Most people with knee arthritis or meniscal tears get pain during an arthritis flare. But knee pain in people with arthritis is sometimes due to bone breakdown — an insufficiency fracture. This condition is now usually termed a subchondral insufficiency fracture, though it was previously called osteonecrosis, or SONK. So what is a subchondral insufficiency fracture of the knee, and why is an early diagnosis so important?
What is a subchondral insufficiency fracture of the knee?
Excessive overloading of the bone beneath abnormal cartilage in the knee causes the bone to soften or break down. Fluid then enters the softened bone, leading to further breakdown and a subchondral fracture — a fracture in the bone just under the cartilage surface.
What causes it?
We most often see a subchondral insufficiency fracture in people in their 50s and 60s. It’s more common in women and in those with low bone mineral density, knee osteoarthritis, or meniscal tears. Less common risk factors include regular cortisone use. Importantly, arthroscopic knee surgery (for example, for a degenerative meniscal tear) can sometimes trigger the very issue we avoid surgery for most degenerative meniscal tears.
Symptoms of an insufficiency fracture of the knee
Most people present with acute pain in one knee, often more severe than usual arthritis pain. The pain usually affects the inside of the knee and may be accompanied by a limp. As it progresses, even short walks become harder. Rest tends to relieve the pain, but it returns once walking resumes, and night pain is common.
On examination, there is often tenderness on the inside of the knee or over the medial femoral condyle. In the worst cases, there’s swelling and restricted joint movement.
Insufficiency fracture of the knee on MRI
We usually start with a plain X-ray. In early cases, the X-ray is often normal; in advanced cases, it shows bone breakdown with flattening of the knee condyle.
If the X-ray is normal, an MRI can detect early swelling of bone marrow oedema within the knee. In more advanced cases, focal areas of bone death are sometimes seen just under the cartilage, along with any knee arthritis, meniscal tears, and meniscal extrusion.
Once diagnosed, we often check bone density with a DEXA scan and run blood tests to rule out low calcium or vitamin D levels.
Insufficiency fracture vs spontaneous osteonecrosis of the knee (SONK): are they the same?
We used to think an insufficiency fracture was simply another name for osteonecrosis (SONK). We now believe they’re different processes: one is a stress (insufficiency) fracture, the other is bone death (necrosis). The two are linked, though — an untreated insufficiency fracture can progress to bone death and SONK, which is exactly why an early diagnosis matters.
Treatment of an insufficiency fracture of the knee
Caught early, this condition responds well to pain-relieving medication (paracetamol or codeine) and rest from weight-bearing activity. We generally suggest protected weight-bearing, with or without crutches, for about six weeks, then a further six weeks of reduced loading. In the second phase, we add lower-limb strengthening — initially non-weight-bearing on machines (knee extensions, knee curls, side-lying hip abduction), progressing to weight-bearing resistance work, including modified yoga and Pilates.
We usually repeat the MRI at 2–3 months to confirm the bone oedema is settling.
Other treatments are more controversial. Hyaluronic acid or PRP injections have been tried to ease pain and aid healing, with mixed results — they’re more likely to help any co-existing arthritis than the fracture itself. Intravenous and oral bisphosphonates show promise in small studies. Still, the evidence is weak, a recent review questioned their role, and they carry side effects including stomach ulcers, jaw necrosis, and atypical femoral fractures — they aren’t FDA-recommended for this condition. Where bone health is poor, optimising it (calcium, vitamin D, and treating osteoporosis) is an important part of management.
When is surgery needed?
We only recommend surgery when symptoms fail to improve or when a late diagnosis leads to bone collapse. Options include keyhole surgery with core decompression or knee replacement.
Frequently asked questions about an insufficiency fracture of the knee
Can knee arthroscopy trigger an insufficiency fracture?
Yes. In some people, arthroscopic keyhole surgery for a meniscal tear can precipitate an insufficiency fracture — another reason to avoid surgery for most degenerative meniscal tears.
How should I modify exercise while it heals?
Generally, stop weight-bearing activity for 4 to 6 weeks. Maintain fitness with swimming and keep your weight in check. After six weeks, begin non-weight-bearing quadriceps, hamstring, and pelvic strengthening, adding modified yoga and Pilates as symptoms settle. Running can usually restart at 2–3 months, depending on the response to rest, often after a repeat MRI confirms healing.
Is an insufficiency fracture the same as avascular necrosis (AVN)?
No. AVN is caused by a loss of blood supply to part of the knee, not a fracture. Both, however, can ultimately lead to bone death.
How long does an insufficiency fracture of the knee take to heal?
Most settle over about 3–6 months with offloading and protected weight-bearing. Larger fractures, or those diagnosed late, take longer, and a repeat MRI is used to confirm the bone is healing before returning to impact.
Does an insufficiency fracture of the knee need crutches?
It depends on the severity of the pain and the size of the fracture. The priority is offloading the knee; crutches achieve this best, but when they aren’t possible, an unloader brace plus reducing walking distance helps shift the load away from the injured area. Your doctor will tailor this to you.
Why is bone health so important in this condition?
Because an insufficiency fracture often reflects bone that can’t cope with normal load. Assessing and treating bone health — bone density, vitamin D, calcium, and osteoporosis, where present — is central to both healing the current fracture and reducing the risk of another.
Final word from Sport Doctor London about a subchondral insufficiency fracture of the knee
Consider this condition in anyone over 50 with sudden, increasing knee pain — particularly against a background of arthritis or meniscal tears. Early treatment with rest, offloading, and pain relief allows healing, though full resolution can take 3–6 months. Getting the diagnosis early is what prevents progression to bone collapse.
If you have sudden inner-knee pain that isn’t settling, Dr Masci can assess you in London, arrange an MRI, and guide treatment. Contact the team here or call +44 (0) 203 488 0350.
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.
Hi,
I have had acute knee pain on the inside of my left knee for about 21 months. I had an MRI 18 months after the initial pain which confirmed a SIFK. Consultant is questioning a SONK. I had an arthroscopy on the inside of the same knee in 2001 for a suspected cartilage tear which wasn’t the case. The fracture is not mending and I’m awaiting the result of a follow up MRI and Bone Density Scan. I like to weight train but I’ve had to stop recently because my knee hurts when load bearing. I’ve had to go off sick from my firefighting role. I’m unsure what the prognosis is. Any advice would be appreciated.
Generally, insufficiency fractures settle with rest and protected loading +/- crutches. Bone health needs to be assessed as well including bone density, vitamin D and calcium. For intractable pain, medications that have been used include bisphosphonates or PTH – although there is no evidence that these medications improve insufficiency fractures.
LM
Your information is very helpful but I would like a little further input please. I’m 69, recently advised I have severe osteoporosis -1umbar -4.1, left hip-3.3 and forearms about the same. Im addressingthis thru dietary changes and supplements by drawing. John neustadt, ortho-bone health specialist, to improve bone health. Possiby BHRT. Also have PsA, TAKING ENBREL, right thr and lumbar surgeries in the past.
I have a left knee medial femoral condyle insufficiency fracture, have been wearing an unloader brace approximately 6 weeks. Walking with brace seems ok but is it at this stage for a long distance, 30 minutes? I do t have the pain unless I take the brace off and keep walking. Thank you. Denise
Dear Denise,
Thank you for your detailed question and for sharing your background — this is clearly a complex situation and I want to give you a considered response.
Regarding the brace and walking: I would continue offloading with the brace for now. The fact that you have pain when you remove it and keep walking is a clear signal that the bone is not yet ready for full unprotected loading. I would be cautious about 30-minute walks without the brace at this stage — keep using it consistently and allow more healing time.
Regarding bone health: improving bone density is absolutely pivotal in your situation, as an insufficiency fracture of this type is a direct consequence of severely compromised bone. Beyond dietary changes and supplements, I would strongly encourage you to discuss medical treatment with your doctor. The two main options are bisphosphonates or parathyroid hormone (PTH) analogues such as teriparatide. My preference in a case like yours — with severe osteoporosis and an active insufficiency fracture — would be parathyroid hormone, as it actively stimulates new bone formation rather than simply slowing bone loss. The main drawback is cost, as it is administered by daily injection and can be expensive. However, I must stress that the evidence for these medications is scant in insufficiency fractures.
Regarding injections into the knee: these are only likely to be useful if you have co-existing osteoarthritis in the joint. I would avoid cortisone injections entirely in this context. If an injection is considered, hyaluronic acid or PRP would be more appropriate options. Like medications, we don’t have good evidence that these injections improve insufficiency fractures but they might help pain from osteoarthritis.
Lorenzo
Hi Lorenzo,
I am a 67yr old fairly active male. I play golf 3 or 4 times a week. I developed a pain on the inside of my knee approx 6 weeks ago. The pain got gradually worse until I could no longer walk without a bad limp & considerable pain. I had an x-ray which showed no abnormality. I was given antibiotics for what may have been an infection, a knee brace and co-codomol.I saw a Consultant rheumatologist 3 weeks after the pain began, and then had an MRI. He diagnosed a left knee femoral condyle insufficiency fracture. He injected the knee with 80mg of Depo-Medrone and lignocaine. I had a Dexa Scan (results for left femur neck was T-score -0.8, BMD 0.933 g/cm2 and total T-score-0.2., BMD 0.976 g/cm2. I was also given an IV infusion of 5mg of zoledronic acid.
What are the possible causes of the insufficiency fracture?
Are the bone density test results normal?
Can osteoporosis be eliminated as the cause?
Could golf (or the amount of golf) be the cause of the insufficiency fracture?
How long after the infusion can I start playing golf again?
Will I need annual IV infusions of zoledronic acid?
Could I suffer further insufficiency fractures in the future? And what would be the likelihood of these be?
Is there anything I should be doing to expedite full recovery?
Is there anything I should be doing in the future to reduce the risk of a recurrence or another fracture elsewhere.
Is there any other advice you could offer?
Thank you for getting in touch and for setting out your history so clearly. A femoral condyle insufficiency fracture is certainly a complex picture.
I’ve outlined the causes in my blog but underlying knee joint pathology is common in addition to problems with bone health (osteoporosis).
Your DEXA results are actually reassuring — a T-score of -0.8 at the femoral neck and -0.2 overall places you in the osteopenia range at most, and your total score is essentially normal. Osteoporosis as the primary driver of your insufficiency fracture is therefore unlikely to be the full explanation. It may be related to knee joint pathology.
I suspect you were given the infusion to treat the insufficiency fracture. However, there is some controversy regarding using infusion for insufficiency fractures. Nevertheless, once the infusion is done and the condition has resolved, I don’t think you will need further treatment. The other controversy is around injections. In general, I would not recommend further cortisone injections. Better options are hyaluronic acid or PRP.
As I outlined in my blog, most cases will settle with a short period of offloading – so that means no golf for a period of time.