, cystic changes, and similar changes appear in the corresponding area of the acetabulum, which can be easily distinguished from ONFH.
3, ankylosing spondylitis involving the hip joint: common in adolescent males, mostly bilateral sacroiliac joint involvement, characterized by HLA-B27 positive, the femoral head remains round, but the joint space is narrowed, disappeared or even fused, so it is not difficult to distinguish. Some patients with long-term application of corticosteroids can be combined with ONFH, the femoral head can appear collapse but often not serious.
4, rheumatoid arthritis: mostly seen in women, the head of the femur remains round, but the joint space is narrowed and disappeared. The joint surface of the femoral head and acetabular bone erosion are common, so it is not difficult to differentiate.
Differential diagnosis of diseases with similar MRI changes
1. temporary osteoporosis (ITOH): It is seen in middle-aged male and female patients with temporary painful bone marrow edema. x-ray shows reduced bone mass in the femoral head, neck and even rotor, and MRI shows uniform low signal in T1-weighted phase and high signal in T2-weighted phase, ranging to the femoral neck and rotor, without banded low signal, which can be differentiated from ONFH. This disease can heal within 3-6 months.
2, subchondral insufficiency fracture: Mostly seen in elderly patients over 60 years old, without obvious history of trauma, showing sudden onset of hip pain, inability to walk and limitation of joint movement. x-ray shows slightly flattening of the upper outer part of the femoral head, T1 and T2 weighted phase of MRI shows subchondral low signal line, surrounding bone marrow edema, T2 lipid suppression phase shows lamellar high signal.
3, pigmented villous nodular synovitis: mostly in the knee joint, hip joint involvement is rare. CT and X-ray may show cortical bone erosion of the femoral head, neck or acetabulum and mild to moderate narrowing of the joint space; MRI shows extensive synovial hypertrophy with uniform distribution of low or moderate signal.
4, femoral head contusion: mostly seen in middle-aged patients with a history of hip trauma, manifesting as hip pain and claudication. mri shows moderate signal in the T1-weighted phase and high signal in the T2-weighted phase within the femoral head, more medially.
5. Synovial herniation pit: This is a benign lesion of synovial tissue proliferation invading the cortex of the femoral neck, MRI shows small round lesions with low signal in T1-weighted phase and high signal in T2-weighted phase, mostly eroding the upper cortex of the femoral neck, usually asymptomatic.