Ultrasound of the Foot

Some sonographers do only the plantar fascia in sagittal scan , trv scan,  and they look for Morton neuroma. Some add the dorsal and the plantar side of the foot , and they focus on the pain area,. Some do each toes- dip ,pip and mt level., looking for effusion, bursa, ganglion cysts of the flexor tendons or extensor tendons, cysts rising from the joints, and other pathologies. Some include the talonavicular joint area for effusion. and the anterior ankle recess . some add the insertion part of the Achilles looking of spur and retro calc bursa. I do all that in 30 minutes spot depending on the patient situation.

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;

• Muscular, tendinous and ligamentous damage (chronic and acute)

• Plantar plates
• Bursitis
• Soft tissue masses such as ganglia, lipomas Morton’s neuromas
• Plantar fascia
• Joint effusions

• Vascular pathology
• Haematomas
• Classification of a mass eg solid, cystic, mixed
• Post surgical complications eg abscess, edema
• Guidance of injection, aspiration or biopsy
• Some bony pathology.

Plantar fascia origin scan plane ; do the upper , middle and lower fascia in sagittal and transverse section. look for cysts, tears, lumps and thickness, hyperemia. and calcification.

Normal plantar fascia origin on the calcaneum. Tension enthesopaphytes are common here. Follow the fibers anteriorly through the arch.

Anterior forefoot; do each toe , dip,pip and mt level.look for effusion, cysts and hyperemia.

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 visualize fully. 

                                             Do transverse section .

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 (7-15 MHZ) 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.

Plantar fascia complex cyst.

For the Plantar Fascia:

Ask the patient to lay  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 . It should be flat and homogeneous.

MID FOOT

Plantar Fibromatosis:
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.

FOREFOOT

Begin by scanning each metatarso-phalangeal joint for effusions, synovial thickenings or ganglia. Assess the extensor and flexor aspects.

Morton’s neuroma V’s Bursa:

Scan in transverse across the plantar aspect of the metatarsal heads.

Utilize the ‘Mulder’s technique’ to elicit a click and visualize 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 inter space. Similarly, a thickened inter metatarsal bursa will be a hypoechoic area between the metatarsal heads but will be compressible and a vascular. It will be seen to bulge out the plantar aspect and correspond to the Mulder’s click. almost always close to an arterial vessel. 

Plantar plates:

Scan in longitudinal over the plantar aspect of the metatarso-phalangeal 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)

plantar fascia tear.

Foreign body

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

plantar fascia thickness possible linear tears.

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.

( Morton Neuroma usually 2nd, 3rd, and 4th).

Joint Abnormalities

• Joint effusions:
• Gout: Abnormal uric acid metabolism resulting in joint inflammation. May see tophaceous gout as a complex echogenic mass (tophus) in the soft

Osteoarthritis: Bony irregularity at the bone ends with joint effusion. When acute the joint will be hyperaemic

• Rheumatoid arthritis: Thickened synovium with a complex ‘thick’ joint effusion, pannus & associated boney irregularity.

Tendon abnormalities

• Check for tendon thickening (compare with other side)
• Fluid in the tendon sheath
• Integrity of the tendon- any tear?
• does the tendon slide freely when mobilized?

• Document the normal anatomy. Any pathology found in 2 planes, including measurements and any vascularity.

Thank you for reading, Keep your us file updated make copies\

Make sure to clean the propes and wear cloves as feet  us sometimes deals with warts and these are contagious , they have the mark of blood dot and skin ulceration, nodule under the pain point and it look like FB inside but with no RING DOWN ARTIFCAT .

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Steve Ramsey, PhD.  MSc Medical Ultrasound.  Calgary, Alberta – Canada