2008 Radiology Exam - Musculoskeletal Case 1

“Cyclone”
14 mo, Male, Belgian
4 views of the right tarsus

Presented for evaluation of right tarsal swelling. Not reported to be lame.

See images below. Click to enlarge.

Radiographic Findings:

• Associated with the distal dorsal intermediate ridge of the tibia are multiple (5) mineralized opacities of variable size and shape with mildly irregular margins. The opacities are clustered together but each is separated from the adjacent opacity and the distal tibia by a radiolucent space. The is a defect in the adjacent contour of the tibial ridge.
• The distal edge of the lateral trochlear ridge of the talus is misshapen with flattened contour, irregular subchondral raduolucencies, and several small indistinct mineralized opacities closely packed in the area.
• In the proximal dorsal subchondral bone of the lateral trochlear ridge of the talus is a 16mm discretely bordered radiolucent lesion – best seen in the DLPMO and PLDMO projections, but can be seen in the lateral view.

Radiographic Diagnosis (Synthesis):

• Osteochondral fragments from the distal intermediate ridge of the tibia and the lateral trochlear ridge of the talus typical of osteochondrosis dissecans of the tarsus.
• Subchondral cystic lesion of the lateral trochlea of the talus.

Recommendations/Management:

• Osteochondrosis dissecans of the tarsus is frequently bilateral and thus if arthroscopic intervention is recommended radiographs of the left tarsus should be done.
• Additional views such as overexposed DP or alternative imaging could be done to further evaluate the subchondral cystic lesion.

Candidate performance:
Candidates had little difficulty in identifying the typical osteochondrosis lesion of the distal tibia and lateral trochlear ridge distal lesion. However there was a significant “satisfaction of search” error in that the majority did not identify the subchondral cystic lesion. Many also mis-identified anatomy, particularly in the DLPMO view where they called the normal contour of the medial distal surface of the talus abnormal (basically the contour effects created by the distal tuberosity of the talus – located on the medial surface of the bone) and equated this with the defect they expected to be present as a consequence of the lateral trochlear distal lesion. In essence the impression was that there was significant lack of recognition of the bone contours in the oblique views. Candidates also did not recommend radiographs of the opposite tarsus, even though they recommended surgical/arthroscopic removal of the identified osteochondral fragments.