CT Arthrogram — Post Intra-Articular Contrast
The injected joint with a margin sufficient to include the capsule and any labral or ligamentous structure in question.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Suspected labral tear of the shoulder or hip when MRI is contraindicated (non-conditional implanted device) or not tolerated.
- Assessment of the articular surface and of glenoid or humeral bone loss in shoulder instability.
- Post-arthroplasty or post-instrumentation joints where metal defeats MRI.
- Suspected intra-articular loose body.
- Assessment of a suspected rotator cuff tear where ultrasound and MRI are both unavailable or non-diagnostic.
Technique
- The injection is a separate image-guided procedure (fluoroscopy, ultrasound or CT) performed immediately before the scan.
- Scan promptly. Intra-articular contrast is resorbed and diluted over time, and delay degrades the study.
- Gentle passive joint movement after injection distributes contrast into the recesses.
- Dual-energy acquisition, where available, allows a virtual unenhanced reconstruction that improves detection of loose bodies and assessment of glenoid bone loss.
Where it goes wrong
- Over-diluting the contrast leaves the joint fluid and the contrast indistinguishable; under-diluting causes streak that obscures the labrum.
- Extravasation into the soft tissues at injection makes the intra-articular volume inadequate and the study non-diagnostic.
- Delay between injection and scanning is the commonest avoidable degradation.
- A joint injected for a therapeutic purpose is not equivalent to an arthrogram; the volume and dilution differ.
- Raising intravenous contrast safety concerns on this protocol is over-flagging: nothing is injected intravenously.
Clinical questions that reach this study
Contrast
None
Dilute iodinated contrast injected INTRA-ARTICULARLY under image guidance before the CT — reported concentrations around 80 mg/mL of iodine and volumes of roughly 10-20 mL depending on the joint. Nothing is given intravenously.
- The contrast agent here is intra-articular, not intravenous. The shared ContrastAgent vocabulary has no intra-articular option, so this protocol declares no systemic agent deliberately: the intravenous contrast safety rules (renal function, metformin) do not apply to an intra-articular injection and must not be raised by it.
- Some centres add a small volume of dilute local anaesthetic, which doubles as a diagnostic anaesthetic response test.
Acquisition
- Reconstruction
- Sub-millimetre acquisition with multiplanar reformats aligned to the joint — radial reformats for the hip labrum, oblique coronal and sagittal for the shoulder.
- Preparation
- Consent for an image-guided joint injection, with the usual counselling about post-procedural discomfort and the small risk of septic arthritis. Skin infection over the puncture site and uncorrected coagulopathy are checked before the injection, not before the CT. Scan promptly after injection, before the intra-articular contrast is resorbed and diluted.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Child-sized technique and contrast dose· radiographer at scan
- Sedation or anaesthesia for a child· nurse pre scan