Diagnosis

Osteochondral Defect

Case Discussion

An osteochondral defect (OCD) is a type of focal osteochondral lesion that may be posttraumatic or secondary to chronic repetitive microtrauma (leading to osteochondritis dessicans in an immature skeleton). In the ankle, an OCD is typically located in the medial or lateral aspects of the talar dome.

It has been well recognized that the mechanism of injury dictates the location of the defect. With dorsiflexion and inversion type injuries, lesions occur anterolaterally. With plantarflexion and inversion type injuries, lesions occur posteromedially.

The Berndt and Harty classification is used to describe talar osteochondral defects.

– Stage 1: Area of subchondral compression

– Stage 2: Partially detached fragment

– Stage 3: Completely detached fragment, but not displaced

– Stage 4: Completely detached and displaced

MRI is highly sensitive and specific for the detection of OCDs and and is accurate in staging of osteochondral lesions. MRI findings of OCDs include hypointensity on T1, variable intensity on T2, and a pathognomonic “rim sign” of fluid signal intensity indicating a potentially unstable fragment.

Lesions may be shouldered (with a portion of normal bone between the OCD and vertical portion of the talus) or non-shouldered (without a portion of normal bone between the OCD and vertical portion of talus). Shouldered lesions versus non-shouldered lesions are important to note in the report, as they have implications regarding management. Shouldered lesions are easier to manage surgically as they have viable subjacent bone available for graft incorporation. 

Note: High signal alone does not indicate an unstable fragment. High signal could also represent fibrovascular change adjacent to an area of osteochondral injury. The high signal needs to be as hyperintense as fluid to represent a potentially unstable fragment. 

The reader should carefully scrutinize for intra-articular loose bodies.

Chronic ankle sprain and ankle instability in general go hand in hand with talar dome OCDs.

Key Images

Osteochondral defect of the medial talar dome in a 24-year-old man complaining of left ankle pain after lifting.

A. Sagittal T1 image of the left ankle shows a hypointense lesion within the posteromedial aspect of the talar dome (red arrow) and flattening of the articular surface.
B. Coronal T1 FSE image shows a non-shouldered hypointense osteochondral lesion of the posteromedial aspect of the talar dome (red arrow).
C. Sagittal PD image shows a lesion within the posteromedial aspect of the talar dome (red arrow) with heterogeneous signal and associated flattening of the articular surface.  There is adjacent osteoedema.
D. Coronal PD image shows a lesion within the posteromedial aspect of the talar dome (red arrow) with heterogeneous signal and associated flattening of the articular surface.  There is adjacent osteoedema. The lesion is non-shouldered and measures approximately 1.0 cm wide and 0.9 cm deep.

References:

  1. Zanon G, Di Vico G, Marullo M. Osteochondritis dissecans of the talus. Joints 2014; 2(3) 115-123
  2. Berndt AL, Harty M. Transchondral fractures (osteochondritis dissecans) of the talus. J Bone Joint Surg Am 1959; 41-A: 988-1020