CT SCANOGRAM

Overview

A CT Scanogram, also known simply as a scanogram or CT length measurement, is a specialized imaging technique performed using computed tomography (CT) to measure the exact length of long bones, most commonly in the lower limbs. Unlike conventional X-rays, a CT scanogram provides highly accurate and reproducible measurements by scanning only specific sections (joints and bone ends) rather than the entire limb. This method is especially useful for evaluating leg length discrepancies, planning orthopedic surgery, assessing limb deformities, and following up after surgical correction procedures. By offering precise and low-radiation measurements, CT scanograms have become a trusted tool in modern orthopedic practice.

Purpose of CT Scanogram

The main objective of a CT scanogram is to obtain accurate measurements of bone lengths and analyze the alignment of limbs. Common clinical indications include:

1. Leg Length Discrepancy

CT scanogram is widely used to measure and document differences in limb length, whether congenital (present from birth) or acquired due to conditions like trauma, infection, or previous surgery.

2. Pre-Operative Planning

Before procedures like limb lengthening, corrective osteotomy, or joint replacement, precise limb measurements help orthopedic surgeons plan the surgery accurately.

3. Post-Operative Assessment

After limb lengthening procedures or fracture fixation, a CT scanogram helps confirm whether the intended correction has been achieved.

4. Congenital and Developmental Disorders

Conditions like developmental dysplasia of the hip (DDH), Blount’s disease, or hemihypertrophy often require serial limb length measurements to monitor progression.

5. Limb Deformity Evaluation

When a patient presents with angular or rotational deformities, CT scanogram assists in planning correction by accurately measuring bone segments.

Procedure for CT Scanogram

A CT scanogram is simple, non-invasive, and typically takes about 10–15 minutes.

Before the Scan

• Usually, no special preparation is required.
• Inform your doctor if you:
  • Are pregnant or suspect pregnancy.
• You may be asked to remove any metal objects, such as jewelry, that could interfere with imaging.

During the Scan

• You will lie flat on the CT scanner table.
• The technologist positions the limb(s) carefully to ensure straight alignment.
• Unlike a routine CT scan, only three specific sections are scanned:
  • The hip joint
  • The knee joint
  • The ankle joint
• These targeted scans are combined digitally to calculate the full bone length.
• The process is painless, and you may be asked to remain still to ensure precise measurements.

After the Scan

• You can resume normal activities immediately.
• A radiologist interprets the scan, and the report with measurements is typically available within 24–48 hours.

Benefits of CT Scanogram

• High Precision: More accurate than manual measurements or full-length X-rays.
• Low Radiation Exposure: Only specific segments are scanned instead of the entire limb.
• Reproducible Results: Ensures consistency across repeated scans, useful for follow-up.
• Quick Procedure: Shorter scan time compared to traditional radiographic methods.
• Improved Surgical Planning: Helps surgeons plan precise corrections, reducing complications.

Conditions Commonly Evaluated with CT Scanogram

• Congenital leg length discrepancy
• Acquired discrepancies (due to fractures, infections, or surgery)
• Post-traumatic deformities
• Angular deformities of the lower limbs
• Pre- and post-operative assessment for limb lengthening
• Limb length changes in conditions like cerebral palsy or scoliosis

Risks and Considerations

CT scanogram is a safe procedure, but it does involve certain considerations:

Radiation Exposure

• Involves ionizing radiation, but since only specific regions are scanned, the dose is significantly lower than a full CT scan or full-length radiograph.

Pregnancy

• Generally avoided unless medically necessary to protect the developing fetus.

Patient Cooperation

• Staying still during the scan is important to avoid measurement errors.

Conclusion

CT Scanogram is a highly valuable, quick, and reliable method for measuring limb lengths and planning orthopedic treatments. Whether you are undergoing evaluation for leg length discrepancy, limb deformity correction, or surgical planning, this technique ensures precise measurements that directly influence treatment decisions. Its combination of low radiation, speed, and accuracy makes it a preferred choice for both adults and children needing serial monitoring. If your doctor recommends a CT scanogram, it’s to ensure your diagnosis and treatments are based on the most accurate and objective data, supporting better surgical outcomes and quality of life.