 Hello everyone and welcome to another video on Indian Radiologist's YouTube channel. I am Dr. Chaitali Pareh, consultant musculoskeletal interventional radiologist and today we'll be discussing on another topic in musculoskeletal radiology which is slightly tricky one and that is MRI anatomy of the finger. I know these are difficult times and many of you are working day in and day out as covid warriors to save a lot many lives. I hope by sharing the knowledge that I have gained through this video I can help you to learn something in these trying times. Hope you like the video. MRI anatomy of finger is really tricky because of the small size of the soft tissue structures of the finger. Two basic things that are needed to report a finger MRI is a good quality scan obtained in appropriate planes and second is you need to be well versed with the anatomy of the finger. Today we'll be discussing both these aspects in the session. Before we start the session let us understand what part of the hand we are going to cover in today's session. So this is the hand okay where you can see the carpal bones, metacarpal bones, proximal phalanges, middle phalanges and distal phalanges. Normally speaking we have five fingers that is you have index two little finger and you have a thumb but however with respect to MRI the thumb and finger need to be dealt with separately and that is because the anatomy of the thumb is slightly different and more importantly because the planes in which you scan the finger cannot be used to scan the thumb and vice versa. So the planning for both of them is different and hence they are considered as separate MRI studies. Thumb we will discuss separately in a later session. Today we'll be discussing the MRI anatomy of the four fingers. So four fingers means 12 joints and that's a huge number. But the good news is if you know the anatomy across any one finger that anatomy is applicable for all the four fingers. So basically all the four fingers have got the same anatomy. So now you only need to understand the anatomy across three joints which is one finger. We will start with the very basics of how to get an MRI scan done because getting a good quality scan in appropriate planes is very very critical particularly for small joints like finger. So if you have a good scan you're more than half the job is done. So first we'll discuss about the coils that can be used followed by positioning for MRI, protocol and planning of MRI then we'll discuss the anatomy of the finger and finally we'll look at the normal MRI appearance. A dedicated finger coil is obviously better than a flex coil. This is the image of a flex coil and all the MRI images that you'll see in today's session have been obtained with a flex coil and you can obtain very good quality images with a flex coil. So dedicated finger coil is not a necessity. If you have it you can use it if not you can get very good images with flex coil. In case you don't have both of them you can use a volume coil like a knee coil for getting the MRI images of the finger. The positioning for an MRI scan of the finger is called the Superman position. This doesn't mean that you're going to fly like a Superman while getting an MRI done. It only means that the scan is done in a prone position with the affected arm above the head just like this. So actually if you'll see it looks similar to a Superman flying in the air except for the flying part. So currently obviously we don't have MRI machines which can help us fly who knows it can happen in the future. In case overhead abduction is painful say because patient has a frozen shoulder. In that scenario patient can lie down in supine position with the arm by the side and the scan can also be performed in that position. So this is how you'll place the hand. So it should be in the prone position with the palm facing downwards. So this is this is the hand that is placed on the coil. Make a point to place a marker at the site of pain or symptom in the patient. Place the marker superficially and do not press down the marker. In case the patient is making some movements you can also tape the finger to the coil. So this is the MRI from two different patients showing the positioning of the marker. This is the wrong method of putting a marker whereas this is the right method. The difference is that this marker is placed superficially whereas this marker has actually been pressed down on the skin and when you do so you will actually deform the underlying structures and miss the injuries. So please inform your staff to put the marker superficially or you can tell the staff to put the marker one centimeter proximal to the site of a pain or the abnormality. So that way you will not even compress the underlying structures and you also know where exactly to look at. So coming down to the protocol first you obtain a stir coronal of the hand that is entire hand from wrist to the finger which is the tip of the finger which is the large FOV to look for the bone and the soft tissue edema and the areas of abnormalities. Once you know the area of abnormality please obtain the rest of the scan with small FOV images. So next is a proton density coronal image in a small FOV wherein you cover from the tip of the finger up to the discol shaft of the metacarpal. Then you have a proton density sagittal image, proton density axial images, T2 part saturated sagittal image and T2 part saturated axial images. Now amongst all these proton density images is a very important image for musculoskeletal imaging. It is really helpful for imaging of the ligaments, tendons, small structures like volar plates, pulleys and everything and even identifying the injuries. T1 weighted image is not required for injuries or internal derangement scans. So this is a proton density image and if you will see the tendon is also visualized better as compared to the T1 and particularly the small triangular black structures which are nothing but the volar plates they are not easily identified on T1 weighted images. But T1 weighted images are needed for imaging of the marrow so T1 weighted images are required for infections and tumours. For the planning first obtain the axial images and then plan the coronal on the axial images so they should be planned exactly along the finger of interest or parallel to the shaft of the finger of interest. And once you obtain the coronal images the sagittal images are planned on the coronal images again along the shaft of the finger of interest. Now ideally you need to include an adjacent normal finger while planning the scan. So when we are planning a coronal image make sure that at least one or two adjacent normal fingers are included. Similarly when you are planning a sagittal image please include at least one adjacent normal finger so your planning should be this. Now this is important because sometimes the injuries to these small structures are difficult to diagnose and when you have an adjacent normal finger you can use it for comparison and come to a diagnosis. So in order to obtain good quality images a 3 Tesla MRI is better than 1.5 Tesla. Please get small FOV images because with large FOV identifying these small structures is very difficult. Call in your application specialist and set appropriate protocols. Ideally you should get 2 to 2.5 millimeter thickness images. Up to 3 millimeter is still acceptable beyond that if you obtain 4 or 5 millimeter thickness images you will miss those thin structures of the fingers and for the same reason you need to have 0 millimeter slice gap so that you don't miss anything. So points to remember place a marker and place it superficially. Imaging planes should be along the finger of interest this is very important because if the planes are not along the finger of interest diagnosis becomes very difficult. Include an adjacent normal finger so that you can compare and come to a diagnosis. So this is the list of all the structures that are present in the finger but this is not how you need to report a scan. So for scan reporting you can divide your anatomy into osteo structures or bones and joints and cartilage. So first look at them and then start looking at the soft tissue structures. The soft tissue structures can be divided into 3 compartments. The first one is the volar compartment, second is dorsal and third is the lateral compartment. The volar compartment comprises of volar plate, flexor tendons and pulleys. This is from deep to superficial. Dorsal compartment you have extensor tendon and sagittal bands and lateral compartment you have the radial and ulnar collateral ligaments. Now flexor tendons are in the volar compartment and they are two of them flexor-digitorum superficialis and flexor-digitorum tropondas. Extensor tendons are on the dorsal compartment and they can be further divided into extrinsic tendons and intrinsic tendons. Extrinsic tendons are those which originate out of the hand say in the forearm or the elbow and insert on the finger. Intrinsic are those which originate in the hand and insert on the finger. So extrinsic comprises of extensor digitorum, extensor inbysis and extensor digiti minimi. Intrinsic you have the interoscia and the lumbar icles. Now this is the image showing the volar compartment and it looks pretty complex. So what we'll do is we'll break down each structure and look at them individually so that we can understand the anatomy well. So this is the diagrammatic image showing the coronal image of the finger and this is the sagittal image of the finger. This is the dorsal. This is the volar and you can see the lamelline. So this is metacarpal, proximal phallines, middle phallines and distal phallines. So the first structure we are looking at is the volar plate which is the deepest structure on the volar aspect. So it is an inverted triangular structure with a broad base attachment to the distal bone and a slender attachment to the proximal bone and they are present at all the joint levels. Next is the flexor digitorum superficialis. Now this is a flexor tendon which is a single tendon up to the base of the proximal phalline and then it divides into two tendon slips which go and attach to the base of the middle phalline. So if you'll see it has an appearance of a tuning fork. I'm sure all of you must have used a tuning fork in your physics experiments back in the school days. So the stem of the tuning fork is the single tendon and after splitting it forms the prongs of the tuning fork. The third structure is the flexor digitorum profundus tendon. Now FDS is superficial to FDP and this relationship is valid till the base of the proximal phallines. After that the FDS divides into two tendon slips and while doing so it forms a loop or a gap in between and FDP passes through this loop and become superficial. So if you'll see that after the division of FDS the FDP becomes superficial to the FDS. As you can see over here the red tendon is the FDP and it is becoming superficial to FDS over here and then it runs all the way up to the distal phallines to attach to the base of the distal phallines. The key to remember that which one splits and attaches to the middle phallines and which one goes and attaches to the distal phallines is S for S that is the superficial is splits and will attach to the middle phallines while the profundus or the FDP tendon will run in the midline and attach to the distal phallines. And the last structure is the pulleys. So you have cruciate and annular pulleys. These are the cross ones are the cruciate pulleys but they're not much important so we'll only discuss the annular pulleys. There are five of them. The odd number pulleys are close to the joints that is the MCP the proximal inter phallinger and the distal inter phallinger joint and the even number pulleys are along the shafts of the phallenges. So A2 is along the proximal phallines and A4 is along the middle phallines. And the function of the pulleys is to keep the flexor tendons in close proximity to the underlying bone particularly when you flex the fingers. Now this is the dorsal compartment. I'm sure this also looks very complex and in fact dorsal or the extensor compartment is more complex as compared to the volar compartment. So as you see again this is the coronal image and this is the sagittal image where this is the volar plates to show you that this is the volar side. So the first structure is obviously the extensor tendon and at the level of the base of the proximal phallings or the mid proximal phallings level the extensor tendon divides into three slips which is one central slip and two lateral bands. Now the central slip runs in the midline goes and attaches to the base of the middle phallings whereas the lateral bands they are reinforced from intrinsic tendons on both the sides. Some of the fibres of intrinsic tendons also go to the central slip but predominantly they go to the lateral band and the lateral band joins with this intrinsic tendon to form conjoined tendon and this conjoined tendon then joins together at the level of the discylinder phalangeal joint and forms a single terminal tendon which goes and attaches to the base of the distal phallings. So the central slip attaches to the middle phallings whereas the lateral bands along with the intrinsic tendon attach to the base of the distal phallings. Now overlying these tendons similar to what you have police in the volar compartment you have got sagittal band and extensor hood on the dorsal compartment. So the sagittal band is a thin band of tissue that lies superficial to the extensor tendon at the level of the metacarpal head. Extensor hood is actually formed by a sheet which is contributed by all of these extensor tendons and triangular ligament is again a thin sheet of tissue that connects the two conjoined tendons distally. So these sagittal bands and extensor hood they prevent the subluxation of the extensor tendon of these the most important structure is the sagittal band. Now let's look at the lateral compartment so again the same diagrammatic representations and laterally you have only two structures that is the radial and the ulnar collateral ligaments. So the collateral ligament on the radial side is the radial collateral ligament whereas on the ulnar side is the ulnar collateral ligament and on the sagittal image you can see that they arise dorsally from the proximal bone and distally they go and attach more on the volar aspect. Now ideally there are two collateral ligaments a proper and the accessory on both the sides but clinically it is not much important and so all you need to know is there are radial and ulnar collateral ligaments you do not bother about the proper and the accessory ones. So let us now look at the normal MRI appearance of the finger the first image that we obtain is a star coronal image of the hand to look at the area of abnormality the next is the flexor compartment on the sagittal sections so this is a proton density sagittal image this is a coronal scout image and this line will help you to guide as to which level we are looking at. So currently we are imaging the middle finger and we're looking at the midline section so in this midline section this is the volar compartment where you can see the entire flex attendance and at the level of the joints you can see there are black inverted triangular structures with a broad base attachment to the distal bone and a thin flimsy attachment to the proximal bone. So these are nothing but the volar plates and volar plates can have intrinsic intermediate signal intensity this should not be mistaken for a tear. Now I know the proximal attachment is very thin but the good news is that the distal attachment is usually torn which has a broad base attachment and so identifying these injuries is not that difficult. So volar plates are the deepest structures on the volar aspect of the finger. Now we look on the sagittal sections and we'll be going from radial to the ulnar side and as we do so the first structure that we see is the radial collateral ligament here again you can see the radial collateral ligament at these two joints. Now we'll directly go to the midline section so here you can see that there are two flex attendance at the level of the proximal phalanx it becomes difficult to differentiate the two tendons after the mid level of the mid phalanx we know that only FDP tendon exits because FDS attaches at this level so this entire tendon is actually the FDP tendon and this is the insertion of FDP tendon on the base of the distal phalanx. Now you cannot see the insertion of FDS tendon on this particular section because FDS divides into two tendon slips and has a paramidline insertion on the middle phalanx so as you go back on the radial side here you can now see the FDS inserting onto the middle phalanx which is the radial slip and again when you go on the ulnar side you can see the ulnar slip that is attaching to the middle phalanx. Now let us look at the extensor compartment on the same sagittal sections so again this is the scout image and we'll be going from radial to ulnar side we'll directly go to the midline section and here you can see on the dorsal aspect this is your extensor tendon and this at this level nearly at the base of the proximal phalanx it divides into three components so the central slip runs in the midline okay so you can see the entire central slip which goes and attaches to the base of the middle phalanx and the other structure that you can appreciate here is the terminal tendon which is formed by joining of the conjoined tendon so this terminal tendon goes and attaches to the base of the distal phalanx. Now if you'll see there is no tendon appreciated in this region this does not mean that there is a tear in the extensor tendon as we know the lateral bands they run in the paramedline region where it is reinforced by the intrinsic tendon to form the conjoined tendon so again as you go slightly on the radial side here you can see the entire lateral band of the conjoined tendon which is on the radial aspect and similarly when you go on the ulnar aspect you can see the same conjoined tendon over here over here you can see this line so please don't just look at one midline section and label a tear of the extensor tendon please look at the paramedline sections to make sure that the lateral bands of the conjoined tendons are intact. Now we'll again look at the flexor compartment but this time on the actual sections so we'll be going from proximal to distal so this is the volar compartment and these are the flexor tendons and this is a thin flimsy structure that is enveloping the tendons this is nothing but the pulley now depending upon the level at which you are looking at you can know which pulley it is so this is at the level of proximal phalanx and hence this is the a2 pulley now as we go further distally here it is actually difficult but you can see that there are two tendons over here so the deeper one is the fdp and the superficial one is the fds and as you go further distally you can see that there is a tendon this fds has split and it is trying to go on the lateral side here you can see that this is the fdp and these two small structures are the fds and as you go further distally now you can see that the fds is trying to go deep to the fdp so basically the fdp is becoming superficial from the loop that is formed by the fds so here you can see that the fdp has become superficial and when you go further distally at the level of the middle phalanx you can see that the fds is inserting to the middle phalanx and the tendon overlying it which is the fdp and now further distally you can identify only one tendon which is your fdp because the fd has has already inserted to the bone and further when you go at the level of the distal phalanx you can see this small flimsy structure this black that that is nothing but the fdp which is inserting onto the distal phalanx and that will be actually better appreciated on the sagittal image over here now let's look at the extensor compartment so again here you can see that these are the intrinsic muscles so these are the interoscii and the muscles between the flexor tendon these are the lumbaricles now in this image which is at the level of the metacarpal head okay this is the extensor tendon and this is the flexor tendon the structure which has intermediate signal intensity seen deep to it that's the volar plate now this is a thin structure which is nothing but a sagittal band so here you can see this is the extensor tendon and this is the sagittal band which goes and attaches to the volar plate so this thin black structure is the sagittal band which goes and attaches to the volar plate and it prevents the subluxation of the extensor tendon now let's go further distally so this is your extensor tendon at this level now you can see three tendons so the one which is dorsal is the extensor tendon whereas the one which is present laterally are the intrinsic tendons so that is the extrinsic extensor tendon and this is at the intrinsic tendons and as you go distally you can see that there is a sheet of black thin black line that is connecting these tendons and this is at the level of the proximal phalange and this is nothing but the extensor hood which connects these tendons and keeps them in place and prevent the subluxation now as you go further distally you can just see one black structure so the central part is the central slip whereas laterally by now you know that the extensor tendon has divided into central slip and lateral bands and laterally the intrinsic tendon have actually come and join the lateral bands and this is nothing but the conjoined tendons so this is the central slip and this are the conjoined tendons and as we go further distally at this level you can see that this is the central slip and it is attaching to the underlying bone over here which can be better appreciated on the sagittal image and distal to this you can only identify your two lateral structures but there is nothing in the midline because the central slip has already attached to the bone so here these two are nothing but the conjoined tendons which run in paramedal line sections and distally again you can appreciate the conjoined tendons and as you go at the level of the base of distal phalanx they have joined to form a single tendon okay and now they are attaching to the base of the distal phalanx here which can again be appreciated on the sagittal image now let's look at the lateral compartment and they'll be better seen on coronal sections so we'll be going from dorsal to volar aspect and as we do so first thing to look on the coronal sections are the bones and the joints because they are very well seen so this is the metacarpal head this is the proximal phalanx middle phalanx and distal phalanx and here you can see the cartilage is also very well seen so this thin gray zone this is the metacarpal cartilage and this gray zone is the proximal phalanx cartilage so the black line is the cortex and the gray zone between the two black lines is the cartilage similarly here also you can identify this thin gray zone which is again the cartilage at the proximal interphalangeal joint so once you've assessed the bones and the joints the next structure is to look at the collateral ligaments and here you can see this black structure or it can have sometimes intermediate signal intensity so these structures which are arising from the dorsal aspect of the proximal bone are the collateral ligaments and as you go on the volar aspect you can see that they are attaching to the distal bone in fact here you can also appreciate that there are two bands so this one and this one and these are the ones what I was talking about as proper and accessory components but again it is not important from clinical point of view so on the radial side you have the radial collateral ligament and on the ulnar side you have the ulnar collateral ligament and you can also correlate these ligaments on axial images so this is the head of the proximal phalanx and here you can see this blacks this intermediate signal intensity structures they are the collateral ligaments again these are the collateral ligaments at the joint level and this is the base of the middle phalanx and here you can see again that they are attaching to the base of the middle phalanx over here so now further points to remember correlate the structures on all the planes in sagittal planes remember all tendon insertions are not seen on mid sagittal sections particularly the lateral bands with the extensor and the fds insertion for the flexor compartment please look at the paramidline sagittal sections carefully and this is a checklist so which structures are better visualized on which sections but please remember to correlate all the structures in all the planes thank you for watching the video and if you like the video please hit the like button and leave your feedback in the comment section if you want us to take any particular topic please do let us know in the comment section also subscribe to the indian radiologist youtube channel and indian radiologist group on other social media platforms to get information regarding future educational videos and if you have any queries regarding this topic please feel free to type in the comment 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