Lower Limb Positioning: Foot Anatomy

The foot has 26 bones in total: 14 phalanges, 5 metatarsals, and 7 tarsals.

The 14 phalanges are divided so that toe 1 has 2 phalanges and toes 2–5 have 3 each.

Digits and metatarsals are numbered 1–5, starting on the medial side of the foot.

1. Head; 2. Body (shaft); 3. Base

1. Calcaneus; 2. Talus; 3. Cuboid; 4. Navicular; 5. Medial (1st) cuneiform; 6. Intermediate (2nd) cuneiform; 7. Lateral (3rd) cuneiform

The calcaneus is the largest and strongest tarsal.

The talus is the second largest tarsal and the only tarsal in the ankle joint.

Navicular

Medial (1st) cuneiform

Intermediate (2nd) cuneiform

Cuboid

The calcaneal tuberosity is at the posterior-inferior heel and is a common site of bone spurs.

The lateral ridge of the calcaneus is the trochlear process, also called the peroneal trochlea.

Sustentaculum tali

The subtalar joint, formed by the calcaneus and talus, is also called the talocalcaneal joint.

Sinus tarsi

False. The proximal portion (base or tuberosity) of the 5th metatarsal is the common fracture site.

MTP joints are at the heads of the metatarsals, whereas TMT joints are at the bases of the metatarsals.

The sesamoid bones of the foot lie on the plantar surface at the head of the 1st metatarsal (1st MTP joint).

The patella is the largest sesamoid bone in the body.

The ankle joint is formed by the tibia, fibula, and talus.

Tibial plafond

Mortise

The lateral malleolus (fibula) sits about 1 cm more posterior and more distal than the medial malleolus (tibia).

The intermalleolar plane is 15°–20° from the coronal plane.

The anterior tubercle is on the distal anterior-lateral tibia.

The tibia is the weight-bearing bone of the lower leg.

The intercondylar eminence of the tibia is also called the tibial spine, and it has medial and lateral intercondylar tubercles.

The tibial plateau (articular facets) slopes 10°–20° posteriorly.

False. The fibula is not part of the knee joint.

The intercondylar fossa (notch) is a deep depression on the posterior distal femur.

The patellar surface of the distal femur, on its anterior side, is also called the intercondylar sulcus or trochlear groove.

The adductor tubercle is on the medial condyle of the femur.

The base of the patella is superior and its apex is inferior.

The cruciate ligaments (anterior cruciate ligament, ACL, and posterior cruciate ligament, PCL) stabilize the knee front-to-back.

The collateral ligaments (medial, MCL, and lateral, LCL) prevent side-to-side movement of the knee.

The menisci are shock absorbers between the femur and tibia.

The infrapatellar fat pad protects the front of the knee.

The two joints of the knee are the femorotibial joint and the patellofemoral joint.

Hinge

Modified condyloid (ellipsoidal)

Gliding (plane)

Saddle (sellar)

Bicondylar

Saddle

Syndesmosis (fibrous)

The minimum source-to-image-receptor distance (SID) for lower limb radiography is 40″ (100 cm).

The kVp range for the lower limb is 50–85, and for the knee it is 65–80.

A grid is used for lower limb parts measuring over 4″.

False. A grid is not required for foot and ankle radiography.

No. Gonadal shielding is still used.

For digital lower limb imaging, center the anatomy to the image receptor (IR) and use four-sided collimation.

For a pediatric patient, immobilize instead of holding the child, and lower the exposure.

Clothing creates artifacts on digital images.

For AP toes, the central ray (CR) is angled 10°–15° toward the calcaneus.

The MTP joint of the toe in question

The shafts of the phalanges are equally concave.

For oblique toes, rotate 30°–45° with the CR perpendicular to the MTP joint.

For oblique toes, toes 1–3 are rotated medially and toes 4–5 are rotated laterally.

Toes 1–3 are imaged lateromedial, whereas toes 4–5 are imaged mediolateral.

For a lateral toe, the CR is centered to the IP joint of toe 1 or the PIP joint of toes 2–5.

For tangential sesamoids, the patient is positioned prone with the foot dorsiflexed.

For tangential sesamoids, the foot is dorsiflexed so the plantar surface is 15°–20° from vertical.

Perpendicular to the IR, tangential to the posterior 1st MTP joint

False. The supine alternative for tangential sesamoids gives more OID and a less sharp image.

The AP foot is also called dorsoplantar (DP), and the PA foot is plantodorsal (PD).

For an AP foot, the CR is angled 10° posterior (toward the heel), perpendicular to the metatarsals.

The base of the 3rd metatarsal

High arch: 15°; low arch: 5°

Near-equal distance between the 2nd–5th metatarsals; 1st–2nd cuneiform joint open

For the AP oblique foot, rotate the foot medially 30°–40° with the CR perpendicular to the IR.

The AP oblique foot with medial rotation is the best projection for the cuboid and most tarsal bones.

False. The lateral oblique foot (30°) best shows the navicular and the 1st–2nd cuneiforms.

AP oblique foot with medial rotation (30°–40°), CR perpendicular at the base of the 3rd metatarsal

For a lateral foot, the knee is flexed about 45° and the foot is dorsiflexed.

Mediolateral

Tibiotalar joint open; distal fibula superimposed by the posterior tibia; metatarsal heads superimposed; 5th metatarsal tuberosity in profile

Weight-bearing foot studies evaluate the longitudinal arches under full body weight.

The weight-bearing AP and lateral foot is the best study for a possible Lisfranc injury.

For the weight-bearing AP foot, the CR is angled 15° posterior to the midpoint between the feet at the base of the metatarsals.

Horizontal, to the base of the 3rd metatarsal

For the plantodorsal (axial) calcaneus, the CR is angled 40° cephalad to the base of the 3rd metatarsal.

If the foot is not perpendicular to the IR on the axial calcaneus, increase the CR angle (30° → 40° fixes foreshortening).

On the axial calcaneus, the sustentaculum tali shows medially.

Plantodorsal (axial) calcaneus: CR 40° cephalad to the base of the 3rd metatarsal

For the lateral calcaneus, the CR is perpendicular, 1″ (2.5 cm) inferior to the medial malleolus.

The lateral malleolus

On a true AP ankle, the lateral mortise should look closed.

If the lateral mortise is open on a true AP ankle, suspect ligament rupture.

For an AP ankle, the CR is perpendicular and centered midway between the malleoli.

For the AP mortise, rotate the leg and foot 15°–20° medially until the intermalleolar line is parallel to the IR.

AP mortise (15°–20° medial rotation)

For the AP mortise, the foot stays plantar flexed, which shows the base of the 5th metatarsal.

On a correct AP mortise, the space around the talus is an even 3–4 mm.

Lateral joint space not open; lateral malleolus over the talus; talus distorted (looks like an AP)

AP mortise: leg and foot rotated 15°–20° medially, foot plantar flexed

For the 45° oblique ankle, rotate the leg and foot 45° medially.

So the calcaneus does not overlap the lateral malleolus

Lateral malleolus; base of the 5th metatarsal

The AP mortise rotates 15°–20° medially with the foot plantar flexed to open the mortise, whereas the 45° oblique rotates 45° medially with the foot dorsiflexed to open the distal tibiofibular joint.

45° oblique ankle: leg and foot rotated 45° medially, foot dorsiflexed

On a lateral ankle, the distal fibula should lie over the posterior half of the tibia.

False. Superimposed malleoli on a lateral ankle make a partial oblique, not a true lateral.

The routine lateral ankle projection is mediolateral, and lateromedial is the alternative.

The base of the 5th metatarsal

False. AP stress views of the ankle show ligament tear or rupture (joint separation).

Inversion; eversion

A physician or other health professional (or weights or straps); lead gloves and apron

For the AP knee, rotate the leg internally 3°–5° so the interepicondylar line is parallel to the IR.

½″ (1.25 cm) distal to the apex of the patella

Under 19 cm: 5° caudad; 19–24 cm: 0°; over 24 cm: 5° cephalad

On a correct AP knee, about half of the fibular head is superimposed by the tibia.

For the AP oblique knee, the whole leg is rotated 45°, with the CR 0° on an average patient.

False. If only one knee oblique is routine, it is usually the medial oblique.

“Medial” and “lateral” oblique name the direction the front of the knee rotates.

In the medial (internal) oblique, the proximal tibiofibular joint is open and the lateral condyles are in profile, whereas in the lateral (external) oblique, the proximal fibula is superimposed by the tibia and the medial condyles are in profile.

For the lateral knee, the patient is in lateral recumbent with the knee flexed 20°–30°.

For the lateral knee, the CR is angled 5°–7° cephalad to superimpose the distal femoral condyles.

A lateral knee needs a cephalad CR because the medial femoral condyle sits lower.

For the lateral knee, the CR is centered 1″ (2.5 cm) distal to the medial epicondyle.

Over-rotation gives less fibular head overlap, whereas under-rotation gives more.

Posterior condyles superimposed; patella in profile; patellofemoral joint open

If the knee cannot flex for a lateral knee, use a horizontal beam.

For the AP weight-bearing bilateral knees, the CR is centered ½″ (1.25 cm) below the apex of the patellae.

For the AP weight-bearing knees, the CR is perpendicular for an average patient, or 5°–10° caudad on a thin patient.

The femorotibial joint spaces (cartilage degeneration), with both knees for comparison

The Rosenberg method is a PA axial weight-bearing projection of the knees.

In the Rosenberg method, the knees are flexed 45° with the patellae against the upright bucky.

False. In the Rosenberg method, the CR is angled 10° caudad, parallel to the tibial facets.

The joint spaces and the intercondylar fossa

Rosenberg method (PA axial weight-bearing): knees flexed 45°, CR 10° caudad

For the Camp-Coventry method, the patient is prone with the knee flexed 40°–50°.

In the Camp-Coventry method, the CR is perpendicular to the lower leg, which is 40°–50° caudad, matching the flexion.

Intercondylar fossa; condyles; tibial plateaus; intercondylar eminence

Camp-Coventry method (PA axial, prone): knee flexed 40°–50°, CR perpendicular to the lower leg

In the Holmblad method, leaning forward 20°–30° gives 60°–70° of knee flexion.

In the Holmblad method, the CR is perpendicular to the IR and lower leg, centered to the mid-popliteal crease.

Straddle a lowered table; rest the affected knee on a stool or chair

Holmblad method: kneeling on all fours, IR under the knee, CR perpendicular to the lower leg

The Béclère method is an AP axial projection for patients who cannot lie prone.

In the Béclère method, the knee is flexed 40°–45° and the CR is perpendicular to the lower leg.

CR angle distorts; OID increased; gonadal exposure rises

Béclère method (AP axial): supine, knee flexed 40°–45°, IR against the posterior thigh and leg

Less OID; less magnification; less distortion

The PA patella is used to check for fracture before flexing the knee.

The mid-patella

More flexion can separate fracture fragments.

The lateral patella is used with the PA projection to evaluate patellar fractures.

For the bilateral Merchant method, the CR is angled 30° caudad from horizontal, midway between the patellae.

For the bilateral Merchant method, the knees are flexed 40° over the table end on a leg support.

The bilateral Merchant method uses an SID of 48–72″ to reduce magnification.

Patellofemoral joint spaces open; patellae and intercondylar sulcus symmetric

Bilateral Merchant method: supine, knees flexed 40°, CR 30° caudad

For the inferosuperior axial (tangential) patella, the CR is 10°–15° from the lower legs, tangential to the patellofemoral joint.

No special equipment; comfortable; quadriceps relaxed

The IR is hard to hold or support if the patient cannot cooperate fully.

Inferosuperior axial (tangential) patella: supine, knees flexed 40°–45°, IR on the thighs

For the Hughston method, the patient is prone and the knee is flexed 50°–60°.

For the Hughston method, the CR is 45° cephalad, tangential to the patellofemoral joint.

Hughston method: prone, knee flexed 50°–60°, CR 45° cephalad

For the Settegast method, the CR is 15°–20° from the lower leg, tangential to the patellofemoral joint.

False. The Settegast method uses knee flexion of 90° or more.

Acute flexion tightens the quadriceps and draws the patella into the intercondylar sulcus.

Before acute flexion for the Settegast or Hobbs method, patellar fracture must be ruled out.

Settegast method: prone, knee flexed 90° or more, CR 15°–20° from the lower leg

Hughston is prone with 50°–60° flexion and a CR of 45° cephalad, whereas Settegast is prone with 90° or more flexion and a CR 15°–20° from the lower leg.

Hobbs modification (superoinferior)

The Hobbs modification uses an SID of 48–50″ to reduce magnification from the increased OID.

Hobbs modification: seated superoinferior, IR under the knees on a step stool, CR perpendicular to the IR

Lisfranc injury (sprain to fracture-dislocation)

Osgood–Schlatter disease

Chondromalacia patellae (“runner’s knee”)

Osteogenic sarcoma is a highly malignant primary bone tumor seen from childhood to young adult.

Osteomalacia is bone softening from lack of mineralization, and it is called rickets in children.

False. Osteomalacia is called rickets in children.

Gout is caused by uric acid deposits in joints, mostly in men.

The common first site of gout is the 1st MTP joint.

Lateral rotation of the lower limb

Increase the CR to 45° caudad (match the flexion).

Hobbs modification (seated superoinferior)