CASE 125
By: Dr. Nizar Al-Nakshabandi MD, FRCPC
HISTORY: 29-year-old boy ankle pain.
What are your findings?
What is the differential diagnosis?
What is the diagnosis?
FINDINGS:
Plain AP radiograph (A) of the ankle joint demonstrates flattening on the medial aspect of the dome of the talus with a subtle lucency and a bony fragment measuring less than 5 mm.
Coronal and sagittal T1 (B & C) respectively show the loose bone fragment to be of low signal intensity with the crater for the dome of the talus (representing the donor site).
Coronal STIR sequence (D) shows both the donor site and the donor-RIM SIGN (non-displaced loose body) of high signal intensity.
DIFFERENTIAL DIAGNOSIS:
· Osteochondritis dissecans (OCD).
· Osteochondral defect/fracture from impaction.
· Stress/insufficiency fracture.
· Avascular necrosis.
· If stuck, you can also include the differential of an epiphyseal lytic lesion, like Geod (subchondral cyst), intraosseous ganglion, chondroblastoma among others but be careful to dismiss each based on the characteristic of the lesion you are seeing now.
DIAGNOSIS:
Stage III OCD of the ankle.
PEARLS AND DISSCUSSION:
The etiology of OCD is uncertain but thought to be from trauma/microtrauma resulting in aseptic loosening of the boney fragment.
Symptoms are variable but usually pain and locking are the most common.
Males are affected two times more than females.
Any age is affected but usually between the 2nd. to 4th. Decade.
OCD STAGING SYSTEM:
| Stage | Findings |
|---|---|
| I |
- Injury limited to articular cartilage - MRI findings: subchondral oedema - X-ray findings: none |
| II |
- Cartilage injury with associated subchondral fracture but without detachment. - Thin sclerotic margin. - X-ray findings: usually none; may see fracture as sclerotic or osteopaenic area |
| III |
- Detached, nondisplaced fragment. - MRI findings: high signal around osteochondral fracture (RIM SIGN) but not displaced - X-ray findings: slight lucency between osteochondral fragment and remainder of the bone |
| IV |
- Osteochondral fragment displaced. - Usually joint effusion present, surrounding fragment and filling donor site - X-ray findings: increased lucency between osteochondral fragment and remainder of the bone, or loose body with donor site irregularity |
| V |
- Subchondral cyst formation - Secondary degenerative change X-ray findings: secondary OA |
FURTHER READING:
1. Hepple S, Winson IG, Glew D. Osteochondral lesions of the talus: a revised classification. Foot Ankle Int. 1999; 20:789-93.
2. Resnick D, Kransdorf MJ. Bone and joint imaging. W B Saunders Co. (2005) ISBN:0721602703.
