The os trigonum syndrome, also known as talar compression syndrome, posterior ankle impingement syndrome, and posterior tibial talar impingement syndrome, is a broad term that refers to symptoms produced by pathology of the lateral tubercle of the posterior talar process. Symptoms include chronic pain with stiffness, tenderness, and edema in the posterior ankle, which are exacerbated by activities that result in extreme plantar flexion.
Different processes can lead to os trigonum syndrome:
- Disruption of the cartilaginous synchondrosis between the os trigonum and the lateral talar tubercle: MRI will show fluid between the os trigonum and the lateral talar process.
- Trigonal process fracture.
- Flexor hallucis longus (FHL) tenosynovitis: The tendon for the FHL is located medial to the os trigonum between the medial and lateral tubercles of the talus. Heavy use of the FHL can result in tenosynovitis by rubbing against the os trigonum.
- Posterior tibiotalar impingement by bone block: A bony protuberance from the calcaneus may articulate with the inferior surface of the os trigonum.
- Intraarticular loose bodies: Just like other joints, synovial osteochondromatosis can affect the posterior subtalar joint or posterior ankle joint capsule.