What Is Osteochondritis Dissecans, and Who Gets It?
Osteochondritis dissecans (OCD) is a condition where a small area of bone just beneath the cartilage surface of the knee loses its blood supply. The affected bone softens, and the cartilage above it may loosen or break away, forming a loose body in the joint. It is most common in physically active adults and younger athletes.
Key takeaways
- OCD affects the subchondral bone, the layer directly beneath cartilage, usually on the inner side of the knee.
- Symptoms include deep knee pain, swelling, and sometimes catching or locking if a fragment comes loose.
- MRI is the primary tool for staging the lesion. Standing imaging can add alignment context that lying-down scans miss.
- Early diagnosis matters. Smaller, stable lesions often respond to rest and activity modification.
- A standing, weight-bearing scan shows how your whole leg alignment may be loading the affected area unevenly.
If you have been told you have osteochondritis dissecans, or you have a knee that aches after sport and occasionally catches, this page explains what is happening inside your joint and how standing imaging fits into the picture.
What does osteochondritis dissecans feel like?
The earliest sign is usually a vague, deep ache inside the knee that gets worse with activity, especially running, jumping or climbing stairs. As the condition progresses, you may notice more specific symptoms.
A dull ache deep inside the knee, usually on the inner side, that flares during and after activity.
The knee may puff up after exercise, taking hours or days to settle.
If a cartilage fragment loosens, it can get caught between the joint surfaces, causing the knee to lock or give way suddenly.
The knee may feel stiff after sitting, and the thigh muscles can weaken over time from reduced use.
Important: if your knee locks completely and you cannot straighten it, or you experience sudden severe swelling, see your GP or attend A&E promptly. A locked knee from a loose body may need urgent assessment.
What causes osteochondritis dissecans in the knee?
The exact cause is not fully understood, but it involves a disruption of blood flow to a small area of subchondral bone, the hard layer directly beneath the joint cartilage. Without adequate blood supply, that patch of bone weakens. Several factors are thought to contribute.
Repeated loading from running, jumping or pivoting sports can damage the blood vessels feeding the bone beneath cartilage.
Some people may have a naturally more fragile blood supply to certain parts of the knee bone, making those spots more prone to damage.
If your leg is angled inward or outward, certain parts of the knee surface carry more weight than they should. This uneven loading can concentrate stress on one area of bone.
Most OCD lesions occur on the medial femoral condyle, the rounded bump on the inner side of the thighbone where it meets the knee. This is the area that bears the most load when you walk, run and land from jumps.
How is osteochondritis dissecans diagnosed?
OCD is usually diagnosed through a combination of clinical examination and imaging. Your doctor will ask about your symptoms, check for tenderness on the inner knee, and may test for swelling or restricted movement.
Standard X-rays can sometimes show an OCD lesion, but they are taken lying down and only give a flat, two-dimensional view. MRI is the key tool for staging the lesion. It shows whether the cartilage cap is intact, how large the affected area of bone is, and whether a fragment is at risk of separating.
When is MRI the right choice? For osteochondritis dissecans, MRI is usually the better tool for seeing the cartilage surface, the bone beneath it, and any fluid signals that suggest the fragment is loosening. EOS standing imaging does not replace MRI for staging OCD. What it does is add alignment context, showing how your full leg loads the knee when you are upright, which a lying-down MRI cannot capture.
Why does leg alignment matter if you have an OCD lesion?
Because the way your leg is aligned changes where force concentrates across your knee. When you lie down for an MRI or standard X-ray, your muscles relax and gravity stops loading the joint. Alignment problems that only appear under your body weight are effectively hidden.
Your body works as a connected chain from your foot through your ankle, knee, hip and spine. If your leg angles slightly inward, more force falls on the inner knee, exactly where most OCD lesions develop. A tilt at the hip or foot can shift loading higher up or lower down the chain, making the knee compensate in ways that concentrate stress on a small area of bone.
A standing, full-leg EOS scan at ScanAlign, low dose standing imaging captures your entire leg from hip to ankle in one image while you bear weight naturally. It uses about 90% less radiation than a standard X-ray, around ten times less. The result gives your specialist a clear picture of your leg alignment under real-life conditions, information that helps guide whether activity changes, bracing or surgical planning is most appropriate.
What are the options if you have osteochondritis dissecans?
Management depends on the size and stability of the lesion, your age, and your activity level. ScanAlign is a diagnostic imaging clinic, not a treatment centre, so we do not provide treatment. What we can do is give you and your specialist the alignment information that helps shape the right plan.
In general terms, the options your doctor may discuss include:
- Activity modification and rest. Reducing impact sports to allow the bone to heal. This is often tried first for stable lesions.
- Physiotherapy. Strengthening the muscles around the knee to support the joint and reduce loading on the affected area.
- Surgery. If the fragment has loosened or detached, surgical options may include fixing it back in place or, if that is not possible, removing the loose body and restoring the cartilage surface. Alignment correction may also be considered if leg geometry is contributing to uneven loading.
Understanding how your leg is aligned under weight helps your surgeon decide whether a straightforward cartilage procedure is enough, or whether the underlying alignment needs addressing at the same time to protect the repair long term.
If you are considering surgery or want your specialist to see your full leg alignment, you can book a standing knee scan and bring the results to your consultation.
Book a free video consultationIs a standing alignment scan right for you?
A standing EOS scan does not replace MRI for staging your OCD lesion. It adds something different: a view of your whole leg alignment under real body weight. Here is a quick guide.
- Have been diagnosed with OCD and want alignment context for your specialist
- Are being considered for surgery and need full-leg measurements
- Have knee pain that has not responded to rest and want to rule out alignment as a factor
- Want a very low-radiation image of both legs for comparison
- Need to see the cartilage surface and bone detail of the lesion itself
- Have soft-tissue symptoms like ligament or meniscus concerns
- Need to stage an OCD lesion for the first time
For younger patients, paediatric imaging at ScanAlign follows specific protocols designed to keep radiation as low as possible.
Frequently asked questions about osteochondritis dissecans
It is a condition where a small patch of bone just beneath the cartilage in the knee loses its blood supply. The bone softens, and the cartilage above it may loosen or break away, creating a loose body inside the joint.
It is most common in physically active people, particularly those involved in running, jumping or pivoting sports. It can occur at any age in adulthood, though it often first appears in younger adults.
A loose body can cause sudden catching or locking, where the knee gets stuck and you cannot straighten it. You may also feel a sharp pain that comes and goes, or a sensation of something moving inside the joint.
Some stable lesions can heal with rest and reduced activity, especially smaller ones. Larger or unstable lesions, particularly those where the cartilage has started to separate, are less likely to heal without surgical help.
MRI is the key investigation for staging the lesion, because it shows the cartilage, the bone beneath it, and any fluid that suggests loosening. Standard X-rays can show the lesion but give less detail. A standing X-ray adds alignment information that neither MRI nor standard X-ray provides.
If your leg is angled so that more weight falls on the inner knee, the area most commonly affected by OCD bears extra stress. Correcting or understanding this alignment can influence treatment decisions, including whether a realignment procedure is needed alongside cartilage repair.
A standing EOS scan captures your entire leg from hip to ankle while you bear your own body weight. This reveals how your bones and joints actually align under load. A standard X-ray is taken lying down, so the muscles relax and gravity does not pull on the joint, potentially hiding alignment problems.
EOS uses about 90% less radiation than a standard X-ray, around ten times less. It is one of the lowest-radiation skeletal imaging methods available.
No. ScanAlign is a private, self-pay clinic, and you can book directly without a GP referral. You start with a free video consultation to check that a standing scan is the right next step for your situation.
Pricing details are on our FAQs and cost page. The free video consultation will confirm exactly what is included for your scan.
Want to see how your knee aligns under your body weight?
Start with a free video consultation. We will check whether a standing scan is the right next step for you and explain exactly what it shows.
Book a free video consultationSources
- Kessler JI, et al. "Osteochondritis Dissecans of the Knee." Journal of the American Academy of Orthopaedic Surgeons, 2014;22(5):297–306.
- Chambers HG, et al. "American Academy of Orthopaedic Surgeons Clinical Practice Guideline on the Diagnosis and Treatment of Osteochondritis Dissecans." JAAOS, 2011;19(5):307–309.
- NHS. "Knee pain." nhs.uk, 2023. Overview of knee conditions including cartilage and bone disorders.
Written by Abbas Dhami (Specialist Diagnostic Radiographer).
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.