1, intermediate and advanced hip osteoarthritis When the joint space is narrowed and subchondral cystic changes appear, it may be confused, but its CT shows sclerosis with cystic changes, and Mill changes are mainly low signal, which can be distinguished accordingly. 2, acetabular dysplasia secondary to osteoarthritis Femoral head wrapping incomplete, narrowing of the joint space, disappearance, osteosclerosis, cystic changes, acetabular corresponding area appears similar changes, easy to distinguish. 3, ankylosing spondylitis involving the hip joint Common in adolescent males, mostly bilateral sacroiliac joint involvement, which is characterized by HLA-B27 positive, the femoral head remains round, but the joint space is narrowed, disappeared or even fused, easy to distinguish. Some patients with long-term application of corticosteroids can be combined with ONFH, the head of the femur can appear collapsed but often not heavy. 4, rheumatoid arthritis Most commonly seen in women, the femoral head remains round, but the joint space becomes narrower and disappears; common femoral head joint surface and acetabular bone erosion, easy to distinguish. 5, chondroblastoma within the femoral head MRI T2WI shows lamellar high signal, CT scan shows irregular osteolytic destruction. 6, temporary osteoporosis (ITOH) can be seen in middle-aged and young people, is a temporary painful bone marrow edema; radiographs show reduced bone mass in the femoral head, neck and even rotor: MRI can be seen as T1WI uniform low signal, T2WI high signal, the range can reach the femoral neck and rotor, no banded low signal, can be distinguished from ONFH. The lesion can be dissipated within 3-12 months. 7, subchondral incomplete fracture Most commonly seen in elderly patients over 60 years old, without obvious history of trauma, showing sudden onset of hip pain, inability to walk, and limited joint movement. x-ray shows slightly flattened external upper 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. 8, hyperpigmented villous nodular synovitis Most often occurs in the knee joint, and hip joint involvement is rare. CT and radiographs 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 a uniform distribution of low or moderate signal. 9, synovial herniation pit This is a benign lesion of synovial tissue proliferation invading the cortex of the femoral neck, MRIT, T1WI low signal, T2WI high signal small round lesion, located in the upper cortex of the femoral neck, usually asymptomatic. 10, bone infarction Osteonecrosis occurring in the long bone stem has different imaging manifestations at different times, MRI manifestations are: ① acute stage: the center of the lesion shows equal or slightly high signal with normal bone marrow in T1WI, high signal in T2WI, long T1 and long T2 signal at the edge; ② subacute stage: the center of the lesion shows similar or slightly low signal with normal bone marrow in T1WI, similar or slightly high signal with normal bone marrow in T2WI, long T1 and long T2 signal at the edge. (3) Chronic stage: T1WI and T2WI both showed low signal.