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MRI Anatomy Review: A Look at the Acetabular Anatomy in the Sagittal Plane

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The sagittal projection of the

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hip, often ignored and overlooked.

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In the sagittal projection, especially

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with very thin-section 3D imaging,

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one or two millimeter cuts, we get our

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best view of the hyaline cartilage.

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And while the femur thickness and the acetabular

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thickness vary from front to back, one thicker

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than the other in the front, the other thicker

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than its neighbor in the back, they should

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add up to approximately 3 millimeters and

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should be uniform as in this young patient.

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As we move forward, the overall

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milieu or proteoglycan content of the

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cartilage changes and it gets darker

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as it transitions into the poinsettia.

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Thorn-like labrum, which should not have, in

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young, healthy individuals, any longitudinal

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signal in it, and should not have any horizontal

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signal going more than 25 percent of the

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depth, and certainly not going through it.

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The posterior portion of the acetabular labral

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cup is deeper, craniad to caudad, or superior

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to inferior, than its counterpart in the front.

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There is a ligament in the front, the

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iliofemoral ligament, and there is a

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capsular ligament in the back, mostly

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composed of the ischiofemoral ligament.

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Now let's do a little scrolling.

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We have a T1-weighted and a heavily water-

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weighted fat-suppressed image, both of which

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have a nice complement of fluid within.

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Let's scroll, shall we?

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And as we scroll, we see the anterior

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capsule, and it has innumerable components.

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It has a component that

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is more medial, not this.

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That is the origin of the rectus femoris

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from the anterior inferior iliac spine.

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It will also have a small origin

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from the anterior acetabular roof,

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which we don't see here as yet.

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But there are the medial and lateral portions of

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the anterior capsule which form the letter Y.

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Here's one limb of the Y,

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here's the other limb of the Y.

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They come down and merge as the

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powerful iliofemoral ligament.

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That little tiny gray slit is the pre-

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labral recess, which may fill with fluid.

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Sometimes this ligament is referred

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to as the ligament of Bigelow.

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The sagittal projection invaluable on its

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own in 20 percent of all labral tears.

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Let's go to our water-weighted fat-

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suppressed image where we see the inferior

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capsule forming the inferior boundary of

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the intra-articular portion of the femur.

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This is important because fractures above

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this level may lead to necrosis, and fractures

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below this level have a better prognosis.

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So you should get in the habit of being

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able to identify where the capsule is.

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This inferior transverse structure,

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not coincidentally, is known

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as the transverse ligament.

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It is said to produce the appearance

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of a Saint Andrew's cross.

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I don't see it.

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There is another thin structure right here,

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which can be confused with a piece of capsular

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anatomy. But it is a pectinosynovial fold.

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It is a variation, a type of synechiae

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or plica, analogous to the one I showed

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you earlier in the paralabral region.

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So in the sagittal projection, we don't

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want to see any signal going longitudinally

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in our labrum or through our labrum.

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And unfortunately, in this case, we do in one

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small locus, right there, a young individual

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with signal going through the labrum,

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although ill-defined—an abnormality, a

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labral tear in a high-performance athlete.

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We want to see a firm, complete black

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triangle, like we see on the far right,

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with no defects from back to front,

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and no defects running longitudinally.

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Let's move on now to the

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beloved coronal projection.

Report

Description

Faculty

Stephen J Pomeranz, MD

Chief Medical Officer, ProScan Imaging. Founder, MRI Online

ProScan Imaging

Tags

Musculoskeletal (MSK)

MRI

Hip & Thigh

Congenital

Bone & Soft Tissues

Acquired/Developmental

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