Os trigonum syndrome/ posterior tibiotalar compression syndrome
Os trigonum:
Secondary ossification center at posterolateral talus (7 - 13 years) and fuses within 1 year. If this forms large lateral talar process, it is called Stieda process. If it fails to fuse, os trigonum is formed. Os trigonum articulates with talus via synchondrosis (7%–14%)
Mechanism:
Avulsion of posterior talofibular ligament, talar fracture or disruption of os trigonum
Repetitive forced plantar flexion
Common in Ballet dancers, footballers
Pathology:
Compression of soft tissues between posterior process of calcaneus and posterior tibia on plantar flexion
Diffuse or focal posterior capsule synovial thickening
Posterior intermalleolar, posterior talofibular ligament, posterior tibiofibular ligament involvement may be seen
Stress fracture of talar process or os trigonum
FHL runs in groove between lateral and medial processes of talus and can be affected leading to stenosing tenosynovitis
Clinical features:
Posterior ankle pain increased by plantar flexion or dorsiflexion
Posterior tenderness anterior to Achilles tendon
Occasionally palpable soft-tissue
Radiographs:
Prominent lateral talar process or os trigonum
CT:
Prominent lateral talar process or os trigonum
Isotope bone scan:
Increased activity
Negative scan excludes diagnosis
MR:
Marrow edema
Fracture - fluid in synchondrosis suggests os trigonum fracture
Posterior capsular or ligament thickening
Gad is good for synovitis
FHL tenosynovitis
USG:
Guided LA + steroid injections is diagnostic and therapeutic
Management:
Physiotherapy
Image guided steroid + local anesthetic injection
Arthroscopic resection of soft-tissue thickening and associated bony abnormality with joint washout
References:
Robinson P et al. Soft-Tissue and Osseous Impingement Syndromes of the Ankle: Role of Imaging in Diagnosis and Management. Radiographics. 2002;22:1457-1469
