Several techniques can be used to perform MR arthrography. All techniques however are based on the presence of an intra-articular contrast-enhancing agent and on distension of the joint. A joint effusion or hemarthrosis, due to an acute or chronic injury of the joint, leads to distension of the joint with the intra-articular fluid acting as a natural contrast agent. Another way to perform an arthrogram is by injecting a saline solution into the joint and injecting Gd intravenously. The most commonly used technique however, is an intra-articular injection of a diluted Gd solution . This results in a high intra-articular signal and therefore a good depiction of the intra-articular anatomy.
Until now no technique was available to perform plastination arthrography. Plastination is a process in which tissues are dehydrated and impregnated with a polymer. It is an excellent method to study anatomy, but as fluids are taken out of the tissues during the process, it is difficult to study intra-articular anatomy. Plastination arthrography could be the solution for this problem. When a polymer is added to the Gd solution there will be a decrease in signal intensity with time because curing of the polymer results in an increasing solidity of the mixture. This decrease in signal intensity goes on until, finally, there is a signal void.
In order to be able to perform MR arthrography, we looked for that specific mixture of Gd and polymer, which would give us the maximum time window to scan before the signal intensity, dropped below a visible level. The mixture showing the highest signal intensity for the longest period of time was the slow-curing polymer with a 1:50 diluted Gd solution. At 50% decrease of the initial signal intensity, this Gd-polymer mixture was still clearly visible. The 50% reduction in signal intensity was reached after 150 min. Since we needed circa 50 min to prepare the Gd–polymer mixtures before we could start MRI scanning, the total available time window before the signal intensity dropped below a visible level added up to 200 min. This gave us ample time to perform the MR imaging.
The most convenient way to perform MR plastination arthrography is with a single intra-articular injection of a mixture of Gd and polymer. Such a mixture did not give a good result in this study. Although the joint could be clearly visualized, the arthrogram was inhomogeneous. As such it was not possible to study the joint lining and syndesmotic recess. There could be a number of reasons for this phenomenon.
First, the ongoing process of curing could be the cause of this inhomogeneous arthrogram. However, this is not likely since all images were acquired within approximately 110 min after we started the preparation of the Gd–polymer while the total available time window amounted 200 min.
Secondly the presence of joint fluid and/or the presence of tissues forming the joint lining may give an additional interaction between the Gd and polymer. This could lead to a faster decrease of signal intensity in the joint than was observed in the test tubes. Moreover the curing process itself may be an inhomogeneous process.
Changing the order of mixing the components of the polymer solution with the hardening component (Biodur Härter E2) added last however, did not result in a more homogenous arthrogram. We therefore changed to a two-step procedure with a conventional MR arthrogram as a first step, followed by an intra-articular injection of a dyed polymer and plastination of the leg.
The obliquely running anterior and posterior tibiofibular ligaments are only partially visible in axial images of the talocrural joint. This may lead to the erroneous interpretation of a rupture of these ligaments. Generally, a ligament is best depicted in a plane along its length. We therefore scanned and sawed the specimen in an oblique plane, which was defined with the aid of markers containing cod oil, which were attached to the skin of the cadaveric leg.
This article shows that the study of clinically relevant anatomical structures clearly improves by using plastination arthrography. This can best be done following the two-step procedure. The first step was the MR arthrogram with a 1:250 diluted Gd solution; the second step was the plastination arthrogram with a dyed polymer. With this technique we achieved an excellent correlation between MR images and plastinated slices of the distal tibiofibular syndesmosis. MR-plastination-arthrography demonstrated the clinically relevant syndesmotic recess, the fat pad, and the tibiofibular ligaments in great detail. This technique can be applied to study the anatomy of any synovial joint. However, it is essential to obtain plastination slices in the same plane as the imaging slices. To optimize this technique for each joint may be a subject for future studies.