Generally, most people with knee arthritis or meniscal tears develop pain from a flare of arthritis. However, knee pain in people with arthritis is sometimes secondary to bone breakdown or insufficiency fracture. This condition is often termed a subchondral insufficiency fracture but used to be referred to as osteonecrosis or SONK. So, what is a subchondral insufficiency fracture of the knee, and why is it essential to diagnose this condition early?
What is a subchondral insufficiency fracture of the knee?
Excessive overloading of the bone under abnormal cartilage in the knee leads to softening or breakdown. Fluid then enters the softened bone leading to further breakdown and a subchondral fracture.
Causes
We often see a subchondral insufficiency fracture in people in their 50s and 60s. This disease is more common in females and those with low bone mineral density, knee osteoarthritis, or meniscal tears. Less common risk factors include regular cortisone use.
Symptoms of insufficiency fracture of knee
Generally, most people present with acute pain in one knee. Symptoms are often more severe than usual knee arthritis pain. The pain usually affects the inside of the knee and may be associated with limping. As the disease progresses, people find it more and more difficult to walk even shorter distances. Rest usually makes the pain better, but the pain returns once walking is resumed. Also, night pain is common.
When your doctor examines your knee, often there is tenderness at the inside of the knee or medial femoral condyle. In worse cases, we see swelling and joint movement restriction.
Insufficiency fracture knee MRI
First, we start with a plain X-ray. In early cases, the X-ray may be normal. However, in advanced cases, we see a breakdown of the bone with flattening of the knee condyle.
If the X-ray is normal, MRI can detect early changes of swelling or marrow oedema on the inside of the knee. In more advanced cases, focal areas of bone death can sometimes be seen just under the cartilage. In addition, we might see knee arthritis, meniscal tears, and meniscal extrusions.
Once diagnosed, we often check bone density with a DEXA scan and blood tests to exclude low Calcium or Vit D.
Insufficiency fracture vs. spontaneous osteonecrosis othe f knee (SONK): are they the same?
We used to think that an insufficiency fracture was another word for osteonecrosis, also called SONK. However, we now believe they are different disease processes. One is a fracture, while the other is bone death or necrosis. Nevertheless, an untreated insufficiency fracture can lead to bone death and SONK.
Treatment of insufficiency fracture knee
If this condition is picked up early, pain-relieving medications (paracetamol or codeine) and rest from weight-bearing activity improve symptoms quickly. Generally, we suggest protected weight-bearing with crutches for about six weeks, followed by a further six weeks of weight-bearing rest. In the second phase, we recommend hamstring and quadriceps exercises, initially non-weight bearing on machines (knee extensions, knee curls, side-lying hip abduction), followed by weight-bearing weight training, including Yoga and pilates.
Usually, we repeat the MRI scan in 2-3 months to ensure the bone odema is settling.
Other treatments are a little more controversial. Hyaluronic acid or PRP injections have been tried to reduce pain and improve healing with mixed results. Intravenous and oral bisphosphonates show promising results in small studies, but we don’t know whether these medications are any better than rest. A recent review questioned the role of bisphosphonates in this condition. Also, bisphosphonates have side effects such as stomach ulcers and jaw necrosis and have not been recommended by the FDA for this condition.
Insufficiency fracture of knee and surgery
We only recommend surgery for the failure of symptom improvement or a late diagnosis when the bone collapses. Surgical options include keyhole surgery with core decompression or knee replacement.
Frequently asked questions
I’ve heard that surgery such as arthroscopy can be a triggering factor. Is this true?
Yes, we know some people who have had keyhole surgery for a meniscal excision can precipitate an insufficiency fracture. Perhaps, this is a reason why you should avoid surgery for early cases.
Do you need to modify exercise during the healing of a subchondral insufficiency fracture?
Yes. Generally, we suggest stopping all weight-bearing activity for at least six weeks. You can maintain fitness with swimming and upper body weight. After six weeks, non-weight-bearing quadriceps, hamstring, and pelvic strengthening can begin. As symptoms settle, adding modified Yoga and Pilates should be fine. It would help if you did not push through the discomfort or pain.
Is an insufficiency fracture the same as avascular necrosis or AVN?
No. AVN is caused by a block to the blood supply of one part of the knee, not a fracture. But ultimately, both conditions can lead to bone death.
Final word from Sportdoctorlondon re subchondral insufficiency fracture of the knee
We need to consider this condition in a person over 50 who presents with sudden and increasing pain in the knee – especially with a background of arthritis or meniscal tears. Early treatment with rest and pain-relieving medications will allow healing, although complete resolution may take 3-6 months.
I have been told I have a tiny subchondral insufficiency fracture to my right knee. Been giving me pain for 6 weeks before diagnosed by MRI. Not sure what to do.
Hi Mark,
As I outlined in the blog, you will need to offload the knee joint. Rest from sport and reduce walking distance. In some cases, you might need crutches. Other treatments are outlined in the blog.
Lorenzo