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Flexor Hallucis Longus Tendon Injury
Corrie M. Yablon, MD; Julia R. Crim, MD
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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

                                    1. Sharpe BD et al: Posterior ankle impingement and flexor hallucis longus pathology. Clin Sports Med. 39(4):911-30, 2020
                                    2. Rajakulasingam R et al: Master knot of Henry revisited: a radiologist's perspective on MRI. Clin Radiol. 74(12):972.e1-8, 2019
                                    3. Rungprai C et al: Disorders of the flexor hallucis longus and os trigonum. Clin Sports Med. 34(4):741-59, 2015
                                    4. Donovan A et al: Plantar tendons of the foot: MR imaging and US. Radiographics. 33(7):2065-85, 2013
                                    5. 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
                                    6. Lui TH: Arthroscopy and endoscopy of the foot and ankle: indications for new techniques. Arthroscopy. 23(8):889-902, 2007
                                    7. 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
                                    8. 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
                                    9. 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
                                    10. Lo LD et al: MR imaging findings of entrapment of the flexor hallucis longus tendon. AJR Am J Roentgenol. 176(5):1145-8, 2001
                                    11. 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
                                    12. 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

                                                                      1. Sharpe BD et al: Posterior ankle impingement and flexor hallucis longus pathology. Clin Sports Med. 39(4):911-30, 2020
                                                                      2. Rajakulasingam R et al: Master knot of Henry revisited: a radiologist's perspective on MRI. Clin Radiol. 74(12):972.e1-8, 2019
                                                                      3. Rungprai C et al: Disorders of the flexor hallucis longus and os trigonum. Clin Sports Med. 34(4):741-59, 2015
                                                                      4. Donovan A et al: Plantar tendons of the foot: MR imaging and US. Radiographics. 33(7):2065-85, 2013
                                                                      5. 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
                                                                      6. Lui TH: Arthroscopy and endoscopy of the foot and ankle: indications for new techniques. Arthroscopy. 23(8):889-902, 2007
                                                                      7. 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
                                                                      8. 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
                                                                      9. 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
                                                                      10. Lo LD et al: MR imaging findings of entrapment of the flexor hallucis longus tendon. AJR Am J Roentgenol. 176(5):1145-8, 2001
                                                                      11. 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
                                                                      12. Wredmark T et al: Os trigonum syndrome: a clinical entity in ballet dancers. Foot Ankle. 11(6):404-6, 1991