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 an insufficiency fracture. This condition is often termed a subchondral insufficiency fracture but was previously 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 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
Most people present with acute pain in one knee, which is 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 increasingly difficult to walk even shorter distances. Rest usually relieves the pain, but it returns once walking resumes. Also, night pain is common.
When your doctor examines your knee, there is often tenderness on the inside of the knee or at the medial femoral condyle. In the worst 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 perform blood tests to exclude low calcium or vitamin D levels.
Insufficiency fracture vs. spontaneous osteonecrosis of the 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 stress 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 of the 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 or without 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 oedema 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 one is better. A recent review questioned the role of bisphosphonates in this condition. Also, bisphosphonates have side effects such as stomach ulcers, jaw necrosis and atypical femoral shaft fractures and have not been recommended by the FDA for this condition.
Insufficiency fracture of knee and surgery
We only recommend surgery when symptoms fail to improve or when a late diagnosis leads to bone collapse. 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 arthroscopic keyhole surgery for a meniscal tear can precipitate an insufficiency fracture. Perhaps this is why you should avoid surgery for most degenerative meniscal tears.
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 four to six weeks. You can maintain fitness by swimming and keeping your upper body weight under control. After six weeks, non-weight-bearing quadriceps, hamstring, and pelvic strengthening can begin. As symptoms settle, adding modified Yoga and Pilates should be fine. Running can ususally be recommenced in 2-3 months, depending on the response to rest. A repeat MRI
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. 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
Dear Lorenzo
I am 44 , have 2 kids , house with stairs , work and keep sane through keeping active!
Eventually had an MRI 3 months ago for knee pain which showed lateral subchondral sclerosis with bone marrow oedema . No mention of fracture. No underlying meniscal issues.
Pain started 11 months ago, ( 8 months pre scan) no clear injury, not improving despite physio/ orthotics. Reduced my normal activity, cut out running . Few days ago severe pain in the superior lateral area of my knee ( relating to location on mri)
Just when extending leg in bed.
Not yet been given a diagnosis. Concerned this could represent an insufficiency fracture.
I do have osteopenia but recent dexa suggest this is improving.
No pain now on walking but concerned about what safe to do . Please grateful for advise
Hi katy,
it can be difficult to diagnose an insufficiency fracture on MRI. Sometimes, cartilage injuries can produce lots of bone swelling and can mimic an insufficiency fracture. I’d suggest you speak to your doctor. You may want to repeat the MRI scan. LM
I have a SIF to my right knee, I have been advised to use crutches for 2-3 months, would a knee brace be any help to me, I’m female and 73
knee brace would help reduce load on the load but crutches are critical.
Thank you for the blog. I was diagnosed with SIF yesterday. I am unable to use crutches due to long term rotator cuff ROM. Will the brace be sufficient?
Yes a brace will help but you’ll need to offload your knee as much as you can ie rest your knee from weight-bearing activity.
What are your thoughts on bone graft to repair subchondral insufficiency fracture left knee
I have been told I have a 4mmx5mm subchondral fracture, I’m only 46, female, hoping it’s from overuse, I took up bouldering and was going to the gym often and jumping down from climbs. But reading about this condition has me pretty freaked out. I have meniscus tears too, but nothing sticking out. It sounds like I should be off my leg as much as possible, but they gave me an unloader brace only. Should I be on crutches? I have stairs all over my house and three kids, so I’m always on the move, but I’m worried I’m making myself worse. They also said I should start physical therapy, I’m starting on may 7, he didn’t think was too soon, what do you think?
4mm x 5mm is a tiny – I suspect you have a small articular cartilage injury with underlying bone marrow oedema rather than a true insufficiency fracture. I’d clarify with your doctor as these conditions are treated differently.
My fx is 19mm and a big meniscus tear this is awful. They say it could take up to 7 months to heal and not to be weight bearing .
I have a root tear meniscus and some arthritis in knee but was running ultra marathons prior the the injury which in hindsight was acute as i felt a pop at the back of my knee in late august. The orthopedic dr I saw told me i was headed for knee replacement suggested and administered one cortisone and three ha injections as only treatment. Now three months later I had some pain reoccur and new ortho told me that likely my root tear should be repaired but ordered new mri which showed new insufficiency fractures in medial femur condyle and tinia plateau. She ordered a medial offloader brace which i need to make an appt to get next week to wear for six weeks then reevaluate. I am nervous that i might worsen things just waiting for the brace. In reading your blog i am wondering why she wouldnt suggest non weight bearing for best healing and whether it would help anything at this point. To say I am frustrated by the first dr treatment approach and resulting fractures is an understatement and now trying hard to understand how best to proceed and avoid knee replacement for as long as I can.
Thanks for your message and for explaining everything so clearly – I can completely understand why you’re feeling frustrated after all of this.
Treatment for a meniscal root tear with associated insufficiency fractures does not always have to be fully non-weight bearing. It really depends on:
how much pain you’re in day to day whether you’re limping or having to compensate heavily when you walk. In many cases, the aim is to reduce load rather than eliminate it completely – for example, shorter walks, flatter surfaces, avoiding impact and deep bending, and sometimes using a brace or walking aid – rather than strict non-weight bearing on crutches for weeks. The medial offloader brace your orthopaedic surgeon has suggested is designed to shift some of the load away from the injured compartment, which can help the bone and joint cope better while things settle.
The question of whether to repair a root tear is quite controversial, especially when there is co-existing osteoarthritis. In more arthritic knees, the potential benefits of root repair are less clear and have to be weighed carefully against the risks, recovery time and your overall goals. That’s why different surgeons sometimes give quite different opinions in this situation.