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Os Trigonum

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Description

  • Medial view of posterior ankle with the presence of os trigonum[1]
    Medial view of posterior ankle with the presence of os trigonum[1]
  • Os trigonum on (a) Lateral foot radiograph; (b) 2D CT; (c) 3D CT[2]
    Os trigonum on (a) Lateral foot radiograph; (b) 2D CT; (c) 3D CT[2]
  • Lateral view of the ankle, with arrow indicating the os trigonum[3]
    Lateral view of the ankle, with arrow indicating the os trigonum[3]
  • The os trigonum is shown in a magnetic resonance exam (black arrow)[4]
    The os trigonum is shown in a magnetic resonance exam (black arrow)[4]
  • Os trigonum seen on lateral ankle radiograph[5]
    Os trigonum seen on lateral ankle radiograph[5]
(A) Lateral weightbearing radiographs obtained preoperatively revealed an os trigonum posterior to the talus (red arrow) compared with that obtained from (B) surgical excision at 6-month follow-up. Additionally, (C) demi-pointe lateral radiograph of the same dancer showed restriction of normal plantarflexion compared with that obtained (D) after follow-up. (E) Magnetic resonance imaging was used to further evaluate the size of the ossicle (red circle), as well as focal edema in the hindfoot of soft tissue structures being impinged.[6]
Illustration of Os Trigonum
Os trigonum and os talotibiale radiograph of the ankle, lateral view shows rounded bones in the anterior aspect of tibia and behind the talus. Os talotibiale (arrow) and os trignum (arrowhead) are suspected. Soft tissue swelling is noted in front of the os talotibiale. On CT of ankle, os talotibiale (arrow) and os trigonum(arrowhead) are visualized. Distal tibia shows spur formation with loose bodies suggestive of arthritis.[7]
Classification and measurements of the os trigonum: (a) Type I os trigonum. (b) Type II os trigonum. (c) Type III os trigonum. (d) Length (point A to B) and width (point C to D) of the os trigonum. (e) The distance between the os trigonum and the most inferior point of the tibia (point E to F) and the distance between the most posterior point of the os trigonum and the most superior posterior point of the calcaneus (point G to H).[8]
Accessory bones: Os Intermetatarseum, Os Supranaviculare, Os Naviculare, Os Supratalare, Os Vesalianum, Os Peroneum, Os Calcaneus Secundarium, Os Trigonum[9]

Names

  • Accessory ossicle of the posterior talus
  • Accessory talar ossicle
  • Posterior talar accessory bone
  • Unfused lateral tubercle of the posterior talar process
  • Secondary ossification center of the posterior talus
  • Os trigonale
  • Plural: ossa trigona

General

Gross Anatomy

  • Located posterior to the talus[10]
  • Represents a failure of fusion of the lateral tubercle of the posterior process

Classification[11]

  • Type I
    • Small, rounded ossicle with the smallest dimensions
    • Least common variant with an incidence of 1.9%
  • Type II
    • Characterized by a larger, more elongated morphology with the greatest overall size.
    • Incidence of 10.5% and represents the largest volume among the three types
  • Type III
    • Common variant (14.7% incidence) and has intermediate dimensions
    • Demonstrates the greatest distance from the os trigonum to the calcaneal tubercle

Epidemiology

  • Variable, found in 7% to 25% of patients
  • Bilateral in 2% of individuals[12]
  • Ossicle usually forms between age 7-13, fuses with talus at age 17[13]

Imaging

Clinical Significance

Clinical Significance

See Also

References

  1. ↑ Preinl, Maciej, et al. "Prevalence and clinical aspects of os trigonum: a meta-analysis: Prevalence and clinical aspects…." Anatomical Science International 100.3 (2025): 287-297.
  2. ↑ Keles-Celik, Nigar, et al. "Accessory ossicles of the foot and ankle: disorders and a review of the literature." Cureus 9.11 (2017).
  3. ↑ Gill, Laura E., and Kevin E. Klingele. "Management of foot and ankle injuries in pediatric and adolescent athletes: a narrative review." Orthopedic research and reviews (2018): 19-30.
  4. ↑ Ráfare, André Limongi, et al. "Os trigonum: a discussion of its role in posterior ankle impingement syndrome and a meta-analysis of its prevalence." Surgical and Radiologic Anatomy 46.7 (2024): 1137-1143.
  5. ↑ Case courtesy of Mohammad Taghi Niknejad, Radiopaedia.org, rID: 91842
  6. ↑ Walsh, Keifer P., et al. "Surgical outcomes of os trigonum syndrome in dancers: a case series." Orthopaedic Journal of Sports Medicine 8.7 (2020): 2325967120938767.
  7. ↑ Kobashi, Y., Y. Tazawa, and S. Suzuki. "Disorders of the accessory bones and sesamoids of the foot and ankle." European Congress of Radiology-ECR 2010, 2010.
  8. ↑ Candan, Busra, Ebru Torun, and Rumeysa Dikici. "The prevalence of accessory ossicles, sesamoid bones, and biphalangism of the foot and ankle: a radiographic study." Foot & Ankle Orthopaedics 7.1 (2022): 24730114211068792.
  9. ↑ Osiowski, Aleksander, et al. "The prevalence and clinical considerations of Os Vesalianum Pedis: A meta-analysis." Foot and Ankle Surgery (2025).
  10. ↑ Karasick, David, and Mark E. Schweitzer. "The os trigonum syndrome: imaging features." AJR. American journal of roentgenology 166.1 (1996): 125-129.
  11. ↑ Fu, Xiaoyong, et al. "Implications of classification of os trigonum: a study based on computed tomography three-dimensional imaging." Medical Science Monitor: International Medical Journal of Experimental and Clinical Research 25 (2019): 1423.
  12. ↑ Uzel M, Cetinus E, Bilgic E, Karaoguz A, Kanber Y. Bilateral Os Trigonum Syndrome Associated with Bilateral Tenosynovitis of the Flexor Hallucis Longus Muscle. Foot Ankle Int. 2005;26(10):894-8. doi:10.1177/107110070502601017
  13. ↑ Incidence and Fusion of Os Trigonum in a Healthy Pediatric Population. (2017) Journal of Pediatric Orthopaedics. doi:10.1097/BPO.0000000000001016
  14. ↑ Anwar, R., and J. E. Nicholl. "Non union of a fractured os trigonum." Injury Extra 36.7 (2005): 267-270.
Created by:
John Kiel on 15 November 2024 15:52:05
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Last edited:
3 March 2026 20:07:14
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