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Posterior Ankle Impingement Syndrome M76.899 726.90


synonyms:Os Trigonum Syndrome, PAIS, talar compression syndrome, os trigonum impingement syndrome, nutcracker syndrome, posterior tibiotalar impingement syndrome (PTTIS. 



  • 726.90 - Enthesopathy of specified site (Capsulitis NOS) 
  • 726.70 - Enthesopathy of ankle and tarsus, unspecified 
  • 726.71 - Achilles bursitis or tendonitis 
  • 729.5 - Pain in limb 
  • 719.57 - Stiffness of joint, not elsewhere classified 

PAIS Etiology / Epidemiology / Natural History

  • Most commonly in ballet dancers, soccer players, basketball players, volleyball players and runners.
  • Can be stress injury from repetitive plantar flexion, or a synchondrosis disruption from a plantar flexion-inversion injury
  • Os Trigonum syndrome: inflammation between the os trigonum and the adjacent talus.  Generally occurs as a result of impingement or compression of the posterior talus with an os trigonum present with the surrounding soft tissues between the tbia and calcaneous.  

PAIS Anatomy

PAIS Clinical Evaluation

  • Posterior ankle pain exacerbated by plantar flexion, such as in pointe technique exercises.
  • Consider fluoroscopically guided local anesthetic injection. Significant relief of symptoms after injection strongly points to that structure as a source of the pain and may have predictive value for surgical treatment.

PAIS Xray / Diagnositc Tests

  • A/P, Lateral and Mortise ankle xrays may be normal.
  • MRI: demonstrates intraosseous edema in the os trigonum and adjacent talus and calcaneous
  • Bone Scan: may demonstrate focal intense Tc-99m uptake in the posterior aspect of the talus and adjacent tibia as well as in the calcaneous. High false-positive rate (Sopov V, Foot Ankle Int 2000;21:822)

PAIS Classification / Treatment

  • Nonsurgical treatment options:  activity modification, stretching, and injection.
  • Os Trigonum syndrome: definitive treatment = excision of the os trigonum via a medial approach. (Abramowitz Y, JBJS 2003;85A:1051).

PAIS Associated Injuries / Differential Diagnosis

PAIS Complications

  • Sural Nerve injury

PAIS Follow-up Care

PAIS Review References

  • (Marotta JJ, AJSM 1992;20:533)
  • Hamilton WG, JBJS 1996;78:1491
  • Wredmark T, Foot Ankle 1991;11:404


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