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Year : 2005  |  Volume : 15  |  Issue : 4  |  Page : 463-466
Images - osteochondritis dissecans of knee : MR Imaging


Department Of Radiodiagnosis, Maulana Azad Medical College And Associated Lok Nayak Hospital, Jawahar Lal Nehru Marg, New Delhi-110002, India

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Keywords: Osteochondritis, MR, Condylar, OCD

How to cite this article:
Singh S, Chowdhury V, Dixit R, Khera G. Images - osteochondritis dissecans of knee : MR Imaging. Indian J Radiol Imaging 2005;15:463-6

How to cite this URL:
Singh S, Chowdhury V, Dixit R, Khera G. Images - osteochondritis dissecans of knee : MR Imaging. Indian J Radiol Imaging [serial online] 2005 [cited 2020 Aug 12];15:463-6. Available from: http://www.ijri.org/text.asp?2005/15/4/463/28774

   Introduction Top


Osteochondritis dissecans (OCD) represents an osseous lesion with secondary involvement of the overlying cartilage. This entity is most frequently seen in adolescents and young adults and refers to fragmentation, and often separation, of a portion of the subchondral bone, typically along the lateral aspect of the medial femoral condyle in the knee [1]. Its nature is that of a transitional zone with chance of healing as well as of progression to an osseous defect. Early detection of osteochondral lesion is desirable because the onset of degenerative arthritis in patients with OCD is estimated to occur 10 years earlier than in normal individuals. Osteochondritis dissecans is generally diagnosed by conventional radiology. Its therapy is determined by the stage of the lesion and MRI has a role in staging the lesion [2]. Knowledge of the fragment stability and presence of an articular cartilage defect is useful in deciding the treatment. This information cannot be determined on plain films or clinical examination. MR imaging is useful in evaluating articular surface defects and lesion stability in patients with osteochondritis dissecans.


   Case report Top


A 36 year old male presented with sudden locking of the right knee associated with pain and swelling. A history of minor trauma could be elicited. A clinical diagnosis of meniscal tear was made and the patient was referred for a MR examination of the knee.

The study revealed a large condylar defect in the lateral aspect of the medial femoral condyle [Figure - 1]. A large defect in the overlying articular cartilage was seen [Figure - 2]. No fragment was evident within the osseous bed. The detached osteochondral fragment was seen within the intercondylar notch [Figure - 3]. Indirect MR arthrogram performed after intravenous injection of gadolinium followed by delayed imaging of the knee revealed the displaced fragment in the notch to be outlined by contrast [Figure - 4].

Based on the these MR findings a diagnosis of osteochondritis dissecans of the knee with displacement of the fragment in the intercondylar notch (loose body) was made. The patient underwent an arthroscopic removal of the fragment.


   Discussion Top


Osteochondritis dissecans (OCD) is a localized affection of an articular surface that may lead from edematous changes in the subchondral bone to progressive detachment and complete separation of an osteochondral fragment from the surrounding subchondral bone [3]. The cause of the lesion is uncertain but it is suggested by some to result from repetitive trauma that produces shear forces across the cartilage. The alternative theory more popular recently is that osteochondritis dissecans is an avascular lesion attributed to an insufficient arterial blood supply to the subarticular trabeculae and poor anastomoses with the neighbouring systems resulting in infarctions of small wedge shaped pieces of bone immediately beneath the articular cartilage. Other proposed causes include mechanical stress, familial dysplasia and fat emboli [1].

Osteochondritis dissecans most commonly involves the knee. Classically lesions are located in the lateral aspect of the medial femoral condyle (55%). Less commonly, lesions involve a central portion of medial femoral condyle (25%). OCD may also effect the lateral femoral condyle (18%) or it may occur bilaterally (24%). The talus is the second most frequent site while the elbow is the third frequent joint affected by OCD [2].

Not infrequently OCD is clinically silent and only incidentally detected radiologically. Exercise related pain during jumping, squatting or stair climbing are frequent complaints. A small effusion can develop but never a haematoma. Since these symptoms cause minimal suffering, the diagnosis is often established only years after the onset of symptoms. Not until the late stage loosening or complete dislocation of the fragment causes locking of the joint.

Radiographic findings include a geographic, subchondral lucency along the medial femoral condyle. Although the radiographic examination generally establies the diagnosis of OCD correctly it is by no means adequate for therapeutic decisions.

Despite its excellent anatomic delineation of the lesion, CT cannot assess the healing potential of OCD.

Assuming an ischaemic theory a scintigraphic description and staging of OCD has been proposed. However with radionuclide scanning, findings between stable and unstable fragments overlap. Radionuclide scanning also provides no anatomic information on articular surface deformity [2].

A staging system for osteochondritis was developed based on arthroscopic findings. In stage 1, the lesion is 1 to 3 cm and the articular cartilage is intact. Stage 2 is characterized by an articular cartilage defect without a loose body. In stage 3, a partially detached osteochondral fragment with or without fibrous interposition is found. Stage 4 demonstrates a loose body with a crater filled with fibrous tissue [4].

MRI plays an important role in detecting the lesion if plain films are normal. A crescentic or ovoid focus of subchondral signal abnormality is evident. The primary concern when evaluating a focus of osteochondritis dissecans is whether the fragment of subchondral bone is unstable (i.e. at risk of evolving into a displaced loose body in the joint) or stable. The most common sign of unstable lesion is a high signal intensity line on T2W images between the fragment and the underlying bone. Other MR imaging signs of instability on T2W images include an articular fracture indicated by joint fluid of high signal intensity passing through the subchondral bone plate, a focal osteochondral defect filled with joint fluid and a 5 mm or larger fluid filled cyst deep to the lesion [5].

The cartilaginous coverage is intact during the early and prognostically favourable stage of OCD. The MRI technique can distinguish lesions with intact cartilage from lesions with focal or linear cartilaginous defects (fissures, tears and clefts). Fluid detected between the fragment and the defect is a certain sign of severely damaged cartilage. The intravenous or intra-articular administration of gadolinium contrast agent has been used as a supplementary MR imaging method in the assessment of osteochondritis dissecans. With intravenous gadolinium there may be enhancement of signal intensity in the zone between the fragment and parent bone which corresponds to histologic evidence of loose fragment and subjacent granulation tissue. The intra-articular contrast (MR arthrography) also results in improvement in accurate assessment of the overlying articular cartilage when compared with standard spin echo and gradient echo sequences.

A proposed classification system is based on these findings and assigns intact cartilage, contrast enhancement and large cystic lesions of more than 5 mm diameter decisive roles [2].

Staging OCD is of utmost importance for prognosis and therapy. MRI stage I (intact cartilage, contact enhancement of the lesion, absent cystic defects) is a condition generally treated conservatively. Cartilage defect with or without incomplete separation of the fragment, fluid around an undetached fragment and a dislodged fragment are MRI findings observed in stage II and require arthroscopy with possible intervention. Thus MRI can non-invasively separate non-surgical from possible surgical lesions reliably and arthroscopy should no longer be obtained for diagnostic purposes [2].

 
   References Top

1.Hughston JC, Hergenroeder PT, Courtenay BG. Osteochondritis dissecans of the femoral condyles. J Bone Joint Surg 1984; 66: 1340-1348.  Back to cited text no. 1  [PUBMED]  
2.Bohndorf K. Osteochondritis (Osteochondrosis) dissecans : A review and new MRI classification. Eur Radiol 1998; 8:103-112.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Stabler A, Glaser C, Reiser M. Musculosckeletal MR : Knee. Eur Radiol 2000; 10:230-241.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.Mesgarzadeh M, Sapega A, Bonakdarpour A, et al. Osteochondritis dissecans : Analysis of mechanical stability with radiography, scintigraphy and MR imaging. Radiology 1987; 165:775-780.  Back to cited text no. 4    
5.De Smet AA, Fisher DR, Graf BK, Lange RH. Osteochondritis dissecans of the knee; value of MR imaging in determining lesion stability and the presence of articular cartilage defects. AJR 1990; 155:549-553.  Back to cited text no. 5  [PUBMED]  

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Correspondence Address:
S Singh
212, Sfs Flats, Phase Iv, Ashok Vihar, Delhi - 110052
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-3026.28774

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    Figures

[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]

    Tables

[Table - 1]



 

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    Introduction
    Case report
    Discussion
    References
    Article Figures
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