Posterior ankle impingement, the dancer’s ankle and os trigonum syndrome — from injection to endoscopic hindfoot debridement.

Posterior ankle impingement is bony or soft-tissue pinching at the back of the ankle on forced plantarflexion. Common causes include an os trigonum, a prominent Stieda process (posterior talar tubercle) or flexor hallucis longus (FHL) tenosynovitis.

It is classically described as the dancer’s ankle — most common in ballet dancers on pointe and demi-pointe — and is also seen in footballers, downhill runners and other athletes with repeated forced plantarflexion.

The story and a positive forced plantarflexion test do most of the work. A lateral X-ray in plantarflexion looks for an os trigonum, MRI shows FHL tenosynovitis and bone oedema, and CT best defines bony anatomy. A positive response to an ultrasound-guided injection is strongly supportive.

Ultrasound-guided steroid injection into the posterior recess or FHL tendon sheath is both diagnostic and therapeutic — a clear symptom response supports the diagnosis, and many patients settle without needing surgery.

It is a two-portal minimally invasive technique — often called the Van Dijk approach — that allows the surgeon to excise an os trigonum, release the FHL tendon and debride the posterior ankle through small incisions, with a much faster recovery than open surgery.

Acute weakness of great-toe flexion after a plantarflexion injury may indicate FHL rupture and needs urgent surgical review. New numbness or motor weakness after surgery, or wound infection, also warrants same-day contact with your surgical team.