Osteochondritis Dissecans of the Knee: What to Know
A healthy, 21-year-old female presents with a 6 month history of persistent knee pain that worsens with activity She undergoes x-rays and juvenile osteochondritis dissecans of the knee is diagnosed. Which of the following is the most common area for juvenile osteochonditis dissecans and what site?
A. knee, medial condyle
B. knee, lateral condyle
C. elbow, capitullum
D. ankle, talus
Osteochondritis dissecans (OCD) is conventionally defined as a focal idiopathic alteration of subchondral bone with risk of instability and disruption of adjacent articular cartilage that may result in premature osteoarthritis . This condition was initially described in 1887 and there are still challenges in regards to proper diagnosis and treatment.
The most commonly affected joint is the knee, followed by the ankle, elbow, shoulder and hip. OCD is divided into juvenile and adult forms, depending on skeletal maturity at diagnosis. The juvenile form of the disease (JOCD) presents in those aged five to 16 years with open growth plates . Most adult lesions are likely unresolved juvenile lesions, but de novo adult OCD has been described .
The causes of OCD are unknown; however, repetitive trauma, inflammation, accessory centers of ossification, ischaemia and genetic factors have been proposed . Boys have more risk of developing OCD in the knee (4 times) and elbow (7 times), whereas girls have more risk of OCD developing in the talus (1.5 times) .
The classic site of knee OCD is the posterior-central aspect of the medial condyle (63.6% to 85%) compared with inferior-central aspect of the lateral condyle (15% to 32.5%), inferomedial aspect of the patella (1.5% to 10%), and trochlea (2%) . OCD usually involves a single site but can be multifocal within one or multiple joints with lesions in different stages. Bilateralism occurs in knees (7.3% to 29%) . Participation in high-level athletics is associated with the development of OCD in the knee (55% to 60%), elbow (84%), and talus (67.4%). Knee and talar OCD cases are commonly associated with soccer, football, and basketball, whereas elbow OCD is often seen in throwing athletes and gymnasts .
history and physical examination
History and physical examination can be challenging with this condition. There may or may not be any history of trauma. The symptoms may be dependent on the location and stage of the lesion. Stable lesions may cause vague symptoms and intermittent pain. Unstable lesions or loose bodies can cause catching, locking and possibly a joint effusion. They tend to worsen with impact activity, cutting or pivoting. A special exam technique for lesions over the medial femoral condyle called the Wilson test has been described. It is proposed that it may reproduce pain with tibial internal rotation during knee extension from 90° to 30° that is relieved with tibial external rotation . There may be restricted range of motion, limping and abnormal limb alignment with unstable lesions or loose bodies .
Plain radiographs are usually the first line imaging modality for OCD and for monitoring treatment response  . Comprehensive views are recommended for knees (anteroposterior, lateral, notch or tunnel, and skyline or sunrise radiographs). Bilateral and standing alignment radiographs should be made with a low threshold to evaluate suspected bilateral disease and malalignment. Characteristic findings in early lesions are contour abnormality and radiolucency at the articular surface. More advanced lesions display a well-circumscribed, variably ossified fragment (progeny) separated from underlying bone (parent) by a crescent-shaped radiolucent line that may later ossify with healing . Radiography can reliably identify lesion location and size but is inaccurate for determining stability and identifying subtle lesions.
Magnetic resonance imaging (MRI) is the gold standard for imaging of OCD . T1-weighted sequences allow lesion size measurement. T2-weighted sequences provide information on articular cartilage integrity, reactive marrow edema in the parent bone, and fluid or cystic changes at the parent-progeny interface. However, high signal intensity around the lesion may ambiguously represent fluid or granulation tissue . Post Gadolinium fat-suppressed T1-weighted sequences can distinguish fluid from granulation tissue but may not correlate with healing .
Figure 2. (a) T2 coronal image of the knee of an osteochondritis dissecans lesion of the medial femoral condyle; note the subchondral bone marrow oedema. (b, c) T1 coronal and sagittal images shows the presence of a large JOCD lesion that affects most of the weight-bearing area of the medial femoral condyle. Adopted from .
Scintigraphy was historically used to detect OCD and assess healing on the basis of perfusion . Despite excellent sensitivity, scintigraphy became obsolete because of the lack of specificity, MRI availability, and radioisotope exposure . Recently, a nonradioactive, non-contrast-enhanced 3-T MRI method, called arterial spin labeling, was demonstrated to visualize distal femoral perfusion similarly to scintigraphy in children with knee OCD .
There are many OCD classifications systems based on the joint involved and the diagnostic modality. To date, a consensus about the most suitable classification system is still lacking. Arthroscopy is the gold standard for determining lesion stability . The first MRI criteria to predict the instability of the OCD lesion were formulated by De Smet et al. in 1990 (high T2-signal intensity line surrounding the lesion, fluidfilled cartilage defect, presence of subchondral cysts, high T2-signal fracture line in articular cartilage) .
In 2013, Chen et al. proposed a new 5 stages classification system adding a three-dimensional (3D) T1-weighted gradient-echo (GRE) MR sequence to the routine protocol to better differentiate fluid from granulation tissue and consequently to better detect unstable lesions. Hussain et al. in 2021, proposed a simpler 3-group classification with a reported excellent intra-rater agreement and moderate inter-rater agreement .
In 1998, Yoshida et al. developed a staging system differentiating JOCD in 4 stages in relation to the natural history of the lesions and introducing a last stage called “healing stage.” In 2003, Hughes et al. revisited previous classifications and developed a 4-stage system with stages 1, 2, and 3 considered stable and with high chance to heal with conservative treatment, whereas Stage 4 required surgery .
The ROCK arthroscopic classification system for the knee is the most comprehensive, including 6 mutually exclusive categories divided into immobile and mobile lesions but omitting salvageability, which requires considering skeletal maturity, prior treatments, and imaging . Contributing to MRI-based systems, Ellermann et al. devised a classification system for juvenile OCD that stages natural history from necrotic epiphyseal cartilage to lesions that are healed or not healed .
In conclusion, the diagnosis of osteochondritis dissecans of the knee should be considered in young, active patients who have knee pain. Early diagnosis and treatment are essential to prevent cartilage destruction and preserve joint function. Several classification systems based on radiographs, MRI, and arthroscopy have been proposed over the years to classify OCD location or severity, focusing on key features to assess lesion stability and healing potential. Arthroscopy, using the more recent ROCK classifications, remains the gold standard to confirm lesion stability while offering the possibility to directly perform the surgical treatment.
The most commonly affected joint is the knee, followed by the ankle, elbow, shoulder and hip. The classic site of knee OCD is the posterior-central aspect of the medial condyle (63.6% to 85%) compared with inferior-central aspect of the lateral condyle (15% to 32.5%), inferomedial aspect of the patella (1.5% to 10%), and trochlea (2%) . OCD usually involves a single site but can be multifocal within one or multiple joints with lesions in different stages. Bilateralism occurs in knees (7.3% to 29%). .
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