DPM Diagnostic Imaging Interpretation 3 — Questions and Answers
Question 1: On CT imaging, which finding best distinguishes a fibrous from an osseous tarsal coalition?
- Non-ossified bridging tissue with irregularity at the joint margins (Correct answer)
- Complete bony trabecular continuity across the joint
- Subchondral cyst formation only
- Joint effusion without bridging tissue
Correct answer: Non-ossified bridging tissue with irregularity at the joint margins
Fibrous coalitions show irregular, non-corticated joint margins without complete bony fusion, whereas osseous coalitions demonstrate trabecular continuity.
Question 2: Which nuclear medicine study is most sensitive for detecting early diabetic foot osteomyelitis before radiographic changes appear?
- Technetium-99m MDP three-phase bone scan
- Gallium-67 scan alone
- Indium-111 labeled WBC scan alone
- FDG-PET/CT (Correct answer)
Correct answer: FDG-PET/CT
FDG-PET/CT offers superior spatial resolution and sensitivity for early osteomyelitis compared to conventional nuclear studies, though labeled WBC scan is also highly specific.
Question 3: The 'lover's heel' or 'policeman's heel' radiographic sign describes a large inferior calcaneal spur; this spur arises from which structure?
- Origin of the intrinsic foot muscles, not the plantar fascia itself (Correct answer)
- Insertion of the Achilles tendon
- Peroneus brevis attachment
- Spring ligament origin
Correct answer: Origin of the intrinsic foot muscles, not the plantar fascia itself
The inferior calcaneal spur arises from the origin of the flexor digitorum brevis and intrinsic muscles at the medial calcaneal tubercle, not directly from plantar fascia.
Question 4: On MRI, Morton's neuroma (interdigital neuroma) appears most characteristically as:
- Low T1, low T2 signal mass in the intermetatarsal space with dumbbell shape (Correct answer)
- High T1 signal mass consistent with lipoma
- Fluid-filled cyst with high T2 signal
- Calcified lesion with signal void on all sequences
Correct answer: Low T1, low T2 signal mass in the intermetatarsal space with dumbbell shape
Morton's neuroma shows low to intermediate T1 and low T2 signal due to fibrous tissue, with a characteristic dumbbell or teardrop shape between metatarsal heads.
Question 5: On a standard AP ankle radiograph, talar tilt measurement evaluates the integrity of which ligamentous complex?
- Lateral collateral ligament complex (ATFL and CFL) (Correct answer)
- Deltoid ligament complex
- Syndesmotic ligaments
- Spring ligament complex
Correct answer: Lateral collateral ligament complex (ATFL and CFL)
Talar tilt under varus stress assesses the lateral collateral ligaments, particularly the ATFL and CFL; greater than 10° tilt indicates instability.
Question 6: Which radiographic view best demonstrates os trigonum and posterior talar process pathology?
- Lateral ankle view in plantar flexion (Correct answer)
- Axial calcaneal view
- Mortise ankle view
- Sesamoid view
Correct answer: Lateral ankle view in plantar flexion
A lateral ankle radiograph taken in forced plantar flexion best profiles the posterior talar process and os trigonum.
Question 7: On Doppler ultrasound of the foot, reduced diastolic flow with a high resistive index in the dorsalis pedis artery most suggests:
- Peripheral arterial disease with distal occlusion (Correct answer)
- Normal variant in a young athlete
- Deep vein thrombosis
- Acute plantar fasciitis
Correct answer: Peripheral arterial disease with distal occlusion
A high resistive index with diminished or absent diastolic flow indicates increased peripheral vascular resistance from distal occlusive arterial disease.
DPM Diagnostic Imaging Interpretation 3
On CT imaging, which finding best distinguishes a fibrous from an osseous tarsal coalition?