|Plantar fascia origin scan plane||Normal plantar fascia origin on the calcaneum. Tension enthesopaphytes are common here. Follow the fibres anteriorly through the arch.|
|Anterior forefoot||Assess the extensor tendons dynamically for pathology. Check the underlying joints (with minimal probe pressure) for effusions.|
|Plantar plate scan plane||The plantar plate is seen arising from the base of the proximal phalanx on the plantar aspect. You should gently extend the toe to visualise fully.|
|Forefoot scan plane|
ROLE OF ULTRASOUND
Ultrasound is used for the soft tissue structures of the foot.
Ultrasound is a valuable diagnostic tool in assessing the following indications;
The thick skin on the sole of the foot will require higher gain and/or power settings. You my need to use a lower frequency probe, particularly at the hind foot.
Use of a high resolution probe (7-15MHZ) is essential when assessing the superficial structures of the foot. Careful scanning technique to avoid anisotropy (and possible misdiagnosis). Beam steering or compounding can help to overcome anisotropy in linear structures such as tendons. Good colour / power / Doppler capabilities when assessing vessels or vascularity of a structure. Be prepared to change frequency output of probe (or probes) to adequately assess both superficial and deeper structures.
For example images, click here to goto the Foot pathology page.
Patient prone on bed, foot flexed with toes on the bed for support. Place the probe over the midline of the heel on the plantar aspect. The toe of the probe towards the heel. The plantar fascia will be seen as a fibrillar structure inserting onto the calcaneum (See pic). It should be flat and homogenous.
The patient will generally present with on or more palpable thickenings in the arch of their foot. Follow the plantar fascia into the arch and look for fusiform, nodular thickenings. They may be subtle and more numerous than can be palpated.
Begin by scanning each metatarso-phalangeal joint for effusions, synovial thickenings or ganglia. Assess the extensor then flexor aspects.
Morton’s neuroma V's Bursa:
Scan in transverse across the plantar aspect of the metatarsal heads.
Utilise the 'Mulder’s technique' to elicit a click and visualise any correlating pathology. This involves gripping across the anterior forefoot whilst scanning the plantar aspect. Use a knuckle of your gripping hand to simultaneously apply pressure between the metatarsal heads as you squeeze across the foot.
A Morton's neuroma will be seen as a non compressible, hypoechoic rounded mass at the metatarsal head interspace. Similarly, a thickened intermetatarsal bursa will be a hypoechoic area between the metatarsal heads but will be compressible and avascular. It will be seen to bulge out the plantar aspect and correspond to the Mulder's click.
Scan in longitudinal over the plantar aspect of the metatarso-phalageal joints. The plantar plate is readily seen as a homogeneous elongated wedge arising from the base of the proximal phalanx extending under the head of the metatarsal
View with the toes slightly extended
Check for tears, calcification and heterogeneity (suggesting degeneration)
Ensure you approach the proposed site of the foreign body from different angles. Some materials will be poorly reflective and almost invisible unless the beam is perpendicular to them. There will usually be a surrounding hypoechoic halo representing an inflammatory reaction
identify the plane of tissue it is in, how close it is to the entry wound and to any blood vessels. It may be helpful to mark the location and orientation of the foreign body on the skin to guide removal.
Hard copy imaging should reflect the anatomy investigated.