Avascular necrosis, commonly abbreviated as AVN, is a condition that causes disabling hip pain due to death of the bone underlying the cartilage on the femoral side of the hip joint. In many instances, the cause of this spontaneous death of the bone is unknown, but the condition can be associated with alcoholism and use of high doses of corticosteroids. High doses of corticosteroids are often used to treat severe cases of asthma, reactive airway disease, or inflammatory conditions like rheumatoid arthritis. The relationship between high dose corticosteroid use and AVN is thought to be related to the fact that corticosteroids cause fat cells to enlarge and this swelling of the fat content in the bone marrow space of the femur may interfere with normal blood flow to the bone. Once the bone is starved of blood, it starts to decay, microfractures appear, and the cartilage starts to delaminate, causing severe pain.
For example, these are the pre-operative xrays of a 29 year old male who had several visits to the emergency department in the 12 months prior to his eventual diagnosis of avascular necrosis. While his xrays were initially thought to be negative, closer inspection of the bone, especially on the lateral view of the hip, reveals a large cyst inside the head of the femur which is indicative of avascular necrosis.
An MRI scan was obtained, confirming the diagnosis. On this image of both hips, large cystic areas can be seen in the femoral heads where the bone has collapsed. The cartilage overlying these cystic areas does not have any support and as a result, the patient has severe hip pain. Here is another view of the femoral head, called the axial view, where the radiologist has placed an arrow pointing to one of the cystic areas in the femoral head caused by AVN.
This patient initially presented with primarily left hip pain, and while he had severe changes in both hips, he chose to have the left hip replaced first. However, within 6 months of having the left hip replaced, he developed crippling right hip pain and went on to have the right hip replaced as well. Both hips were replaced using a minimally invasive direct anterior approach to total hip replacement. In both hips the Stryker Accolade stem was used on the femoral side and conventional metal cobalt chrome heads were used with highly crosslinked X3 polyethylene liners, also from Stryker. This is an xray taken in the post-anesthesia care unit or recovery unit, after the second hip replacement, showing bilateral hips.
Time will tell how well these hips perform. This patient is very young, and he chose to have hip replacements over the other alternatives for the surgical management of AVN, which include core decompression and bone grafting. Our hope is that advances in the bearing surfaces for total hip replacements and improved metallurgy on the both the femoral and the acetabular side of the joint will result in implants that last at least 15 to 20 years, but much of the longevity of these two hips will depend upon his activity level and how much impact he puts on these hips.