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open license. Please read the
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Type:
Educational Exhibit
Keywords:
MR, CT, Conventional radiography, Musculoskeletal system, Musculoskeletal bone, Normal variants, Education and training
Authors:
J. Saraiva, C. Bilreiro, L. Silva, C. Carneiro, B. M. Q. Santos, M. O. E. Castro; Portimão/PT
DOI:
10.1594/ecr2016/C-1827
Findings and procedure details
This presentation reviews the reported symptomatic accessory ossicles and suggests guidelines on their imaging diagnosis while attempting to provide some clinical-radiological correlation.
We provide our own examples of the more commonly symptomatic ossicles:
1.
os odontoideum;
2.
Accessory Navicular;
3.
os acromiale;
4.
os subfibulare;
5.
os trigonum;
6. Carpal Boss;
7.
os calcaneus secundarius;
8.
os peroneum;
9.
os intermetatarseum.
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666542?maxheight=300&maxwidth=300)
Fig. 1: Locations of the more common symptomatic ossicles: 1. os odontoideum; 2. Accessory Navicular; 3. os acromiale; 4. os subfibulare; 5. os trigonum; 6. Carpal Boss; 7. os calcaneus secundarius; 8. os peroneum; 9. os intermetatarseum.
1.
Os Odontoideum
Location |
Unfused dens axis fragment,
adjacent to C2 vertebral body.
|
General Incidence |
|
Symptoms
|
Atlantoaxial instability (anterior or posterior atlantoaxial subluxation) is common.
May lead to substantial spinal canal narrowing and spinal cord compression at the level of C1.
|
Causes / Risk Factors |
|
Imaging |
MRI narrowing...
|
Differential Diagnosis
|
Assymptomatic os odontoideum : well corticated convex of upper margin of atlas body(arrowhead).
Hypertrophic and rounded anterior atlas arch(arrow).
-Type 2 odontoid Fracture: flattened,
sharp,
uncorticated upper margin of atlas body(arrowhead).
Normal half moon- shaped anterior atlas arch.
|
Notes
|
|
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666043?maxheight=300&maxwidth=300)
Fig. 12: os odontoideum
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666044?maxheight=300&maxwidth=300)
Fig. 13: os odontoideum
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666041?maxheight=300&maxwidth=300)
Fig. 10: os odontoideum
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666042?maxheight=300&maxwidth=300)
Fig. 11: os odontoideum
2. Accessory navicular
Location |
Adjacent to the medial side of the navicular bone.
|
General Incidence |
~10% (range 4-21%) of the population |
Symptoms
|
medial side foot pain (os naviculare syndrome) |
Causes / Risk Factors |
Pain is worsened by walking,
running and other weight-bearing activities.
If large,
it can protrude outwards and cause friction against footwear. |
Imaging |
A medial navicular eminence is best visualised on the lateral-oblique view.
Symptomatic accessory navicular bones can appear bright on bone scan and bone marrow oedema is best seen on MRI.
|
Differential Diagnosis
|
|
Notes
|
Acute pain can be managed with corticosteroid injection and immobilisation.
In refractory cases surgical management can be an option. |
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666038?maxheight=300&maxwidth=300)
Fig. 7: Accessory navicular
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666040?maxheight=300&maxwidth=300)
Fig. 9: Accessory navicular
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666039?maxheight=300&maxwidth=300)
Fig. 8: Accessory navicular
3. Os Acromiale
Location |
Unfused accessory center of ossification of the acromion of the scapula
|
General Incidence |
1 - 15% |
Symptoms
|
Shoulder pain
|
Causes / Risk Factors |
It may cause shoulder impingement,
rotator cuff tear or degenerative AC joint disease |
Imaging |
On conventional radiography is best seen on axillary views.
On MRI it can easily be mistaken for the normal acromioclavicular joint. |
Differential Diagnosis
|
- normal AC joint
- degenerative ossification
- acromion fracture
|
Notes
|
|
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666523?maxheight=300&maxwidth=300)
Fig. 18: os acromiale
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666522?maxheight=300&maxwidth=300)
Fig. 17: os acromiale
4. Os Subfibulare
Location |
Ajacent to the tip of the lateral malleolus of the ankle
|
General Incidence |
very rare |
Symptoms
|
Can cause painful syndromes or degenerative change in response to overuse and trauma.
The ossicle itself may fracture.
|
Causes / Risk Factors |
There are two hypotheses:
- It's an unfused accessory ossification center.
- It's an avulsion fracture attributable to pull of the anterior talofibular ligament.
|
Imaging |
|
Differential Diagnosis
|
Avulsion fracture of the lateral malleolus |
Notes
|
|
5. Os Trigonum
Location |
Posterior to the talus
|
General Incidence |
~7 % |
Symptoms
|
Posterior ankle impingement (PAI) syndrome
|
Causes / Risk Factors |
It origins on a failure of fusion of the lateral tubercle of the talus |
Imaging |
Best characterized on MRI,
signal characteristics of the affected region include:
T1: low signal in areas of bony bruising
T2/STIR: high signal posterior to ankle in areas of bone bruising
PD/PD fat saturated: high signal posterior to the ankle
|
Differential Diagnosis
|
- avulsion fracture of lateral tubercle of talus (Shepherd fracture)
- fracture of Stieda process
|
Notes
|
|
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666500?maxheight=300&maxwidth=300)
Fig. 15: os trigonum
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666135?maxheight=300&maxwidth=300)
Fig. 14
6. Carpal Boss
Location |
- os styloideum is located dorsally between the trapezoid,
capitate and 2nd and 3rd metacarpal base.
- os trapezium secundarium is located between the trapezium and the base of the first metacarpal,
developing as an appendage to the tubercle of the trapezium.
|
General Incidence |
~2.0 % (os styloideum) |
Symptoms
|
Degenerative joint disease
|
Causes / Risk Factors |
|
Imaging |
|
Differential Diagnosis
|
|
Notes
|
|
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/665720?maxheight=300&maxwidth=300)
Fig. 3: os trapezoideum secundarium
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/665719?maxheight=300&maxwidth=300)
Fig. 2: os trapezoideum secundarium
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/665721?maxheight=300&maxwidth=300)
Fig. 4: os styloideum
7. Os Calcaneus secundarius
Location |
anterior calcaneal process
|
General Incidence |
5% |
Symptoms
|
ankle pain
|
Causes / Risk Factors |
|
Imaging |
|
Differential Diagnosis
|
bifurcated ligament avulsion fracture of the anterior calcaneal process. |
Notes
|
|
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/666501?maxheight=300&maxwidth=300)
Fig. 16: os calcaneus secundarius
8. Os Peroneum
Location |
lateral plantar aspect of the cuboid
|
General Incidence |
very common,
seen in up to 26% of feet |
Symptoms
|
Os peroneum syndrome includes fracture,
peroneus longus tenosynovitis and peroneus longus tendon tear.
|
Causes / Risk Factors |
|
Imaging |
|
Differential Diagnosis
|
- os vesalianum
- apophysis of the 5th metatarsal
- avulsion fracture (pseudo-Jones fracture)
|
Notes
|
|
9.
Os Intermetatarseum
Location |
Typically positioned dorsally between the bases of the first and second metatarsals but has been reported to occur near the metatarsal heads or between the fourth and fifth metatarsal bases.
|
General Incidence |
~4% (range 1-7%) |
Symptoms
|
dorsal midfoot pain
|
Causes / Risk Factors |
|
Imaging |
It can have a variety of shapes:
- round
- oval
- bean-shaped
- linear
- resemble a rudimentary metatarsal
|
Differential Diagnosis
|
|
Notes
|
It can be classified into three basic types:
- free standing: it is a completely independent ossicle,
and it does not show any osseous or articular connection with any structure
- articulating: it may form a synovial joint with first or second metatarsal or the medial cuneiform
- fused: it forms a spur that is seen as a bony projection in the first and second intermetatarsal space
|
|
|
|
|
|
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/665735?maxheight=300&maxwidth=300)
Fig. 5: os intermetatarseum
![](https://epos.myesr.org/posterimage/esr/ecr2016/133526/media/665736?maxheight=300&maxwidth=300)
Fig. 6: os intermetatarseum