43-year-old patient with longstanding left medial malleolar pain. The region is highly sensitive to pressure and friction, with a reported VAS pain score of 8. Symptoms may have developed or persisted in relation to altered or compensatory gait due to longer-standing knee symptoms on the same side.
Ultrasound examination included the medial malleolus, tarsal tunnel structures including the tibialis posterior, flexor digitorum longus, flexor hallucis longus and flexor retinaculum, all components of the deltoid ligament, the talocrural joint, extensor tendons including tibialis anterior, extensor hallucis longus and extensor digitorum, the extensor retinaculum, and possible local bursae.
Ultrasound examination of the left medial malleolar region shows no local fluid collection, bursitis, ganglion-like lesion, hematoma, or evident soft tissue mass.
There is focal thickening of fibrous tissue at the attachment and crossing region where structures of the flexor retinaculum, possibly superficial extensor retinacular fibers, and components of the deltoid ligament converge around the medial malleolus.
Dynamic ultrasound assessment suggests that ankle movement provokes the patient’s symptoms. The imaging pattern and dynamic pain response suggest local mechanical irritation caused by friction and traction forces at this fibrous attachment complex.
No clear deltoid ligament rupture is identified. The tarsal tunnel tendons and other scanned superficial soft tissue structures do not show a specific structural abnormality based on the provided findings.
The diagnostic certainty is limited because this is an unusual presentation and the ultrasound findings are not fully specific. In the setting of high pain intensity and longstanding symptoms, pathology outside the direct diagnostic range of ultrasound should also be considered, including bone marrow edema or stress reaction of the medial malleolus.
1. Final diagnosis
Atypical ultrasound appearance with focal thickening and irritation of fibrous tissue at the left medial malleolus, most consistent with mechanical irritation of a retinacular/deltoid attachment complex. There are no ultrasound signs of bursitis, local fluid collection, soft tissue mass, or clear ligament rupture.
2. Differential diagnosis
The most likely differential consideration is local enthesopathic or friction-related irritation of the fibrous attachment complex around the medial malleolus. Other considerations include irritation of superficial retinacular fibers, mild deltoid ligament enthesopathy, local irritation or compression of small cutaneous nerve branches, and mechanical overload secondary to altered gait. Bursitis, ganglion, hematoma, and clear ligament rupture are less likely based on the ultrasound appearance. If severe pain persists, osseous pathology such as bone marrow edema or stress reaction of the medial malleolus should be considered.
3. Teaching points
The medial malleolar region contains several closely related ligamentous, retinacular, tendinous, and neurovascular structures. Focal pain in this area may arise from subtle friction or traction at fibrous attachment zones, even when no fluid collection or discrete mass is visible. Dynamic ultrasound can help correlate symptoms with movement, but nonspecific fibrous thickening should be interpreted cautiously, especially in atypical presentations with high pain intensity.
4. Injury/disease information
Mechanical irritation around the medial malleolus may occur when local pressure, footwear friction, altered ankle mechanics, or compensatory gait increases traction and compression at retinacular or ligamentous attachment sites. Chronic irritation may lead to focal fibrous thickening and marked tenderness. Because ultrasound is strongest for superficial soft tissue assessment and limited for bone marrow, cartilage, and deep intra-articular pathology, MRI can be considered when symptoms are severe, persistent, or disproportionate to ultrasound findings.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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