Avascular necrosis is the death of bone areas due to a lack of blood supply The lack of blood supply leads to death of the cells in these areas and thus failure of the bone to repair any tiny crack that occurs in it. This eventually leads to bone collapse and deformity of the femoral head.
The blood supply to a part of bone can be interrupted if the bone is broken or the hip joint becomes dislocated. Avascular necrosis of bone can be due to long-term use of steroid medications and excessive alcohol intake. Some diseases also cause avascular necrosis e.g. sickle cell anemia. It usually affects men between the ages of 30 and 60.
In the early phases of the disease the patient may not have any symptoms, but as the disease progress there is usually pain in the hip joint with limitation of the range of movement. Pain is usually exacerbated by walking and relieved by rest.
On examination, passive internal and external rotation of the extended leg ("log roll test") may elicit pain that is consistent with an active capsular synovitis.
In early cases, plain x-ray of the hip may appear normal, but later it will show collapse of the head and its deformity with loss of its sphericity.
MRI is the study of choice in patients who demonstrate signs and symptoms that are suggestive of AVN but whose radiographs are normal. MRI may detect disease as early as 5 days subsequent to an ischemic insult. MRI may show early osteonecrosis that did not even cause symptoms (for example, whether osteonecrosis is developing in the opposite hip joint).
In early cases, before there is any deformity of the femoral head, the surgeon may do a surgery called “core decompression”. This procedure involves drilling one hole into the femoral head to relieve pressure in the bone and create a channel for new blood vessels to nourish the affected areas of the bone. Core decompression is often supplemented with bone grafting to enhance mechanical support and augment healing.
Core decompression achieves the best results when osteonecrosis is diagnosed in its early stages, before the bone collapses. In many of these patients, the bone heals within few months and regains its blood supply after core decompression. During this time, a walker or crutches will be needed to prevent putting stress on the damaged bone.
If the head was already deformed, the patient is treated by pain killers, limiting the physical activities and using crutches to keep weight off your joint.
In advanced cases not responding to other forms of treatment, total hip replacement is the most commonly performed and successful surgery done as it relieves pain and restores function in 90% to 95% of patients.