🩻 TOACS FCPS Station · Scanogram for Leg Length Discrepancy
📷 Scanogram – Leg Length Discrepancy
🔍 Key imaging features:
- ✓ Three separate exposures – hips, knees, ankles
- ✓ Long cassette with radiopaque ruler – accurate measurement
- ✓ Anatomical leg length – from femoral head to talar dome
- ✓ Quantifies discrepancy – guides treatment decision
- ✓ Lower radiation than CT – but less information on 3D anatomy
📋 Clinical scenario (examiner prompt)
A 12‑year‑old boy is brought to the orthopedic clinic with a limp and complaint of right leg feeling shorter than the left. His mother noticed the limp over the past year. On examination, there is a pelvic tilt on standing; a block test reveals a 3 cm discrepancy. The child has no history of trauma or infection. A scanogram (see image) is ordered to quantify the anatomical leg length and assess growth potential. Bone age is 12 years.
🧑⚕️ Examiner tasks · TOACS
1. Identify the purpose of the imaging study (scanogram for leg length discrepancy).
2. Describe the scanogram technique (three exposures, long cassette, ruler).
3. Explain the clinical significance (quantifies LLD, guides treatment: shoe lift, epiphysiodesis, lengthening).
4. Discuss management based on findings (predict LLD at maturity, epiphysiodesis if 2-5 cm, lengthening if >5 cm).
🎯 Expected answers (for examiners)
- • Imaging study: Scanogram (orthoroentgenogram) for leg length discrepancy
- • Technique: Three separate exposures of hips, knees, and ankles on a long cassette with a radiopaque ruler; measures anatomical leg length from femoral head to talar dome
- • Indications: Symptomatic LLD (>2 cm), limp, pelvic tilt, scoliosis; planning for epiphysiodesis or lengthening
- • Interpretation: The current LLD is measured. Bone age (left wrist) is used to predict remaining growth. Growth remaining: distal femur ~9 mm/yr, proximal tibia ~6 mm/yr.
- • Treatment: <2 cm: observe or shoe lift; 2-5 cm with growth remaining: epiphysiodesis; >5 cm: lengthening; >18-20 cm with foot deficiency: amputation
- • Alternative imaging: EOS (lowest radiation, 3D, but not all centers have it); CT scanogram (higher radiation); plain radiographs (less accurate)
• Purpose: Accurate measurement of anatomical leg length
• Technique: 3 exposures (hips, knees, ankles) on long cassette + ruler
• Advantage: More accurate than clinical measurement
• Disadvantage: Radiation exposure (higher than clinical, lower than CT)
• Alternative: EOS (lowest radiation, biplanar)
• Treatment: Guided by predicted LLD at skeletal maturity
⚡ Quick FCPS‑style MCQ
A 12-year-old with a limp and a block test positive for 3 cm LLD. A scanogram confirms 3 cm anatomical discrepancy. Bone age is 12 years. The most appropriate management is:
A. Observation only B. Shoe lift C. Epiphysiodesis of distal femur and proximal tibia D. Limb lengthening📌 Topic summary · Scanogram for Leg Length Discrepancy
3-exposure LLD measurement
Hips, knees, ankles + ruler
Symptomatic LLD >2 cm
Observation or shoe lift
Epiphysiodesis
Lengthening
| Feature | Scanogram (Orthoroentgenogram) |
|---|---|
| Definition | Radiographic measurement of anatomical leg length using three separate exposures |
| Technique | Hips, knees, and ankles imaged on a long cassette with a radiopaque ruler; single exposure per joint |
| Measurement | Distance from femoral head to talar dome (or medial malleolus) |
| Indications | Leg length discrepancy causing symptoms (limp, pelvic tilt, low back pain); preoperative planning |
| Advantages | Accurate, reproducible, lower radiation than CT |
| Disadvantages | Radiation exposure; does not provide 3D anatomy |
| Alternative | EOS (lowest radiation, biplanar, 3D); CT scanogram (higher radiation) |
| Treatment based on predicted LLD | <2 cm: observe/shoe lift; 2-5 cm: epiphysiodesis; >5 cm: lengthening; >18-20 cm: amputation |