MR arthrogram solution

MR arthrogram solution is a gadolinium-containing mixture injected into a joint for MR arthrography. 

Terminology

Fluoroscopy, ultrasound or CT guidance can be used to cannulate a joint, which is then injected with the MR arthrogram solution.  MR arthrogram solutions differ in different institutions, but will broadly contain a mixture of gadolinium, diluted with saline and iodinated contrast medium and/or local anesthetic.  Commonly used is a 1 in 200 dilution of gadolinium, i.e. 0.1 mL in 20 mL ¹.

Suggested MR arthrogram solution mixtures for fluoroscopic/CT guided injections ^ref:

• 0.1 mL gadolinium

• 9.9 mL 0.9% saline

• 5 mL iodinated contrast medium

• 5 mL longer-acting local anesthetic / 5 mL 0.9% saline

Suggested MR arthrogram solution mixture for ultrasound-guided injections ^ref:

• 0.1 mL gadolinium

• 9.9 mL 0.9% saline

• 5 mL longer-acting local anesthetic / 5 mL 0.9% saline

Iodinated contrast medium can be substituted for 0.9% saline, however, its inclusion will enable the practitioner to assess joint distention and for extra-articular injection.  It is not required for ultrasound-guided procedures.

Local anesthetic use is more controversial, with many shown to be chondrotoxic at typical therapeutic doses, particularly lidocaine ^2,3.  Of all routinely available anesthetics, ropivacaine at concentrations of 0.5% appears safest ³.  Their addition in a small quantity, offer a diagnostic benefit with the patient keeping a pain diary after their injection. 

Radiographic features

MRI

• T1: high signal

• T2: high signal (fluid)

MRI sequences performed will be predominantly fat-saturated T1 sequences, thus leaving the T1 high signal gadolinium to outline or extend into a labral or meniscal tear.

Insufficiently-diluted gadolinium can result in the ‘black contrast effect’ resulting in low signal (black) fluid on all sequences ⁴.

Iatrogenic gas bubbles will have similar appearances to intra-articular loose bodies, therefore needles and tubes should be primed before injection.

Radiology report

The arthrogram injection report should include:

• the total injected volume of the MR arthrogram solution

• the amount and concentrations of solutions used to make the MR arthrogram solution

Practical points

• MR arthrogram solutions differ in different institutions, and it is time well spent familiarising with local ‘recipes’ before undertaking

• 3 T MRI techniques have much improved labral and meniscal (including TFCC) imaging and many institutions will first perform non-arthrographic imaging before considering MR arthrography, particular for hip joints 

• joint volumes differ and the injected volume of the MR arthrogram solution should reflect the size of the joint, i.e. hip 10-12 mL and wrist 2-3 mL

• confirming an intra-articular needle position first with only iodinated contrast medium will reduce the chance of extra-articular gadolinium, which can interfere with interpretation although more experienced practitioners may opt to only inject the MR arthrogram solution

• if intra-articular injection is confirmed first with only iodinated contrast medium, care must be taken in small joints i.e. wrist, so as not to fill the joint then leaving no room for the MR solution

• using a 20 mL for the clear MR arthrogram solution will identify it from other clear solution syringes such as local anesthetic for the skin and iodinated contrast medium, often in 5 mL and 10 mL syringes