12.2 Lower Limb & Pelvic Girdle Positioning (Foot, Ankle, Leg, Knee, Femur, Pelvis, Hip)

12.2 Lower Limb & Pelvic Girdle Positioning (Foot, Ankle, Leg, Knee, Femur, Pelvis, Hip)

Foot & Calcaneus Positioning

Radiographic examination of the lower extremity begins distally at the foot and heel. The foot comprises fourteen phalanges, five metatarsals, and seven tarsal bones (calcaneus, talus, navicular, cuboid, and three cuneiforms).

Foot Projections

1. AP (Plantodorsal) Projection

   • Patient & Part Position: Supine or seated on the table with the knee flexed and the plantar surface of the foot placed flat on the IR.
   • Central Ray (CR): Angled 10 degrees posteriorly (toward the heel), centered at the base of the third metatarsal.
   • Rationale for Angle: The longitudinal arch of the foot tilts the tarsometatarsal joints; a 10-degree posterior angle directs the central ray perpendicular to these joint spaces, preventing anatomical foreshortening.

2. AP Oblique Projection

   • Positioning: From the flat plantar position, rotate the foot and lower leg 30 to 40 degrees medially.
   • Diagnostic Feature: Opens the spaces around the lateral tarsals, demonstrating the cuboid, sinus tarsi, third cuneiform, and 3rd through 5th tarsometatarsal joint spaces free of superimposition.

3. Lateral Foot Projection

   • Positioning: Rotate the patient onto the affected side in a mediolateral position until the foot is in a true lateral orientation (plantar surface perpendicular to IR). Dorsiflex the foot 90 degrees to the leg.
   • Diagnostic Feature: Demonstrates the calcaneus, talus, and tarsal interspaces in profile, along with metatarsal base overlap.

Calcaneus (Heel) Projections

1. Axial Plantodorsal Projection
   • Positioning: Patient supine or seated with leg extended. Dorsiflex the foot using a strap or band so the plantar surface is perpendicular to the IR.
   • Central Ray (CR): Angled 40 degrees cephalad (toward the head/knee), entering the plantar surface at the base of the 5th metatarsal.
   • Diagnostic Feature: Demonstrates the entire calcaneus, calcaneotalar (subtalar) joint, and sustentaculum tali without foreshortening.
2. Lateral Calcaneus: Patient on affected side, calcaneus centered to IR, CR perpendicular to 2.5 cm inferior to medial malleolus.

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Ankle & Lower Leg (Tibia-Fibula) Positioning

Ankle Projections & Joint Geometry

1. AP Ankle

   • Patient supine, leg extended, foot dorsiflexed to 90 degrees.
   • CR perpendicular to mid-way between malleoli.
   • Anatomy: Medial talomalleolar joint space open; lateral joint space superimposed due to overlapping fibula.

2. AP Mortise Oblique (15° to 20° Medial Oblique)

   • Positioning: Supine, leg extended. Rotate the entire leg and foot medially 15 to 20 degrees until the intermalleolar line (an imaginary line connecting the tip of the lateral malleolus and medial malleolus) is parallel to the IR.
   • Diagnostic Criterion: The entire ankle mortise joint space (medial, superior, and lateral talar joint spaces) is open and visualized without superimposition of the lateral malleolus over the talus.

3. AP 45° Medial Oblique Ankle

   • Leg rotated 45 degrees medially. Demonstrates the distal tibiofibular joint space open.

4. Lateral Ankle

   • Patient on affected side, lateral malleolus resting on IR, dorsiflex foot 90 degrees.
   • Fibula superimposed over the posterior half of the tibia; tibiotalar joint open.

Lower Leg / Tibia-Fibula (AP & Lateral)

• AP Tibia-Fibula: Patient supine, leg extended, foot dorsiflexed. Include both ankle and knee joints (minimum 3-5 cm beyond joint lines).
• Lateral Tibia-Fibula: Patient turned on affected side, knee flexed 45 degrees. Both joint spaces must be included.

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Knee & Axial Patellar Projections

Standard Knee Views

• AP Knee: Patient supine, leg extended. Measure distance from anterior superior iliac spine (ASIS) to tabletop to determine CR angle:
  • $< 19\ ext{ cm}$ (thin pelvis): CR angled 3-5 degrees caudad.
  • $19 - 24\ ext{ cm}$ (average pelvis): CR perpendicular (0 degrees).
  • $> 24\ ext{ cm}$ (large pelvis): CR angled 3-5 degrees cephalad.
  • CR enters 1.25 cm inferior to patellar apex.
• Lateral Knee: Patient on affected side, knee flexed 20 to 30 degrees. CR angled 5 to 7 degrees cephalad to align the larger medial femoral condyle over the lateral condyle, preventing joint space closure.

Specialized Intercondylar Fossa & Patellar Views

1. Intercondylar Fossa / Tunnel Views (Camp-Coventry & Holmblad Methods)
   • Camp-Coventry Method: Patient prone, knee flexed 40 or 50 degrees. CR angled 40 or 50 degrees caudad (perpendicular to lower leg), exiting the popliteal fossa.
   • Holmblad Method: Patient kneeling on table ("all-fours"), leaning forward so femur forms a 60-70 degree angle with table. CR perpendicular to IR.
   • Diagnostic Feature: Projects the intercondylar fossa (tunnel) free of patellar superimposition, evaluating joint mice (loose bodies) and osteochondritis dissecans.
2. Settegast Method ("Sunrise" / Axial Patella)
   • Positioning: Patient prone or supine, knee flexed 90 degrees.
   • Central Ray: Angled 15 to 20 degrees cephalad (tangential to patellofemoral joint space).
   • Diagnostic Feature: Demonstrates patellofemoral joint space, patellar subluxation, and vertical patellar fracture lines.

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Pelvis & Hip Positioning (Routine & Trauma)

AP Pelvis

• Patient Position: Patient supine, arms across chest.
• CR: Perpendicular to IR, centered midway between ASIS and symphysis pubis (approx. 5 cm inferior to ASIS).
• Critical Leg Positioning: Rotate lower limbs and feet 15 to 20 degrees medially.
• Anatomical Rationale: Natural femoral neck orientation exhibits anteversion (pointing anteriorly). Medial rotation turns the femoral necks parallel to the image receptor, fully elongating the necks and placing the greater trochanters in profile laterally, while hiding the lesser trochanters behind the femoral shafts.

Hip Projections (AP, Frog-Leg, Trauma Lateral)

1. AP Hip
   • Rotate leg 15-20 degrees medially. CR directed to femoral neck (located 6.3 cm distal along a perpendicular line bisecting the midpoint between ASIS and symphysis pubis).
2. Modified Cleaves Method (Frog-Leg Lateral Hip)
   • Patient Position: Abduct affected thigh 40 to 45 degrees laterally from vertical, flexing knee.
   • Diagnostic Feature: Non-trauma view demonstrating lateral profile of femoral head, neck, and trochanteric region.
   • CONTRAINDICATION: Strictly contraindicated in suspected hip fracture or acute dislocation!
3. Danelius-Miller Method (Axiolateral Cross-Table Trauma Lateral Hip)
   • Clinical Indication: Mandatory lateral projection for trauma patients with suspected femoral neck fracture.
   • Patient Position: Supine on table. Flex and elevate uninjured leg high on a support structure out of the primary beam.
   • Equipment Orientation: Place IR vertically against the lateral aspect of the affected hip/flank.
   • Central Ray: Horizontal CR angled perpendicular to the long axis of the femoral neck (entering groin region).
   • Diagnostic Feature: Demonstrates acetabulum, femoral head, neck, and trochanters in lateral profile without manipulating or adducting/abducting the injured limb.

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Lower Extremity Positioning Summary Guide