When “Ankle Sprain” Isn’t a Sprain: A Hidden Extensor Digitorum Longus Tear
- Carlos Jimenez
- Oct 14
- 2 min read
A 25-year-old soccer player presented two days after an ankle inversion and plantarflexion injury during play. He described tripping over an opponent’s foot and twisting his ankle, leading to sharp lateral ankle pain and swelling.
Initial X-ray was normal no fractures, only soft-tissue swelling. But high-resolution musculoskeletal ultrasound revealed something unexpected.
Ultrasound Findings
Using a 6–22 MHz linear probe, long- and short-axis scans with dynamic maneuvers were performed.
Ligaments (ATFL, CFL): Intact
Peroneal, tibialis anterior, and extensor hallucis longus tendons: Normal
Extensor digitorum longus (EDL):
Focal tear of the epimysium (fascia) near the lateral malleolus
~6 mm fascial gap with muscle herniation into subcutaneous tissue at rest
Dynamic dorsiflexion reduced the herniation confirming a true myofascial hernia
Partial fiber tears and small hematomas around the myotendinous junction
Subtle cortical irregularity (small fracture) of the lateral malleolus not seen on X-ray
MRI done later confirmed partial muscle tear but failed to demonstrate the fascial defect or herniation, reinforcing ultrasound’s diagnostic advantage. Normal EDL Appearance (Long Axis)
The extensor digitorum longus (EDL) shows a smooth, continuous fibrillar pattern from muscle to tendon.
The echogenic fascial line (epimysium) is intact and uninterrupted over the lateral malleolus (LM).
The tendon fibers remain linear and compact without bulging or focal discontinuity.
Serves as the baseline reference to highlight the fascial defect and herniation seen on the injured side
Abnormal Long-Axis (LAX) View
Demonstrates a discontinuity in the echogenic fascial line (epimysium) of the extensor digitorum longus (EDL) over the lateral malleolus (LM).
There’s a focal bulge of muscle fibers protruding through the fascial gap labeled “hernia.”
The fascial defect and superficial muscle herniation are clearly visible at rest, confirming a myofascial rupture.
Abnormal Short-Axis (SAX) View
Confirms a ~6 mm fascial defect (measured between dotted calipers) with subcutaneous muscle herniation.
Fibula and tibia landmarks show the anatomical context — the lesion sits just anterior to the lateral malleolus.
Dynamic testing (dorsiflexion) reduces the herniation, verifying that the finding is true herniation, not a static mass.
Mechanism & Discussion
Most lateral ankle sprains injure the ATFL or CFL, but this case shows a rare isolated injury of the EDL
a dorsiflexor and evertor of the ankle.
During forceful plantarflexion-inversion, the EDL contracts eccentrically against resistance, producing:
A fascial rupture (epimysial tear) → herniation
A partial muscle tear near the myotendinous junction
Muscle hernias are often missed clinically and under-detected on MRI because they can reduce with position or probe pressure.
High-resolution ultrasound enables real-time visualization of these dynamic changes.
Clinical Insights
Not all “ankle sprains” are ligament injuries check the dorsiflexors and evertors.
Dynamic ultrasound is key: muscle herniation often disappears during contraction.
MRI may miss small fascial defects ultrasound remains the first-line tool for acute soft-tissue ankle injuries.
Early diagnosis prevents chronic pain or misdirected rehab and allows safe return to play.
Citation
Bordoloi Deka J, Deka N, Shah M, Bortolotto C, Draghi F, Jimenez F. Isolated partial tear of extensor digitorum longus tendon with overlying muscle herniation in acute ankle sports injury: role of high-resolution musculoskeletal ultrasound. Journal of Ultrasound. 2022;25:369–377.
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