Sinus tarsi syndrome is a frequently overlooked cause of persistent lateral ankle pain after ankle sprains — the subtalar canal fills with scar tissue, producing chronic aching at the outside of the foot that fails to resolve with standard ankle sprain treatment. Dr. Tom Biernacki, DPM, at Balance Foot & Ankle in Howell and Bloomfield Hills, Michigan, evaluates and treats sinus tarsi syndrome with corticosteroid injection, orthotics, and arthroscopic debridement when needed.

Quick Answer: What Is Sinus Tarsi Syndrome?

The sinus tarsi is a small canal between the talus and calcaneus (heel bone) in the lateral hindfoot, containing ligaments, nerves, and fatty tissue. Sinus tarsi syndrome (STS) occurs when this space becomes inflamed, scarred, or impinged — typically after an ankle sprain — producing a characteristic dull aching at the lateral hindfoot that worsens on uneven ground, with prolonged standing, and on the morning after activity. It affects approximately 70% of patients with chronic ankle sprain symptoms who have persistent lateral ankle pain despite normal ankle ligament examination. It responds well to ultrasound-guided cortisone injection and custom orthotics; refractory cases benefit from arthroscopic sinus tarsi debridement.

Anatomy: The Sinus Tarsi and Its Contents

The sinus tarsi (tarsal sinus) is a conical space between the talus superiorly and the calcaneus inferiorly, located at the anterior aspect of the subtalar joint just anterior to the lateral malleolus. Its contents include: the interosseous talocalcaneal ligament (ITCL), the cervical ligament, the posterior and anterior subtalar joint recesses, multiple proprioceptive nerve endings (three branches of the peroneal nerve supply sinus tarsi sensory function), and a pad of fatty areolar tissue. The sinus tarsi is directly adjacent to the subtalar joint — inflammation in the sinus tarsi invariably involves the posterior subtalar joint capsule and vice versa. The ITCL is torn in approximately 50–70% of significant lateral ankle sprains, and the resulting scar formation in the sinus tarsi is the primary structural basis of chronic STS.

Causes and Mechanisms

The most common cause of sinus tarsi syndrome is a previous lateral ankle sprain — particularly Grade 2 or 3 sprains where significant subtalar motion occurred at the time of injury. Scar tissue filling the sinus tarsi after ligament healing impinges on the remaining normal tissue and nerve endings with subtalar motion, producing chronic pain. Additional causes include: rheumatoid arthritis and inflammatory arthropathies affecting the subtalar joint; hindfoot valgus deformity (flat feet with calcaneal valgus) that chronically impinges the lateral sinus tarsi with every step; tarsal coalition (a rare congenital fusion of subtalar bones causing rigid restriction) causing sinus tarsi overload on the mobile side; and degenerative subtalar joint arthritis producing synovitis that extends into the sinus tarsi space.

Diagnosis: Clinical Signs and Imaging

The sinus tarsi point tenderness test is the most reliable clinical sign — direct palpation with the thumb over the sinus tarsi entrance (approximately 1–2cm anterior and inferior to the lateral malleolus, just lateral to the extensor digitorum brevis muscle origin) reproduces the patient’s characteristic pain. This finding has approximately 90% sensitivity for STS in patients with chronic ankle pain. Subtalar range of motion is typically restricted and painful compared to the contralateral side. The subtalar stress test (passive inversion of the hindfoot while stabilizing the ankle joint) produces sinus tarsi pain rather than lateral ligament pain — a key distinction from lateral ankle sprain. MRI shows sinus tarsi edema and obliteration of the normal fatty tissue by scar and fibrosis. Ultrasound is useful for guided injection targeting and demonstrates subtalar joint effusion in inflammatory cases.

Treatment: Cortisone Injection and Orthotics

First-line treatment for sinus tarsi syndrome is ultrasound-guided cortisone injection directly into the sinus tarsi space. This is a technically specific injection — the sinus tarsi must be precisely targeted with ultrasound guidance to ensure the medication reaches the inflamed tissue rather than the adjacent ankle joint or peroneal tendon sheath. Success rate for 1–2 injections: approximately 70% achieve significant pain reduction lasting 3–6 months. Concurrent custom orthotic management addresses the underlying biomechanical cause — hindfoot valgus (flat foot) is corrected with a medial heel post, reducing the chronic impingement that perpetuates sinus tarsi inflammation. Physical therapy focusing on subtalar proprioceptive training reduces the neurological hypersensitivity from peroneal nerve impingement within the sinus tarsi. For STS secondary to inflammatory arthritis, disease-modifying therapy coordinated with rheumatology is essential.

Arthroscopic Sinus Tarsi Debridement

Arthroscopic debridement of the sinus tarsi is indicated for STS that has failed 2–3 corticosteroid injections and 6 months of orthotic management. The procedure uses two small portals at the lateral hindfoot — the scope enters through one portal and the shaver through the other — to remove the scar tissue, synovium, and damaged ITCL from the sinus tarsi space. Any associated posterior subtalar joint pathology (synovitis, loose bodies) is addressed simultaneously. Recovery is faster than open sinus tarsi surgery: weight-bearing in a walking boot by day 2–3, transition to athletic shoes at 3–4 weeks, return to full activity at 6–8 weeks. Success rate: approximately 80% at 2 years. Arthroscopic debridement for STS secondary to subtalar arthritis has lower success rates and may require progression to subtalar fusion if symptoms recur.

Sinus Tarsi Syndrome vs Lateral Ankle Sprain: Why STS Is Missed

Sinus tarsi syndrome is frequently missed because it follows the same mechanism (ankle inversion sprain) and produces the same general region of pain (lateral ankle) as a lateral ankle ligament sprain. The key distinctions that separate STS from residual ankle sprain: STS pain is specifically at the sinus tarsi (anterior to the lateral malleolus, not at the ATFL attachment); the anterior drawer test is negative (ankle ligament laxity is absent); uneven ground specifically aggravates STS (subtalar motion challenge) while lateral ankle sprains are more aggravated by ankle dorsiflexion; and the subtalar stress test reproduces sinus tarsi pain while the ankle ligament stress test does not. Patients who have been told their “ankle sprain” has not healed after 3+ months should be evaluated for STS — it requires specific injection therapy, not continued rest and ankle ligament rehabilitation.

Book a Sinus Tarsi Evaluation in Michigan

Dr. Tom Biernacki, DPM, evaluates sinus tarsi syndrome, chronic ankle pain, and all subtalar conditions at Balance Foot & Ankle in Howell (4330 E Grand River Ave, Howell MI 48843) and Bloomfield Hills (43494 Woodward Ave #208, Bloomfield Hills MI 48302). Same-day appointments, ultrasound-guided injections available. Call (810) 206-1402 or book online →.

Medically reviewed by Dr. Tom Biernacki, DPM — podiatric physician and surgeon, Howell and Bloomfield Hills, Michigan.

Dr. Tom Biernacki, DPM

Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.