Glossary
CT scan of the knee
Quick answer
A knee CT scan uses X-rays and a computer to build detailed cross-sectional and 3D images of bone. It is used for complex fractures, planning revision ACL surgery, measuring kneecap alignment and checking implants, rather than for ligaments or the meniscus, explains Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.
What to expect
You lie on a table that moves through a ring-shaped scanner. The scan itself takes only a few minutes and is quiet compared with MRI, and the ring is open, so claustrophobia is rarely a problem. You need to keep still. A CT uses more radiation than a plain X-ray, so it is ordered only when the extra detail will change the plan. Contrast is not usually needed for the knee.
What it tells the surgeon
- Fractures: CT shows how many pieces there are and how much the joint surface has sunk in a tibial plateau or kneecap fracture, which guides surgery.
- Revision ACL: it measures the position and widening of old bone tunnels, which may need bone grafting before a new reconstruction.
- Kneecap instability: it measures the TT-TG distance and rotation, helping decide whether a tibial tubercle osteotomy is needed.
- Knee replacement: it can assess component rotation and loosening when a replaced knee is painful.
CT or MRI?
MRI is better for soft tissues such as ligaments, meniscus and cartilage, and uses no radiation. CT is better for fine bone detail and is less affected by metal. Sometimes both are needed.
Frequently asked questions
Why did my surgeon order a CT instead of an MRI?
Because the question is about bone: the shape of a fracture, old tunnels or the alignment of the kneecap. CT answers these more clearly.
Is the radiation from a knee CT dangerous?
The knee is far from radiation-sensitive organs and the dose is modest, but it is higher than an X-ray. That is why CT is used only when it will change treatment.
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