Os trigonum: secondary ossification center at posterolateral talar process with intervening synchondrosis
Stieda process: fused os trigonum at posterolateral talar process
Os trigonum syndrome = compression of bone and soft tissue between posterior malleolus and calcaneus caused by forceful repetitive plantar flexion; may impinge upon FHL
FHL impingement syndrome: os trigonum, large posterior process, or fracture of posterior process of talus limits gliding of FHL through fibroosseous tunnel at posterior process of talus
FHL impingement may also occur at knot of Henry or at intersesamoidal ligament
Check-rein deformity: tethering of FHL by flexor retinaculum
Due to scar from previous injury
Master knot of Henry
Site at plantar aspect of foot where FHL crosses flexor digitorum longus (FDL)
Tendon sheaths communicate here
Tendon disease at this point may entrap medial plantar nerve
IMAGING
Radiographic Findings
MR Findings
Ultrasonographic Findings
Other Modality Findings
Imaging Recommendations
DIFFERENTIAL DIAGNOSIS
PATHOLOGY
General Features
Relevant Anatomy
CLINICAL ISSUES
Presentation
Demographics
Treatment
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
Selected References
Sharpe BD et al: Posterior ankle impingement and flexor hallucis longus pathology. Clin Sports Med. 39(4):911-30, 2020
Rajakulasingam R et al: Master knot of Henry revisited: a radiologist's perspective on MRI. Clin Radiol. 74(12):972.e1-8, 2019
Rungprai C et al: Disorders of the flexor hallucis longus and os trigonum. Clin Sports Med. 34(4):741-59, 2015
Donovan A et al: Plantar tendons of the foot: MR imaging and US. Radiographics. 33(7):2065-85, 2013
O'Loughlin P et al: Fracture of the medial tubercle of the posterior process of the talus: magnetic resonance imaging appearance with clinical follow-up. HSS J. 5(2):161-4, 2009
Lui TH: Arthroscopy and endoscopy of the foot and ankle: indications for new techniques. Arthroscopy. 23(8):889-902, 2007
Michelson J et al: Tenosynovitis of the flexor hallucis longus: a clinical study of the spectrum of presentation and treatment. Foot Ankle Int. 26(4):291-303, 2005
Na JB et al: The flexor hallucis longus: tenographic technique and correlation of imaging findings with surgery in 39 ankles. Radiology. 236(3):974-82, 2005
Renard M et al: Intermittent dislocation of the flexor hallucis longus tendon. Skeletal Radiol. 2003 Feb;32(2):78-81. Epub 2003 Jan 23. Erratum in: Skeletal Radiol. 32(10):608-9, 2003
Lo LD et al: MR imaging findings of entrapment of the flexor hallucis longus tendon. AJR Am J Roentgenol. 176(5):1145-8, 2001
Inokuchi S et al: Closed complete rupture of the flexor hallucis longus tendon at the groove of the talus. Foot Ankle Int. 18(1):47-9, 1997
Wredmark T et al: Os trigonum syndrome: a clinical entity in ballet dancers. Foot Ankle. 11(6):404-6, 1991
Related Anatomy
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Related Differential Diagnoses
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References
Tables
Tables
KEY FACTS
Terminology
Imaging
Top Differential Diagnoses
Pathology
Clinical Issues
TERMINOLOGY
Abbreviations
Flexor hallucis longus (FHL)
Definitions
Os trigonum: secondary ossification center at posterolateral talar process with intervening synchondrosis
Stieda process: fused os trigonum at posterolateral talar process
Os trigonum syndrome = compression of bone and soft tissue between posterior malleolus and calcaneus caused by forceful repetitive plantar flexion; may impinge upon FHL
FHL impingement syndrome: os trigonum, large posterior process, or fracture of posterior process of talus limits gliding of FHL through fibroosseous tunnel at posterior process of talus
FHL impingement may also occur at knot of Henry or at intersesamoidal ligament
Check-rein deformity: tethering of FHL by flexor retinaculum
Due to scar from previous injury
Master knot of Henry
Site at plantar aspect of foot where FHL crosses flexor digitorum longus (FDL)
Tendon sheaths communicate here
Tendon disease at this point may entrap medial plantar nerve
IMAGING
Radiographic Findings
MR Findings
Ultrasonographic Findings
Other Modality Findings
Imaging Recommendations
DIFFERENTIAL DIAGNOSIS
PATHOLOGY
General Features
Relevant Anatomy
CLINICAL ISSUES
Presentation
Demographics
Treatment
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
Selected References
Sharpe BD et al: Posterior ankle impingement and flexor hallucis longus pathology. Clin Sports Med. 39(4):911-30, 2020
Rajakulasingam R et al: Master knot of Henry revisited: a radiologist's perspective on MRI. Clin Radiol. 74(12):972.e1-8, 2019
Rungprai C et al: Disorders of the flexor hallucis longus and os trigonum. Clin Sports Med. 34(4):741-59, 2015
Donovan A et al: Plantar tendons of the foot: MR imaging and US. Radiographics. 33(7):2065-85, 2013
O'Loughlin P et al: Fracture of the medial tubercle of the posterior process of the talus: magnetic resonance imaging appearance with clinical follow-up. HSS J. 5(2):161-4, 2009
Lui TH: Arthroscopy and endoscopy of the foot and ankle: indications for new techniques. Arthroscopy. 23(8):889-902, 2007
Michelson J et al: Tenosynovitis of the flexor hallucis longus: a clinical study of the spectrum of presentation and treatment. Foot Ankle Int. 26(4):291-303, 2005
Na JB et al: The flexor hallucis longus: tenographic technique and correlation of imaging findings with surgery in 39 ankles. Radiology. 236(3):974-82, 2005
Renard M et al: Intermittent dislocation of the flexor hallucis longus tendon. Skeletal Radiol. 2003 Feb;32(2):78-81. Epub 2003 Jan 23. Erratum in: Skeletal Radiol. 32(10):608-9, 2003
Lo LD et al: MR imaging findings of entrapment of the flexor hallucis longus tendon. AJR Am J Roentgenol. 176(5):1145-8, 2001
Inokuchi S et al: Closed complete rupture of the flexor hallucis longus tendon at the groove of the talus. Foot Ankle Int. 18(1):47-9, 1997
Wredmark T et al: Os trigonum syndrome: a clinical entity in ballet dancers. Foot Ankle. 11(6):404-6, 1991
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