Glossary
Subchondral insufficiency fracture
Quick answer
A subchondral insufficiency fracture is a small crack in the bone just under the joint cartilage, caused by normal loads on bone that cannot cope. It typically causes sudden, severe knee pain without a clear injury, often in people over fifty, explains Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.
What it means
Subchondral means beneath the cartilage. Insufficiency means the bone is not strong enough for everyday load, rather than being hit hard. The fracture usually sits in the medial femoral condyle or tibia, and MRI shows a thin dark line with surrounding bone marrow oedema.
It used to be called spontaneous osteonecrosis of the knee, or SONK. It is often linked to a meniscal root tear or extrusion, reduced bone density, or a recent increase in activity.
Why it matters
The pain can be out of proportion to what an X-ray shows, so it is easy to miss early. Pain is often worst at night and when standing. Many small fractures heal well if protected. Larger ones, or those where the bone surface collapses, can lead to rapid arthritis in that part of the knee.
Recognising it early also matters because keyhole meniscus surgery in this setting can make things worse.
How it is treated
Treatment usually starts with reduced weight-bearing on crutches for several weeks, pain relief and a check of bone health, including vitamin D. An unloading brace may help. A repairable meniscal root tear may be fixed. If the joint surface collapses, osteotomy or partial or total knee replacement may be needed later.
Frequently asked questions
Why did my knee start hurting without an injury?
In an insufficiency fracture, normal walking is enough to crack bone that is weakened or overloaded, often because the meniscus is no longer protecting it.
Will it heal?
Many small lesions heal over a few months with protected weight-bearing. Follow-up MRI or X-rays show whether healing is on track.
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