| Introduction |
 Up to 40 accessory ossicles and multiple sesamoids have been described in the foot and ankle- Definition
- accessory ossicles
- are secondary ossification centers that remain separated from the normal bone
- sesamoids
- are bones that are incorporated into tendons and move with normal and abnormal tendon motion
- Most common ossicles
- os trigonum
- accessory navicular (os tibiale externum)
- os intermetatarseum
- Most common sesamoids
- os peroneum
- located in the peroneus longus tendon
- hallux sesamoids
- located in the flexor hallucis brevis tendon at the base of the 1st metatarsal head
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| Classification |
| |
| Accessory Ossicles and Sesamoids of the Foot and Ankle |
| Accessory bone |
Prevalence |
Clinical significance |
Differential Diagnosis
|
Image |
| Os trigonum |
10-25% |
Posterior ankle impingement, FHL entrapment |
Shepherd's fracture
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|
| Type II accessory navicular |
2-12% |
Posterior tibial tendon dysfunction |
Navicular tuberosity avulsion frx, type I accessory navicular |
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| Os subfibulare |
2% |
Painful os subfibulare |
Lateral malleolus avulsion frx |
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| Os peroneum |
9-20% |
Painful os peroneum, fracture, diastasis |
Painful os vesalianum, bipartite os peroneum |
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| Os vesalianum |
2% |
Painful os vesalianum |
Avulsion frx of the 5th metatarsal base |
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| Hallux sesamoids |
~100% |
Fracture, stress fracture |
Bipartite tibial sesamoid |
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| Os Trigonum |
 Definition
- sesamoid bone representing the seperated posterolateral tubercle of the talus
- usually asymptomatic, but can become symptomatic and cause os trigonum syndrome
- Epidemiology
- incidence
- 10-25% of the population have os trigonum
- commonly symptomatic in ballet dancers due to extreme plantar flexion ("en pointe" toe position)
- Pathophysiology of os trigonum syndrome
- repetitive microtrauma (ankle plantarflexion)
- may present as a stress fracture
- acute forced plantarflexion
- may present as an acute fracture
- Associated conditions
- FHL tenosynovitis or entrapment
- Anatomy
- osteology
- the secondary ossification center forms posterior to the talus between 8-13yrs
- normally fuses with talus within 1yr
- if the ossicle fails to fuse, it articulates with the talus through a synchondrosis
- the os lies lateral to FHL, tibial nerve, PTT, and posterior tibial artery
- Presentation
- symptoms
- pain in "en pointe" position
- physical exam
- pain with passive ankle plantar flexion
- swelling and tenderness over FHL
- Imaging
- radiographs
- recommended views
- lateral radiograph with foot in plantar flexion
- findings
- shows os trigonum impinged between posterior tibial malleolus and calcaneal tuberosity
- os trigonum can be round, oval or triangular and of variable size
- MRI
- findings
- shows os trigonum and associated inflammation and edema in FHL tendon
- Differential diagnosis
- fracture of the posterior process of the talus (Shepherd's fracture)
- Treatment
- nonoperative
- NSAIDS, rest, immobilization, restricted weightbearing
- operative
- surgical excision
- indications
- if nonoperative management fails
- techniques
- through open lateral approach or posterior ankle arthroscopy
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| Os Tibiale Externum (Accessory navicular) |
 See Accessory Navicular 
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| Os Subfibulare |
 Definition
- small piece of bone adjacent to inferior fibula
- Epidemiology
- Pathoanatomy
- may represent avulsion fx of ATFL that secondarily ossifies
- or accessory ossification center
- Presentation
- symptoms
- may be asymptomatic
- may have ankle pain (symptomatic os subfibulare)
- may be associated with chronic ankle instability and present with recurrent ankle sprains
- signs
- focal tenderness and swelling at the site of the ossicle
- laxity with anterior drawer and inversion/eversion stress testing
- Imaging
- radiographs
- recommended views
- standard ankle series (weightbearing AP, lateral, mortise)
- varus stress view
- findings
- accessory ossicle
- talar tilt on varus stress view
- suggesting ankle instability
- increased separation of os fragment from fibula tip
- Differential diagnosis
- acute lateral malleolus avulsion fracture (by the ATFL)
- Treatment
- nonoperative
- NSAIDS, rest, immobilization, restricted weightbearing
- indications
- initial treatment for symptomatic os subfibulare
- operative
- surgical excision
- indications
- failed nonoperative management
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| Os Peroneum |
 Definition
- sesamoid bone found within the peroneus longus tendon near the base of the 5th MT
- may represent avulsion or rupture of peroneus longus
- Epidemiology
- incidence
- 9-20% of adults
- bilateral in 60%
- bipartite in 30%
- Pathophysiology of injury or fracture
- direct trauma
- indirect trauma (sudden inversion and supination)
- associated with peroneus longus tendon rupture
- Imaging
- radiographs
- findings
- normal os peroneum
- acute os peroneum fracture
- peroneus longus rupture
- MRI
- findings
- normal os peroneum
- acute os peroneum fracture
- peroneus longus rupture
- Differential diagnosis
- painful os vesalianum
- bipartite os peroneum
- Treatment
- nonoperative
- NSAIDS, rest, immobilization, restricted weightbearing
- indications
- initial treatment for painful os peroneum syndrome
- minimally displaced os peroneum fractures
- operative
- surgical excision
- indications
- painful os peroneum syndrome (with minimal tendon involvement) refractory to conservative treatment
- os peroneum fracture with displaced fragments
- surgical excision and repair of peroneus longus tendon or tenodesis to peroneus brevis
- indications
- os peroneum associated with peroneus longus tendon rupture
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| Hallux Sesamoids |
- See Sesamoid Injuries of the Hallux
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Please Rate Educational Value!
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Qbank (1 Questions)
TAG
(OBQ11.253)
A 17-year-old ballet dancer presents with 5 months of pain in the posterior aspect of the right lower extremity that is exacerbated with the ballet position shown in Figure A. Her symptoms returned with ballet activity following a 1 month course of full rest, nonsteroidal anti-inflammatory medication, and physical therapy. On physical examnination she has no tenderness at the insertion of the achilles tendon at the calcaneus. Radiographs are shown in Figure B and a MRI is shown in Figures C-E. Which of the following options is the most appropriate next step in treatment?
Review Topic
DISCUSSION:
The history, examination, and imaging studies are consistent with os trigonum syndrome and is most appropriately surgically treated with arthroscopic or open excision. An os trigonum can cause impingement with plantar flexion of the foot, especially in ballet dancers. The FHL tendon runs through a fibro-osseous tunnel posterior to the hindfoot formed by the posterolateral (os trigonum) and posteromedial tubercle of the talus.
Maquirriain presents a Level 5 review stating that patients with os trigonum syndrome report chronic or recurrent posterior ankle pain caused or exacerbated by forced plantar flexion or push-off maneuvers, such as may occur during dancing, kicking, or downhill running.
Van Dijk presents a Level 5 review of his clinical experience with hindfoot impingement and states that arthroscopic excision of an os trigonum yields good/excellent results in 80% of patients at 2-5 year follow-up.
Illustration A and B are 2 different hindfoot arthoscopy images of a left hindfoot in the prone position that have important landmarks labelled. It is important to know the location of the FHL as the neurovascular bundle is found just medial to the FHL. Illustration C shows a video of a left ankle posterior ankle arthroscopy demonstrating the os trigonum and its relationship to the FHL and Illustration V shows the posterior ankle following arthroscopic removal of the os trigonum.
REFERENCES:
1.
Maquirriain J. Posterior ankle impingement syndrome. J Am Acad Orthop Surg. 2005 Oct;13(6):365-71. Review.
PMID:16224109 (Link to Abstract)
2.
Niek van Dijk C. Anterior and posterior ankle impingement. Foot Ankle Clin. 2006 Sep;11(3):663-83. Review.
PMID:16971256 (Link to Abstract)
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Please Rate Educational Value!
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3.0
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Average 3.0 of 4 Ratings
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Videos
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Shows posterior ankle arthroscopy of left ankle following os trigonum excision
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6/14/2012
175 views
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Shows an os trigonum of a left ankle viewed with posterior ankle arthroscopy wit...
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6/14/2012
613 views
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See More Videos
Groups
Level of Evidence 5 and Other Journal Articles (includes Case Reports, Expert Opinions,
Personal Observations, and Biomechanic Studies)
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Maquirriain J. Posterior ankle impingement syndrome. J Am Acad Orthop Surg. 2005 Oct;13(6):365-71. Review.
PMID:16224109 (Link to Abstract)
-
Niek van Dijk C. Anterior and posterior ankle impingement. Foot Ankle Clin. 2006 Sep;11(3):663-83. Review.
PMID:16971256 (Link to Abstract)
Textbooks
- Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
- AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
- Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
- Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
- Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
- Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
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