X-rays and MRI scans are essential tools in diagnosing and grading osteochondritis dissecans. Doctors also use them to guide treatment and evaluate the outlook for the condition.
Osteochondritis dissecans (OCD) is a rare joint condition that most often develops in active teenagers. In OCD, a small part of the end of a bone that’s nearest to a joint loses its blood supply and begins to die. The condition typically affects only one joint — often your knee, elbow, or ankle. Usually, there’s no clear cause.
The fragment of diseased bone and its attached cartilage might stay in place and eventually heal, or the fragment might break off, interfere with regular joint function, and cause long-term joint problems.
Accurately assessing the position and attachment of the diseased bone and cartilage fragment is very important when evaluating your symptoms and outlook.
Doctors use medical imaging tests such as X-rays, MRIs, and CT scans to best diagnose and evaluate OCD. These tests can also help guide treatment.
Why do doctors use imaging in osteochondritis dissecans?
No blood test, physical sign, or exam maneuver can definitively diagnose OCD.
Doctors use a variety of imaging tests to find the injured area of bone and cartilage , diagnose OCD, and differentiate the condition from other bone injuries or diseases.
Imaging also plays a major role in treatment planning. Using imaging tests, doctors can see whether your OCD lesion is stable (likely to remain attached and heal with supportive care) or unstable (in need of surgery).
Doctors also use imaging studies to monitor your progress and healing.
What is the most common site of osteochondritis dissecans?
OCD most commonly affects the knee, which is involved in 75% of all cases.
OCD can happen at any joint, but the most common locations are:
- Medial knee: where the end of your thigh bone ( femur ) meets your knee joint (this is the most typical location)
- Lateral elbow: where your lateral upper arm bone ( humerus ) meets your elbow joint
- Ankle: where your shin meets your foot, at the mid-upper portion of your talus bone
What types of imaging do doctors usually use in osteochondritis dissecans?
Doctors most frequently use X-ray and MRI scans to evaluate OCD.
X-ray
X-rays are usually the first tests doctors order, and they’re generally excellent at imaging bone. But in the earliest stages of OCD, X-rays may not clearly show the area of damage.
For the most common OCD lesions of the knee, special X-ray views, such as the notch view, can better show the parts of the joint typically affected by OCD.
X-rays can also help doctors check the closure of the childhood growth plates, which are located at the ends of bones.
But X-rays can’t evaluate cartilage or the stability of attached OCD fragments.
MRI
MRI uses a magnet to generate detailed images. MRI is very accurate, detecting OCD with almost 100% sensitivity . Healthcare professionals can also use MRI to evaluate bone and cartilage.
In growing children, MRI can be particularly useful when differentiating typical bone maturation from OCD lesions.
MRI can also determine the stability of the bone and cartilage fragments in OCD, which is vital information for your treatment plan. Additionally, MRI can show whether joint fluid is tracking below your cartilage and into bone, which could be cause for concern.
The great value of MRI is in determining whether surgery is necessary and which type of surgery would be best, depending on the size and stability of the lesion. it can also help doctors differentiate between OCD and similar conditions, such as avascular necrosis and a subchondral insufficiency fracture.
But MRI tests are often lengthy and require cooperation and no movement. They may sometimes require the use of a contrast dye, which is injected into your knee, for a full assessment.
Less commonly used imaging techniques
CT scans are X-ray-based tests that are good for imaging bone. Compared with standard X-rays, they offer a higher resolution, greater detail, and multiple views through the joint.
However, they involve more radiation exposure and, like X-rays, can’t evaluate the joint cartilage.
Your doctors may recommend CT scanning after surgical repair of OCD to check on the health of the repositioned bone fragment.
Radionuclide bone scans track patterns of radioactive isotope uptake. They may be helpful for evaluating OCD in people with open growth plates.
What does osteochondritis dissecans look like on radiographic imaging?
(A) X-ray, (B) CT, and (C) MRI images of the same knee show different features of osteochondritis dissecans. Department of Orthopedic Surgery, Hirosaki University Graduate School of Medicine, Aomori, Japan CC BY-NC-ND 4.0
Department of Orthopedic Surgery, Hirosaki University Graduate School of Medicine, Aomori, Japan CC BY-NC-ND 4.0
This X-ray image of osteochondritis in the knee shows a buildup of fluid in the bone marrow. Pil Kang, Public domain, via Wikimedia Commons
Different MRI enhancements can reveal specific features of osteochondritis dissecans, such as bone marrow edema and cartilage fragments. Hemke R. Contrast-enhanced MRI features in the early diagnosis of Juvenile Idiopathic Arthritis. Eur Radiol. 2015 CC BY-NC 4.0
Hemke R. Contrast-enhanced MRI features in the early diagnosis of Juvenile Idiopathic Arthritis. Eur Radiol. 2015 CC BY-NC 4.0
X-ray imaging can show bone fragments in the knee from osteochondritis dissecans. BSIP SA / Alamy Stock Photo
What are the most common radiographic findings of osteochondritis dissecans?
X-ray findings
At first, the affected area of bone may not be visible. When it appears, it looks like an indistinct radiolucent (dark) spot.
As OCD progresses, X-rays may show distinct dark areas of dying bone ringed by white calcifications or sclerosis (hardening).
If the fragment of diseased bone and cartilage breaks apart and separates from the host bone, the fracture will appear as a dark line surrounded by healing tissue. Doctors can also see the bony portion of the loose fragment on an X-ray.
MRI findings
MRI can help doctors accurately diagnose OCD. But MRI scans are also crucial for determining the status and stability of the dissected bone fragment and its cartilage coating.
A stable OCD lesion is one that is likely to remain in its usual place, aligned to the host bone. It may recover blood supply and heal on its own with rest and physical therapy.
MRI scans of stable lesions may still show changes in the bone and cartilage, with a dull rim of signal behind the fragment, indicating that it’s still partially attached. MRI with gadolinium contrast can evaluate the blood supply to the bony fragment and determine its viability.
In an unstable OCD lesion, the affected bone and cartilage fragment is detached and likely to dislocate from the rest of your healthy bone.
When this happens, the dissected fragment can enter the free joint space and cause problems with your joint function. The exposed unprotected area of the host bone can also develop early onset arthritis. Unstable OCD lesions are likely to require surgical treatment.
On an MRI scan, the best indicator of instability is the bright line of high signal intensity between the diseased bone and cartilage fragment and the underlying host bone. There may also be other signs, such as fluid-filled cysts in the host bone below the OCD fragment or a linear high intensity signal passing completely through the affected cartilage.
Osteochondritis dissecans MRI grading
In addition to assessing whether an OCD lesion is stable or unstable, doctors often grade or stage OCD lesions depending on MRI findings. Scientists have devised at least 13 grading systems, each with different criteria. Most have four or five grades, with instability increasing with higher grade numbers.
In one widely used system , doctors grade OCD lesions as follows:
- Grade 1: intact cartilage (stable)
- Grade 2: non-movable cartilage fragment (stable)
- Grade 3: partially attached, movable fragment (unstable)
- Grade 4: completely detached fragment (unstable)
Takeaway
Osteochondritis dissecans (OCD) is a rare bone condition that most often affects the knee joint in active adolescents. Getting an accurate diagnosis and starting treatment are important, as unstable OCD bone and cartilage fragments can cause significant joint symptoms and contribute to early onset osteoarthritis .
When signs and symptoms of OCD are present, doctors use medical imaging studies — most commonly X-ray and MRI — to make a diagnosis and evaluate the characteristics of the condition.
If you or your child receives an OCD diagnosis, your doctor will also rely on imaging studies to:
- monitor the progression of the condition
- monitor your response to treatment
- evaluate your recovery
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