Os Trigonum Syndrome or Posterior Ankle Impingement (PAI)

Main Article Content

Pornthep Mamanee, MD
Nathapon Chantaraseno, MD
Somsak Geraplangsub, MD


Os Trigonum is an normal variant of an accessory bone found posterior to the talus. The os trigonum is present in around 5-15% of normal feet. Usually it is asymptomatic, until there is a minor to blunt injury on the anterior aspect of the foot. The injury becomes painful on the hyperplantarflexion test. The pain is located at posterolateral aspect of the ankle associated with swelling known as the ‘os trigonum syndrome’1,2 or posterior ankle impingement (PAI).


Download data is not yet available.

Article Details

How to Cite
Mamanee P, Chantaraseno N, Geraplangsub S. Os Trigonum Syndrome or Posterior Ankle Impingement (PAI). BKK Med J [Internet]. 2014 Feb. 20 [cited 2023 Dec. 10];7(1):94. Available from: https://he02.tci-thaijo.org/index.php/bkkmedj/article/view/219633
Medical Images


1. Sainani IN, Lawande AM, Pawar A, et al. Posterior ankle impingement syndrome due to os trigonum. Appl Radiol 2011;40:28-30.
2. Karasick D, Schweitzer ME. The os trigonum syndrome: imaging features. AJR Am J Roentgenol 1996;166:125-9.
3. Kose O, Okan AN, Durakbasa MO, et al. Fracture of the os trigonum: a case report. J Orthop Surg (Hong Kong) 2006;14:354-6.
4. American College of Foot and Ankle Surgeons (ACFAS). Os Trigonum Syndrome (Accessed December 15, 2013, at https:// www.foothealthfacts.org/footankleinfo/os_trigonum_syndrome.htm?terms=os%20trigonum).
5. American Academy of Orthopaedic Surgeons (AAOS). Posterior Tibial Tendon Dysfunction. (Accessed December 15, 2013, at https://orthoinfo.aaos.org/topic.cfm?topic=A00166).