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My first lecture of about 45 minutes in length will deal

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with disorders of the sacroiliac joint.

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We're gonna emphasize the anatomy of the sacroiliac joint

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and nearby structures.

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We're gonna talk a bit about methods of imaging

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and disease distribution and characteristics.

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To give you some specific objectives, I list three here.

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Number one, to invest, investigate the anatomy

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of the sacroiliac interosseous space,

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including the true sacroiliac joint

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and the adjacent ligaments

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that connect the sacrum and ileum.

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Number two, to review the various imaging methods

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that are used to investigate disorders

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of this particular area, emphasizing MR imaging.

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And then the third objective

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to document the characteristic distribution

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and morphologic features of these disorders,

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particularly in the spondyloarthropathies.

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So let's get started

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and talk briefly about the anatomy of this particular area.

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You'll note on my illustration on the right

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that I'm showing you that the entire space

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between sacro manum is considered the sacroiliac

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interosseous space,

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and only a portion of that is the sacroiliac joint.

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This is an interesting joint synovial at birth,

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although later in life, it fills with fibrous tissue.

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It consists of the irregular articular surfaces

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of the sacrament ileum, okay, with areas of depressions

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and of elevations.

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And because of that, this is the joint

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with limited mobility.

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It represents, again, a portion of

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that sacroiliac interosseous space.

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To give you an idea of the overall anatomy

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of this particular interosseous space,

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here I'm providing you with a transverse section

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through the very top aspect of

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that interosseous space shown in the picture on your right.

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And you can see in this particular area,

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we can see in orange the interosseous sacroiliac ligament.

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This is one of the strongest ligaments in the entire human

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body, and it's the major bond connecting sacro manum.

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There are other ligaments nearby,

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shown in the picture on your right.

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The anterior and posterior sacroiliac ligaments are

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among those other ligaments.

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Now, if we look at sections,

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transverse sections at a little lower level, levels two,

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three, and four, you can see in fact that we have areas

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that are synovial, areas that are ligamentous,

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or areas that only one of those is present.

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At the very top, you can see the synovium portion

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of the joint shown in yellow,

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representing the anterior aspect of the interosseous space

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with ligaments behind.

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As we go to level three, you can see the width

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of the synovial space and ligamentous

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Space becomes approximately equal.

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And then as we go to the bottom, we can see in fact

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that most of what we're seeing here with CT is going

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to be the synovial line space.

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So you can imagine if your task is

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to aspirate this particular joint to go

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and find fluid within the synovial joint, you would do best

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to aspirate the joint in a lower portion

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of the articulation.

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Now, there's another interesting aspect about it,

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and here's a coronal section of the sacroiliac joint

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that we did years ago.

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And it points out, in fact, at the top,

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the ligamentous portion of the interosseous space.

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And below it, the true synovial lined articulation know

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how the cartilage differs on the two portions of the joint.

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On the sacral side, we deal with thick,

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relatively healthy highline cartilage.

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And on the ileal side, we can, we deal with fibro cartilage.

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One of the interesting facts

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that I learned early on in my residency in radiology is

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that disease processes tend to begin

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and dominate on the ileal aspect of this joint,

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including ankylosing spondylitis.

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And now you can perhaps understand why,

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because on that ileal side, the cartilage is thinner

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and it's made of fibrocartilage and not hylan cartilage.

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These are pictures taken from the literature

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to show you the surrounding ligaments about this particular

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region of the human body.

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On your left, you can see in fact,

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the anter posterior siliac ligaments.

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They're outlined by arrows, the sacral spinous

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and sacral tubus ligament shown by arrowhead and asterisk.

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And on your right, a transverse section

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through the hemi pelvis showing you the posterior siliac

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joint in front of it, the interosseous ligament,

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then the true synovial joint,

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and in front the anterior S sacroiliac ligament.

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And in front of those, the sacral tubus

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and sacral spinous ligaments can be seen.

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Now, this is an articulation

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that has many different anatomic variations.

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I take the image on your left from a very nice review

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of this recently in skeletal radiology

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to point out about nine such anatomic variations.

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The arrows point to the two

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that I'm gonna emphasize in the next slide.

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Okay? And that is the accessory S sacroiliac joint

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and the ileo sacral complex.

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So let's look at these.

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The accessory sac joint is present about 10

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to 15% of persons.

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And it represents a second articulation

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that is located posterior,

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connecting the very posterior aspects of the, uh,

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ileum and sacrum.

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And here's what it would look like.

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And for those of you who do a lot of CT

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of the sacroiliac interosseous space, you're very familiar

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with this appearance, the one on the right,

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the images on the right, perhaps something that you're not

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as aware about,

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and that is something that is called the Iliosacral complex

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seen in up to 5% of persons.

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It relates to a very large projection from the ileum

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that extends into a concavity in the sacrum.

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And in the cases that I've seen of this,

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there's often bone sclerosis

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and irregularity at this site of anatomic variation.

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I wanted to show you an example of what

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that looks like here.

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Again, taken from the literature showing you

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with conventional radiography on your left and with CT

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and MR, the dramatic changes that you may see with

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Iliosacral complex.

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And indeed, I can tell you

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that sometimes when you view this particularly on mr,

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you will mistake this for evidence of s sacroiliitis.