This is a question I often hear from young patients facing Total Hip Arthroplasty for osteonecrosis of the femoral head. At an age when they should be working and exercising at their peak, it is only natural to want to save one's own joint by any means possible once the topic of an artificial joint comes up.
To state the conclusion first, there are certainly patients who, by catching the condition early, can avoid or delay joint replacement surgery. But early detection does not mean every patient can avoid surgery. The real value of early diagnosis lies in securing the time to assess the risk of progression and choose the right treatment before the femoral head collapses.
Osteonecrosis of the femoral head is a disease in which impaired blood flow to the femoral head causes bone cells to die. It is often described as "bone rotting," but it is more accurately understood as something closer to "a bone infarction." At first, the shape of the femoral head is preserved, but once the weakened bone beneath the joint surface can no longer bear the load, a subchondral fracture develops, and the femoral head eventually collapses.
The crescent-shaped shadow seen on X-ray, known as the "crescent sign," indicates this subchondral fracture. ARCO (Association Research Circulation Osseous), the international academic body that studies osteonecrosis of the femoral head, treats the presence of a subchondral fracture or collapse as a key criterion for staging the disease. If neither a subchondral fracture nor collapse is present, the case is classified as Stage II; if either occurs, it is classified as Stage III. In other words, the crescent sign is not simply an imaging finding — it is a signal that structural collapse has begun.
In the early stages, X-rays can still appear normal, which is why magnetic resonance imaging (hereafter MRI) results are so important. MRI helps detect necrosis before the femoral head collapses and confirms the size, location, and bone marrow edema of the lesion. In general, a small lesion located more medially carries a lower risk of progression, while a large lesion involving the lateral weight-bearing area carries a higher risk.
But treating real patients over many years teaches you that size and location alone cannot perfectly predict a single person's future. Some patients are diagnosed before collapse yet progress rapidly within a few months and end up needing joint replacement surgery, while others, even after annual X-rays confirming necrosis on the opposite side following surgery on one hip, show almost no change for 10 or 15 years. The risk of progression can be predicted, but a patient's individual "timetable" cannot be known with precision.
This disease also frequently appears in both hips. Surgery on one side is not the end of the story. When patients return for regular follow-up after surgery, I check not only the operated hip but the opposite side as well. Long-term follow-up is especially important when necrosis has already been confirmed on the opposite side.
In carefully selected patients before collapse, core decompression may be considered. Some patients, particularly those with bone marrow edema and severe pain, experience meaningful pain relief. But pain improving and preventing collapse of the femoral head are not the same thing. No current treatment can restore necrotic bone to normal or reliably prevent collapse in every patient.
On the other hand, once the crescent sign appears and the femoral head has collapsed to the point where walking is difficult and daily life is significantly restricted, the outcome of joint-preserving surgery becomes far less certain. At this stage, total hip arthroplasty is the most predictable treatment for relieving pain and restoring function.
Ultimately, early diagnosis is not about rushing patients into surgery. It exists so that patients who can simply be monitored avoid unnecessary surgery, patients who would benefit from conservative treatment do not miss the right window for it, and patients whose joint has already collapsed do not delay joint replacement surgery for too long.
Securing the time to make the most appropriate choice for each patient before the femoral head collapses — that is the greatest meaning of early diagnosis.
<Written by Song Sang-ho, Director of Wellton Hospital | Edited by Jang In-sun, Health Kyunghyang reporter>
FAQ
Q1. Can early detection of osteonecrosis of the femoral head prevent joint replacement surgery?
A1. There are certainly patients who can avoid or delay surgery through early detection, but this is not true for every patient. The real value of early diagnosis is securing the time to assess the risk of progression and choose the right treatment before the femoral head collapses.
Q2. What does the crescent sign indicate?
A2. The crescent-shaped shadow seen on X-ray, called the crescent sign, indicates a subchondral fracture. ARCO, the international academic body, uses the presence of a subchondral fracture or collapse as a key criterion for staging, and the sign indicates that structural collapse has begun.
Q3. If core decompression relieves pain, does that also prevent collapse?
A3. No. Pain relief and preventing collapse of the femoral head are not the same thing. No current treatment can restore necrotic bone to normal or reliably prevent collapse in every patient.
