Age / Sex : 15 / M

Chief complaint: Left knee pain (onset: 1 year ago)  

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한 개만 보내주시기 바랍니다)

Courtesy: 이민희 (Lee, Min Hee) 울산의대 서울아산병원 (University of Ulsan College of Medicine, Asan Medical Center)

Osteochondritis dissecans of the knee (femoral condyle)

Discussion

Findings: On AP projection of both knees, there is a focal bony fragmentation in the lateral (inner) aspect of medial condyle of left femur. Some sclerotic change is seen along the margin of the parent bone. A corresponding lesion is identified on coronal proton density- weighted MR image. High signal intensity rim is not evident at the interface between the bony fragment and the adjacent bone.

Differential Diagnosis:

1. Spontaneous osteonecrosis of the knee, which occurs in older patients and almost invariably in the weight-bearing portion of the medial femoral condyle

2. Fragmentation that may be associated with neuropathic osteoarthropathy

3. Normal grooves of the femoral condyles

Diagnosis: Osteochondritis dissecans of the knee (femoral condyle)

Discussion:

Osteochondritis dissecans is characterized by fragmentation and possible separation of a portion of the articular surface. Men are affected more frequently, and symptom onset at adolescence is the most frequent, although the age range is variable. Regarding the location, medial femoral condyle is involved in 85% (classic location is the inner aspect of medial femoral condyle, 65%) and lateral condyle in 15%. The pathogenesis has not been definitely established.  In about 50% of cases, it has been reported that a significant history of knee trauma was present.

MR imaging is a favored modality for evaluation that can identify the location, size and depth of the lesions, and any associated intraarticular bodies. Major concern is the determining the stability of the fragment (ie, stable or unstable/loose). The best indicators of instability were known as the presence of fluid encircling the fragment or focal cystic areas beneath the fragment. High signal intensity, indicative of fluid or granulation tissue at the interface of the fragment and the parent bone on T2-weighted MR images proved to be strong, but not infallible, evidence of an unstable lesion. De Smet et al. summarized the MR imaging signs of instability of osteochondritis dissecans on T2-weighted images: the presence of a line of high signal intensity at the interface between the osseous fragment and the adjacent bone, a focal osteochondral defect filled with joint fluid, and a 5-mm or larger fluid-filled cyst deep to the lesion. MR arthrography may have advantage, because the fluid extending through the cartilaginous defect and into the base of the fragment depends not only on the extent of the chondral damage but also on the amount of joint fluid.

References:

1.      Resnick D. Traumatic disorders of bone. In: Resnick, Kang, Petterklieber. Internal derangements of joints. 2^nd ed. Philadelphia, Pa: Saunders, 2007; 315-322

2.      De Smet AA, Ilahi OA, Graf BK. Untreated osteochodritis dissecans of the femoral condyles: prediction of patient outcome using radiographic and MR findings. Skeletal Radiol 1997;26:463-467