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<v ->There also are accessory ossicles that can develop.

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The function of these small accessory bones

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are not really well-known.

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We see them most commonly in the foot.

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They relate to a normal variance that relate themselves

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to unfused primary or secondary ossification centers.

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And although I don't know their function,

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I do know that they can become symptomatic.

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So let's look at a few symptomatic accessory ossicles

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about the foot in particular.

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The first is the accessory navicular bone.

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These are often typed into three categories,

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the type I is a small ossicle

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within the tibialis posterior tendon itself.

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The type II is accessory ossification center

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that is connected to the parent navicular bone

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by cartilaginous tissue.

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It's often bigger and closer to the navicular bone

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as shown here.

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And the type III looks like a fused type II

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with the navicular bone

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producing what is known as the cornuate navicular bone.

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Now the one in my experience that tends to be most painful

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is the type II because of the abnormal movement

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between the accessory ossification center

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and the navicular bone.

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Another accessory ossicle is the os trigonum.

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This occurs adjacent to the posterior process of the talus

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located laterally adjacent to or intimate

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with the posterolateral tubercle of that process.

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And it's also intimate

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with the flexor hallucis longus tendon

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that is located itself between the two tubercles,

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the lateral and medial tubercles.

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So we diagnose a problem with this when it is enlarged,

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when it is oedematous,

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when it appears to narrow the distance

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between the posterior aspect of the tibial plafond

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and the top of the calcaneus,

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when there's edema in either one of those sites

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or a cystic change.

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And another interesting finding is tenosynovial fluid

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about the flexor hallucis longus tendon shown here

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that stops abruptly at the level of the os trigonum.

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Now as you know,

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fluid in that tendencies is extremely common

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but generally goes below the os trigonum.

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So when you see it isolated above that level,

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you may wanna consider the os trigonum may be symptomatic.

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And as you might imagine

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because of the intimate relationship

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between the tendon and the os trigonum,

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tears partial or complete.

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Here's a complete tear shown by the blue arrows,

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kinda occur within that tendon with proximal retraction

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of the torn end.

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Look at the size of the os in this case,

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and how it narrows the interosseous space

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and the posterior aspect of the ankle.

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(keyboard clicks)

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Another and very interesting accessory ossification center

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is a triangular area of bone

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that is intimate with the sustentaculum tali.

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Now the sustentaculum tali is a fancy name

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for one of the facets of the calcaneus.

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I'd remind you there are three facets on the talus.

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There are three facets on the calcaneus.

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The middle facet of the calcaneus is known in fact,

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as the sustentaculum tali.

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And indeed, this is what that os looks like.

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It can painful because of abnormal motion,

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and it may be a component of a specific type

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of talocalcaneal coalition.

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It's known as an extra-articular type

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because you see it's located a little further posteriorly

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than the typical coalition

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of the middle facets of the talus and calcaneus.

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The os intermetatarseum is uncommon.

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It's found between the bases

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of the first and second metatarsals.

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Here's what it looks like in a sagittal image.

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It can be painful,

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can produce paresthesias in this case,

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it's edematous indicating that it might be painful.

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And a very interesting one

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that I didn't know about until a few years ago,

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in fact, thought this was an old fracture

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when I saw a case like this,

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is a bipartite medial cuneiform,

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and this is what it looks like.

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And as you know,

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a lot of things attach to the medial cuneiform.

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So when you have a bi or partition one,

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they may attach to one or the other of the partitions

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or sometimes to both,

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for example, the Lisfranc ligament

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has components that attach both to the dorsal

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and plantar portion.

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Abnormal motion may occur at the site of partition.

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This can be painful.

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As we move away from the foot,

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we end up looking at the shoulder region

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and here we deal with the os acromiale.

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Now to understand what that is,

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you have to realize that during development,

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there are three ossification centers

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that occupy the acromion,

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the distal one,

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the pre-acromion ossification center,

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a larger one known as the meso-acromion,

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and then a even larger one located more posteriorly

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is the meta-acromion ossification center.

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And the typical scenario that occurs

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during normal development is the pre-acromion

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and meso-acromion ossification centers first fuse,

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and then later that fuse area will then fuse

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with the meta-acromion ossification center

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typically the ages of 18 to 25 years.

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If that fusion does not occur,

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you end up with a classic os acromiale shown over here.

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Now there are other patterns of os acromiale,

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but this is the most common pattern that we see.

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There's a school of thought that says,

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"This is a very significant finding

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because what will occur in certain movements of the arm

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is the deltoid will depress a large os acromiale

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leading to impingement on the rotator cuff."

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But there's another school of thought that says

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it's overrated and that the importance of an os acromiale

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to shoulder symptoms,

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and specifically to pathology of the rotator cuff

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is not that clear.

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In any case, just to show you what it might look like,

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this is what a painful os acromiale might look like,

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and this is what normal ossification looks like.

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More serrated irregular area of separation

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as opposed to the transverse type of appearance

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you see with an os acromiale.

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Also in the upper extremity

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one of my favorite accessory ossification centers,

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this is the os styloideum.

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It's a separate ossicle found at the basis

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of the second and third metacarpals,

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it too may become edematous and painful.

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As to here you can see what it looks like

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with radiographs and with MR.

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And there may be pain at the adjacent metacarpal base

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as you can see here,

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and even in the carpal bone.

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So this is a painful os styloideum.

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And to finish our discussion of ossicles that may be painful

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the os hamuli proprium which can simulate

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a fracture of the hook of the hamate

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typically occurs in this area not up higher.

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It tends to be right here.

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This becomes important.

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If your hand surgeon

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is considering doing carpal tunnel surgery.

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Knowledge of this particular finding may influence

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the way he does that surgery.

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This is what it looks like on the MR.

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And then another one, os calcanei secundarium.

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And this one is problematic because as you know,

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fractures involving the anterior process

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of the calcaneus occur in this region.

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And telling what is a post-traumatic abnormality

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from a developmental abnormality can be difficult

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in that particular region.