Extensor hallucis longus tendon entrapment

Case contributed by Nicholas Sharobeem

Presentation

Left lower extremity deformity following motor vehicle collision

Patient Data

Age: 50 years
Gender: Female

There are acute comminuted fractures of the distal tibia and fibula, with equivocal intra-articular extension of the distal tibial fracture. The proximal tibial segment protrudes through the skin medially on the AP view and a distal fragment protrudes through the skin anteriorly on the lateral view, consistent with open fracture. A chronic healed fracture of the distal tibial diaphysis is noted.

CT was performed after closed reduction and external fixation, with improved alignment of the distal tibial and fibular fractures compared to the initial radiographs. However, there is entrapment of the extensor hallucis longus tendon, which is located completely within the fractured distal tibia. This is best appreciated on the axial and sagittal images with soft tissue windows. There are locules of gas within the distal tibia. An external fixation pin is present in the mid tibial diaphysis. 

There is no definite intra-articular extension of the distal tibial fracture. There is no entrapment of the other tendons. Chronic healed fractures of the distal tibial and fibular diaphyses are noted.

Case Discussion

The radiographs and CT show comminuted fractures of the left distal tibia and fibula. Although MRI would be better for evaluation of tendons, the tendon silhouettes are visible on CT with appropriate windowing. It is important to examine the tendons on CT when there are adjacent fractures to make sure there is no tendon entrapment. This case is a great example of tendon entrapment on CT, with the entrapped tendon completely within the fractured bone. It is unclear if the interposition occurred with the initial trauma or with subsequent external fixation. It is important to recognize this abnormal course so that the tendon can be released prior to internal fixation. Failure to recognize this abnormality would likely lead to tendon tear or functional impairment.

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