All you may need to know about ONFH

1. What is ONFH?

2. What are the risk factors of ONFH?

3. What are the clinical manifestations of ONFH?

4. How is ONFH diagnosed?

5. How is ONFH treated?

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1.    What is ONFH?

Osteonecrosis of femoral head (ONFH) is featured by the pain, function limitation and dysfunction of the hip joint, and the structural change and collapse of the femoral head, caused by the repair of partial death of bone cells and bone marrow components, subsequent to the stasis of femoral head vein, and/or the damage or interruption of arterial blood supply.

2.    What are the risk factors of ONFH?

ONFH is frequently related with glucocorticoids (sugar metabolism regulating hormones secreted by the adrenal cortex) use, alcohol consumption and trauma, which can cause a state of ischemic hypoxia and irregular metabolism in femoral head, inducing necrosis and repair of bone tissues, increasing the instability of biomechanical structural instability and eventually necrosis of femoral head.

The correlation of glucocorticoids and alcohol is relatively more complex. They can induce abnormal lipid metabolism and fat accumulation in bones, abnormality of bone marrow cell differentiation and osteogenesis, high blood viscosity and intravascular coagulation, and capillary regeneration dysfunction, resulting in intraosseous pressure increase and intramedullary microcirculation disorder. Meanwhile, trauma, the fracture of femur neck for example, can directly cause vascular rapture and interrupt the blood supply of femur head, and therefore contributing to the ischemic hypoxia state.

Besides, other factors including sex, age, smoking, BMI and drastic air pressure change are also related to ONFH. The incident rate of ONFH is statistically higher in men of middle-age than other groups. Studies have shown that smoking can significantly increase the risk of ONFH, as it can also affect the blood supply of the hip joint by causing vessel contraction and capillary thrombus formation. Groups of high BMI show a higher ONFH incident rate. Occupations involving working under high air pressure, such as divers and miners, are also closely related to ONFH, as the accumulation of nitrogen in bone marrows may finally cause osteonecrosis.

3.    What are the clinical manifestations of ONFH?

At the early stage, ONFH shows no typical symptoms; they can be pain or soreness in the hips, groin or knee, which can be relieved after rest. As the disease progresses, the pain becomes acute and the limb is shortened due to the collapse of the femoral head, resulting walking difficulty, hip joint function limitation and/or limping.

4.    How is ONFH diagnosed?

The diagnosis of ONFH bases mainly on imaging results, including X-ray, CT and MRI. With X-ray, diseases of the cartilage can be distinguished, such as osteoarthritis, ankylosing spondylitis (AS) and rheumatoid arthritis, and etc., though it is difficult to confirm ONFH at the early stage, since the symptoms are too atypical to tell.

CT can sense the micro changes in bone structure and is valuable to early diagnosis of ONFH. MRI is efficient both in early diagnosis and staging of ONFH.

Besides, the hip joint motion range test and the Patrick sign test, as well as laboratory tests can also provide valuable references for ONFH diagnosis.

There are different staging standards of ONFH, though the ARCO system is most widely applied. ONFH is classified into 4 stages mainly basing on image results, and then treated accordingly.

5.    How is ONFH treated?

ONFH can be treated with non-surgical and surgical measures.

For early and middle stage ONFH patients, or patients that are under contradictory conditions for surgery, non-surgical measures can be adopted, which include: anti-coagulators, vessel dilators, and lipid lowering drugs; osteoclast inhibitors and osteoblast promotors, physiotherapy, shock wave, immobilization and traction, and so on.

Surgical measures can be divided into two types: femoral head preserving surgery and hip replacement. The preservation of femoral head is often suggested to patients of early stages and young age, who can hopefully recover the blood supply of femoral head and avoid or delay hip replacement after the surgery. The femoral head preserving surgery can be core decompression, implantation, bone grafting and osteotomy. When the preservation of femoral head becomes impossible, a hip replacement is necessary, which can be the replacement of the femoral head(s) or the whole hip joint.

Meanwhile, general suggestions for ONFH patients can be beneficial, including management of body weight and blood lipid level, restraining from alcohol and tobacco, regular diet and proper exercise. Besides, for patients of one-side ONFH not of trauma cause, the other side of the hip joint shall be regularly examined to avoid delayed discovery of possible ONFH.