RADIOGRAPHIC ANATOMY AND NORMAL PARAMETERS
|
In this epigraph, we review the most common radiographic projections used to image the foot and ankle. Other complementary projections are infrequently used nowadays and have often been replaced with CT and MRI as the next step.
Anteroposterior projection of the ankle
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850220?maxheight=300&maxwidth=300)
Fig. 1: Evaluate the tibiotalar joint and the medial mortise (lateral mortise obscured due to superimposition of distal fibula and talus). Johnson angle is the angle between axis of tibia and tibial plafond.
Lateral projection of the ankle
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850221?maxheight=300&maxwidth=300)
Fig. 2: Evaluate the tibiotalar, subtalar, calcaneocuboid, and talonavicular joints. The pre-Achilles fat pad appears as a triangular radiolucency delimited posteriorly by the anterior surface of the tendon, and inferiorly by the calcaneal tuberosity. A tendon tear, ankle and calcaneal fractures may obscure this fat pad.
Calcaneal projection and Böhler angle
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850222?maxheight=300&maxwidth=300)
Fig. 3: The Böhler’s angle is the angle formed by: 1) A line from the highest point of the posterior margin of the calcaneus to the highest point of the posterior calcaneal tuberosity; and 2) A line connecting the posterior superior facet with the upper margin of the anterior process. The normal range is 20º-40º. Calcaneal fractures with talus impaction disrupt the subtalar joint and distort this anatomical angle to less than 20º.
Dorsoplantar projection of the foot
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850242?maxheight=300&maxwidth=300)
Fig. 4: Evaluate the metatarsophalangeal and interphalangeal joints. Review the alineation between the medial cortex of the 2nd metatarsal and the medial cortex of the middle cuneiform (best view to identify Lisfranc’s injury). The first intermetatarsal angle or metatarsus primus adductus angle (1) is the angle between the longitudinal axes of the 1st and 2nd metatarsal bones. The hallux valgus or hallux abductus angle (2) is formed by the longitudinal axis of the 1st proximal phalanx and the longitudinal axis of the 1st metatarsus.
Lateral projection of the foot
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850262?maxheight=300&maxwidth=300)
Fig. 5: Evaluate the ankle, subtalar, calcaneocuboid, and talonavicular joints. Examine the foot articulation angle (1) and the angle between the tangent to the lower edge of the calcaneus and the tangent to the lower edge of the 5th metatarsal (2). The plane of support (blue) is the line connecting the most inferior point of the tuberosity of the calcaneus with the most inferior point of the 5th metatarsal head. The calcaneal inclination angle (3) is the angle between the plane of support and the calcaneal inclination axis (it is decreased in pes planus and increased in rearfoot cavus).
Medial oblique projection of the foot
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850225?maxheight=300&maxwidth=300)
Fig. 6: Evaluate the 3rd-5th metatarsal bones (they appear without superimposition), navicular, cuboid, talar head, tarsal sinus, and transverse talar joint.
ANATOMIC VARIANTS AND ACCESORY OSSICLES
|
Many sesamoid bones and accessory ossification centers may be present in the foot, and can be mistaken with fractures.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850275?maxheight=300&maxwidth=300)
Fig. 7: Accesory ossicles of the foot. 1. os trigonum. 2. os peroneum. 3. os vesalianum. 4. os supratalare. 5. accessory navicular bone. 6. os supratalare. 7. cuboideum secundarium. 8. os intermetatarseum.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850226?maxheight=300&maxwidth=300)
Fig. 8: The accessory navicular bone is the most common accessory ossicle in the foot. It is positioned medial and dorsal to the navicular bone. The posterior tibial tendon inserts on this ossicle in the majority of cases. Three types of accessory navicular have been described (figure).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850227?maxheight=300&maxwidth=300)
Fig. 9: The os trigonum is a commonly found accessory ossicle located near the lateral tubercle of the posterior process of the talus.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850229?maxheight=300&maxwidth=300)
Fig. 10: The os intermetatarseum is located between the bases of the two first metatarsal bones. It can be confused with calcification of the intermetatarsal artery.
There are other anatomical variants, such as the presence of sesamoid bones or developmental abnormalities, some of which may simulate pathologic conditions.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850228?maxheight=300&maxwidth=300)
Fig. 11: The sesamoid of the 1st metatarsal is bipartite in one-third of cases. This may not be confused with a fracture (trauma in the sesamoids may result in subtle fractures, avascular necrosis, or stress reaction).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850230?maxheight=300&maxwidth=300)
Fig. 12: Synostosis is the osseous union of two adjacent bones. Synostosis of the metatarsals is extremely rare. Most of the cases are congenital between the base of the 4th and 5th metatarsal (figure), and less commonly between the 1st and 2nd metatarsals.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850231?maxheight=300&maxwidth=300)
Fig. 13: Polydactyly is the presence of supernumerary digits on the hands or feet.
STRUCTURAL AND DEVELOPMENTAL DISORDERS |
This section includes the study of tarsal coalitions, plantar arch abnormalities, congenital talipes equinovarus and hallux valgus.
Tarsal coalition
Developmental fusion between two or more bones in the midfoot and hindfoot. The majority are talocalcaneal or calcaneonavicular. Cases can be associated with peroneal spastic flatfoot, vague foot pain, limited subtalar movement, and pes planus.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850232?maxheight=300&maxwidth=300)
Fig. 14: The C-sign is a classic radiologic finding of a talocalcaneal (subtalar) coalition in the foot lateral view, which consist in a C-shaped line formed by the medial outline of the talar dome and the inferior outline of the sustentaculum tali, created by the overlap of the talus and the fused facets. The image shows a talocalcaneal coalition with the C-sign (curved line), confirmed in Computed Tomography (arrowheads point the abnormal joint).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/850315?maxheight=300&maxwidth=300)
Fig. 15: The anteater nose sign relates to an anterior tubular elongation of the anterior calcaneal process (arrows), which approaches or overlaps the navicular bone. It is indicative of calcaneonavicular coalition.
Plantar arch abnormalities
Pes Planus (flatfoot) exists when the calcaneus does not maintain its usual degree of dorsiflexion (calcaneal-5th metatarsal angle higher than 170º). It can be flexible or rigid.
Pes cavus is an augmented longitudinal arch of the foot (calcaneal-5th metatarsal angle lesser than 150º).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852082?maxheight=300&maxwidth=300)
Fig. 16: Pes Planus (calcaneal-5th metatarsal angle higher than 170º).
Congenital talipes equinovarus (clubfoot)
Clubfoot is a none-reducible deformity composed of:
- Hindfoot equinus (fixed plantar flexion of the calcaneus).
- Hindfoot varus (decreased talocalcaneal angle).
- Forefoot adductus (medial deviation of the metatarsal).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852083?maxheight=300&maxwidth=300)
Fig. 17: Clubfoot with hindfoot equinus (yellow), hindfoot varus (blue) and forefoot adductus (red).
Hallux Valgus
Lateral angulation of the great toe in relation to the first metatarsal (typically acquired, although precise etiology is uncertain). The metatarsophalangeal angle measures more than 15º for moderate disease and more than 40º for severe.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852084?maxheight=300&maxwidth=300)
Fig. 18: In hallux valgus, the metatarsophalangeal angle measures more than 15º (22º in this patient).
Rheumatoid arthritis
Inflammatory arthropathy with symmetric appendicular distribution. The foot (specially MTP joints) is affected in 90% of patients. The rheumatoid factor is usually positive.
The main radiology findings are joint effusions, soft tissue swelling, juxta-articular osteopenia, marginal osseous erosions, symmetric joint space reduction, and subluxations.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852112?maxheight=300&maxwidth=300)
Fig. 19: Two cases of advanced rheumatoid arthritis with malalignment and subluxations (rectangles). Notice the erosive changes of multiple joints (arrows), most pronounced at the first MTP joint (with hallux valgus deformity), the joint space narrowing and the juxtaarticular osteopenia (arrowheads).
Juvenile idiopathic arthritis
This category includes different conditions classified based on the number and type of joints involved, symptoms, and appearance of specific antibodies. The ankles and feet are involved in 90% of patients. Radiographic features may include soft tissue swelling, osteopenia, periostitis, growth delay, joint space narrowing, erosions, and ankylosis.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852113?maxheight=300&maxwidth=300)
Fig. 20: Two radiographs of the same patient (20 years), showing juxtaarticular osteopenia (blue), joint space narrowing, erosions (green), periosteal new bone formation (red) and ankylosis (yellow).
Psoriatic arthritis
Radiographic findings are asymmetric involvement of hands and feet, normal bone density, bone proliferation, involvement of DIP joints, distal phalangeal erosion, and joint space widening. The skin changes commonly precede the articular abnormalities. The distribution differs from rheumatoid arthritis (distal in psoriatic arthritis).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852159?maxheight=300&maxwidth=300)
Fig. 21: Two patients with psoriatic arthritis. The images show significant involvement of DIP joints, distal phalangeal erosions (arrows), and bone proliferation (arrowheads).
Metabolic arthritides
- Gouty arthritis.
- Calcium Pyrophosphate Dihydrate Deposition Disease.
- Hydroxyapatite Deposition Disease.
- Hemochromatosis.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852160?maxheight=300&maxwidth=300)
Fig. 22: Gouty arthritis is the most frequent crystal-induced arthropathy, with predilection for the lower extremities. Typical radiologic findings are erosions (arrows) and tophi (circle). The erosions are well-defined punched-out litic lesions (rat bite erosion). Tophi is a deposit of urate crystals which manifests as a soft-tissue swelling and can eventually erode the underlying bone with overhanging edges and well-defined sclerotic borders.
Connective tissue disease arthropathy
Many connective tissue pathologies can cause articular disorders, including scleroderma, systemic lupus erythematosus, dermatomyositis, and mixed connective tissue diseases, among others.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852161?maxheight=300&maxwidth=300)
Fig. 23: The radiograph of this female patient showed a markedly asymmetric acro-osteolysis, periarticular osteoporosis, erosions, and severe destruction and resorption of the MTP joints (rectangle). The patient was diagnosed with scleroderma.
Charcot neuropathic osteoarthropathy
Progressive destructive joint abnormality in patients with a loss of deep sensation and proprioception, resulting in repetitive injury, malalignment, erosions of articular surfaces, subchondral sclerosis, fractures, fragmentation, and joint disorganization. Diabetes is the most habitual cause. There are two patterns of this disease: atrophic and hypertrophic.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852162?maxheight=300&maxwidth=300)
Fig. 24: Loss of ankle mortice congruence and disorganization, osteophytes, subchondral sclerosis, multiple bone fragments, and erosion around the joint space. Destruction of calcaneum and resorption of proximal tarsal bones with soft tissue swelling. Findings in relation to neuropathic osteoarthropathy.
Osteomyelitis
Inflammation and infections involving bone. In the foot, trauma is the most common mechanism. The first radiographic findings are the soft tissue changes (often subtle). Later, it may appear regional osteopenia, periostitis, lytic areas, or loss of trabecular architecture.
In some cases, the infection does not lead to necrosis but instead causes sclerotic changes (Garré’s sclerosing osteomyelitis).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852206?maxheight=300&maxwidth=300)
Fig. 25: Diabetic patient with a soft-tissue infection. Radiographs showed lytic areas and destruction of the 4th-5th distal and middle phalanxes (circles), congruent with an extension of the infection to bone (osteomyelitis).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/852207?maxheight=300&maxwidth=300)
Fig. 26: 22-year-old patient with a history of stabbing trauma near the second finger. The radiograph showed sclerotic changes in the second proximal phalanx (rectangle). MRI demonstrated bone edema (arrowheads) and mild associated synovitis (arrow). These findings suggest Garré’s sclerosing osteomyelitis.
TUMORS AND TUMOR-LIKE LESIONS |
Bone and soft-tissue tumors are classified according to the tissue of origin. Bone tumors of the ankle and foot are uncommon, accounting for around 3% of all primary bone tumors.
Conventional radiographs are the initial study of choice, being a reliable predictor of the histological nature of the tumor.
Benign Bone Tumors
Osteoid osteoma:
- Very common.
- Talar neck and subtalar region of calcaneus.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854019?maxheight=300&maxwidth=300)
Fig. 27: An oblique radiograph showed a well-circumscribed lucent region and adjacent sclerosis (circle). Subsequent CT demonstrated a lucent nidus with surrounding sclerotic reactive bone and a central sclerotic dot (arrows).
Osteoblastoma:
- Uncommon. Predilection for foot and ankle.
- Talar neck.
Chondroblastoma:
- Uncommon.
- Epiphyseal or subarticular location (talus and calcaneus).
- Translucent, with well-defined (often-sclerotic) margins.
- Mineralization is uncommon. Septation is common.
Enchondroma:
- Common, but less in the foot and ankle than the digits of the hand.
- Well-defined, expansile, lytic.
- May contain punctate or stippled calcifications.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854020?maxheight=300&maxwidth=300)
Fig. 28: A lateral radiograph showed a well defined lytic lesion with sclerotic borders (arrows), associating chondroid calcifications (arrowheads). It did not cause bone destruction or periosteal reaction.
Osteochondroma:
- Very common.
- Metatarsals.
Subungual exostosis:
- First toe the most frequent.
- Lack of marrow continuity and cartilage cap (not true osteochondromas).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854022?maxheight=300&maxwidth=300)
Fig. 29: Exostosis at the medial and dorsal aspect of the distal first phalanx (arrows).
Simple bone cyst:
- Anterior third of calcaneus.
- Well-defined lytic lesion often with a sclerotic rim.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854023?maxheight=300&maxwidth=300)
Fig. 30: A lateral radiograph showed a well defined geographic lucent lesion with a narrow zone of transition in the anterior aspect of the calcaneus (arrowheads). CT demonstrated a unicameral bone cyst.
Intraosseous lipoma:
- Anterior third of calcaneus.
- Often incidental finding.
- Well defined, radiolucent lesion with a thin sclerotic rim.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854024?maxheight=300&maxwidth=300)
Fig. 31: A lateral radiograph showed a well defined geographic lucent lesion with a narrow zone of transition in the anterior aspect of the calcaneus (arrows). CT demonstrated an intraosseous lipoma.
Malignant Bone Tumors
Osteosarcoma:
- Uncommon.
- Intraosseous and osteoblastic.
- Metastatic disease is common.
- Aggressive moth-eaten or permeative pattern of bone destruction and usually soft-tissue extension.
Chondrosarcoma:
- Majority involve the distal tibia and fibula (in the foot, calcaneus, talus, and metatarsals).
- Centrally located with a geographic pattern of bone destruction.
- Endosteal erosion, cortical destruction, and expansion.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854025?maxheight=300&maxwidth=300)
Fig. 32: Radiographs showed a lytic lesion in the distal tibia (circle), with intralesional chondroid calcifications (ring and arcs pattern), and periosteal reaction (arrowheads). Notice also the associated pathologic fracture (arrow). MRI and biopsy supported the diagnosis of chondrosarcoma.
Metastases:
- Rare. Primary tumors are mostly colon adenocarcinoma, kidneys, lung, bladder, and breast.
- The majority are purely osteolytic (prostatic are usually sclerotic, and breast, bladder, and gastrointestinal primaries may be lytic, sclerotic or mixed).
- Cortical destruction is invariably present.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854026?maxheight=300&maxwidth=300)
Fig. 33: Radiographs showed a lytic lesion that occupied the epiphysis and the distal diaphysis of the first metatarsal, associating poorly defined borders and destruction of the cortex. The extension study demonstrated a primary kidney tumor (arrows).
Soft Tissue Tumors
Soft-tissue lesions are only seen if they display mass effect, bone or joint involvement, or mineralization.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854027?maxheight=300&maxwidth=300)
Fig. 34: The radiograph showed a partially calcified nodule in the soft tissues adjacent to the base of the 5th metatarsal (circles). The MRI findings and evolution were consistent with the diagnosis of pilomatrixoma.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/854028?maxheight=300&maxwidth=300)
Fig. 35: The radiograph showed a soft tissue swelling ahead of the ankle joint (arrow), without affecting the underlying bone. MRI showed the presence of a well defined mass in that location, hypointense in T1 and T2-weighted images, and with marked enhancement after the administration of contrast (arrowhead), compatible with pigmented villonodular synovitis.
TRAUMA AND OVERUSE SYNDROMES |
There are multiple publications about the classic ankle and foot fractures, as well as their classifications. Reviewing this topic is not one of the objectives of this educational poster.
Instead, we review some specific entities that can be diagnosed in radiography and may be easily overlooked by less experienced professionals.
Stress fractures
Fractures that occur after repetitive stress on a normal bone. Most of them involve the lower extremity (more than 80% affect the tibia, fibula, metatarsals, and calcaneus).
Radiographs are usually normal in the acute phase. Later, the findings can include: loss of cortical density, increasing sclerosis or periosteal reaction.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/860453?maxheight=300&maxwidth=300)
Fig. 36: Stress fractures of metatarsals (arrowheads point periosteal reaction), fibula (arrows point loss of cortical density and periosteal reaction), and tibia (void arrows point linear sclerosis).
Osteochondritis dissecans
Fragmentation and possible separation of an osteochondral portion of the articular surface. Osteochondritis dissecans (OCD) commonly involves the talar cartilage (medial or lateral corner). The most accepted theory is that OCD is caused by a single or multiple traumatic events, leading to detachment of the fragments. OCD of the ankle is often associated with a ligamentous injury.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/860454?maxheight=300&maxwidth=300)
Fig. 37: Radiographic classification of osteochondral lesions of the talus (I: a small area of subchondral compression, II: partial fragment detachment, III: complete fragment detachment but not displaced, IV: displaced fragment). We show three cases of osteochondritis dissecans (arrowheads).
Müller-Weiss syndrome
The idiopathic osteonecrosis of the navicular bone in adults (in children it is named Köhler disease).
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/860455?maxheight=300&maxwidth=300)
Fig. 38: The oblique and AP radiographs of the same patient depicted deformity and sclerosis of the navicular, which adopted the classic “comma-shaped deformity” due to the collapse of the lateral part of the bone. The findings were confirmed in Computed Tomography (arrowhead).
Sudeck's arthropathy (Complex Regional Pain Syndrome)
This syndrome usually follows trauma (whose severity does not correlate with the severity of the symptoms). The principal imaging finding is the patchy or aggressive appearance of osteopenia (involving medullary and cortical bone) and soft tissue swelling, not associated with bone erosion nor joint space narrowing.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/860456?maxheight=300&maxwidth=300)
Fig. 39: Patient with aggressive osteopenia (circle) following trauma (ankle fracture), without bone erosion or joint space narrowing, compatible with complex regional pain syndrome.
Soft tissue injuries
Careful observation of the soft tissue structures on the lateral radiographs can assist in detecting subtle soft tissue injuries.
Ankle effusion is demonstrated as a teardrop-shaped mass anterior (more frequent) or posterior to the tibiotalar joint.
Hemorrhage in the pre-Achilles (Kager) fat pad can occur with Achilles tendon injury, showing distortion of this fat pad. This finding can also be seen in the ankle and calcaneal fractures. Tendon thickening and calcaneal changes may also suggest Achilles tendinopathy or tears.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/860457?maxheight=300&maxwidth=300)
Fig. 40: Teardrop-shaped “masses” anterior and posterior to the tibiotalar joint (arrows), compatible with articular effusion.
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/860458?maxheight=300&maxwidth=300)
Fig. 41: Distortion of the Kager (pre-Achilles) fat pad (circle), in a patient with acute tendon rupture.
ADVANCED IMAGING MODALITIES |
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/865551?maxheight=300&maxwidth=300)
Fig. 42
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/865552?maxheight=300&maxwidth=300)
Fig. 43
![](https://epos.myesr.org/posterimage/esr/ecr2020/154105/media/865553?maxheight=300&maxwidth=300)
Fig. 44