Multiplanar Musculoskeletal CT

Figure 1

History: 23-year-old male with left ankle pain. The patient was referred to Main Street Radiology for a non-contrast ankle CT.

Findings: There is a 2.3cm osteochondral lesion at the dome of the talus medially, with a 1.3cm loose fragment depressed within the defect. In addition, cyst formation is seen beneath the loose fragment within the body of the talus.

(Figure #1 Coronal Image)
(Figure #2, Sagittal Image)
(Figure #3 Axial Image)
(Figure #4 3D Image)

Figure 2

Discussion: Osteochondral lesion of the talus is considered the chronic phase of a compressed or avulsed talar dome fracture. The most common sign/symptom is persistent ankle pain after an inversion injury. The clinical profile includes chronic ankle pain/sprain, stiffness, swelling, ecchymosis, clicking, locking, giving way, and reduced motion.

The average age at presentation is 25 years, but is also known to occur in the fifth and sixth decades. The lesion is not common in children. The lesion is more common in males (67%) than females (33%).

The etiology of the lesion is thought to be related to direct trauma or repetitive microtrauma. Trauma and a predisposition to talar dome ischemia with increased joint pressures, forces synovial fluid into the fracture site and prevents healing. The subchondral fracture is then susceptible to avascular necrosis.

Figure 3

The natural history and prognosis, without treatment, include joint stiffness, ankle instability and degenerative arthritis. There is a staging pattern based on non-contrast CT criteria which includes:

Stage I: A cystic lesion with an intact roof.
Stage IIA: A cystic lesion with communication with the talar dome.
Stage IIB: An open articular surface lesion and nondisplaced fragment.
Stage III: A non-displaced lesion and lucency.
Stage IV: A displaced fragment.

Both conservative and/or surgical treatments are available. Conservative treatment is utilized with Stage I and II lesions. They include reduced activity, with limited ankle motion for Stage I lesions. Casting is performed with acute Stage II lesions. Surgical treatment is performed with Stage III + IV lesions. They included free fragment excision, curettage, drilling, and abrasion arthroplasty.

Figure 4

At MSR, joint and extremity CT examinations are performed on a 16-detector spiral CT utilizing 0.75 mm slices. The acquisition of sub-millimeter slices results in near-isotropic resolution, which enables reconstruction of images at any plane or angle from the original data set without losing resolution. Sagittal, coronal and 3D images are routinely generated from the original axial scan. With older technology, to obtain high quality images at a different plane, second set of images must be obtained after repositioning the patient, resulting in higher radiation dose to the patient. This new technology available at MSR results in highest quality images with less radiation to the patients.