|ECR 2019 / C-1829|
|Magnetic resonance imaging in plantar pain|
Findings and procedure details
Anatomy of the foot
Twenty-six bones of the foot the structural support of the foot, separated in the three main sections of the foot: forefoot, midfoot, hindfoot.
The forefoot consists of five metatarsals and fourteen phalanges, the bones of each toe being the proximal phalanx, the middle phalanx and the distal phalanx, except the first finger that has only proximal and distal phalanges.
Between these bones, there is a joint that allows the movement of the foot, and they are the metatarsophalangeal joint, proximal interphalangeal joint, and distal interphalangeal joint.
The midfoot consists of five bones with joint surfaces that articulate each other; these bones are the navicular, cuboid, three cuneiform bones.
The fourth and fifth metatarsals are articulated with the cuboid bone, the first, second and third metatarsals are articulated with the respective cuneiform bones. All are wrapped in a capsule or Lisfranc joint. The talonavicular and calcaneocuboid joints form the Chopart joint.
The Hindfoot, the tibia articulates and the dome of the talus form the Tibiotalar joint, the talus articulates with the calcaneus, and form the subtalar joint; It has three surfaces of articulation with three separate facet joints.
The plantar fascia is an important stabilizer in the foot, originates from the plantar surface of the calcaneus and attaches to the plantar surfaces of the five metatarsal heads and proximal phalanges of the toes. The sole of the foot is made up of four layers of muscles, vessels, and nerves.
The causes of plantar pain can be classified as degenerative, traumatic, joint diseases, and infections.
It is an inflammation that affects the plantar aponeurosis and the perifascial structures. It is characterized by deep chronic pain in the subcalcaneal area and on the medial aspect of the plantar surface of the foot.
The etiology includes repetitive microtrauma, foot deformities, obesity, degenerative changes, and rheumatic diseases.
Patients have heel pain that is exacerbated when walking or after a period of inactivity.
MRI in sagittal and coronal planes is the ideal image method for its evaluation; the findings are thickening of the fascia greater than 4 mm, increased signal intensity intrasubstance, edema of the perifascial soft tissues and bone insertion in the calcaneus.
The enthesophytes originate from the tuberosity of the calcaneus, usually appear by chronic microtrauma, which generates periostitis and calcification.
MRI can show the enthelophytes of the calcaneus associated with anomalies of the plantar aponeurosis.
Rupture of the plantar fascia
The rupture of the plantar fascia may be secondary to the progression of chronic plantar fasciitis or some acute trauma related to sports.
Patients can not elevate the heel and have plantar ecchymosis. Most ruptures are located at the proximal end of the fascia at the level of the calcaneus insertion,
The MRI shows the plantar fascia with disruption, the presence of fluid, soft tissue edema and in some cases lesion of the flexor digitorum muscle.
The fracture of the calcaneus occurs mainly due to trauma. Pain is the most common symptom and is associated with edema and erythema; Sometimes a hematoma that extends distally to the sole of the foot can be formed and is known as "Mondor's sign."
The MRI shows the linear fracture trace of the hypointense behavior in the T1 sequence, with an increase in the signal intensity of the surrounding bone marrow in the T2 and STIR sequences.
Flexor Tendon Tear Distal
Distal rupture of the flexor tendon of the fingers can occur acutely during excessive dorsiflexion of the distal phalanges of the big toe, in an iatrogenic manner or by repetitive microtrauma.
In MRI the characteristic findings are increased synovial sheath fluid in the area of rupture, loss of continuity of the tendon fibers and incomplete ruptures retraction, edema of peritendinous soft tissues.
3) Joint diseases
Charcot neuropathic osteoarthropathy
Neuropathic osteoarthropathy is a frequent complication of diabetes mellitus; It is a progressive disease that affects the bones, joints and soft tissues of the foot.
The acute phase is characterized by edematous and erythematous foot, with hypoesthesia. The vascular flow is normal, and the pulses are palpable.
In the inactive or chronic phase, hyperemia and hyperthermia decrease and deformity occur. Calluses and plant ulcers can form, which can lead to infection, cellulitis, osteomyelitis and finally amputation.
MRI is the most sensitive imaging method to detect the early stages of neuroarthropathy, shows soft tissue edema, joint effusion, edema of the bone marrow, contrast reveals enhancement of bone marrow and periarticular soft tissues. In the chronic phase, bone deformity and fragmentation is observed, joint effusion with mild bone marrow edema and without soft tissue edema.
Gout is caused by the deposition of sodium urate crystals in joints and soft tissues. The first metatarsophalangeal joint is the most affected.
The characteristics by MRI are not very specific, joint effusion with synovial thickening, bone erosions and formation of periarticular gouty tophi; the administration of contrast medium shows periarticular enhancement, especially in patients with acute symptoms. Gout can be confused with rheumatoid arthritis or septic arthritis, so clinical correlation and serum urate level are usually necessary.
Rheumatoid arthritis commonly affects the feet at the level of the metatarsophalangeal joints. It presents with pannus formation that is inflammatory synovial tissue.
In magnetic resonance the intensity of the pannus varies in acute phases usually hyperintense in T2 sequences by vascular proliferation, in chronic stages, it is hypointense and is associated to hemosiderin deposit by a proliferation of fibrous tissue. Joint erosion, thinning of articular cartilage, the presence of subchondral cysts, bone edema, and joint effusion are also observed.
4) Non-neoplastic soft tissue lesions and neoplasms
Morton's neuromas are not true neoplasms, but interdigital perineural fibrosis and nerve degeneration; therefore the term fibroid of Morton is more exact.
It occurs between the heads of the metatarsals, commonly in the third interdigital space between the third and fourth fingers.
It is more common in middle-aged people, with a higher prevalence in women, probably related to the use of high-heeled shoes. The most accepted etiology is as a result of the compression of the interdigital nerve against the intermetatarsal ligament.
The pain of the metatarsal head radiating to the fingers is the most classic symptom.
In the magnetic resonance, it has dumbbell morphology, its isointense behavior about the muscle in the images weighted in T1, isointense or hypointense about the fat in the images weighted in T2; the contrast allows to delimit the lesion by having variable enhancement.
Plantar fibromatosis is a benign superficial fibroblastic proliferation, but locally aggressive that is located in the plantar fascia.
Clinically it presents as one or several palpable nodules on the sole of the foot. These nodules generate pain, contracture and inability to wander.
In the MRI it is presented as a poorly defined nodule in the deep aponeurosis, shows low to an intermediate intensity of the signal in T1 and T2 sequences, in some occasions, it can have hyperintense behavior in T2 due to a low amount of fibrous tissue. Contrast administration reveals variable enhancement that extends along the plantar aponeurosis.
Epidermoid cysts are produced by the proliferation of keratin-producing epidermal cells. Appearance in the extremities is rare, being more common in the plantar region.
In MRI it is observed as a well defined cystic lesion, isointense to the muscle in T1 sequence, hyperintense in T2, with the administration of contrast they have annular enhancement of the wall.
They are rare in this location. Among the most common neoplasms are the tumors of the nervous sheath, the imaging characteristics are nonspecific, generally of hypointense or isointense behavior in T1 and T2 sequences, hyperintense in STIR and with variable enhancement with the administration of contrast medium.
Lipomas are also common and have isointense signal behavior about fat with all sequences.
The complications of diabetic foot are diverse in the white tissue, joints, muscles, tendons and blood vessels.
White tissue infection and osteomyelitis are quite common in the diabetic foot, timely diagnosis is essential, improves quality of life and avoids complications such as amputation.
In general, the infectious processes of the diabetic foot are spread directly by a skin ulcer.
In MRI ulcers are seen as an alteration in the continuity of the skin and soft tissue defects.
Acute ulcers may have a high intensity in T2 sequences, with a peripheral enhancement, due to the presence of granulation tissues.
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