Ultrasound of the Foot: Morton's Neuroma and Plantar Fasciitis — Technique, Criteria, and Differential Diagnosis
Examination Technique
When suspecting plantar fasciitis, the patient is placed in a prone position with slight knee flexion and dorsiflexion of the ankle, with the foot resting on the toes on the couch. The plantar fascia is assessed primarily in the longitudinal, as well as in the transverse plane at the anteromedial edge of the calcaneus (medial tubercle). For the dorsal part of the foot, the patient lies on their back with the knee bent and the sole on the couch.
In clinical suspicion of Morton's neuroma, pressure with the probe can be applied to reproduce the patient's symptoms. Manual medial and lateral compression of the forefoot during plantar transverse scanning (Mulder's maneuver) often displaces the neuroma in the plantar direction, accompanied by a palpable click and improves visualization.
Criteria and Measurements
Plantar Fasciitis
The diagnosis is based on the thickening of the plantar fascia at the anteromedial edge of the calcaneus. According to the source, mild thickening around 4.7 mm corresponds to mild fasciitis, and pronounced thickening around 6.7 mm indicates severe fasciitis. Exact threshold values for normal [to be clarified].
| Degree | Fascia Thickness |
|---|---|
| Mild Fasciitis | ~4.7 mm |
| Severe Fasciitis | ~6.7 mm |
Morton's Neuroma
The ultrasound appearance of Morton's neuroma should be distinguished from other interdigital soft tissue formations. Dynamic examination of the forefoot using the sonographic Mulder's sign correlates with MRI and surgical data. Numerical criteria for neuroma size in fragments are not provided [to be clarified].
Differential Diagnosis
The key point is to correctly identify the neuroma and distinguish it from the intermetatarsal bursa. The intermetatarsal bursa is located on the dorsal surface of the interdigital nerve and, unlike the neuroma, usually flattens upon compression. Other indications and differential diagnoses include plantar fibroma, ganglia, osteoarthritis, gout, ligament injury, plantar fascia rupture, plantar plate injury, and stress fracture.
Treatment Interventions Under Ultrasound Guidance
For Morton's neuroma, an injection of steroid and local anesthetic (e.g., 40 mg of methylprednisolone and 5 ml of 0.5% bupivacaine) is performed via a plantar longitudinal approach with a 23-G needle; if unresponsive, a steroid with alcohol/radiofrequency ablation is used. For forefoot bursitis, a steroid injection is performed via a plantar approach. For plantar fasciitis, PRP injection after dry needling with a 21-G needle is described.
Frequently asked questions
How to differentiate Morton's neuroma from the intermetatarsal bursa?
The bursa is located on the dorsal surface of the interdigital nerve and usually flattens upon compression, whereas the neuroma shifts plantarly with a palpable click upon compression (Mulder's maneuver).
Which maneuver improves the visualization of Morton's neuroma?
Mulder's maneuver — manual medial and lateral compression of the forefoot during plantar transverse scanning relative to the metatarsal bones.
What fascia thickness values correspond to degrees of fasciitis?
According to the source, ~4.7 mm corresponds to mild, and ~6.7 mm to severe plantar fasciitis at the anteromedial edge of the calcaneus.
In which plane is the plantar fascia assessed?
Primarily in the longitudinal, as well as in the transverse plane; the patient is in a prone position with dorsiflexion of the ankle.
What medications are used for injection in Morton's neuroma?
Steroid and local anesthetic (e.g., 40 mg of methylprednisolone and 5 ml of 0.5% bupivacaine) via a plantar longitudinal approach with a 23-G needle; if ineffective, a steroid with alcohol or radiofrequency ablation.