Lower Extremities
Ankle
Anatomy
Students should be able to identify the following structures on radiographic images:
Metatarsals, Tarsals, Calcaneous (os calcis), Talus, Cuboid, Navicular, 1st cuneiform, 2nd cuneiform, 3rd cuneiform, Metatarsophalangeal joints, Tarsometatarsal joints, Tibia, Fibula, lateral malleolus, medial malleolus, mortise, anterior tubercle
Routine Projections (ARRT Required)
AP Ankle
CR Location & Positioning
- SID: 40″
- Patient position: Supine, leg fully extended
- Adjustments: Foot dorsiflexed so plantar surface is vertical; no rotation (intermalleolar line not parallel to IR here)
- CR: Perpendicular, midway between malleoli
- Pt. Instructions: Hold still
- Exposure: 60–70 kVp
Evaluation Criteria
- Coverage: Distal 1/3 of tibia and fibula, talus, and proximal metatarsals
- Rotation checks: Medial mortise closed, lateral mortise partially open; tibiofibular joint partially superimposed
- Motion checks: Sharp trabecular pattern, cortical margins distinct
- Technique checks: Soft tissue and joint space visible, no artifacts
- Clinical aim: Baseline view for fractures, alignment, and joint space narrowing
AP Mortise Ankle
CR Location & Positioning
- SID: 40″
- Patient position: Supine, leg fully extended
- Adjustments: Internally rotate entire leg 15–20° so intermalleolar line is parallel to IR
- CR: Perpendicular, midway between malleoli
- Pt. Instructions: Hold still
- Exposure: 60–70 kVp
Evaluation Criteria
- Coverage: Distal tibia/fibula, talus, proximal metatarsals
- Rotation checks: All 3 sides of mortise joint (medial, lateral, superior) open without overlap
- Motion checks: Sharp trabecular markings
- Technique checks: Even exposure of distal tibia/fibula and talus
- Clinical aim: Best projection for ankle joint evaluation (fractures, dislocations, arthritis)
AP Oblique (45° Medial) Ankle
CR Location & Positioning
- SID: 40″
- Patient position: Supine, leg extended
- Adjustments: Internally rotate entire leg and foot 45°
- CR: Perpendicular, midway between malleoli
- Pt. Instructions: Hold still
- Exposure: 60–70 kVp
Evaluation Criteria
- Coverage: Distal tibia/fibula, talus, calcaneus
- Rotation checks: Distal tibiofibular joint open, lateral mortise open; medial mortise closed
- Motion checks: Sharp trabecular margins, no blurring
- Technique checks: Proper contrast to show tibiofibular articulation
- Clinical aim: Detect distal tibiofibular joint injury, high ankle sprain
Lateral (Mediolateral) Ankle
CR Location & Positioning
- SID: 40″
- Patient position: Supine, turned toward affected side
- Adjustments: Knee flexed, lateral aspect of ankle against IR, dorsiflex foot
- CR: Perpendicular, directed to medial malleolus
- Pt. Instructions: Hold still
- Exposure: 60–70 kVp
Evaluation Criteria
- Coverage: Distal tibia/fibula, talus, calcaneus, base of 5th metatarsal
- Rotation checks: Distal fibula superimposed over posterior half of tibia; tibiotalar joint open
- Motion checks: Sharp trabecular markings, posterior borders of tibia/fibula distinct
- Technique checks: Adequate density, soft tissue visible
- Clinical aim: Fractures/dislocations, ankle alignment, calcaneus and talus in profile.
Supplemental Projections
Weight-Bearing AP Ankle
CR Location & Positioning
- SID: 40 inches
- Patient position: Erect, standing on IR with weight evenly distributed between both feet.
- Adjustments: Feet positioned parallel and centered to IR; ensure full dorsiflexion if possible.
- CR: Perpendicular to midway between malleoli.
- Pt. Instructions: Remain still, normal breathing.
- Exposure: 60–70 kVp
Evaluation Criteria
- Coverage: Distal tibia/fibula, talus, and ankle mortise.
- Rotation checks: Medial and lateral mortise joints appear open and symmetric.
- Motion checks: Sharp trabecular markings, no motion blur.
- Technique checks: Adequate penetration through ankle mortise; uniform brightness.
- Clinical aim: Demonstrates alignment and joint-space narrowing under physiologic load; evaluates ankle instability or post-traumatic arthritic change.
Weight-Bearing Lateral Ankle
CR Location & Positioning
- SID: 40 inches
- Patient position: Erect, standing on IR with affected ankle centered.
- Adjustments: Opposite foot placed slightly behind; weight evenly distributed.
- CR: Horizontal beam, perpendicular to medial malleolus.
- Pt. Instructions: Hold still, normal breathing.
- Exposure: 60–70 kVp
Evaluation Criteria
- Coverage: Distal tibia/fibula, talus, calcaneus, and joint space.
- Rotation checks: Distal fibula superimposed over posterior tibia; talar domes aligned.
- Motion checks: Sharp cortical and trabecular detail.
- Technique checks: Adequate exposure to visualize joint-space narrowing and subtalar articulation.
- Clinical aim: Demonstrates mortise alignment and subtalar relationship under full weight bearing; used for instability, arthrosis, and alignment evaluation.
Hows & Whys of Ankle Radiography
Anatomy
- What bones form the ankle mortise?
The tibia, fibula, and talus. - What type of joint is the ankle mortise?
A diarthrodial hinge joint. - What type of joint is the distal tibiofibular articulation?
An amphiarthrodial (slightly movable) joint.
Positioning
- Why is dorsiflexion of the foot required in ankle imaging?
To prevent the calcaneus from overlapping the lateral malleolus and to open the joint space. - Which projection places the intermalleolar line parallel to the image?
Mortise - Why is a 15–20° medial rotation used for the mortise projection instead of 45°?
Because this rotation aligns the intermalleolar line parallel to the IR, opening the mortise uniformly. - Why is the 45° oblique performed in addition to the mortise?
It demonstrates the distal tibiofibular joint open, helpful in diagnosing syndesmotic injuries or “high ankle sprains.” - Why is the lateral ankle essential?
It provides a profile view of the talus, calcaneus, and distal tibia/fibula relationship.
Technique & Image Evaluation
- How can you tell the foot was dorsiflexed on the oblique and mortise views?
The calcaneus does not superimpose the lateral malleolus. - How much of the lower leg should be included on ankle images?
The distal 1/3 - How do you know an ankle AP was not rotated?
The medial mortise should be closed, lateral mortise partially open, and tibiofibular joint partially superimposed. - How do you know the ankle mortise projection was positioned correctly?
The medial, lateral, and superior mortise joint spaces are all open without overlap. - How can you tell the difference between an AP, Oblique, and Mortise projection?
- AP: Medial mortise open, lateral mortise closed
- Oblique (45° medial): Distal tibiofibular joint open, lateral mortise open
- Mortise (15–20° medial): Entire mortise joint open
- How do you know the lateral ankle was positioned correctly?
The distal fibula is superimposed over the posterior half of the tibia, and the talus sits centered in the ankle mortise. - What error is indicated if the fibula is too anterior on a lateral ankle?
The ankle was under-rotated (not turned lateral enough). - What error is indicated if the fibula is too posterior on a lateral ankle?
The ankle was over-rotated (too much lateral). - How do you confirm exposure was appropriate on ankle imaging?
The cortical outlines and trabecular markings are sharp, soft tissue margins are visible, and no motion blur is present.
Clinical Applications
- Why are both AP Oblique and Mortise projections important for trauma?
Together, they evaluate both the mortise and distal tibiofibular joint spaces, helping to identify subtle fractures and ligamentous injuries. - Why are weight-bearing ankle projections sometimes ordered?
They demonstrate joint space narrowing, alignment abnormalities, or subtle instability that may not appear non-weight-bearing.
