There are many causes of forefoot pain, many of which are well diagnosed with both ultrasound and MRI. Frequently a combination of diagnoses may co-exist. Accurate diagnosis assists the clinician in determining the most helpful treatment options.
Plantar plate disruption (images 1 -4)
The metatarsophalangeal joint plantar plates are major stabilisers and form part of the plantar capsule. The plantar plates provide strength and support during ambulation . Disruption can lead to toe deformities. The normal plantar plate is a slightly hyperechoic broad-curved band which protects the metatarsal head and inserts onto the proximal phalanx. Plantar plate tears typically appear as hypoechoic defects. The torn plantar plate is often swollen and hypervascular in the acute phase of degeneration.
Morton's Neuroma/ intermetatarsal bursitis (images 5 & 6)
A Morton's neuroma is caused by mechanical damage to the interdigital nerve, resulting in perineural fibrosis. On ultrasound it commonly appears as an ovoid hypoechoic mass, although the shape and echogenicity may vary . Intermetatarsal bursitis appears as a hypoechoic or anechoic zone in a normally echogenic webspace, generally dorsal to the interdigital nerve, although sometimes enveloping it. This soft tissue collection may become complex and heterogeneous with time. Dynamic assessment of a webspace will show poor compressibility of a neuroma and high compressability of a bursitis (note: complex bursa may mimic a neuroma). Treatment options include ultrasound guided cortisone or alcohol injection (image 6).
Adventitial bursitis is acquired bursitis in the metatarsal fat pad as a result of trauma . Sonographically these areas may either be ill-defined or focal collections. These are generally compressable and hypoechoic, although complex collections may appear heterogeneous.
Joint effusions are compressable anechoic collections best seen on the dorsal aspect of metatarsophalangeal joints. Synovial proliferation appears on ultrasound as a thickening of the synovial layer. Hypervascularity and bone erosions may also be present .
- Gregg JM, Schneider T, Marks P. MR imaging and ultrasound of metatarsalgia--the lesser metatarsals. Radiol Clin North Am 46(6):1061-78, 2008
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